DEVELOPMENT OF MALE REPRODUCTIVE-SYSTEM AND SEXUAL TRANSFORMATION IN NEMATODE CAENORHABDITIS-ELEGANS

The small free-living nematode C. elegans is usually found as a hermaphrodite, but occasionally true males appear in the population. Gonadogenesis is described in the normal male and in a temperature-sensitive sex transformer mutant. Male and hermaphrodite gonads develop from morphologically identical primordia. The small primordial gonad lies on the ventral side of the worm in the coelomic cavity. The gonadial primordium contains 4 nuclei at parturition. As this primoridium develops in a hermaphrodite it produces a double-armed, mirror symmetrical gonad that produces first sperm and then eggs. In the male this primoridium develops into an asymmetrical structure composed of a ventrally located testis, a loop region, a seminal vesicle and a vas deferens. The male gonad presents a linear sequence of nuclei in successive stages of spermatogenesis beginning with a mitotic region in the testis, followed by clearly distinguishable stages of meiosis throughout the loop region to the seminal vesicle. A temperature-sensitive sex transformer mutant, tsB202, was isolated, which carries an autosomal recessive mutation in linkage group II that at restrictive temperature transforms an XX hermaphrodite into a phenotypic male, complete with a normal male gonad and vestigial external genitalia. These transformed males are classified as pseudomales because they do not exhibit mating behavior. Temperature shift experiments determined the specific temporal sequences of gonadogenesis, oogenesis and spermatogenesis. Proper manipulation of the temperature regimen causes intersex production. In 1 intersex, a male gonad complete with sperm, seminal vesicle and vas deferens also contains oocytes. In another produced by the complementary temperature shift, a hermaphrodite-shaped gonad develops that produces only sperm and no oocytes.