Genes required for Drosophila nervous system development identified by RNA interference.

RNA interference was used to screen 3,314 Drosophila double-stranded RNAs, corresponding to approximately 25% of Drosophila genes, for genes that affect the development of the embryonic nervous system. RNA-interference-mediated gene silencing in Drosophila embryos resulted in loss-of-function mutant phenotypes for 43 genes, which is 1.3% of the genes that were screened. We found 18 genes that were not known previously to affect the development of the nervous system. The functions of some of the genes are unknown. Other genes encode protein kinases, transcription factors, and signaling proteins, as well as proteins with other functions.

Towards understanding the polycystins.

Autosomal dominant polycystic kidney disease (ADPKD) is a very common inherited disease caused by mutations in PKD1 or PKD2 genes characterized by progressive enlargement of fluid-filled cysts and loss of renal function [1]. Previous studies proposed a role for human polycystin-1 in renal morphogenesis acting as a matrix receptor in focal adhesions and for polycystin-2 as a putative calcium channel [2, 3]. The genome of Caenorhabditis elegans contains 2 new members of the polycystin family: lov-1, the homolog for PKD1; and pkd-2, the homolog for PKD2 [4; this paper]. Mutation analysis in C. elegans showed similarly compromised male mating behaviors in all single and double lov-1 and pkd-2 mutants, indicating their participation in a single genetic pathway. Expression analysis localized LOV-1 and PKD-2 to the ends of sensory neurons in male tails and to the tips of CEM neurons in the head, consistent with functions as chemo- or mechanosensors. Human and C. elegans PKD1 and PKD2 homologs, transfected into mammalian renal epithelial cells, co-localized with paxillin in focal adhesions suggesting function in a single biological pathway. Based on the role of polycystins in C. elegans sensory neuron function and the conservation of PKD pathways we suggest that polycystins act as sensors of the extracellular environment, initiating, via focal adhesion assembly, intracellular transduction events in neuronal or morphogenetic processes.

PRKX, a phylogenetically and functionally distinct cAMP-dependent protein kinase, activates renal epithelial cell migration and morphogenesis.

The human protein kinase X gene (PRKX) is a member of an ancient family of cAMP-dependent serine/threonine kinases here shown to be phylogenetically distinct from the classical PKA, PKB/Akt, PKC, SGK, and PKG gene families. Renal expression of the PRKX gene is developmentally regulated and restricted to the ureteric bud epithelium of the fetal metanephric kidney. Aberrant adult kidney expression of PRKX was found in autosomal dominant polycystic kidney disease. PRKX kinase expression markedly activated migration of cultured renal epithelial cells in the presence of cAMP; this effect was blocked by cell treatment with the PKA inhibitor H89 and was not observed in PKA-transfected cells. In addition, expression of PRKX kinase activated branching morphogenesis of Madin-Darby canine kidney cells in collagen gels even in the absence of cAMP and/or hepatocyte growth factor, an effect not seen with either PKA expression or expression of a mutant, kinase-inactivated PRKX. These results suggest that the PRKX kinase may regulate epithelial morphogenesis during mammalian kidney development. Because another member of the PRKX gene family (the Dictyostelium discoideum gene KAPC-DICDI) also plays a role in cellular migration, these studies suggest that regulation of morphogenesis may be a distinctive property of these genes that has been conserved in evolution that is not shared with PKA family genes.