1 CLEAVAGE
Dec 18, 2015
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CLEAVAGE
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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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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.
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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
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Frog
7http://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 crescent2. Major axes of embryo3. Position of dorsal lip4. Position of first cleavage
furrow
Wilhelm Roux, 1885
L R
Ant
Pos
Dor
Ven
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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?
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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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A
V
A
V
Sagittal view
View of animal pole
View of vegetal pole
STARFISH CLEAVAGE - EQUAL HOLOBLASTIC
IIIIIIIIVV
~32 cell stage
Meiosis complete at ovulation Isolecithal, oligolecithal, microlecithal egg
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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
II
2 cell stage4 cell stage
IIIII
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 telolecithalFrog blastula
18 hr
A
V
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Structure of the chicken (bird) shelled egg
Polylecithal or megalecithal egg (huge amount of yolk)
Blastodisc
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AVIAN CLEAVAGE - DISCOIDAL
IIIIIIIIVV
Yolk
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
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A
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Polyinvagination
Delamination
Movie of delamination in digital lab manual
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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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19http://www.erin.utoronto.ca/~w3bio380/lecture/Lect11/L11.htm
Human embryo cleavage and cavitation.