Circadian regulation of the lark RNA-binding protein within identifiable neurosecretory cells

Molecular genetic analysis indicates that rhythmic changes in the abundance of the Drosophila lark RNA-binding protein are important for circadian reg ulation of adult eclosion (the emergence or ecdysis of the adult from the p upal case). To define the tissues and cell types that might be important fo r lark function, we have characterized the spatial and developmental patter ns of lark protein expression. Using immunocytochemical or protein blotting methods, lark can be detected in late embryos and throughout postembryonic development, from the third instar larval stage to adulthood. At the late pupal (pharate adult) stage, lark protein has a broad pattern of tissue exp ression, which includes two groups of crustacean cardioactive peptide (CCAP )-containing neurons within the ventral nervous system. In other insects, t he homologous neurons have been implicated in the physiological regulation of ecdysis, Whereas lark has a nuclear distribution in most cell types, it is present in the cytoplasm of the CCAP neurons and certain other cells. wh ich suggests that the protein might execute two different RNA-binding funct ions. Lark protein exhibits significant circadian changes in abundance in a t least one group of CCAP neurons, with abundance being lowest during the n ight, several hours prior to the time of adult ecdysis. Such a temporal pro file is consistent with genetic evidence indicating that the protein serves a repressor function in mediating the clock regulation of adult ecdysis, I n contrast,we did not observe circadian changes in CCAP neuropeptide abunda nce in late pupae, although CCAP amounts were decreased in newly-emerged ad ults, presumably because the peptide is released at the time of ecdysis, Gi ven the cytoplasmic localization of the lark RNA-binding protein within CCA P neurons, and the known role of CCAP in the control of ecdysis, we suggest that changes in lark abundance may regulate the translation of a factor im portant for CCAP release or CCAP cell excitability. (C) 2000 John Wiley & S ons, Inc.