Oogenesis

Oogenesis is the process of generating functional oocytes from an undifferentiated germ cell. In most animal species, oocytes arrest during meiotic prophase. The completion of meiosis and the preparation of the oocyte for fertilization are triggered in response to intercellular signaling in a process called meiotic maturation. During meiotic maturation, the oocyte transitions to metaphase of meiosis I, the nuclear envelope breaks down, the cortical cytoskeleton undergoes rearrangement, and the meiotic spindle is assembled. By contrast, in C. elegans, the processes of meiotic maturation, ovulation, and fertilization are temporally coupled. Meiotic maturation is triggered by major sperm protein (MSP), which acts as a hormone. In turn the maturing oocyte signals its own ovulation. During ovulation the oocyte passes through the spermatheca becoming fertilized on the way to the uterus.

Spermatogenesis

Spermatogenesis is the process of generating functional sperm from an undifferentiated germ cell. In C. elegans, spermatogenesis occurs in both males and hermaphrodites. In both sexes, the germ line initiates spermatogenesis during the L4 larval stage. In the male, spermatogenesis continues throughout adulthood. In the hermaphrodite, however, during the adult stage the germ line ceases spermatogenesis and switches to oogenesis. Sperm made by the hermaphrodite are stored and used for self-fertilization of the hermaphrodite's oocytes. Hermaphrodite sperm differ from male sperm in size with male spermatids being much larger than those of the hermaphrodite. In addition, spermiogenesis is regulated by sex-specific mechanisms. Unlike other sperm-bearing organisms, C. elegans and other nematodes spermatozoa move by a unique crawling mechanism using a single pseudopod. The major sperm protein (MSP), instead of actin, is the main cytoskeletal fiber used in the pseudopod.