Bio 325 Exam 1 Terminology

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Four Principles of von Baer

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1)General Features of a large group of animal appear earlier in development than do the specialized features of a smaller group.

2) Less general characters develop from the more general, until finally the most specialized appear.

3)The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them

4) The early embryo of a higher animal is never like a lower animal, but only like its early embryo.

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Epithelial Cells

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Tightly connected to one another in sheets or tubes

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Mesenchymal Cells

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Unconnected to one another and operate as independent units

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Cell Lineages

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Following individual cells to see what those cells become

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Fate Map

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"map" larval or adult structures onto the region of the embryo from which they arose

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Ways to study embryos

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Direct observation: Used with embryos with relatively few cells and cytoplasm is distinguishable in different blastomeres

Dye Marking: Vital Dyes, inject in area of cytoplasm but tend to fade as further cell division occurs. Fluorescent Dyes, more intense then vital

Genetic Labeling: Use chimeric embryos. Also you can use a virus to inject DNA for the creation of GFP.

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Neural Crest

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transient band of cells that joins the neural tube and epidermis

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Homologous

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Underlying similarities are derived from common ancestry

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Analogous

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Same function but different ancestry

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Malformation

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Abnormalities caused by genetic events

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Disruptions

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Abnormalities caused by exogenous agents

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Teratogens

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Agents responsible for disruptions

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Selective Affinity

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-inner surface of the ectoderm has a positive affinity for mesodermal cells and negative affinity for the enoderm, while the mesoderm has positive affinities for ectoderm and endoderm

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Differential Adhesion Hypothesis

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if the strength of A-A connections is greater B-B or A-B connections, sorting will occur with A-A being central

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Cadherins

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calcium-dependent adhesion molecules, they are critical for segregation of cell types

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Catenins

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anchor cadherins to cell cyto-skeleton

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Cadherin Related Functions

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1) External Domains serve to adhere cells together
2) cadherins link to help and assemble the actin cytoskeleton
3) can serve as signaling molecules that change a cells gene expression

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Trophoblast Cells

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Outer Cells that bind to uterus

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Inner Cell Mass

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The inner cells that will generate the embryo and eventually the mature organism

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First differentiation in mammalian development

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trophoblasts from inner cells mass

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Induction

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interaction at close range between two or more cells or tissues of different histories and properties

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Inducer

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The tissue that produces a signal that changes the cellular behavior of the other tissue

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Paracrine Factors

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Proteins made by a cell or group of cells that alter the behavior or differentiation of adjacent cells

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Responder

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the tissue that is being induced

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Competence

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The ability to respond to a specific inductive signal

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Wnt 1

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Is a part of the 15 members in gene family in vertebrates. Appears to be active in inducing the dorsal cells of the somites to become muscle and is involved in the specification of the midbrain cells

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Canonical Pathway

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wnt interacts with frizzled protein which binds disheveled. Once disheveled is active it inhibits GSK3(glycogen synthase kinase), if active prevents disassociation of B catenin from APC protein(responsible b catenin degradation) When the wnt pathway is active B catenin can enter the nucleus where it binds to Lef/Tcf protein which activates gene transcription

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Non Canonical Pathways

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Alternative pathways: one offects cytoskeleton by activating disheveled which interacts with Rho GTPase which can activate the kinases that alter the cytoskeleton. Another pathway can activate a phospholipase from frizzled and this can release Ca ions from the endoplasmic reticulum which in turn can activate enzymes, transcription and translation factors

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What is included in the TGF-B superfamily?

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TGF-B family
activin family
Bone Morphogenic Proteins(BMP)
vg1 family and others

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TGF-B family is important for what?

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regulating the formation of the extracellular matrix between cells ands for regulating cell division.

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BMP4

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-can cause bone formation
-can cause cell death
-can specify epidermis

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BMP7

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-important in neural tube polarity, kidney development and sperm formation

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Commitment

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The Cell will become a certain cell type

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Specification

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A cell is capable of differentiating autonomously

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Determination

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A cell is capable of differentiating to autonomously even when its placed in another part of the embryo

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First Mode of Commitment

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Autonomous Specification, the blastomere inherits a set of transcription factors from the egg cytoplasm

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Morphogenetic Determinants

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The cytoplasm is not homogeneous. These things will be at the bottom of the vegetal pole

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Mosaic embryos

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they develop like a mosaic, where each cell develops independently without cell to cell interaction

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Conditional Specification

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the ability of cells to achieve their respective fates by interactions with other cells

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Germ Plasm Theory

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embryo develops autonmously, proven wrong by dividing the embryo

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Morphogen

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Diffusable biochemical molecule that can determine the fate of a cell by its concentration

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Syncytium/syncytial specification

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nuclei divide in the cytoplasm but the cell doesn't divide.

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Gray Crescent

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The region where gastrulation will begin. It gets divided in the first cleavage for many species.

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Morula

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An amphibian embryo containing to 16 to 64 cells

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Two major functions of blastocoel

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1) permits cell migration during gastrulation
2) prevents cells beneath from influencing the cells above it

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Mid-Blastula transition

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different genes begin to be transcribed in different cells, the cell cycle acquires gaps phases, and the blastomeres acquire the capacity to become motile

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VegT

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helps to direct vegtal cells to become endoderm and the cells above it to become mesoderm

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Bottle Cells

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The cells at the grey crescent during the invagination. The main body of each cell is displaced toward the inside of the embryo while maintaining contact with the outside surface by way of slender neck.

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Marginal Zone

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the region surrounding the equator of the blastula. Where gastrulation begins in the frog.

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Vegetal Rotation

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places prospective pharyngeal endoderm cells adjacent to blastocoel immediately above involuting mesoderm

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Dorsal Lip of the blastpore

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Where migrating cells reach and are then involuted. The cells here are always changing

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Prechordal Plate

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precursor of head mesoderm, first cells to involute

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Chordamesoderm

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will form the notochord and the second type of cells to be involuted

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Notochord

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transient mesodermal rod that play an important role in inducing and patterning the nervous system

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yolk plug

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the little piece of vegetal/endoderm cells left but is eventually internalized

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Convergent Extension

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cell movement resulting in tissue elongation via intercalation of adjacent cells in an epithelial sheet to form a narrower, longer strip of tissue.

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What forces drive convergent extension?

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1) polarized cohesion, the involuted mesodermal cells send out protrusions to contact one another
2) differential cell cohesion, specific cadherins become active to place cells
3) calcium flux,

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Noninvoluting marginal zone(NIMZ)

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dorsal portion that doesn't involute extends rapidly toward the blastopore

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Mesodermal Mantle

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remainder of the body mesoderm, that doesn't include noto chord and somites, enters through ventral/lateral lips

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Two major functions of vegetal cells

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1) differentiate into mesoderm
2) induce cells immediately above them to become mesoderm

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What happens when VegT is knocked out?

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VegT activates the zygotic transcription of genes encoding several members of TGF-B superfamily including vg1 and nodals so no mesoderm is induced. endoderm as well is not induced

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Spemann experiment dividing embryo along cleavage

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sides with grey crescent will develop fully

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Which tissue is the only autonomously determined in the early gastrula?

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dorsal blastopore lip

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Organizer

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the dorsal lip cells and there determinants, notochord and head mesoderm, because
1)induced host cells ventral tissues to change there fates to form a neural tube and dorsal mesodermal tissue
2)they organized host and donor tissues into a secondary embryo with clear anterior-posterior and dorsal-ventral axes

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Primary embryonic induction

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key induction where progeny of dorsal lip induce the dorsal axis and neural tube

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Nieuwkoop Center

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dorsal most vegetal cells of the blastula that are capable of inducing the organizer

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What gives the dorsal most vegetal cells their special properties?

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B-Catenin, a multifunctional protein that can act as an anchor for cell membrane cadherins or as nuclear transcription factor, in the embryo by maternal mRNA

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how does B-catenin become localized specifically to the side opposite sperm entry?

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Glycogen synthase kinase 3(GSK3) destroys b-catenin. It can be deactivated by GSK3 binding protein (GBP) and Disheveled. these bothe travel along the micro tubulues and prevent b-catenin destruction on the dorsal side. wnt11 pathway is also necessary.

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What happens if wnt11 is knocked out?

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Organizer fails to form

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Where is wnt11 located in oocyte?

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vegetal cortex

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B-catenin/Tcf3 complex

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converts tcf3 repressor into activator of transcription.

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Tcf3 binding malfunction to b-catenin

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no dorsal structures formed

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twin and siamois

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homeodomain transcription factors and are expressed in the organizer immediately following mid blastula transition. activated by tcf3/b-catenin. initiate formation of the organizer and enode transcription factors for: goosecoid, xlim1, paracrine factor antagonists(Noggin, Chordin, Frzb, Cerberus)

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What if vg1 is depleted?

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lacks notochord and organizer gene expression

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Xbra

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gene encoding a transcription factor that instructs cells to become mesoderm

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nodal gradient

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during late blastula a nodal gradient is expressed throughout the endoderm, low conc. ventral, high conv. dorsal
low concentration =ventral mesoderm
medium conc= lateral mesoderm
high conc= +vg1 become organizer

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Four major functions of the organizer

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1) ability to self-differentiate dorsal mesoderm(pre-chordal plate,chordamesoderm, etc.)
2)ability to dorsalize the surrounding mesoderm into paraxial(somite-forming) mesoderm when it would otherwise form ventral mesoderm
3)ability to dorsalize the ectoderm and induce formation of the neural tube
4)ability to initiate the movements of gastrulation

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four cell types organizer contributes to

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Pharyngeal entoderm, head mesoderm,dorsal mesoderm, and dorsal blastopore lip

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concerning neural tissue and bmp

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1) the "default fate" of the ectoderm is to become neural tissue
2)certain parts of the embryo induce the ectoderm to become epidermal by secreting bmps
3)organizer tissues secretes things that block bmps so surrounding ectoderm can become neural

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BMP inhibitors

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noggin, chordin and follistatin

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noggin major fuctions

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induces dorsal ectoderm to form neural tissue, dorsalizes mesoderm that would otherwise be ventral
bmp inhibitor

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chordin info

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localized in dorsal blastopore lip and later in notochord
bmp inhibitor

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Follistatin

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transciped in lip and notochord, inhibits activin and bmp

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Anti dorsalizing morphogenic protein (ADMP)

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anatgnostic relationship with organizer like bmp

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BMP4 Restricted

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Restricted to the ventral lateral Marginal zone
graded levels of bmp4 activates different genes

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Organizer Specification ability

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specifies brain and spine tissue

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Ectoderm protein combinations

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BMP+WNT= epidermal
WNT alone = trunk and spinal
Blocked both = Head and brain

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Frzb

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binds wnt proteins
excess frzb cause embryo to lack ventral/ posterior structures becomes a big head

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Dickchopf

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interacts directly with wnt
lacks makes deformed heads with no forebrain

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Insulin like growth factor(IGF)

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required for formation of head and neural tube
inserted in ventral mesoderm causes ectopic heads