Analysis of Biological Development (K. Kalthoff)

Updates to Topic 06: Cell Fate, Potency, and Determination

Answers to Questions in Text

Cellularization and Determination in Drosophila (p. 131/132)

  1. Why is Drosophila melanogaster a favorable organism for the experiment outlined in Fig. 6.6? Answer: Because of the wealth of available mutants that produce easily detectable phenotypes in groups of potentially disorganized cells.
  2. In the Drosophila embryo, a significant restriction in the potency of blastoderm cells occurs around the time of cellularization. Can you think of a process at the cellular level that becomes restricted as a result of cellularization and may be related to cell potency? Answer: The plasma membranes formed during cellularization inhibit the exchange of large, water-soluble molecules, such as RNAs and proteins. These molecules are involved in the control of gene expression, which is likely to affect cell potency.

Transdetermination (p. 141/142)

  1. Would the outcome of Hadorn's experiment have been different if he had begun his serial transplantation experiment with a wing imaginal disc instead of a genital imaginal disc? Answer: Yes, because the transdeterminations from wing to other imaginal structures are less frequent, as indicated by the lengths of the arrows in Fig. 6.21. Hadorn might have terminated the experiment before the first transdetermination occurred.
  2. Do you see any similarities between the transdeterminations observed by Hadorn and the homeotic mutations discussed in Section 1.4? Answer: Yes. For instance, the transdetermination from haltere to wing resembles the Ultrabithorax phenotype shown in Fig. 1.21. Likewise, the transdetermination from antenna to leg mimicks the Antennapedia phenotype shown in Fig. 1.22.
  3. How can one test the hypothesis that transdetermination may occur in groups of cells rather than in single cells? Answer: A prediction derived from this hypothesis is that a transdetermined area of epidermis may encompass more than one cell clone. This can be tested by marking cell clones in imaginal discs as shown on p. 128 before subjecting the discs to the serial transplantations that cause transdetermination. If a patch of transdetermined cells would straddle the boundary between a marked clone and the unmarked “background” territory then the transdetermination would have had to occur in at least one marked cell and one adjacent unmarked cell.


Clarifications and Corrections

p. 126, legend to Fig. 6.3 should end "...when cells have become smaller."

p. 138, 2nd to last paragraph, line 4 from below, should read "and, in some instances, the difference between dorsal and"

New Review Articles

Mumm J.S. and Kopan R. (2000) Notch signaling: From the outside in. Devel. Biol. 228: 151-165

New Research Articles

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