Imaginal disc-autonomous expression of a defect in sensory bristle patterning caused by the lethal(3)ecdysoneless¹ (l(3)ecd¹) mutation of Drosophila melanogaster

The temperature-sensitive mutation l(3)ecd¹ of Drosophila melanogaster is known to autonomously impair the ability of the larval prothoracic gland to produce the steroid molting hormone ecdysone in response to stimulation by the tropic neuropeptide prothoracicotropic hormone. It is shown that autonomous expression of the l(3)ecd¹ mutation in metamorphosing imaginal tissues disrupts the spatial pattern of sensory bristles. Transfer of homozygous mutant animals to the restrictive temperature at the time of pupariation resulted in the elimination of sensory microchaetae and macrochaetae. This effect was specific to the sensory bristles; nonsensory bristles were not eliminated, nor were other types of innervated cuticular sense organs. In the case of the dorsal thoracic macrochaetae, normal ecd gene function is required during an early period of bristle development (0-18 hr after puparium formation at 20°C). It is during this period that important determinative events take place in developing imaginal tissues that are responsible for the establishment of bristle progenitor cells. It is proposed that the ecd gene product may be required for the response of certain classes of cells to specific, regulatory signals.