Transcript Chapter 10- Amphibians

Chapter 11- Fish and mammals
• Zebrafish are becoming the sweetheart of developmental
biologists
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Large broods
Breed year-round
Easy and cheap
Transparent embryos
Develop outside mother
Early development complete in 24 hours
A. Cleavage
1st
12 divisions are
sychronous to form
_____________
6
1
Three cell populations
1. __________
_____ (EL)
2. ____layergives rise to
embryo proper
Blastoderm is
perched on a
large ________
Fig. 11.1
3. ____________
layer (YSL)
Fig. 11.2
B. Gastrulation
Epiboly
Deep cells migrate to
outside then encase
entire yolk
Recall Epiboly
from Ch 9
Movement not by crawling, but by YSL cells expansion and
pulling EL cells along
1. Enveloping
layer (EL)
Embryonic
shield
epiblast
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)
B. Gastrulation (cont.)
Animal
Ventral
Head
The hypoblast cells extend in both
directions to form the notochord
precursor
Dorsal
Ectoderm
Trunk
Tail
Vegetal
Fig. 11.3
Mesoderm
Endoderm
Fig. 11.2 -A zebrafish fate map
C. Axis formation
1. Dorsal ventral axis-
As with the amphibian __________ (Organizer), the embryonic shield:
1. Establishes the _______________ axis
• Converts lateral/ventral medoderm to
dorsal mesoderm (notochord)
• Convert ectoderm to neural rather
than epidermal
2. Forms the ______________
precursor
B-catenin
samois
goosecoid
BMP
inhibitors
e.g.
Chordino
C. Axis formation
1. Dorsal ventral axisAs 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
Fig. 11.6
B-catenin
samois
goosecoid
BMP2
Chordino
Embryonic shield
4. Acquires its function from _________ accumulation
in nearby cells
•B-catenin accumulates in _____ cells
•______________is activated
BMP
inhibitors
e.g.
Chordino
C. Axis formation (cont.)
2. _________________ axisIn 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
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 _________
4. Implant in
______
2. fertilization
1. Egg released from _____
Fig. 11.20
Mammalian Development
A. Cleavage
Distinctions of mammalian cleavage
1. Slow- ______ hrs per cleavage
2. 2nd cleavage is ______________
3. Marked __________ in early cell
division
4. Cleavage at 2nd division requires
newly made ________ from zygoteAmphibians
5. ____________ (marked cell
huddling) occurs at 8 cell stage
Mammals
Fig. 11.21-rotational
cleavage in mammals
compaction
Fig. 11.23- Compaction at 8 cell stage (______ in humans)
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 ______________.
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
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
_________________.
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
Embryo’s blood vessels
Fig. 11.27-Blastocyst
invading uterus
Chorion
Villi
Embryo chorion
Mother’s Placenta
Mothers blood vessels
Blood vessels feed
embryo, but blood
cells do not mix
Fig. 11.31
C. Anterior-posterior axis formation
Two signaling centers
1. _______________________ (AVE)
2. _________ (Organizer)
These work together
to form
___________.
Fig. 11.34 These are on opposite sides of a
“cup” structure
Node produces _____ and ________
AVE produces ______ and Otx-1
Knock-out of
one of these
results no
_________
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 ____________
_________.
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 ___________
Hox gene rules
1. Different sets of Hox genes
are required for __________
of any region of the
_____________________ axis
Hoxa-2 KO- _______ missing, duplicate incus
Incus
Hoxa-3 KO- thymus, ______________ malformed
Stapes
2. Different members of a paralogous group may
specify different ___________ in a given region
st
ExampleHoxd-3 KO = deformed ______ (1 vertebra)
Hoxa-3/Hoxd-3 _______ KO- atlas and neck
cartilage nearly absent
3. A hox gene KO causes defects in the _____________ of that gene’s expression
Retinoic Acid has a profound effect on development
Recall amphibian
development (Ch. 10)
Structure of retinoic acid
(not in textbook)
Fig. 10.41
RA
Retinoic acid activates mammalian _____ genes
Lacks all
distal
vertebra
Wild-type
mouse embryo
RA-treated
mouse embryo
Hox gene
Retinoic acid bind a receptor,
then the complex binds
promoter of a hox gene
Retinoic acid is likely
produced in the _____,
and perhaps more time
spent in the node dictates
more ___________
specification
D. Dorsal-ventral axis formation
Dorsal axis forms from ICM cells near
_____________
Inner cell
mass (ICM)
Trophoblast
Blastocoel
Ventral axis forms from ICM cells
near _____________
Fig. 11.32
Fig. 11.42
E. Left-right axis formation
Note that mammals are ___________
Two levels of regulation1. 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