Bio 110 Lec Chapter 47 Animal Development

Front 1

Preformation

Back 1

- early view for how animal dveloped from egg

- embryo contained all of its descendants as a series of successively smaller embryos w/in embryo

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Epigenesis

Back 2

- early view for how animal developed from egg

- originally proposed by Aristotle

- embryo gradually emerged from a formless egg

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Acrosomal reaction

Back 3

- first part of fertilization

(1) sperm comes into contact with egg's jelly coat

(2) acrosmal vesicle in head of sperm releases hydrolytic enzymes via exocytosis

(3) acrosomal process (in head of sperm) elongates, penetrating jelly coat

(4) protein coating tip of process attaches to specific receptors on vitelline layer (just external to plasma membrane), providing specificity for fertilization

(5) enzymes of acrosomal process digest vitelline layer materials

(6) tip of proess contacts egg plasma membrane, and sperm and egg's plasma membranes fuse

Front 4

Fast block to polyspermy

Back 4

- when sperm and egg plasma membranes fuse, sperm nucleus enters cell

- causes depolarization of plasma membrane that prevents other sperm cells from uniting with the egg

Front 5

Cortical reaction

Back 5

- second part of fertilization

- changes in egg's cortex caused by fusion of egg and spem membranes

(1) signal transduction pathway causes release of Ca2+ from egg cell ER

(2) signal transduction pathway also causes IP3 to be produced, which opens ligand-gated calcium channels on ER

(3) Ca2+ concentration increases, activating cell, and sperm cnucleus within the egg merges with egg nucleus -> DNA replication

(4) cortical granules in egg fuse with plasma membrane and release their contents into the perivitelline space outside

(5) fertilization membrane prevents entry of additional sperm

Front 6

Cortical granules

Back 6

- special vessicles of egg, contents include:

- enzymes which separate vitelline layer from plasma membrane

- mucopolysaccharides which produce an osmotic gradient -> stimulates osmosis in perivitelline space, causing it to swell

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Fertilization membrane

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- when perivitelline space swells, vitelline layer is elevated

- vitelline layer hardened by granule enzymes

- prevents entry of additional sperm

Front 8

Slow block to polyspermy

Back 8

- consists of fertilization mmbrane and other changes to egg's surface

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Zona pellucida

Back 9

- location on egg capacitated (enhanced, motile) sperm cell must reach for process to continue

- extracellular matrix of egg

- network of cross-linked filaments formed by different glycoproteins

(1) ZP3: acts as a sperm receptor by binding to complementary molecule on surface of sperm head -> stimulates acrosomal reaction -> acrosomal rxn exposes a sperm membrane protein that binds and fuses with egg membrane

Front 10

Cleavage

Back 10

- succession of rapid mitotic cell dvisions that partitions the zygote into many smaller cells: G1 and G2 virtually skipped

- first part of establishing animal body plan

- very little gene transcription occurs, embryo does not grow

- first two divisions are vertical -> divide embryo into four, then eight cells

- deuterostomes have radial cleavage -> upper tier arranged directly over lower

- protostomes have spiral cleaveage -> UT aligned with grooves in between cells on lower tier

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Blastomeres

Back 11

- smaller cells comprising zygote cytoplasm

- each has a nucleus

- cytoplasm is heterozygous, so differing cytoplasmic components

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Yolk

Back 12

- stored nutrients in egg

- yolk gradient is a key factor in determining polarity and cleavage factor in frogs and other animals

- large amounts impede cell division: animal hemisphere cells smaller than vegetal for amphibians

- in sea urchins and many others, blastomeres about equal due to small amounts of yolk

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Vegetal pole

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- has higest concentration of yolk

- in frogs, vegetal hemisphere is light yellow due to yellow yolk

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Animal pole

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- opposite vegetal pole

- has lowest concentration of yolk

- where polar bodies are budded from cell

- marks anterior part of embryo

- in frogs, animal hemisphere is gray due to presence of melanin granules in outer cytoplasm

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Gray crescent

Back 15

- At fertilization, plasma memberane and outer cytoplasm of amphibian eggs rotate towards point of sperm entry

- may be due to reorganization of cytoskeleton arond centriole introduced bnby sperm

- gray crescent is located near egg equator, on side opposite sperm entry

- if equally distributed during cleavage, will develop into two tadpoles

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Morula

Back 16

- solid ball of cells resulting from continuation of cleavage

Front 17

Blastocoel

Back 17

- fluid-filled cavity that develops within morula as cleavage continues

- centrally located in blastula in sea urchins due to equal cell divisions, otheriwise, in animal hemisphere

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Blastula

Back 18

- hollow ball of cells resulting from blastocoel

Front 19

Meroblastic cleavage

Back 19

- when cleavage is confined to a small disc of yolk-free cytoplasm at animal pole

- in eggs with large amounts of yolk (birds, reptiles

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Holoblastic cleavage

Back 20

- when complete division of eggs occurs

- little to moderate amounts of yolk

Front 21

Gastrulation

Back 21

- rearrangement of cells that transforms blastula to a three-layered embryo

- cellular changes occur: in motility, cell shape, and cellular adhesion to other cells and molecules of ECM

- some cells move to a more interior location

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Gastrula

Back 22

- three-layered embryo with primitive gut

Front 23

Ectoderm

Back 23

- outermost layer of gastrula

- result in nervous system (from neural crest along border where neural tube breaks off) and outer layer of skin

- forms from cells remaining on surface after involution, aside from yolk plug

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Endoderm

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- lines archenteron

- results in lining of digestive tract and associated organs (e.g. liver, pancreas)

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Mesoderm

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- partly fills space fbetween ectoderm and endoderm

- results in kidneys, heart, muscles, inner layer of skin, and mosto other organs

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Invagination

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- in sea urchins, when vegetal pole cells form a flattened plate that buckles inward in gastrulation

- in frogs,when cluster of cells buries inward

- invaginated plate undergoes rearrangement to form archenteron

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Archenteron

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- primitive gut

- has blastopore and second opening that will form mouth end of rudimentary digestive tube

- in sea urchins, results into ciliated larva afterwards

Front 28

Blastopore

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- where archenteron opens to surface

- will beome anus

- in frogs, small crease forms on blastula where blastopore will form

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Dorsal lip

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- upper edge of blastopore that results from external tuck of invagination

- forms where gray crescent was originally located

- Spemann and Mangold discovered it acts as a primary organizer: sets up interact in between chordamesoderm and overlying ectroderm

- chordamsoderm -> notochord, when transplanted neural plate will develop in abnormal location

Front 30

Involution

Back 30

- in which cells on surface of embryo roll over dorsal lip and move into the embryo's interior away from the blastopore

- cells continue to migrate along the blastocoel

-> organization and layering of migrating internal cells, into mesoderm and endoderm

- wider blastopore lip eventually forms a complete circle

Front 31

Yolk plug

Back 31

- group of large, food-laden cells from the vegetal pole

Front 32

Organogenesis

Back 32

- development of rudimentary organs from germ layers

- first evidence is morphogenetic changes (folds, splits, condensation) in layered embryonic tissues

- in frogs, end result is an aquatic, herbivorous tadpole

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Notochord

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- in chordates

- dorsal mesoderm above archenteron condenses

- elongates, stretching embryo lengthwise

- functions as core around which mesoderm cells forming the vertebrae gather

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Neural tube

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- ectoderm above notocord thickens to form neural plate

- neural plate sinks and rolls itself into a neural tube

- will form brain and spinal chord

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Somites

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- blocks of mesodermal cells from which vertebrae and axial skeleton muscles develop

- arises from condensed stips of mesoderm lateral to notochord

Front 36

Amniotes

Back 36

- embryos which develop in amnion or fluid-filled sac in uterus

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Blastodisc

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- cap of divided yolk-free cytoplasm that rests on large undivided yolk mass

- equivalent to hollow ball stage in frogsd

Front 38

Primitive streak

Back 38

- in avian development, groove produced by movement of epiblast (upper of blastocoel) cells towards midline of blastodisc, then detachment and inward movement towads yolk

- located in upper cell layer along anterior-posterior axis

- some cells in epiblast move from primitive streak -> blastocoel to form mesoderm; others ionvade hypoblast and contribute to endoderm

- hypoblast cells segregate from endoderm

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Extraembrionic membranes

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- in avians, primary germ layers form four: yolk sac, amnion, chorion, and allantois

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Yolk sac

Back 40

- encloses a fluid-filled cavity but no yolk

- membrane is site of early blood cell fomaion -> cells later migrate to endryo

Front 41

Amnion

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- forms as a dome above epiblast

- encloses embryo in a fluid-filled cavity

Front 42

Chorion

Back 42

- in humans, forms trophoblast

- surrounds embryo and all extraembryonic membranes

Front 43

Allantois

Back 43

develops from outpocketing of gut

- develops from outpocketing of gut- is incorporated into umbilical cord, where it forms BV that transport oxygen and nutrients from placenta to embryo and waste productsfrom embryo to placenta

- is incorporated into umbilical cord, where it forms BV that transport oxygen and nutrients from placenta to embryo and waste productsfrom embryo to placenta

Front 44

Blastocyst

Back 44

- 100 cells around a cetral cavity, forms around 7 days post-fertilization

Front 45

Inner cell mass

Back 45

- protrudes into one end of cavity

- will develop into embryo and some extraembryonic membranes

- forms a flat disc with an epiblast and hypoblast similar to birds during implpantation

- epiblast -> embryo, hypoblast -> yolk sac

Front 46

Trophoblast

Back 46

- outer epithelium surrounding cavity

- will form fetal part of placenta with mesodermal tissue

- secretes enzymes that enable blastocyst implantation

- thickens and extends projections into endometrium

- arrangement into trophoblast: no longer totiponet

Front 47

Convergent extension

Back 47

- cells of a tissue layer rearrange themselves such that cell becomes narrower as it lengthens

Front 48

Cell adhesion molecules (CAMs)

Back 48

- substances on a cell surface that contribute to selective association of certain molecules

- vary in amount or chemical identity among various cells -> regulate morphogenetic moveents and tissue building

Front 49

Cadherins

Back 49

- class of CAM that require presence of calcium to function

- expressed in tissue-specific manner as development proceeds

Front 50

Fate map

Back 50

- shows which parts of embryo are derived from each region

- Vogt in 1920s used nontoxic dyes to color amphibian blastula surface -> sectioned embryo

- modern techniques can mark indiviual blastomere and follow it to mitotic descendants, like in C. elegans

- found that (1) certain founder cells generate specific tissue (2) developmental potential of cell becomes limited over time

Front 51

Pattern formation

Back 51

- establishment of body plan is prerequisite to organogenesis

- animal-vegetal: anterior-posterior

- grey crescent: faces dorsal

- left-right: bisected grey crescent

- has molecular basis: bone morphogenic protein 4 (BMP4) exclusively active on ventral side

Front 52

Positional information

Back 52

- control pattern fromation

- set of molecular cues that indicate cell's location relatie to other cells

- provided by regional gradients of polypeptides caused by differential gene expression (e.g. FGF, Sonic hedgehog_

Front 53

Apical epidermal ridge (AER)

Back 53

- produces several proteins of fibroblast growth factor (FGF) family, which serve as inducing signals

- Assign embryonic tissue position along proximal-distal axis (shoulder -> fingertip)

Front 54

Zone of polarizing activity (ZPA)

Back 54

- point of reference for anterior-posterior axis

- releases Sonic hedgehog protein growth factor, inducing signal

- near ZPA: posterior structures (e.g. pinkie) fathest ZPA: anterior structures (e.g. thumb)