Cystic canal mutants in Caenorhabditis elegans are defective in the apicalmembrane domain of the renal (excretory) cell

The excretory cell extends a tubular process, or canal, along the basolater al surface of the epidermis to form the nematode renal epithelium. This cel l can undergo normal tubulogenesis in isolated cell culture. Mutations in 1 2 genes cause excretory canal cysts in Caenorhabditis elegans. Genetic inte ractions, and their similar phenotypes, suggest these genes may encode func tionally related proteins. Depending upon genotype and individual canal, de fects range from focal cysts, flanked by normal width segments, to regional cysts involving the entire tubule. Oftentimes the enlarged regions are con voluted or partially septated. In mutants with very large cysts, renal func tion is measurably impaired. Based on histology and ultrastructure, canal c ysts likely result from defects of the apical membrane domain. These mutant s provide a model of tubulocystic disease without hyperplasia or basement m embrane abnormalities. Similar apical mechanisms could regulate tubular mor phology of vertebrate nephrons. (C) 1999 Academic Press.