Fig. 1. Polarity of the C. elegans germline and the genetic pathway involved in maintaining the stem cell population. (A) Diagram of germline organization of a young adult hermaphrodite gonad arm. Distal germ cells (proliferative zone; green), enter meiotic prophase as they move proximally (red). The somatic distal tip cell (DTC) caps the very distal end. (B) Genetic pathway that regulates the decision to enter meiosis [adapted from Kadyk and Kimble (Kadyk and Kimble, 1998)]. The GLP-1/Notch signaling pathway inhibits the activities of gld-1 and gld-2. (C) Distal end of a wild-type adult gonad arm showing GLD-1 spatial patterning (red; GLD-1-specific antibodies). The same arm stained with DAPI (blue), to reveal nuclear morphology. Arrowheads indicate approximately where transition zone nuclei are first seen. (D) Graph (roughly aligned with C) showing distal GLD-1 accumulation averaged from 11 gonad arms stained with GLD-1 specific antibodies (see Materials and methods). x-axis is the distance in cell diameters from the DTC. y-axis is the relative intensity of antibody staining in arbitrary units. (E) Genetic screen used to identify genes that function with gld-1 in regulating entry into meiosis. Animals homozygous for a gld-2(null), carrying a free duplication (gaDp1) that contains gld-2(+), were mutagenized to generate mutations in genes (m). Animals [m(–)] are recovered from siblings containing gaDp1 and are either homozygous or heterozygous for m(–).