1. Chapter 47 Animal Development
Nicole Gallup

2. Embryonic Development
Genomes of zygote and differences btwn early embryonic cells determine development
Cytoplasmic Determinants – Uneven distribution of maternal substances in the unfertilized egg
Differences between cells because of their location in the embryo
Cell Differentiation – specialization of cells form and function, caused by gene expression
Morphogenesis – process by which an embryo takes shape and cells are in the appropriate locations

3. Embryonic Stages Fertilization – When Gametes (sperm and egg) unite
Cleavage – Rapid Cell divisions after Fertilization. S phase (DNA synthesis) and M phase (mitosis). Skips protein synthesis
Gastrulation – Morphogenetic phase  Drastic rearrangement of the cells of the blastula. Forms a three-layered embryo with a primitive gut.
Organogenesis – When regions of the three-layered embryo develop into fundamental organs

4. Fertilization Vocab
Acrosomal Reaction - discharge of a sperm’s acrosome when it is near the egg
Acrosome – Vesicle at the tip of sperm, helps sperm penetrate the egg
Fast Block to Polyspermy – Depolarization of egg membrane after sperm binds to vitelline layer. Prevents more sperm from entering
Fertilization Envelope - the changed vitelline layer – prevents other sperm from entering the egg
Slow Block to Polyspermy – Formation of fertilization envelope and other changes, opposite of Fast block, lasts longer

5. Fertilization
Fertilize externally – eggs and sperm are released at the same time.
Sperm touches egg’s jelly coat – triggering release of acrosome – hole is formed in jelly
Acrosomal process forms – protrudes from sperm, penetrates jelly coat, binds to receptors on egg cell – aka acrosomal reaction
Hole made in vitelline layer – allows contact and fusion of gamete plasma membranes – membranes depolarize forming Fast block
Sperm nucleus enters cytoplasm of egg – then slow block forms

7. Cleavage Vocab Blastomer – smaller cells that the embryo divides into
Morula – cluster of cells after the first 5-7 divisions
Blastocoel – a fluid filled cavity
Blastula – hollow ball of cells
Yolk – stored nutrients – distributed differently in all embryos
Vegetal Pole – The pole that the yolk is most concentrated
Animal Pole – Opposite pole, very little yolk

8. Cleavage
After fusion of gametes cytoplasm rearranges forming 1 body axis. Other axes form later
First 2 divisions are meridional (Vertical) = 4 blastomers of equal size
Third division is equatorial (Horizontal) = 8 blastomers of unequal size – Animal hemisphere = small cells, Vegetal hemisphere = lager cells
Blastula is located in the Animal Hemisphere

10. Gastrulation Vocab Gastrula – 3 layered Embryo
Germ Layers – The 3 layers produced.
Ectoderm – Outer layer
Endoderm – Inner Layer
Mesoderm – Partly fills space between Ecto and Endo
Invagination – When cells fold inward
Archenteron – Primitive Gut
Blastopore – Opening in the archenteron, develops into the anus.

11. Gastrulation
Complicated mechanics – Large amount of yolk & blastula is more than 1 cell thick
Begins on back side of Blastula – cells begin to invaginate in the line along the region
Dorsal Lip – The Dorsal side of the blastopore
Lip extends and invagination continues until the two ends on the blastopore meet on the ventral side
Involution – When future endoderm and mesoderm cells on the surface roll over edge of the lip into the interior of the embryo

12. Gastrulation
Inside – cells move away from blastopore and become germ layers and blastocoel collapses
Yolk Plug – Large food-laden endodermal cells surrounded by blastopore
End of Gastrulation, circular lip of blastopore encircles plug, cells on surface becomes the ectoderm
Anus forms from the blastopore and mouth develops at the opposite end.

14. Organogenesis Vocab Notochord – Formed from dorsal mesoderm
Neural Tube – when neural plate curves inward – rolling into itself
Neural Crest – band of cells along border of Neural tube
Somites – Paired blocks of mesoderm lateral to notochord

15. Organogenesis First organs to take shape – neural tube and notochord
Signals from notochord to ectoderm cause ectoderm to become neural plate
Cells from neural crest migrate to all parts of the body – form peripheral nerves, teeth, skull bones
Some somites become wandering cells – go to new locations.
Organogenesis continues – cell differentiation continues to refine organs

16. Neural Plate formation
Neural Tube Formation
Somites

17. Morphogenesis
Major aspect of development in animals – involves movement of cells.
Changes in shape involve reorganization of the cytoskeleton. Cytoskeleton drives cell migration.
Cells that move 1st drag others behind them – directs movement of a sheet if cells
Convergent Extension – morphogenetic movement – cells of tissue layer rearrange, sheets become narrow (converge) and become longer (extend)

18. Extracellular Matrix
Extracellular Matrix (ECM) – Mixture of secreted glycoproteins outside plasma membrane of cells – trigger/guide movement
Some ECMs promote migration, providing specific molecular anchorage for moving cells
Others keep cells on correct paths – inhibiting migration – use nonmigratory cells
Cell Adhesion Molecules (CAMs) – glycoproteins – help cell migration and stable tissue structure
Cadherins – important cell-to-cell adhesion molecule.

19. Developmental Fate of Cells
Development requires a combo of morphogenetic changes and the timely differentiation of cells in specific location
2 general principles
Early cleavage divisions – Embryonic cells must become different from each other
Once initial cells asymmetries are set up, subsequent interactions among the embryonic cells influence their fate – usually causing changes in gene expression

20. A Cell’s Fate
Fate Maps – diagram of embryonic development – reveals future development of individual cells/tissues
A cell’s fate can be changed by moving the cell to a new location
2 Important conclusions
Specific tissues of the older embryo can be attributed to certain early “founder cells”
As development proceeds a cell’s developmental Potential becomes restricted

21. Establishing Cellular Asymmetries
Establishing basic body plan is 1st step in morphogenesis – a prerequisite for the development of tissues/organs
Totipotent – describes a cell that can become any part of an organism
Zygote’s pattern of cleavage affects the fate of cells
Progressive restriction of potency is a feature of development in all animals
The tissue-specific fates of cells in late gastrula are fixed

22. Inductive Signals
Cell division creates cells that differ from each other  the cells then influence each other’s fate (induction)
Pattern Formation – development of an animal’s spatial organization, arrangement of organs/tissues – influenced by inductive signals
Positional Information – Molecular cues – control pattern formation

23. Limbs Limbs begin as bumps of tissue called Limb buds
Buds – consist of a core of mesoderm tissue covered by a layer of ectoderm – 2 organizer locations affect limb’s development
Apical Ectodermal Ridge (AER) – 1 organizer – thickened area of ectoderm at the tip of the bud
Zone of Polarizing Activity (ZPA) – other organizer – block of mesodermal tissue located underneath ectoderm – posterior side of the bud is attached to body

24. Citations http://www.vcharkarn.com/uploads/0/80.jpg