The Caenorhabditis elegans germline is composed of mitotically dividing cells at the distal end that give rise to meiotic cells more proximally. Specification of the distal region as mitotic relies on induction by the somatic distal tip cell and the
glp-1 signal transduction pathway. However, the genetic control over the transition from mitosis to meiosis is not understood. In this paper, we report the identification of a gene,
gld-2, that has at least two functions in germline development. First,
gld-2 is required for normal progression through meiotic prophase. Second,
gld-2 promotes entry into meiosis from the mitotic cell cycle. With respect to this second function,
gld-2 appears to be functionally redundant with a previously described gene,
gld-1 (Francis, R., Barton, M. K., Kimble, J. and Schedl, T. (1995) Genetics 139, 579-606). Germ cells in
gld-1(o) and
gld-2 single mutants enter meiosis at the normal time, but germ cells in
gld-2 gld-1(o) double mutants do not enter meiosis. Instead, the double mutant germline is mitotic throughout and forms a large tumor. We suggest that
gld-1 and
gld-2 define two independent regulatory pathways, each of which can be sufficient for entry into meiosis. Epistasis analyses show that
gld-1 and
gld-2 work downstream of the
glp-1 signal transduction pathway. Therefore, we hypothesize that
glp-1 promotes proliferation by inhibiting the meiosis-promoting functions of
gld-1 and
gld-2.