Organisms use circulating diuretic hormones to control water balance (osmolarity), thereby avoiding dehydration and managing excretion of waste products. The hormones act through G-protein-coupled receptors to activate second messenger systems that in turn control the permeability of secretory epithelia to ions like chloride. In insects, the chloride channel mediating the effects of diuretic hormones was unknown. Surprisingly, we find a pentameric, cys-loop chloride channel, a type of channel normally associated with neurotransmission, mediating hormone-induced transepithelial chloride conductance. This discovery is important because: 1) it describes an unexpected role for pentameric receptors in the membrane permeability of secretory epithelial cells, and 2) it suggests that neurotransmitter-gated ion channels may have evolved from channels involved in secretion.

The E2F family of transcription factors are evolutionarily conserved regulators of the cell cycle that can be divided into two groups based on their ability to either activate or repress transcription. In Drosophila, there is only one "activator" E2F, dE2F1, which provides all of the pro-proliferative activity of E2F during development. Interestingly, the de2f1 gene can be transcribed from multiple promoters resulting in six alternate transcripts. In this study, we sought to investigate the biological significance of the alternate transcriptional start sites. We focused on the de2f1 promoter region where tissue and cell-type specific enhancer activities were observed at the larval stage. While a genomic deletion of this region, de2f1(ΔRA), decreased the overall expression level of dE2F1, flies developed normally with no obvious proliferation defects. However, a detailed analysis of the de2f1(ΔRA) mutant eye imaginal discs revealed that dE2F1 is needed for proper cell cycle exit. We discovered that dE2F1 expression during G1 arrest prior to the differentiation process of the developing eye is important for maintaining cell cycle arrest at a later stage of the eye development. Overall, our study suggests that specific alternate transcripts of "activator" E2F, dE2F1, may have a dual function on cell cycle progression and cannot simply be viewed as a pro-proliferative transcription factor.

Pentameric ligand-gated ion channels (pLGICs) constitute a large protein superfamily in metazoa whose role as neurotransmitter receptors mediating rapid, ionotropic synaptic transmission has been extensively studied. Although the vast majority of pLGICs appear to be neurotransmitter receptors, the identification of pLGICs in non-neuronal tissues and homologous pLGIC-like proteins in prokaryotes points to biological functions, possibly ancestral, that are independent of neuronal signalling. Here, we report the molecular and physiological characterization of a highly divergent, orphan pLGIC subunit encoded by the pHCl-2 (CG11340) gene, in Drosophila melanogaster We show that pHCl-2 forms a channel that is insensitive to a wide array of neurotransmitters, but is instead gated by changes in extracellular pH. pHCl-2 is expressed in the Malpighian tubules, which are non-innervated renal-type secretory tissues. We demonstrate that pHCl-2 is localized to the apical membrane of the epithelial principal cells of the tubules and that loss of pHCl-2 reduces urine production during diuresis. Our data implicate pHCl-2 as an important source of chloride conductance required for proper urine production, highlighting a novel role for pLGICs in epithelial tissues regulating fluid secretion and osmotic homeostasis.