The DM domain protein MAB-3 is required for the proper differentiation of the V5- and V6- derived neuroblasts that give rise to the V rays of the adult male. In addition to expression in the V ray lineage,
mab-3::gfp rescuing reporters are expressed in a variety of head and tail neurons (Yi et al., abstract). Male-specific expression of
mab-3::gfp in ADF and CEM in the head and the T neuroblasts in the tail suggests that MAB-3, while dispensable for lineage execution, may be important for full differentiation and function of these neurons. To determine whether MAB-3 mediates differentiation of these neurons, we examined the effects of a
mab-3(0) mutation on the expression of three genes that are coexpressed with
mab-3::gfp in the male nervous system. The first of these genes,
srd-1, encodes a putative chemosensory receptor protein expressed male-specifically in the ADF neurons and in one of the ray 9 neurons (1). In
mab-3(0) mutants,
srd-1::gfp is not expressed in ray 9, but is expressed in ADF. We also examined expression of two polycystic kidney disease homologues,
lov-1, which is required for normal male mating behavior, and
pkd-2.
lov-1::gfp and
pkd-2::gfp are expressed in the CEMs, the hook neuron HOB and the ray neurons in wild-type males (2).
mab-3(0) mutations eliminate
lov-1::gfp expression in the CEMs, but do not affect expression of
lov-1::gfp in the tail.
pkd-2::gfp is expressed normally in both the CEMs and tail neurons in
mab-3(0) mutants. This requirement for MAB-3 gene regulation in sensory neurons of the head and tail is consistent with a function for MAB-3 in male-specific sensory behaviors including detection of hermaphrodites. To determine whether MAB-3 is necessary for detection of hermaphrodites, we used a leaving assay developed by Lipton and Emmons (3). In this assay, wild-type males plated with paralyzed hermaphrodites on a small bacterial lawn remain on the lawn, while those plated with paralyzed males leave at a highly reproducible rate. This difference in behavior between males plated with hermaphrodites and those plated with males suggests that wild-type males detect a hermaphrodite-derived cue that retains them on the lawn. The difference in leaving rate cannot be attributed to mating, nor does it require the V rays;
mab-5(lf) males, which lack V-rays and are unable to mate, leave males more quickly than they leave hermaphrodites, indicating that they are able to detect hermaphrodites. In contrast,
mab-3(0) males leave hermaphrodites and males at equal rates, indicating that they are not sensitive to the hermaphrodite cue that retains
mab-5(lf) and wild-type males under the same conditions.
mab-3(0) males respond normally to volatile attractants and repellants, excluding the possibility that the
mab-3(0) hermaphrodite detection defect may be caused by a general sensory defect unrelated to sexual attraction. To determine whether loss of
lov-1 expression in the CEMs is responsible for the
mab-3(0) hermaphrodite detection defect, we tested
lov-1(
sy582del) males in the leaving assay.
lov-1(
sy582del) males are able to distinguish hermaphrodites from males, indicating that
lov-1 function in the CEMs is not necessary for detecting the hermaphrodite cue in this assay. It is possible that
lov-1 carries out a MAB-3 regulated function separate from hermaphrodite detection or redundant with other targets of MAB-3 regulation. We are currently doing a microarray screen and testing candidate genes to identify other MAB-3 targets which may function in mating behavior (Thoemke et al., abstract). 1. Troemel et al. (1995). Cell 83: 207-218 2. Barr and Sternberg (1999). Nature 401: 386-389 3. Lipton and Emmons (1999). Worm Breeder's Gazette 16(1): 56