Class VI myosins are essential for hearing in mammals and are thought to be vesicle motors in Drosophila, where they play roles in spermatogenesis and cellularization during embryogenesis. Myosin VI localizes to the brush border of epithelial cells in mammalian kidney and to the leading edge and Golgi network in fibroblasts. The C. elegans genome contains two class VI myosins encoded by
hum-3 (heavy chain of unconventional myosin, J. Molec. Biol. 272: 523) and
hum-8 . We have used chemical mutagenesis of large populations of animals coupled with PCR detection using gene-specific primers and multiple rounds of sib selection to isolate single animals with deletion mutations within the class VI myosin genes. The deletion in
hum-3 removes 2 kb from the core of the motor domain and is most likely a loss-of-function allele. The 1kb
hum-8 deletion is also within the motor domain. These strains are presently being outcrossed to remove background mutations. Preliminary evidence indicates that homozygous
hum-3 mutant animals are partially to completely sterile, producing 0 to 4 progeny while heterozygous
hum-3 /+ siblings produce normal broods. DIC observation of sterile animals reveals that oocytes are packed tightly in the gonad but do not divide and thus are unlikely to have been fertilized. Morphology of the spermatheca is abnormal. The
hum-3 promoter was used to drive expression of the green fluorescent protein (GFP) in cells which normally express
hum-3 . GFP is expressed in a small number of cells which appear to be neurons based on the long thin processes they extend along the length of the animal, as well as in a few cells within the pharynx and in the tail. We are in the process of identifying these cells. No expression was evident in the gonad, where the transgene may be silenced. Complex array injections are in progress to look for germ line expression of
hum-3 .
hum-8 promoter fusions are expressed predominately in the gut of the worm, as well as in the pharynx and in other, as yet unidentified, cells. Phenotypic analysis of
hum-8 mutant animals is in progress. These mutants are not sterile. The
hum-3 and
hum-8 mutants provide a unique opportunity to determine the full range of class VI myosin function in a multicellular organism.