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. FGF signalingb. Hox expressionc. Wnt signalingd. Sonic Hedgehog signaling

What might induce the expression of Shh only in the posterior region of each limb bud ?

a. Hox gene expressionb. FGF signalingc. BMP signalingd. Wnt signaling

Original ZPA

In a limb with duplicated digits (produced by an ectopic ZPA), why are the extra digits produced in mirror image?

Extra ZPA

a. Shh diffuses toward the center, so the higher concentration at the center induces two Digit 2s

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.

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 intoa. dorsal cells in the limbb. ventral cells in the limbc. anterior cells in the limbd. posterior cells in the limbe. distal cells in the limbf. 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 outgrowthii. duplication of A-P structuresiii. loss of A-P patterningiv. posteriorization of digitsv. D/V axis disruptedvi .Limb identity alteredvii. 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 outgrowthii. duplication of A-P structuresiii. loss of A-P patterningiv. posteriorization of digitsv. D/V axis disruptedvi .Limb identity alteredvii. 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 outgrowthii. duplication of A-P structuresiii. loss of A-P patterningiv. posteriorization of digitsv. D/V axis disruptedvi .Limb identity alteredvii. 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 outgrowthii. duplication of A-P structuresiii. loss of A-P patterningiv. posteriorization of digitsv. D/V axis disruptedvi .Limb identity alteredvii. 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 cellb. Somite-derived cellc. Cartilage stem celld. Hematopoetic stem cell

Bones in the limb derive froma. axial mesodermb. somitic mesodermc. sclerotomed. lateral plate mesoderme. ventral mesodermf. 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. The limb would be truncated along the proximal-distal axisb. The limb would have ventral structures on the dorsal sidec. The limb would have dorsal structures on the ventral sided. a and be. a and c Wnt7a (dorsal ectoderm) and Radical Fringe

Lmx-1b (dorsal mesenchyme) Proximal Distal EN-1 (ventral ectoderm)

Placement of the AER depends on correct localization of D/V genes!

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 madec. An extra digit 2 would be maded. 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 organb. Signaling between ectodermal and endodermal

parts of the organc. Signals from nearby developing structuresd. A and Be. 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 beatingb. If they both loopedc. If they both expressed left and right-specific

heart moleculesd. If they both expressed markers for ventricular

and atrial myosin