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120 Cards in this Set
- Front
- Back
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What are the structures of the sperm?
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Sperm: haploid nucleus, no cytoplasm, acrosome, and acrosomal process
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When does the egg complete meiosis?
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The first meiotic division is complete, the second meiotic division progresses to metaphase and then stops. When fertilization occurs meiosis 2 will be completed
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What are the events of fertilization in sea urchin and mammals?
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Sea Urchin:
1. sperm contacts jelly layer 2. Acrosomal Reaction 3. digestion of jelly layer 4. binding to vitelline envelope 5. fusion of acrosomal process membrane and egg membrane Mammals: 1. Sperm activate by female reproductive tract (heat and ph) 2. sperm binds to zona pellucida 3. acrosomal reaction 4. sperm lyses hole in zona 5. sperm and egg membranes fuse |
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How do gametes find eachother for mammals and sea urchin? Explain sea urchin mechanism
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In mammals the heat gradient and a pH gradient activates a dynein ATPase (sperm motor protein)
Chemotaxis – a gradient of chemicals secreted by the egg jelly (sea urchin) MECHANISM: Resact is secreted by egg jelly and binds to a resact receptor on sperm membrane, binding activates receptors guanylyl cyclase activity, it forms cGMP, which binds to calcium channels, there is an influx of calcium into the sperm which drives sperm motility |
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How is species-specificity insured? Sea urchin and mammals?
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Sea Urchin: Bindin is a protein on the acromion process that has a species specific receptor on the vitelline membrane.
Mammals: a protein coats the zona pellucida that the sperm’s SED1 protein interacts with |
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How is polyspermy prevented? Sea urchin and mammals…
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1. FAST BLOCK – when sperm binds to egg it causes a cascade that opens Na channels, which leads to a depolarization of the egg membrane. Sperm can only bind to the membrane when it is -70.
2. SLOW BLOCK – when sperm binds to vitelline envelope causes a wave of Calcium release across egg membrane leading to the cortical granules to fuse with the cell plasma membrane and exocytose its enzymes. Proteases break bonds the PM has with the vitelline envelope and forms a fertilization envelope and removes excess sperm. |
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What are the events of egg activation? Provide the mechanism
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Sperm bind egg (either bindin contacts receptor in sea urchin OR sperm and egg membranes fuse in mammals) and causes a wave of calcium release from the endoplasmic reticulum.
MECHANISM: a tyrosine kinase activates Phospholipase C, which cleaves PIP2 into IP3 and DAG. IP3 binds to calcium shuttles on the ER membrane, allows calcium to leave the ER and rush into the cytoplasm. Calcium release can lead to the exocytosis of cortical granule and the inactivation of a MAP kinase |
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How is egg metabolism activated?
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Binding of the sperm can activate a phospholipase C, which leads to IP3 binding to calcium channels in the ER, the influx of Ca into the cytoplasm inactivates a MAP kinase that will lead to the restoration of the mitotic cell cycle. Also DAG leads to the activation of PKA which opens Na/H exchange channels, which causes and increase in the pH of the cell, which can stimulate protein synthesis, DNA replication, and cytoplasmic movements
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How do the pronuclei find eachother?
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After sperm and egg membranes fuse the sperm centriole extends its microtubules and integrates them with the egg’s to form an aster. Then the two pronuclei can migrate toward eachother and fuse.
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What is required for sperm to achieve fertilization in mammals?
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Sperm must undergo capacitation while in the female reproductive tract.
MECHANISM: cholesterol is removed from sperm PM which causes Bicarbonate channels to open and bicarb rushes in. Bicarb binds to adenylate cyclase which forms camp from AMP. cAMP activates PKA which activates Protein Tyrosine Kinsase which, with the help cellular hyperpolarization due K leaving the cell, leads to sperm capacitation |
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Cleavage pattern for Sea Urchin, Snails, Tunicates, Nematodes?
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Sea Urchin: Radial Holoblastic
Snails: Spiral Holoblastic Tunicates: Bilateral Holoblastic Nematodes: Rototational Holoblastic |
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Explain Cleavage in Sea Urchin Embryos
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Radial cleavage separates animal and vegetal poles
-Vegetal containing cells become mesomeres which become macromeres and micromeres -micromeres at the tip of vgetal pole |
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What are the details of the Fate Maps of Sea Urchins?
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• at 60 cell stage, cells are specified but not committed
• animal half gives rise to ectoderm • macromeres give rise to ectoderm, endoderm, coelom (mesoderm), nonskeletogenic mesenchyme • micromeres become skeletogenic mesenchyme and contribute to larval coelom |
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In sea urchin how are skeletogenic mesenchyme cells autonomously determined?
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Maternal determinants Disheveled and B-Catenin are inherited in the vegetal pole and are sequestered in micromeres – help designate micromeres as skeletogenic mesenchyme
-Disheveled prevents degradation of B-catenin -B-catenin combines with TCF txn factor -txn factor OTX and B-catenin/TCF enhance Pmar1 genes -Pmar1 represses HesC, another repressor. so active Pmar1 means no HesC which means activation of genes HesC was repressing -B-catenin/TCF activates txn of Blimp1 -Blimp1 activates paracrine and autocrine signal Wnt8 which will activate txn of the micromere’s own B-catenin genes |
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In sea urchin’s how are cells conditionally specified?
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Micromeres produce paracrine and juxtacrine factors that tell neighboring cells to become endoderm and to invaginate
-an inducing signal called Early Signal (ES) that tell adjacent cells to have nonskeletogenic mesenchyme or endoderm -a juxtacrine protein Delta is activated when HesC is repressed by Pmar1 -Delta activates Notch proteins on adjacent cells -Notch tells cells to become nonskeletogenic mesenchyme |
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In sea urchins, how is the AP axis specified?
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The Animal-Vegetal axis is the AP axis
-Vegetal region has maternal components necessary for posterior development -Ectoderm, endoderm, nonskeletogenic mesenchyme, and skeletogenic mesenchyme line up along the Animal-vegetal (AP) axis |
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In sea urchins, how is the DV or LR axis specified?
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-Sea urchins don’t really have a Left right axis or a dorsal ventral axis but one side of the embryo usually has the origination of the oral pole
-the oral pole originates on the side of the embryo where Nodal is expressed |
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What are the steps of gastrulation in Sea Urchin?
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-Ingression of the skeletogenic mesenchyme
-invagination of the archenteron |
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What mechanisms are used in the sea urchin during ingression of the skeletogenic mesenchyme?
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Micromeres change shape, loose affinity for neighbors and for the hayaline membrane, and gain affinity for proteins that line the blastocoel such as Fibronectin
-micromeres enter the blastocoel -they extend filopodia and eventually fuse into syncytial cables to form spicules -the ectoderm secretes VFGF paracrine factors -the equatorial belt between endoderm and ectoderm has FGF paracrine factor -skeletogenic mesenchyme cells migrate to the points of VEGF and FGF synthesis and align in a ring |
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What are the steps to archenteron invagination in sea urchins?
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-Stage 1: as skeletogenic mesenchyme cells enter blastocoel, cells at bottom flatten and thicken to form a vegetal plate. The vegetal plate invaginates into the blastocoel and stops almost half way. Creating the archenteron and the blastopore.
o Migration is due to actin collecting in apical ends of vegetal cells, thus constricting the ends, causing them to constrict and pucker inward. o 1st group to invaginate are non-skeletal mesenchyme o 2nd layer becomes midgut o 3rd layer becomes the hindgut and anus -Stage 2: extension of archenteron length by changing shape and migrate into a thin sheet by convergent extension -Stage 3: initiated by tension from non-skeletogenic mesenchyme cells at tip of archenteron o They extend filopodia to a specific part of the ventral blastocoel wall and pull the archenteron up o Opening of the archenteron is the mouth o Opening of the blastopore is the anus |
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What is important about spiral cleavage? What animal studied uses it?
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cleavage at oblique angles, forming a spiral arrangement, and form a tighter ball, gastrulation starts after fewer cell divisions
Snails |
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In snails, what controls the orientation of cleavage?
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Maternal cytoplasmic factors such as Nodal, Pitx
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In snails how is the LR axis insuced?
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LR axis is defined by the Nodal family of paracrine factors. Nodal activates genes on the sides of embryos to induce coiling patterns.
-Nodal induces expression of Pitx txn factor in neighboring blastomeres |
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In snails, what 2 ways are cells autonomously specified? Provide an example of each
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1. mRNAs for txn factors and paracrine factors are associated with centrosomes and thus placed in particular cells
-From the four cell stage to the eight cell stage, the production of dpp mRNA is evident at one centrorsome of pair forming mitotic spindle -Dpp attends centrosome in macromere -Dpp (a TGFb molecule) encodes a BMP-like paracrine factor that is critical for development -Dpp specifies a dorsal ventral axis 2. Molecules are bound to the polar lobe region of the egg -Polar lobe is the extrusion of cytoplasm that occurs before the first cleavage -Polar lobe is inherited by only one of two daughter cells – ends up in only the D blastomere -Polar lobe is responsible for autonomously inducing endoderm and mesodermal organs -Contains determinants for proper cleavage rhythm and cleavage orientation of D blastomere -Polar lobe is responsible for turning on a MAP kinase which is required to specify the cell fates of adjacent cells Contains determinants needed for specifying dorsal ventral axis |
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What are the mechanisms of gastrulation in Snails?
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Epiboly
micromeres at animal cap multiply and overgrow the vegetal macromeres, leaving only a small blastopore slit at the vegetal pole |
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What is important about cleavage in Tunicate?
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• First cleavage plane establishes the earliest axis of symmertry in the embryo, separating it into left and right axis
• Asymmetrical cleavage, posterior blastomeres are always smaller than anterior cells • CAB (centrosome-attracting body) directs asymmetrical cleavage and attracts particular mRNAs so that those mRNAs are placed in posterior most cell o Integrates cell patterning with cell determination |
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In tunicates, what establishes the LR axis?
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The first cleavage defines the LR axis, Nodal becomes expressed in left side epidermis of the tunicate.
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In tunicates, explain the structure of the oocyte and what happens upon fertilization? What are the cell fates?
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-Oocyte has central gray cytoplasm that is surrounded by a yellow cortical layer. A clear substance (chorion) accumulates around the yellow cytoplasm
-Upon sperm entry, yellow and clear cytoplasms move to the vegetal hemisphere. The male pronucleus migrates up along the future posterior, yellow cytoplasm migrates with it, forming a yellow crescent -Movement depends on microtubules and a calcium wave • Yellow crescent becomes tail muscles or mesoderm • Clear cytoplasm becomes ectoderm • Slate gray become endoderm • Light gray become neural tube and notochord |
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In tunicates, which cells are autonomously specified and how are they specified?
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Gut endoderm, muscle, and ectoderm are all autonomously specified
Yellow cytoplasm contains the maternal elements needed to form certain tissues by selectively activating or inactivating genes -Muscle: The mRNA encoding Macho1 txn factor is high in vegetal hemisphere and migrates with the yellow crescent into the posterior vegetal region. Macho1 gives rise to muscle cells -Endoderm: localization of B-catenin (a txn factor) in the vegetal pole activates the synthesis of endoderm txn factors |
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In tunicates, what cells are conditionally specified and how are they specified?
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Heart, neural chord, and nervous system
Posterior muscle cells are specified by interactions with endoderm cells -FGF is secreted by the endoderm cells -Macho1 and FGF: gives no notochord induction and instead you get muscle and mesenchyme - No Macho1 and FGF – you get nerve chord and notochord -FGF only – activates cascades that block muscle formation and you get endoderm |
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In tunicates, how is the DV axis determined?
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The cap of cytoplasm at the vegetal pole is filled with stuff involved in cell specification
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in tunicates, how is the AP axis determined?
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AP axis is determined during migration of oocyte cytoplasm
o Vegetal cap is repositioned to the posterior region of the embryo |
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What are the 5 mechanisms for gastrulation in tunicates?
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• Invagination of the endoderm,
o Constriction of vegetal margin of cells • involution of mesoderm, o mesoderm cells involute over blastopre lips, and move inside the embryo • epiboly of ectoderm that brings close at the bottom and forms a blastopore • elongation along AP axis • convergent extension seen in intercalation and migration of notochord cells, it extends along the AP body axis |
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How is cleavage different in nematodes?
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-asymmetrical division produces differentiated descendants and stem cells
-fist division is along the ap axis forming an anterior founder cell and a posterior stem cell -founder cell = EMS |
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In nematodes, how is the AP axis determined?
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the elongated axis of the egg defines AP axis
-position of sperm pronucleus determines posterior pole -sperm enters and initiates cytoplasmic movements -PAR proteins and sperm protein CYK4 activates GTPases in egg that activates the eggs actin to move PAR3 and MEX5 proteins anteriorly and PAR2 posteriorly. -PAR proteins localize P-granules (tln factors responsible for germ cell specification) in the posterior end so they only enter the posterior stem cell line and eventually designate the gametes of the adult |
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in tunicates, how is the DV axis specified?
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Division of the AB cell causes squeezing that causes the posterior founder cell to slide above the EMS cell – the cell that slid becomes the future dorsal side and the EMS cell becomes the ventral side
-Maternal APX-1 (DELTA) is sequestered in the posterior cells binds to protein GLP-1 (NOTCH) on anterior founder cells -Initiates the dorsal ventral axis |
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In tunicates, how is the LR axis specified?
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when MS blastomere contacts half of the grandaughters of the ABa cell which distinguishes the left side of the body
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In tunicates, what are the mechanisms of autonomous specification?
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Posterior Stem cell lineages contain cytoplasmic factors from the P-granules that are localized in the posterior cells
-Maternally expressed SKN-1 can control the fate of EMS blastomere (becomes the posterior pharynx) -Maternal protein POP-1 -Maternal protein PAL-1 |
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In tunicates, what are the mechanisms of conditional specification?
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-In EMS cell, maternal protein SKN-1 activates MED-1 and MED-1 (txn factors)
-Maternal protein POP-1 inactivates MED-1 and MED-2 preventing the cells from having an endodermal fate. POP-1 activates TBx-25 txn factor in MS cell. -TBX-25 activates PHA-4 and HLH-1 necessary for determining Pharynx and Muscle (mesoderm) -TBX-25 inactivates maternal protein PAL-1 -PAL-1 txn factor is responsible for activating genes for ectoderm -Maternal APX-1 (DELTA) is sequestered in the posterior cells binds to protein GLP-1 (NOTCH) on anterior founder cells -Initiates the dorsal ventral axis -Maternal paracrine factor MOM-2 (Wnt) is sequestered in the posterior stem cells, and binds MOM-5 (frizzled) on the EMS cell |
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what is important about nematode gastrulation?
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occurs early, cells migrate from ventral side to center where they divide and form a gut
cells fuse together to form syncytial cells containing many nuclei |
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define fertilization
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fusion of the gametes
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define cleavage
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cell divides into blastomeres
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define blastomere
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cell that makes up an early embryo
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define blastula
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the whole clump of blastomeres
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define gastrulation
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blastomeres rearrange forming three germ layers
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define organogenesis
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cells interact and form tissues
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define metamorphosis
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larva mature
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gametogenesis
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gametes are released
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define blastocoel
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fluid filled cavity in blastula
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define blastopore
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point 180 degrees opposite point of entry of sperm where dimple formes
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define holoblastic
pattern of cleavage
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where entire egg is divided into smaller cells
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define meroblastic
pattern of cleavage
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where part of egg becomes embryo and other part is the yolk used for nutrition
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define mesoderm
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cells migrating through the blastopore, become connective tissue, blood, heart, skeleton, gonads, kidneys
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define ectoderm
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cells on outside enclosing entire embryo... becomes epidermis, brain and nerves
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define endoderm
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large yolky cells that become the gut, respiratory system
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define somites
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become the back muscles, spinal vertebrae, and dermis
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define notochord
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rod of mesoderm in most dorsal portion of embryo, signals ectodermal cells above it that they are not becoming epidermis but will form a tube to become nervous system, cells transform into neural tube
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define oviparity
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born from eggs
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define vivparity
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live birth
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define oviviparity
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egg that hatches inside
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comparitive embryology
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how anatomy changes during the development of different organisms
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what are the two major cell types in an embryo?
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epithelial (tightly connected in sheets or tubes) and mesenchymal (unconnected and operates as independent units)
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what is a chimeric embryo
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can create embryos in which the same organism contains cells with different genetic constitutions
allow identification of structures arising from donor tissue and which is from host
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what is vital dye staining vs. fluorescent dye
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apply dye to region of interest
allows you to trace the fates of different areas
dyes can become diluted after each cell division and become more difficult to see
fluorescent dye is intense and doesnt fade
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what is a transgene
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infect the cells of an embryo with a virus whose genes have been altered such that they express the gene for a fluorescently active protein
altered gene is a transgene because it contains DNA from another species
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what is the difference between homologous structures and analogous structures
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homologs - are similarities that arise from being derived from a common ancestor
analogs - are similarities that arise from performing a similar function rather then arising from a common ancestor |
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what is genomic equivalence... how do we know
it means that the genes are the same in every cell type
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somatic cell (cloning) nuclear transfer
-a single differentiated cell can direct the development of all organs
-put the nucleus of one cell in another cell and you get a clone.
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are cloned animals normal
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no
-many developed diseases due to differences in methylation between chromatin of zygote and of the differentiated cell -differences in size and temperament |
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how do we get differential gene transcription
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all cells have the same genes, how do we get different tissues
- histones tightly bound means no txn -tissue specific genes are activated by local interruption of histone repression - histone tails can be methylated, phosphorylated, acetylated, or ubiquitinated, loosening histones, activating txn |
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what is the structure of a eukaryotic gene
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promoter (where RNA polymerase binds and txn initiates)
TATA box AUG is the tln start site transcript contains introns and exons stop sequence |
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How can translation of specific transcripts be blocked?
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Bicoid can act as an activator or a repressor
-bicoid can bind to specific 3’UTR regions and block the assembly of ribosome recruitment factors -bicoid is prevalent in anterior region of embryo, therefore it blocks posterior genes from being translated in the anterior |
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What are micro RNAs and how do they work?
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Small RNA complements of a specific message of mRNA
They regulate translation by binding to matching regions of mRNA and prevent translation |
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what is selective affinity?
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endoderm has positive affinity for mesoderm and negative affinity for ectoderm cells, and they change during development
cells arrange to minimize surface tension and have proteins with different affinities |
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what are cadherins?
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calcium dependent adhesion molecules that establish and maintain intercellular connections
important for spatial segregation of cells interact with cadherins on other cells |
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what are the four families of paracrine factors?
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1. FGF
2. Hedgehog 3. Wnt 4. TGF-b |
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how does the RTK pathway work? example
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binding of the ligand leads to autoposphorylation of the tyrosine kinase receptor
an adaptor protein is activated adaptor protein activates an intermediate protein intermediate protein activates RAS by exchanging GDP for GTP RAS activates Raf Raf activates Mek Mek activates Erk Erk enters the nucleus and posporylates a txn factor Active or inactive txn facto regulates txn MITF and melanocyte migration |
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how does the JAK-STAT pathway operate? example
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prolactin bind to receptor
JAK protein bound to receptor is phosphorylated JAK2 phosphorylates STAT5 STAT5 dimerizes with itself and enters the nucleus STAT5 dimer binds to specific regions of DNA Binding to DNA activates txn of casein gene FGFR3 uses a JAk-STAT receptor to activate growth factors in gartilage growth |
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how does the Hedgehog pathway operate? example
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hedgehog protein binds to receptor patched
patched is normally bound to a signal transducer called smoothened thus inhibiting it Patched releases smoothened and it is now active Smoothened inactivates PKA and Slimb -with these inactive they can no longer phosphorylate Ci which acts as a repressor Ci can enter the nucleus and act as a txn activator Sonic hedgehog is expressed in nervous system and gut and limb buds |
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explain the 3 pathways that Wnt operates? Example?
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Wnt ligand binds to frizzled receptor
Frizzled activates disheveled Disheveled binds to a prickie wichis is bound to the PM Disheveled then activates Rac and RhoA which coordinate the cytoskeleton and regulate gene expression Wnts can also bind frizzled, which causes the release of Ca, which leads to calcium dependent gene expression Wnts can also bind to receptor firzzled Frizzled activates disheveled Disheveled will inhibit GSK3 GSK3 can no longer prevent dissociation of b-catenin from APC Therefore b-catenin is free to associate with TCF TCF and B-catenin activate txn Important in kidney development and female sex determination |
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explain the pathway for tgf-b operation?
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TGFB ligand binds to type 1 and type 2 receptors
Type 2 receptors phosphorylates the type 1 receptor Type 1 receptor phosphorylates smad Smad is active and regulate txn |
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explain the notch pathway? Example
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delta, serrate, or jagged can bind to notch on adjacent cell
notch changes its conformation cytosolic region of notch is cleaved by a protease the cleaved region enters the nucleus and binds to a txn factor activates txn notch is important for specification of vulva in the nematode fibronectin is a notch protein |
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in drosophila how is the egg activated
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before fertilization
at ovulation, calcium channels are opened allowing meiosis to resume |
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explain fertilization of drosophila
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sperm enters the already organizing egg through the micropyle, a hole at the dorsal anterior region. the entire sperm, including tail must enter the egg before pronuclear fusion can occur
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how is polyspermy prevented in drosophila
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sperm have very long tails to compete with other sperm
the micropyle can only fit one sperm at a time no cortical granules |
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what is the cleavage pattern for drosophila
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superficial cleavage, a large mass of centrally located yolk confines cleavage to the cytoplasmic rim of the egg
karyokinesis occurs without sytokinesis to produce a single cell with many nuclei |
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which species studied has pole cells
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drosophila
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explain cellurization.. what species... basic steps
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drosophila
during nuclear division, about 5 nuclei reach the surface of the posterior pole of the embryo. they become enclosed by cell membrane and generate the pole cells (eventually give rise to gametes) later, the oocyte plasma membrane folds inward between the nuclei, eventually partitioning off each somatic nucleus into a single cells later the rate of invagination increases at the basal end of the cell |
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what is a mid-blastula transition
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when maternal mRNAs are degraded and zygotic mRNAs are put into use
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what are the steps to drosophila gastrulation
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1. mid-blastula transition
2. mesoderm folds in to produce the ventral furrow (becomes a ventral tube) 3. endoderm invaginates to form ant and post ends of ventral furrow 4. pole cells are internalized along with endoderm 5. fromation of the cephalic furrow 6. ectoderm undergo convergetn extension as they migrate toward ventral midline to form a germ band 7. segmentation begins and germ line retracts |
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how is the anterior-posterior axis specified in drosophila
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specified before fertilization
oocyce nucleus moves to the posterior end and synthesizes gurken, which binds to torpedo receptors on posterior follicle cells, thus stimulating their differentiation into posterior follicle cells posteior follicle cells activate PKA that orients the MTs so they grow towards the posterior end then nucleus migrates along MTs toward the anterior end and dynein motor protein moves bicoid mRNA (from nurse cells) along MTs towards anterior end while kinesin moves nanos mRNA (from nurse cells to posterior end) kinesin motor protein also moves oskar mRNA along MTs toward posterior end oskar binds to nanos mRNA and activates txn of Oskar protein |
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how is the dorsal ventral axis specified in drosophila
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before fertilization
after posterior follicle cells are activated and active MT growth, the nucleus migrates along the MTs toward the anterior end and closer to the dorsal surface gurken is synthesised by the nucleus and reaches follicle cells along dorsal axis - signaling them to become dorsal follicle cells torpedo receptor inhibits pipe expression, a protein that is made in ventral follicle cells |
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what is the mechanism for dorsal ventral patterning in drosophila?
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dorsal cells recieve gurken,
which binds to torpedo, which inhibits expression of Pipe in ventral cells pipe is expressed pipe activates nudel Nudel activates factor x factor x activates gastrulation defective (gd) gd activates snake snake activates easter easter activates spatzle spatzle actives toll toll activates tube and pelle tube and pell phosphorylates cactus bound to dorsal cactus is inactivated and dorsal is activated dorsal enters the nucleus and activates genes for ventralization |
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What initiates gastrulation in drosophila?
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Dorsal in the ventral length of the embryo activates snail, twist, rhomboid, fgf8, and the fgf8 receptor.
Dorsal inhibits proteins that encode for dorsal structures |
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what regulates the left right axis in drosophila?
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actin microfilaments
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what are the steps of gene signaling in segmentation and AP axis specification in drosophila?
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maternal gradients activate or inactivate Gap genes
gap genes activate pair rule genes pair rule genes activate segment polarity genes segment polarity genes regulate homeotic genes |
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what are the maternal genes important for AP specification and segmentation in drosophila?
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1. maternal genes bicoid and nanos are transported on microtubules to be concentrated in anterior and posterior respectively
2. bicoid activates translation of maternal protein hunchback and inactivates translation of maternal protein caudal caudal and hunchback mRNAs are distributed throughout the oocyte nanos inactivates tln of gap gene hunchback 3. maternal protein torso generates unsegmented extremities of the anterior posterior axis – torso is an tyrosine kinase receptor torso-like protein activates torso in the anterior and posterior regions of the oocyte membrane. Products of the RTK pathway diffuse into cytoplasm and inactivate groucho Active groucho (inactive in terminal regions) inhibits two gap genes that specify termini of the embryo |
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what is a morphogen?
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substances that differentially specify the fates of cells by different concentrations.
Exmple = bicoid (concentrated in anterior leads to formation of head and trunk structures) |
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how do gap genes work? Give an example of one?
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gap genes are either activated or deactivated by the maternal protein gradient. Then levels of gap genes inactivate and regulate other gap genes
their inhibitory relationships arrange their expression in parasegments example = hunchback, tailess, emty spiracles, kruppel |
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how do segment polarity genes work? Give an example
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mediates intreactions between cells by reinforcing the parasegmental periodicity established by earlier txn factors and by establishing cell fates within each parasegment
each parasegment has only one cell that expresses wingless (wnt) and one cell that expresses hedgehog this is regulated by engrailed engrailed expressing cells form the anterior boundary of each parasegment engrailed is active in cells that will express hedgehog the expression of engrailed is dependent on the concentrations of the pair rule genes engrailed, wingless, cubitus interruptus, hedgehog, patched |
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how do homeotic genes work? Give an example
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• pair rule and gap genes interact to regulate the homeotic selector genes
o gap genes hunchback and kruppel repress expression of homeotic AbdA and AbdB genes. Inhibition prevents these genes from specifying abdomen in the head and thorax. • Expression is refined and maintained by interactions whereby their protein products prevent the transcription of neighboring hom-c genes • homeotic genes have an antennapeida complex and a bithroax complex • together the AC and the BC make the HomC or the homeotic gene complex o Gap gene hunchback activates homeotic antennapedia gene o The genes are arranged in the same order as their transcriptional expression • homeotic genes specifiy the characteristic structures of each segment |
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what forms of cleavage do amphibians and zebra fish employ?
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amphibians:
radial holoblastic zebra fish: discoidal meroblastic |
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what drives ectoderm epiboly in amphibians and zebrafish?
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amphibians:
expansion and cell division differential cell cohesion fibronectin along blastocoel zebrafish: pulled by yolk |
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what is the organizer in amphibians? zebrafish?
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amphibians: dorsal lip of the blastopore
zebrafish: embryonic shield |
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how is the organizer specified in amphibians? zebrafish?
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amphibians: Dorsal signal, B-catenin accumulates by gray crescent due to inhibition of GSK3 inhibitor disheveled. B-catenin combines with tcf3 and they activate twin and siamois. they enhance txn of goosecoid, chordin, noggin, frzb, and cerberus. Vegetal signal, TGFb like proteins VegT and Veg1 are sequestered in the vegetal hemisphere, they activate low levels of nodal-like in absence of b-catenin and high levels of nodal-like in prescence of b-catenin. high levels of nodal-like leads to creation of the organizer
Zebrafish: b-catenin combines with TCF3 that will activate FGF, a BMP inhibitor, Squint (nodal-like), and bozozok (siamois) which is a BMP and Wnt inhibitor. bozozok and squint activate organizer genes like chordino, goosecoid, noggin and dickkopf |
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what does the organizer tissue become in amphibians? zebrafish?
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dorsal and neural tissue
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what are the functions of the blastocoel
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permits migration during gastrulation
prevents the cells beneath it from interacting prematurely with cells above |
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anterior genes
posterior genes dorsal genes ventral genes |
anterior:
Wnt inhibitors: cerberus, dickkopf, frzb IGF cyp26 (RA inhibitor) BMP inhibitors Posterior: BMP (follistatin, noggin, chordin) Wnts FGF RA OTX |
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left right patterning in amphibians and zebra fish
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nodal is expressed in the left side of the embryo
nodal turns on pitx2 |
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what is the nodal structure in zebra fish
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kupffers vessicle has cilia that control left right asymmetry. nodal cilia beat in clockwise manner
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what type of cleavage in chick embryos
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discoidal meroblastic
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what are the steps to chick gastrulation
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1. islands of hypoblast cells and a congregation of hypoblast cells around Koller’s sickle.
2. just prior to primitive streak formation, the hypoblast island cells have coalesced to form the primary hypoblast layer, which meets endoblast cells and primitive streak cells at Koller’s sickle. 3. the secondary hypoblast cells migrate anteriorly. 4. the primitive streak cells form a third layer that lies between the hypoblast and epiblast cells. 5. the primitive streak has become a definitive region of the epiblast, with cells migrating through it to become the mesoderm and endoderm. 6. primitive streak lengthens toward the anterior end and hensens node at the anterior most point of the primitive streak becomes the head 7.cells migrate through the anterior primitive streak due to FGF signaling (fgf8 repels migrating cells away from the streak) |
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how is the anterior posterior axis determined
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hens reproductive tract rotates the egg and thus the yolk shifts so that its lighter components are under one side of the blastoderm. This side becomes the posterior marginal zone where primitive streak formation begins. The posterior marginal zone produces a Wnt and Vg1 which activate nodal
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what is the chick organizer?
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hensen’s node because its cells become the prechordal plate, they can induce and pattern embryonic axis, and it has the same genes as amphibian organizer and zebrafish (goosecoid)
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how does the chick organizer work?
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secretes BMP inhibitors like chordin, noggin, and nodal to dorsalize the ectoderm and mesoderm
secretes FGF to specify mesoderm, separate mesoderm from neurulation due to a gene called Churchill that activates smads |
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how does the left right axis form in chicks?
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sonich signaling turns on cerberous on the left but not the right
activin signaling is active on right witch blocks sonic left lateral plate expression of nodal which turns on pitx2 |
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what type of cleavage is seen in mammals?
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rotational holoblastic
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what is different about mammalian cleavage?
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compaction occurs where embryos change cell affinity for one another to form a very compact ball. After this the cells pump fluid into the center of the cell mass to give rise to the blastocoel. The blastocoel separates inner cell mass cells on one side and trophoblast cells on the other
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in mammals how is the icm distinct from the trophectoderm?
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on apical cells, there is an unknown signal that inactivates hippo signaling and activates Yap. Yap enters the nucleus and binds to txn factor Tead4 which turns on txn of cdx2, a protein that is present in trophectoderm
in the absence of an apical signal hippo is active and activates lats. Lats phosphorylates Yap which is then degraded and therefore there is no txn of cdx2. No cdx2 leads to specification as inner cell mass. |
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how does gastrulation occur in humans?
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primitive streak forms at the future posterior, migrating anteriorly and then regressing. Ones that go all the way to the bottom will displace hypoblast and become endoderm. Ones ending up in the middle become mesoderm
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how is mouse organizing center different from mammals?
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there are two: the node (needed to make trunk and head, forms primitive streak, secretes chordin) and the AVE (needed to make trunk, blocks nodal in anterior to get head, also expression of genes that block WNT signaling like dickkpof and cerberous, otx required for head formation is expressed anteriorly
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