Upload
amy-bater
View
219
Download
5
Tags:
Embed Size (px)
Citation preview
Chapter 16- Tetrapod limb development
“It is one thing to differentiate the chondrocytes and osteocytes that synthesize the cartilage and bone matrices; it is another thing to produce those cells in a temporal-spacial orientation that generates a functional bone.”
“How is it that the fingers form at one end of the limb and nowhere else?”
“How is it that the little finger forms at one edge of the limb and nowhere else?”
We will use limb development to examine the larger question of morphogenesis
5 weeks 11 weeks
5 weeks 7 weeks 11weeks
Feet
Hands
Human development
Morphogenic rules• These rules appear to be the same in all tetrapods
Example- Grafted mammalian limb bud will direct formation of chick limbs
• These rules must follow a _______________ coordinate system
Dimension
1. ________________ (hip-toe)
2. _________________ (thumb-pinky)
3. _________________ (knuckle-palm)
Proteins families involved
_______________
_______________
_________
Fig. 11.36- Hox genes are organized in a _______________ that concurs with _________________ structures
This is referred to as the ____________
Recall from Chapter 11- Hox genes dictate _______________ axis development
Also recall that ____________ has a profound effect on development by activating _____gene expression
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
_______
Hox gene
Retinoic acid bind a _______, then the complex binds promoter of a ________
RA receptorRA
Another unusual observation-
Experiment- Amputate tadpole tail, then soak the stump in ___
Limb development initiates from __________ of _____________ of _____________ mesoderm and from ___________
Fig. 14.1- mesoderm lineages
Somatic layer of ___________ mesoderm
_______
How does a _____develop?
Limb bud
Result- Several _____ develop
What dictates forelimb from hindlimb?• Transcription factor ____ is expressed in mouse ________
• Transcription factor ____ is expressed in mouse _________
• Loss of one copy of _____ gene in humans results in __________________
•If Place FGF-soaked bead near forelimb bud, generate a _____ ______
•If Place FGF-soaked bead near hindlimb bud, generate a __________________
Observations-
Thus, FGF _______ to make a limb, but tbx5 and tbx4 instruct ______ of limb
•If Place FGF-soaked bead between hindlimb and forelimb buds, generate a ___________
Normal
FGF bead inserted
Fig. 16.5
Fig. 16.5F -Chimera limb from FGF bead placed between limb buds-
Fig. 16.5E Extra wing from FGF bead placed near forelimb bud
The apical ectodermal ridge (AER) is a critical structure
The _______ ____________ (AER) is a critical structure
AER removed
AER duplicated
AER replaced with leg
mesoderm
AER replaced with other mesoderm
AER is required for: 1) ______________, 2) _______________
axis formation,3) ______ axes
specification
Forelimb AER experiments
Fig. 16.8
Generating the ______________ axis
Limb devel.ceases
Duplicate wing
chimera
Limb devel.ceases
AER replaced by FGF bead
normal
Hox genes specify two things-1. Where the limb _______ (recall chapter 11)
2. Whether a cell will become a ________ (humerus), ________ (Ulna and radius) or an __________ (metacarpels and digits)
Fig. 16.1
Example- If KO Hoxa-11 and Hoxd–11 in mouse, no _________________
Fig. 16.14
Example- Humans with defective HOX-13display ________________
Generating the _____________________ axis
Ulna,RadiusHumerous
Scalpula
MetacarpelsDigits
9 10 11 12 13
What dictates thumb-pinky orientation??
1. A group of cell located near ____________ region of limb bud- called __________________________ (ZPA) directs polarity
Specifying the anterior-posterior limb axis the proximal-distal axis
2. These cells in the ZPA express __________________ (Shh)
If place Shh bead in anterior limb bud…
…then observe second set of __________
Extra set
Normal
3. Sonic hedgehog (Shh) activates __________ genes
Hoxd genes specify _____________
orientationFig. 6.15
Evidence
Specifying the _____________ limb axis
The surrounding ectoderm signal dorsal-ventral axis
•_____ activates ______expression in mesenchyme
•_____ is required to specify ______cell fate
•Lmx1 mutant humans have loss of _________, ________________•May also have “____________”
All three axes are ________________
Ectoderm secretes ____…
..which maintains ____ expression in ___..
..which activates ___ genes in limb bud..
..which specifies _____________ limb axis.