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Question 1

Cartilage (bone-forming tissue) and connective tissue of the vertebrate limb form from:

a) the ectodermal epithelium of the limb bud.

b) the mesodermal mesenchyme of the limb bud, derived from lateral plate ectoderm.

c) mesodermal cells that migrate into the limb bud from the somites.

d) the progress zone.

e) the polarizing region.

Question 2

Which of the following correctly describes the sequence of events by which the position of limbs along the antero-posterior axis of vertebrates is specified?

a) Hox gene expression in the mesoderm activates Wnt signaling, which turns on FGF expression and formation of the limb bud.

b) Wnt signaling activates Hox gene expression, which turns on FGF expression and formation of the limb bud.

c) FGF expression in the mesoderm activates Wnt signaling, which turns on Hox gene expression and formation of the limb bud.

d) Hox gene expression in the mesoderm activates FGF signaling, which turns on Wnt expression and formation of the limb bud.

e) FGF expression in the mesoderm activates Hox genes, which turn on Wnt and formation of the limb bud.

Question 3

Removal of the apical ridge leads to:

a) regeneration of the entire limb bud from underlying mesoderm.

b) formation of structures proximal to the apical ridge, but no formation of new distal structures.

c) degeneration of the limb bud.

d) regeneration of a new apical ridge from adjacent epidermal tissue.

e) continued development in the progress zone, once the apical ridge has induced progress zone formation.

Question 4

The grafting of a second polarizing region into the anterior of a limb bud results in:

a) degeneration of the bud.

b) formation of a second bud at the site of the graft.

c) formation of extra copies of the anterior-most digit, digit 2, is the only possible result.

d) formation of extra copies of the posterior-most digit, digit 4, is the only possible result.

e) a new axis can be formed if the second polarizing region is large, and a second full set of digits can form with mirror-image orientation to the normal set of digits.

Question 5

In Chapter 4, it was proposed that activation of Hox genes along the antero-posterior axis in vertebrates might be related to the time spent in Henson's node as it retreats posteriorly: cells expressing anterior Hox genes spend the least amount of time in the node, while cells expressing posterior Hox genes have spent progressively more time in the node. What aspect of limb development may involve a similar mechanism?

a) The amount of time spent near the polarizing region may control limb identity along the antero-posterior axis.

b) The amount of time spent in the apical ridge may determine identity along the proximo-distal axis.

c) The amount of time spent in the progress zone may determine which Hox genes are expressed along the proximo-distal axis of the growing limb, and hence the identity of structures formed.

d) The amount of time spent in the limb bud may determine whether a forelimb or a hindlimb forms.

e) The amount of time spent in the limb bud determines whether an anterior digit or a posterior digit develops.

Question 6

The muscle-forming cells of the vertebrate limb come from:

a) the ectodermal epithelium of the limb bud.

b) the mesodermal mesenchyme of the limb bud, derived from lateral plate ectoderm.

c) mesodermal cells that migrate into the limb bud from the somites.

d) the progress zone.

e) the polarizing region.

Question 7

Cells of the muscle forming region of the somite, the myotome, express Pax3; Pax3 activates expression of myoD and myf5, but muscle differentiation does not occur until the cells stop dividing. When they enter the limb bud, Pax3 is downregulated, division ceases, and differentiation begins. At this point, what gene is the next to be activated as the cells differentiate into muscle?

a) Hoxd13

b) myogenin

c) mrf4

d) Wnt

e) FGF

Question 8

If apoptosis in the developing limb were blocked, what feature of a normal limb would not form?

a) The bones and muscles would not form.

b) The overlying epidermis would not form.

c) The proximo-distal patterning would not occur normally.

d) All the bones would form as the same structure.

e) The digits would be connected by webbing, and would not be separated.

Question 9

In thinking about the development of the wing imaginal disc of Drosophila, what is the significance of "compartments"?

a) A compartment is a signaling center that controls antero-posterior patterning.

b) Compartments are developmental units, in that the wing forms from the 'wing compartment'.

c) Compartments are epithelial sacs, set aside during embryogenesis, that will give rise to adult structures such as wings after metamorphosis.

d) Since cells in adjacent compartments have different lineage histories, adjacent compartments can adopt different fates and differentiation patterns, as in the formation of the anterior and posterior portions of the wing blade.

e) Compartments are morphologically similar whose ultimate identity becomes specified after their formation by the homeotic selector genes.

Question 10

Engrailed comes to be expressed in posterior compartments during Drosophila embryogenesis; what is the consequence of engrailed activation of hedgehog (Hh) signaling from the posterior compartment of the wing disc?

a) Hh activates decapentaplegic (Dpp) signaling at the compartment boundary; Dpp then acts as a morphogen to pattern the development of veins in the wing blade.

b) Hh signaling from the posterior compartment specifies the adjacent compartment as an anterior compartment.

c) Hh signaling in the posterior compartment acts as a morphogen to pattern the posterior portion of the wing.

d) Hh signaling controls the identity of the Imaginal discs, in this case, specifying the disc as the wing disc.

e) Hh signaling plays no crucial role, since it is Dpp signaling that is important.

Question 11

Keeping in mind the fact that genes are often named for the phenotype of a mutation in that gene, what might be the phenotype of a mutation of the Distal-less gene of Drosophila?

a) Mutations of distal-less would fail to pattern the wing veins along their antero-posterior axis.

b) Distal-less mutants would form only distal structures, like the tarsus (distal end) of the legs without a coxa (proximal end).

c) Distal-less mutants would form only proximal structures, like the coxa (proximal end) of the legs without a tarsus (distal end).

d) Distal-less mutants would fail to form the signaling center that controls dorso-ventral patterning.

e) Mutants in distal-less would have altered patterns of gene expression throughout the leg disc.

Question 12

The development of drugs to block the activity of vascular endothelial growth factor (VEGF) has been applied to the control of the growth of cancers. What is the rationale for such a strategy?

a) VEGF acts as a growth factor to stimulate the growth of many solid tumors.

b) Tumor cells produce VEGF to stimulate angiogenesis in their vicinity, and tumors cannot continue to grow without this supply of blood.

c) Blocking VEGF prevents vasculogenesis in the embryo, and if done properly prevents cancer later in life.

d) VEGF causes blood vessels to grow toward cancers, which kills the cancer due to too much blood.

e) VEGF is a key controller of the adoption of tumor phenotypes by cells, so blocking it will help control cancer.

Question 13

Heart development begins as:

a) a folding process in the mesoderm below the notochord that is exactly like neural tube formation.

b) an outgrowth of the endoderm above the gut that forms a tube that will become the heart.

c) a pair of tubes in the lateral plate mesoderm that move together and fuse to form a single tube that will become the heart.

e) cells from the somitic myotome, which migrate ventrally and form the heart.

Question 14

Teeth form from:

a) mesoderm, since they are clearly akin to bone.

b) ectodermal epidermis, since they are clearly related to fingernails and toenails.

c) endoderm, since they reside in the mouth, an extension of the gut.

d) a combination of oral epithelium and neural crest-derived mesenchyme in the jaw.

e) neural tube, since they sure can hurt when something's wrong.

Question 15

Hedgehog signaling at the compartment boundary in the Drosophila wing disc leads to the expression of what signaling molecule in the adjacent anterior cells?

a) engrailed

b) wingless

c) decapentaplegic

d) sonic hedgehog

e) BMP-4

Question 16

The segmental identity of imaginal discs is determined by:

a) Hox genes

b) gap genes

c) segment polarity genes

d) maternal genes

e) pair-rule genes

Question 17

The heart forms from:

a) dorsal ectoderm

b) lateral plate mesoderm

c) endoderm

d) mesenchyme

e) Henson's node

Oxford University Press, Online Resource Centre, Chapter 09.

Chapter 09

Instructions