1. 1 CLEAVAGE

2. 2 http://biodev.obs-vlfr.fr/recherche/biomarcell/ascidies/Anim-fromegg.htm Ciona intestinalis http://www.mun.ca/biology/scarr/Garstang_Hypothesis.htm http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=.07EmbIt9ELpT-YFA1rDieIO4AMQFlmlIwWj

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4. 4 E. G. Conklin, 1905 - In Styela partida, cells that contain yellow crescent pigment form muscle (mesoderm) http://sdb.bio.purdue.edu/AboutThisSite/conklin.article.html Swalla & Jeffery, 1995 - showed that a maternally derived mRNA was segregated into cells containing yellow crescent pigment.

5. 5 Clear cytoplasm = ectoderm Yellow cytoplasm = mesoderm Dark gray cytoplasm = endoderm Light gray cytoplasm = neural tube and notochord. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=.0f0icUJoQpTbPzZ-do7pAF-n3I2E18sYrYZ

6. 6 Frog

7. 7 http://www.md.huji.ac.il/~yisraeli/embryology/embryo.html Frog 5-10 min after fertilization Second polar body 15-30 min after fertilization Pronuclei will fuse 1.5 - 2 hr after fertilization Point of sperm fusion with egg determines: 1.Position of grey crescent 2.Major axes of embryo 3.Position of dorsal lip 4.Position of first cleavage furrow Wilhelm Roux, 1885 LR Ant Pos Dor Ven

8. 8 1.In some species, the cytoplasm of the zygote is very organized. 2.That maternally derived cytoplasmic information is sequestered into specific cytoplasmic compartments. 3.The end result - maternal mRNAs end up in specific groups of cells - determines those cells eventual fate a.the cells containing the yellow pigment cytoplasm of Stylea’s embryos form muscle b.the cells of the frog embryo that contain gray crescent cytoplasm become the chordamesoderm and eventually the notochord. What do these experiments tell us?

9. 9 1.Decrease cell size 2.Increase cell number - allows for formation of blastocoel in many species by a process called cavitation. 3.In some cases, distribution of maternal cytoplasmic information to specific groups of cells 4.Beginning of Differentiation - as cleavage proceeds, you reach a point where the blastomeres are no longer totipotent 5.Synthesis of embryo derived mRNA for direction of future development begins during cleavage. Mammals - starts after a few cleavage divisions; Frogs - starts during late blastula stage Purposes of cleavage

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11. 11 A V A V Sagittal view View of animal pole View of vegetal pole STARFISH CLEAVAGE - EQUAL HOLOBLASTIC I I II III IV V ~32 cell stage Meiosis complete at ovulation Isolecithal, oligolecithal, microlecithal egg

12. 12 1st - 3.5 hr 2nd - 4.5 hr 3rd - 5.5 hr A Sagittal view View of animal pole View of vegetal pole UNEQUAL HOLOBLASTIC (may be meroblastic cleavage, but not always) Amphibians - meroblastic, unequal starting with 3rd cleavage division V I I 2 cell stage 4 cell stage II III 8 cell stage IV 16 cell stage V 32 cell stage http://www.luc.edu/depts/biology/dev/stages.htm http://www.its.caltech.edu/~bi12/2003/movies/xclvgtop.mov Ovulated as primary oocyte. First meiotic division completed in oviduct, second after fertilization. Mesolecithal vs telolecithal Frog blastula 18 hr A V

13. 13 Structure of the chicken (bird) shelled egg Polylecithal or megalecithal egg (huge amount of yolk) Blastodisc

14. 14 AVIAN CLEAVAGE - DISCOIDAL I I II III IV V Yolk Looking down on the animal pole. Discoidal cleavage is a type of meroblastic cleavage Ovulated as primary oocyte. Meiosis I completed almost immediately after ovulation. Meiosis 2 completed after fertilization. 1st - 3 hr 2nd - 3.5 hr 3rd - 4 hr 4th - 4.5 hr 5th - 5 hr A

15. 15 A

16. 16 Polyinvagination Delamination Movie of delamination in digital lab manual

17. 17 SUPERFICIAL CLEAVAGE - INSECTS pole plasm http://www.luc.edu/depts/biology/dev/insect.htm Superficial cleavage is a type of meroblastic cleavage

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19. 19 http://www.erin.utoronto.ca/~w3bio380/lecture/Lect11/L11.htm Human embryo cleavage and cavitation.