Analysis of Biological Development (K. Kalthoff)

Updates to Topic 27: Hormonal Control of Development


Answers to Questions in Text

Chromosome Puffing in Drosophila Metamorphosis (pp. 730-732)

  1. How could Ashburner and coworkers have inhibited protein synthesis, and how could they have tested whether the inhibition was indeed working as intended? Answer: By using translational inhibitors, such as cycloheximide. To test which inhibitor concentration was required to completely inhibit protein synthesis, they could have added a radiolabeled amino acid to the culture medium and determined rate of incorporation into proteins at different inhibitor concentrations.
  2. What particular type of protein might the investigators have had in mind to block the synthesis of? Answer: Transcription factors.
  3. The investigators explain the failure of late genes to become activated in the presence of protein synthesis inhibitors by postulating that the activation process itself depends on newly synthesized proteins. Wouldn't it be equally reasonable to assume that (a) puffing depends on ATP or some other donor of chemical energy and (b) inhibiting protein synthesis makes cells “sick” so that their energy production is diminished? Answer: The latter hypothesis would not explain why some early puffs failed to regress “on schedule” after addition of inhibitor.

Early Regulatory Genes in Drosophila Metamorphosis (pp. 735/736)

  1. How could White and coworkers have tested whether DHR3 is not only sufficient but also necessary for inhibiting early genes, such as E74A+ and BR-C+? Answer: By obtaining mutants with loss-of-function alleles in DHR3+. If DHR3 is necessary for inhibiting early genes, the latter should be expressed beyond their normal time, that is, in mid-prepupae (see Fig. 27.14). The normal inhibition of the early genes should be restored by a DHR3+ transgene.
  2. If the two-hybrid assay had failed to show binding between DHR3 and EcR, what would have been an alternative mechanism to account for the precocious inhibition of E74A+ expression by the heat shock-driven DHR3+ transgene? Answer: DHR3 and EcR might have bound competitively to the same ecdysone response element (EcRE). To test this possibility, one would use a test for direct binding between DHR3 and EcRE, such as protection of EcRE by DHR3 against breakdown by DNase, immunoprecipitation of labeled EcRE with antibody against EcR, or reduced electrophoretic mobility of EcRE in the presence of DHR3.

Comments

Clarifications and Corrections

p. 721, legend to Fig. 27.4, line 6 should read: "The proximal (cranial) portion of the Wolffian duct..."

New Review Articles

Sanchez R., Nguyen D., Rocha W., White J.H., Mader S.. (2002) Diversity in the mechanisms of gene regulation by estrogen receptors. Bioessays 24: 244-254

Nef S. and Parada L.F. (2000) Hormones in male sexual development. Genes Dev. 14: 3075-3086.

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