Control of germline proliferation is necessary for normal germline development and fertility. How this control is achieved is not fully understood. Products involved in this process in C. elegans have been identified genetically [1, 2, 3, 4, 5] and molecular evidence for three genes,
lag-2,
glp-1, and
lag-1 suggest their possible roles in the control of germline proliferation. GLP-1, a Notch family transmembrane receptor, is thought to transduce a proliferative signal from the distal tip cell (DTC) to germ cells in the distal gonad [6, 7, 8]. The DTC signal is encoded by the
lag-2 product, a Drosophila Delta and Serrate homolog [9, 10, 11].
lag-1, a Drosophila Suppressor of Hairless homolog, is a potential DNA binding protein [11, 12]. To identify genes encoding negative regulators of the
glp-1 signalling pathway, we screened for enhancer mutations that confer a tumorous phenotype in a sensitized
glp-1 genetic background,
glp-1(
oz112oz120).
glp-1(
oz112oz120) was identified as a cis intragenic revertant of
glp-1(
oz112gf), a novel
glp-1(gf) mutation which results in constitutive activation of the
glp-1(
oz112gf) receptor. Fortuitously, the
oz120 mutation (Gly1057Asp) is identical to another
glp-1 allele,
q231ts [1, 13].
oz112oz120 and
q231 have a temperature-sensitive Glp phenotype; at restrictive temperature (25oC) the germ lines are Glp, but at permissive temperature (15oC) the animals are fertile. Analysis of the
glp-1(
oz112oz120) germline phenotype at 15oC suggests these animals retain residual
oz112gf activity, since there is a low frequency (0.05%) of gonad arms with a late-onset tumorous phenotype. We reasoned this sensitized
glp-1 genetic background could be used to identify mutations that reduce the activity of a negative regulator of the
glp-1 signalling pathway, producing an enhancement in the weak late-onset tumorous phenotype of
glp-1(
oz112oz120). In a pilot screen (2160 haploid genomes) for recessive tumorous mutations in the
glp-1(
oz112oz120) background at 15oC, we identified three mutations that cause a
glp-1(
oz112oz120) dependent tumorous germline phenotype. These loci are called teg genes (tumorous enhancers of
glp-1(
oz112oz120)). None of the Teg mutants display a germline phenotype when separated from
glp-1(
oz112oz120). We are currently mapping these mutations on the basis of their enhancer phenotype. Progress will be reported. [1] Austin and Kimble, 1987. Cell 51:589-599; [2] Maine and Kimble, 1989. Development 106:133-143; [3] Lambie and Kimble, 1991. Development 112:231-240; [4] Maine and Kimble, 1993. Genetics 135:1011-1022; [5] Qiao et al., 1995. Genetics 141:551-569; [6] Yochem and Greenwald, 1989. Cell 58:553-563; [7] Austin and Kimble, 1989. Cell 58:565-571; [8] Crittenden et al., 1994. Development 120:2901-2911; [9] Tax et al., 1994. Nature 368:150-154; [10] Henderson et al., 1994. Development 120:2913-2924; [11] reviewed in Artavanis-Tsakonas et al., 1995. Science 268:225-232; [12] S. Christenson and J. Kimble, personal communication; [13] Kodoyianni et al., 1992. Mol Biol Cell 3:1199-1213.