Systematic Search for the Genes that Program Sex Behavior in Caenorhabditis elegans

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We have undertaken to isolate mutants defective in sex behavior in the nematode C.elegans. The him-5 mutant of C.elegans gives rise to high frequency of males in its offsprings. The plg-1 mutant males deposit gelatinous material (called plug) around the vulva of hermaphrodites after sperm transfer. Double mutant him-5 plg-1 was treated with mutagen and mating-deficient mutants were isolated as those that fail to deposit plug. We isolated 39 such mutants. The mating behavior of C.elegans males consists of four steps : "response to contact", "turning", "vulva location" and "spicule insertion". Among the mutants isolated, 14 had defect in response to contact, 23 had defect in turning, and 5 had defect in vulva location. Some of them had defects in multiple steps. Twenty of the mutants had morphological abnormalities in the tail, which is important for the male mating behavior. Male tail has 9 pairs of sensory organs called rays. The abnormalities observed in the mutants include fusion of rays and deletion of rays. Six mutants seemed to have defects in extension and/or retraction of their spicules, which are important for sperm transfer. Abnormalities in the sensory neurons were revealed by staining with fluorescent dye DiO in 11 of the mutants without gross morphological defects. The mutants isolated in this study will be useful in elucidating the genetic control of the development of male-specific structure and function.