Although the ray sensilla of C. elegans males are all very similar in cellular composition and shape, different classes of rays can be defined on the basis of neurotransmitter usage, ray morphology, and attachment sites within the fan cuticle. We have proposed that each ray possesses a distinct identity that regulates these aspects of ray development. This proposal is based on a number of mutations that result in attachment of rays at ectopic locations, fusions of rays, and changes in ray morphologies. These include mutations in
mab-18,
mab-21,
sma-3, and an unmapped mutation,
bx28. These genes may regulate the specification of ray identities or may encode cell recognition molecules that are required during ray assembly.
mab-18(
bx23)X results in fusions between rays 4 and 6. The fused ray is present in the normal ray 4 location. When rays 4 and 6 do not fuse, the morphologically thickened ray 6 is missing, and an ectopic, slender ray is present adjacent to ray 4. Posterior seam cell lineages are not affected by
mab-18(
bx23). We have interpreted the change in ray morphology as an indication of a transformation in ray identity.
lin-20(
e1796) males express an identical fused-ray phenotype. We have not been able to separate the Lin (postembryonic HO divisions, etc., Ed Hedgecock, pers. comm.) and Mab phenotypes of
lin-20(
e1796).
mab-18(
bx23) does not express the
lin-20 phenotype.
mab-18/lin-20 animals express the Mab, but not the Lin, phenotype. Therefore,
lin-20(
e1796) is, or harbors, a second allele of
mab-18.mab- 21
(bx41 &
bx53)III result in a 4 to 6 fusion identical to that of mab- 18. As in
mab-18 males, an unfused slender ray 6 is occasionally observed adjacent to ray 4.
mab-21 also results in frequent 5 to 7 fusions. No changes in ray morphology are apparent in rays 5 and 7 when they are not fused. 5 to 7 fusions are never observed in
mab-18 males.
mab-21; press the
mab-21 phenotype.
mab-20(
bx24)I results in 1 to 2, 3 to 4, and 8 to 9 fusions. Larger fusions involving rays 1 through 4 and 6 also occur. The only change apparent in the fused rays is that rays 1, 2, and 4 extend to the edge of the fan, the normal ray 3 attachment point.
sma-2(
e502)III and
sma-3(
e491)III result in 4 to 5, and 6 to 7 fusions. When rays 6 and 7 do not fuse, a thick ray 7 is present, anterior of its normal location. Occasionally, fusions of rays 5, 6, and 7 are observed, and in some males, an unfused, thickened ray 5 is present. Thus,
sma-2 and
sma-3 mutations appear to result in frequent 7 to 6 identity transformations, and occasional 5 to 6 identity transformations. Mutations in other sma genes do not result in fused rays. However,
sma-4(
e729) males lack V-derived rays and have posterior alae, a phenotype like that of
mab-5.
bx28 results in fusions of rays 8 and 9. In wild-type males 8 and 9 fuse 10% of the time. In
bx28 males, this frequency increases to 95%.