Chapter 11- Fish and mammals

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Chapter 11- Fish and mammals

• Zebrafish are becoming the sweetheart of
  developmental biologists

• Large broods
• Breed year-round
• Easy and cheap
• Transparent embryos
• Develop outside mother
• Early development complete in 24 hours

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A. Cleavage
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Three cell populations
1st 12 divisions are sychronous to form
_____________
1. __________ _____ (EL)
2. ____layer- gives rise to embryo proper
Blastoderm is perched on a large ________
Fig. 11.1
3. ____________ layer (YSL)
Fig. 11.2
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B. Gastrulation
Recall Epiboly from Ch 9
Deep cells migrate to outside then encase entire
yolk
Epiboly
Movement not by crawling, but by YSL cells
expansion and pulling EL cells along
Embryonic shield
epiblast
1. Enveloping layer (EL)
hypoblast
2. Deep cells
Fig. 11.3
3. YSL cells
YSL
6 hrs post-fertilization

• 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)

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B. Gastrulation (cont.)
The hypoblast cells extend in both directions to
form the notochord precursor
Animal
Head
Ventral
Dorsal
Ectoderm
Trunk
Fig. 11.3
Tail
Vegetal
Mesoderm
Endoderm
Fig. 11.2 -A zebrafish fate map
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C. Axis formation
1. Dorsal ventral axis-
As with the amphibian __________ (Organizer), the
embryonic shield

• Establishes the _______________ axis
• Converts lateral/ventral medoderm to dorsal
  mesoderm (notochord)
• Convert ectoderm to neural rather than epidermal

B-catenin
samois
goosecoid
2. Forms the ______________ precursor
BMP inhibitors e.g. Chordino
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C. Axis formation
1. Dorsal ventral axis-
As with the amphibian dorsal lip (Organizer), the
embryonic shield

• 3. Secretes proteins to inhibit BMP from inducing
  ectoderm to become epidermis
• This inhibiting molecule is called ___________
• If mutate ________, no neural tube is formed

B-catenin
samois
Fig. 11.6
goosecoid
BMP2
BMP inhibitors e.g. Chordino

• 4. Acquires its function from _________
  accumulation in nearby cells
• B-catenin accumulates in _____ cells
• ______________is activated

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C. Axis formation (cont.)
2. _________________ axis-
In amphibians , the
anterior-posterior axis is formed during
oogenesis This axis is stabilized during
gastrulation by _____________ ____________________
____.
_________ neural inducing signal (from ectoderm
cells)
Fig. 11.6
__________ neural-inducing signal ( from mesoderm
cells)
3. ________________ axis -
Not much known, but involves ______ family
signaling molecules
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Mammalian Development
Tough to study!!

• ______ diameter (1/1000th volume of frog egg!)
• Few in number ___________
• Develops within mother
• Cleavage events take _____ hours each
• Development occurs en route to ___________

3. Cleavage during migration down _________
2. fertilization
4. Implant in ______
1. Egg released from _____
Fig. 11.20
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Mammalian Development
A. Cleavage
Distinctions of mammalian cleavage

• Slow- ______ hrs per cleavage
• 2nd cleavage is ______________
• Marked __________ in early cell division
• Cleavage at 2nd division requires newly made
  ________ from zygote

Fig. 11.21-rotational cleavage in mammals
5. ____________ (marked cell huddling) occurs at
8 cell stage
compaction
Fig. 11.23- Compaction at 8 cell stage (______ in
humans)
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A. Cleavage (cont.)
16 cell embryo is termed _______

• external cells will become ___________, which
  will become the _________
• Internal cells will become _____________ (ICM),
  or the ______________

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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B. Gastrulation
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)

Epiblasts form ______________
epiblasts
Hypoblasts (from ICM) line the ________- these
give rise to ______________________.
hypoblasts
blastocoel
Fig. 11.28- Day 15 human embryo
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B. Gastrulation (cont.)
Mammalian ______ and ______ cells arise from
epiblasts that migrate through primitive streak
E-cadherin attachment is mechanism
Direction of migration
_____________
_____________
Fig. 11.28- Day 16 in human
Fig.11.11- Chick gastrulation- similar to
mammalian
Those cells that migrate through the ____________
will become the _________________.
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B. Gastrulation (cont.)
Extraembryonic membrane Formation
Trophoblast cells (originally termed
cytotrophoblast) gives rise to multinucleated
____________________
Uterine wall

• These syncytiotrophoblasts
• secrete proteolytic enzyme to invade
  __________________
• Digest uterine tissue
• Mothers blood vessels contact the
  syncytiotrophoblast cells
• Embryo produces its own blood vessels

Fig. 11.27-Blastocyst invading uterus
Embryos blood vessels
Blood vessels feed embryo, but blood cells do not
mix
Chorion Villi
Embryo chorion
Mothers Placenta
Fig. 11.31
Mothers blood vessels
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C. Anterior-posterior axis formation

• Two signaling centers
• _______________________ (AVE)
• _________ (Organizer)

These work together to form ___________.
Fig. 11.34 These are on opposite sides of a cup
structure
Node produces _____ and ________
Knock-out of one of these results no _________
AVE produces ______ and Otx-1
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C. Anterior-posterior axis formation
The Hox genes specify _________________ polarity
These 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
____________ _________.
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C. Anterior-posterior axis formation (cont.)
Fig. 11.36- Hox genes are organized in a linear
sequences that concurs with posterior to anterior
structures
This is referred to as the ___________
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Hox gene rules
1. Different sets of Hox genes are required for
__________ of any region of the
_____________________ axis
Hoxa-2 KO- _______ missing, duplicate incus
Hoxa-3 KO- thymus, ______________ malformed
2. Different members of a paralogous group may
specify different ___________ in a given region
Hoxd-3 KO deformed ______ (1st vertebra)
Example
Hoxa-3/Hoxd-3 _______ KO- atlas and neck
cartilage nearly absent
3. A hox gene KO causes defects in the
_____________ of that genes expression
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Retinoic Acid has a profound effect on development
Recall amphibian development (Ch. 10)
Structure of retinoic acid (not in textbook)
Fig. 10.41
Hox gene
RA
Retinoic acid bind a receptor, then the complex
binds promoter of a hox gene
Retinoic acid activates mammalian _____ genes
Retinoic acid is likely produced in the _____,
and perhaps more time spent in the node dictates
more ___________ specification
Lacks all distal vertebra
Wild-type mouse embryo
RA-treated mouse embryo
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D. Dorsal-ventral axis formation
Dorsal axis forms from ICM cells near
_____________
Inner cell mass (ICM)
Ventral axis forms from ICM cells near
_____________
Blastocoel
Trophoblast
Fig. 11.32
Fig. 11.42
E. Left-right axis formation
Note that mammals are ___________
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