We are continuing to map and microinject cosmids in order to clone several exc genes. Mutants in these genes exhibit excretory canals that swell into large fluid-filled cysts, rather than maintain the normal narrow tubular shape. Other cloned exc genes (
exc-4,
exc-5,
exc-7,
sma-1, and
let-653) encode proteins that regulate the diameter of the excretory canals, and determine the cytoskeletal structure of the apical surface of the canal and other epithelial tissues. At present we are focusing our efforts on the
exc-1,
exc-2,
exc-3, and
exc-9 genes. The first three of these have been genetically mapped to narrow regions, and microinjection has begun to attempt to rescue the mutant phenotypes. We narrowed the position of
exc-1 on LGX via 3-factor cross between
eat-20 and
lin-15, a region covered by just 7 cosmids. At present,
exc-1 appears to be rescued by cosmid C02C6, which encodes three novel genes and
dyn-1 (encoding dynamin).