Chapter 11- Fish and mammals
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Transcript of Chapter 11- Fish and mammals
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Chapter 11- Fish and mammals• Zebrafish are becoming the sweetheart of developmental
biologists
Fig. 11.1
• Large broods• Breed year-round• Easy and cheap• Transparent embryos• Develop outside mother• Early development complete in 24 hours
1
6
Blastoderm is perched on a
large ________
1st 12 divisions are sychronous to form _____________
3. ____________ layer (YSL)
Three cell populations1. __________
_____ (EL)
2. ____layer- gives rise to embryo proper
Fig. 11.2
A. Cleavage
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Fig. 11.3
B. Gastrulation
EpibolyDeep cells migrate to outside then encase entire yolk
Movement not by crawling, but by YSL cells expansion and pulling EL cells along
• A ________ is formed either by _________ of superficial cells or by _______• These combine with superficial epiblast cells to form the _______________ (function equivalent of the dorsal lip in amphibians)
1. Enveloping layer (EL)
2. Deep cells
3. YSL cells
hypoblast
epiblastEmbryonic shield
6 hrs post-fertilization
YSL
Recall Epiboly from Ch 9
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Fig. 11.3
B. Gastrulation (cont.)
The hypoblast cells extend in both directions to form the notochord precursor
Animal
Vegetal
Ventral Dorsal
Head
TailTrunk
Fig. 11.2 -A zebrafish fate map
Ectoderm
Mesoderm
Endoderm
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C. Axis formation1. Dorsal ventral axis-
1. Establishes the _______________ axis• Converts lateral/ventral medoderm to
dorsal mesoderm (notochord)• Convert ectoderm to neural rather
than epidermal
2. Forms the ______________ precursor
As with the amphibian __________ (Organizer), the embryonic shield:
B-catenin
samois
goosecoid
BMP inhibitors
e.g. Chordino
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C. Axis formation
Fig. 11.6
1. Dorsal ventral axis-
As with the amphibian dorsal lip (Organizer), the embryonic shield:
4. Acquires its function from _________ accumulation in nearby cells
•B-catenin accumulates in _____ cells •______________is activated
BMP2
3. Secretes proteins to inhibit BMP from inducing ectoderm to become epidermis
•This inhibiting molecule is called ___________• If mutate ________, no neural tube is formed
Chordino
Embryonic shield
B-catenin
samois
goosecoid
BMP inhibitors
e.g. Chordino
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C. Axis formation (cont.)
Fig. 11.6
3. ________________ axis -
In amphibians , the anterior-posterior axis is formed during oogenesisThis axis is stabilized during gastrulation by _____________ ________________________.
_________ neural inducing signal (from ectoderm cells)
__________ neural-inducing signal ( from mesoderm cells)
2. _________________ axis-
Not much known, but involves ______ family signaling molecules
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Mammalian Development
• ______ diameter (1/1000th volume of frog egg!)• Few in number ___________• Develops within mother• Cleavage events take _____ hours each• Development occurs en route to ___________
Tough to study!!
1. Egg released from _____
2. fertilization
3. Cleavage during migration down _________
4. Implant in ______
Fig. 11.20
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Mammalian Development
1. Slow- ______ hrs per cleavage2. 2nd cleavage is ______________3. Marked __________ in early cell
division4. Cleavage at 2nd division requires
newly made ________ from zygote
Distinctions of mammalian cleavage
Fig. 11.21-rotational cleavage in mammals
Fig. 11.23- Compaction at 8 cell stage (______ in humans)compaction
5. ____________ (marked cell huddling) occurs at 8 cell stage
A. Cleavage
Amphibians Mammals
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16 cell embryo is termed “_______”
•external cells will become ___________, which will become the _________•Internal cells will become _____________ (ICM), or the ______________
A. Cleavage (cont.)
This marks 1st differentiation event in mammalian development
At 64 cell stage, an internal cavity appears and the embryo is termed a ___________, ready for implantation onto uterus wall
The ______________ (recall ch. 7) must be shed in order to implant• Blastocyst ____ a small hole in zona using the enzyme _______
Note- attachment of embryo to oviduct wall is called a ______________.
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Similar to __________ and birds
•Mammalian embryo relies on __________ for nutrients, not yolk•Thus, the embryo must have a specialized organ to accept nutrients- called the ___________•The chorion induces uterine cells to become a _________ (rich in blood vessels)
B. Gastrulation
Fig. 11.28- Day 15 human embryo
Hypoblasts (from ICM) line the ________- these give rise to ______________________.
Epiblasts form ______________
blastocoel
hypoblasts
epiblasts
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Mammalian ______ and ______ cells arise from epiblasts that migrate through primitive streak
E-cadherin attachment is mechanism
Fig.11.11- Chick gastrulation- similar to mammalian
Fig. 11.28- Day 16 in human
_____________ _____________
Those cells that migrate through the ____________ will become the _________________.
B. Gastrulation (cont.)
Direction of migration
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Extraembryonic membrane FormationTrophoblast cells (originally termed “cytotrophoblast”) gives rise to multinucleated ____________________
These syncytiotrophoblasts: • secrete proteolytic enzyme to invade
__________________• Digest uterine tissueMothers blood vessels contact the
syncytiotrophoblast cellsEmbryo produces its own blood vessels
Uterine wall
Fig. 11.27-Blastocyst invading uterus
Blood vessels feed embryo, but blood cells do not mix
Mothers blood vessels
Embryo chorion
Mother’s Placenta
Chorion Villi
Embryo’s blood vessels
Fig. 11.31
B. Gastrulation (cont.)
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C. Anterior-posterior axis formation
Two signaling centers1. _______________________ (AVE)2. _________ (Organizer)
Fig. 11.34 These are on opposite sides of a “cup” structure
These work together to form
___________.
Node produces _____ and ________
AVE produces ______ and Otx-1Knock-out of one of these results no
_________
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The Hox genes specify _________________ polarityThese are homologous to _________ gene complex (Hom-C) of __________
Recall that the Hom-C genes are arranged in the same order as their expression pattern on anterior-posterior axis
Mammalian counterparts are clustered on____________________ .
Equivalent genes (Hoxb-4 and hoxd-4) are called a ____________ _________.
C. Anterior-posterior axis formation
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Fig. 11.36- Hox genes are organized in a linear sequences that concurs with posterior to anterior structures
This is referred to as the ___________
C. Anterior-posterior axis formation (cont.)
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Hoxa-3 KO- thymus, ______________ malformed
Hoxa-2 KO- _______ missing, duplicate incus
Incus
Stapes
1. Different sets of Hox genes are required for __________ of any region of the _____________________ axis
Hoxd-3 KO = deformed ______ (1st vertebra)
Hoxa-3/Hoxd-3 _______ KO- atlas and neck cartilage nearly absent
2. Different members of a paralogous group may specify different ___________ in a given region
Hox gene rules
3. A hox gene KO causes defects in the _____________ of that gene’s expression
Example
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Retinoic Acid has a profound effect on development
Structure of retinoic acid (not in textbook)Fig. 10.41
Recall amphibian development (Ch. 10)
RA
Retinoic acid activates mammalian _____ genes
Wild-type mouse embryo
RA-treated mouse embryo
Lacks all distal
vertebra
Retinoic acid is likely produced in the _____, and perhaps more time
spent in the node dictates more ___________
specification
Hox geneRetinoic acid bind a receptor,
then the complex binds promoter of a hox gene
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D. Dorsal-ventral axis formation
Inner cell mass (ICM)
Dorsal axis forms from ICM cells near _____________
Ventral axis forms from ICM cells near _____________
Blastocoel
Fig. 11.32
Trophoblast
E. Left-right axis formation
Note that mammals are ___________
Fig. 11.42
Two levels of regulation-1. Global- an ____ gene defect results
in all ______ on the wrong side
2. Organ-specific- an ___gene defect causes the axis of an organ to change
Organs are located in specific locations