The acquisition of competence is a key mechanism for refining global signals to distinct spatial and temporal responses. The molecular basis of competence, however, remains poorly understood. Here, we show that the beta FTZ-F1 orphan nuclear receptor functions as a competence factor for stage-specific responses to the steroid hormone ecdysone during Drosophila metamorphosis. beta FTZ-F1 mutants pupariate normally in response to the late larval pulse of ecdysone but display defects in stage-specific responses to the subsequent ecdysone pulse in prepupae. The ecdysone-triggered genetic hierarchy that directs these developmental responses is severely attenuated in beta FTZ-F1 mutants, although ecdysone receptor expression is unaffected. This study define beta FTZ-F1 as an essential competence factor for stage-specific responses to a steroid signal and implicates interplay among nuclear receptors as a mechanism for achieving hormonal competence.

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Steroid hormones trigger a wide variety of cell-specific responses during animal development, but the mechanisms by which these systemic signals specify either cell division, differentiation, morphogenesis or death remain uncertain. Here, we analyze the function of the steroid-regulated genes betaFTZ-F1, BR-C, E74A, and E93 during salivary gland programmed cell death. While mutations in the betaFTZ-F1, BR-C, E74A, and E93 genes prevent destruction of salivary glands, only betaFTZ-F1 is required for DNA fragmentation. Analyses of BR-C, E74A, and E93 loss-of-function mutants indicate that these genes regulate stage-specific transcription of the rpr, hid, ark, dronc, and crq cell death genes. Ectopic expression of betaFTZ-F1 is sufficient to trigger premature cell death of larval salivary glands and ectopic transcription of the rpr, dronc, and crq cell death genes that normally precedes salivary gland cell death. The E93 gene is necessary for ectopic salivary gland cell destruction, and ectopic rpr, dronc, and crq transcription, that is induced by expression of betaFTZ-F1. Together, these observations indicate that betaFTZ-F1 regulates the timing of hormone-induced cell responses, while E93 functions to specify programmed cell death.

Drosophila larvae are attracted to a wide variety of chemical stimuli. The olfactory response to ethyl acetate, a powerful attractant, was found to be surprisingly well conserved across a variety of different wild-type strains. Strain differences are documented, however, both in attraction to ethyl acetate and in another chemosensory behavior: avoidance of an aversive stimulus. As a means of analyzing the extent of genetic heterogeneity within strains, one wild-type population, Canton-S, was screened for variant X chromosomes. An enrichment procedure was characterized and used to make the screening more efficient. Lines homozygous for individual X chromosomes were established, and all were found to exhibit a strong olfactory response, although evidence was found for variation among them. The olfactory response was found to be conserved through an extended period of larval development, including the final period during which larvae leave the culture medium in preparation for metamorphosis. The results are discussed in terms of the genetic basis of the response and the use of single-gene mutations as a means of dissecting olfactory system function.