Transcript MCDB 4650 Class 19 Patterning of the Limb

MCDB 4650
Limb Patterning
Which of the following is the most likely candidate for
activating the expression of the different Tbx genes in
the mesenchyme?
a.
b.
c.
d.
FGF signaling
Hox expression
Wnt signaling
Sonic Hedgehog signaling
What might induce the expression of Shh only
in the posterior region of each limb bud ?
a. Hox gene expression
b. FGF signaling
c. BMP signaling
d. Wnt signaling
In a limb with duplicated digits (produced by an ectopic
ZPA), why are the extra digits produced in mirror image?
a. Shh diffuses toward the center,
so the higher concentration at
the center induces two Digit 2s
Original
Extra ZPA
b. High Shh concentration induces
Digit 4, so there are Digit 4s
closest to each ZPA
c. The cells on either end are
prespecified to make digit 2, 3,
or 4
d. Digit 4 requires Shh; the other
digits form in the absence of
Shh.
ZPA
Which axis of limb development is
dependent on FGF?
a. proximal-distal
b. anterior-posterior
c. dorsal ventral
When thinking about the dorsal-ventral axis
of the limb, the dorsal side is best
represented by:
a. the palm of the hand
b. the back of the hand
c. the side of the hand
According to the progress zone model of limb
development, the cells that leave the progress
zone first (early in limb development), develop
into
a. dorsal cells in the limb
b. ventral cells in the limb
c. anterior cells in the limb
d. posterior cells in the limb
e. distal cells in the limb
f. proximal cells in the limb
The bones of the limb (humerus, radius,
ulna, and carpals) are derived from the
a. notochord
b. somites
c. lateral plate mesoderm
d. ectodermal epithelium
The proximal-distal identity of cells within the
limb is determined by
a. Notch-Delta signaling
b. FGF expression
c. Shh expression
d. Hox expression
In each of the following situations, select all answers that
are correct. What would happen to limb development
if
An embryo had a loss of function mutation in gene radical
fringe?
i. loss of AER; no or reduced proximal-distal
outgrowth
ii. duplication of A-P structures
iii. loss of A-P patterning
iv. posteriorization of digits
v. D/V axis disrupted
vi .Limb identity altered
vii. limb placement along body altered
In each of the following situations, select all answers that
are correct. What would happen to limb development
if
An embryo had overexpression of Tbx4 throughout the
flank of the developing embryo.
i. loss of AER; no or reduced proximal-distal
outgrowth
ii. duplication of A-P structures
iii. loss of A-P patterning
iv. posteriorization of digits
v. D/V axis disrupted
vi .Limb identity altered
vii. limb placement along body altered
In each of the following situations, select all answers that
are correct. What would happen to limb development
if
An embryo had a loss of function mutation in Engrailed 1.
i. loss of AER; no or reduced proximal-distal
outgrowth
ii. duplication of A-P structures
iii. loss of A-P patterning
iv. posteriorization of digits
v. D/V axis disrupted
vi .Limb identity altered
vii. limb placement along body altered
In each of the following situations, select all answers that
are correct. What would happen to limb development if
An embryo had high levels of sonic hedgehog expression
throughout the limb.
i. loss of AER; no proximal-distal outgrowth
ii. duplication of A-P structures
iii. loss of A-P patterning
iv. posteriorization of digits
v. D/V axis disrupted
vi .Limb identity altered
vii. limb placement along body altered
The cell that mineralizes the bone called the osteoblast is which type of
cell? (choose the best answer)
a. Lateral plate mesodermal cell
b. Somite-derived cell
c. Cartilage stem cell
d. Hematopoetic stem cell
Bones in the limb derive from
a. axial mesoderm
b. somitic mesoderm
c. sclerotome
d. lateral plate mesoderm
e. ventral mesoderm
f. ectoderm
Of the following, which experiment best tests the
hypothesis that cells in the limb bud have a
pre-specified fate?
a. Remove AER, see what cells types are made
b. Mark distal cells in an early limb bud and see
if they become distal cells in the limb
c. Remove factors required for proliferation; see
what cell types are made
d. Transplant just the AER from an older limb
bud to tip of younger limb bud
What would happen to the developing limbs in a mouse
that was homozygous mutant for Engrailed 1?
a.
b.
c.
d.
e.
The limb would be truncated along the proximal-distal axis
The limb would have ventral structures on the dorsal side
The limb would have dorsal structures on the ventral side
a and b
a and c
Wnt7a (dorsal ectoderm) and Radical Fringe
Lmx-1b
(dorsal mesenchyme)
Proximal
Distal
Placement of the AER depends
on correct localization of
D/V genes!
EN-1 (ventral ectoderm)
If Shh did not act as a morphogen but still affected
limb development, what result would you have
expected from a bead of Shh implanted on the
anterior side?
a. No change, still would be mirror image duplication of
digits
b. An extra digit 4 would be made
c. An extra digit 2 would be made
d. The duplication would occur but would not be a mirror
image
Normal formation of organs often relies upon:
a. Signaling between epithelium and mesenchymal parts
of the organ
b. Signaling between ectodermal and endodermal parts of
the organ
c. Signals from nearby developing structures
d. A and B
e. A and C
If you a produce a chick with cardia bifida by
separating the two heart primordia, what
experiment would convince you that each of
the two heart were complete, functioning
hearts rather than two half hearts?
a. If they were both beating
b. If they both looped
c. If they both expressed left and right-specific
heart molecules
d. If they both expressed markers for ventricular
and atrial myosin