Mutations in the C. elegans maternal-effect genes
clk-1,
clk-2,
clk-3, and
gro-1 are highly pleiotropic resulting in an average slowing of development, adult rhythmic behaviors, reproduction, as well as in an extended life span. Here we will present the genetic and molecular characterization of the gene
clk-2. This gene is defined by one recessive mutation,
qm37, which was isolated in a screen for viable maternal-effect mutations (Hekimi et al., 1995). At 20C, the duration of embryonic and post-embryonic development of
clk-2(
qm37) mutants is lengthened and adult behaviors such as defecation, pharyngeal pumping, and egg laying are slower. In addition, they live long. In contrast, at 25C,
clk-2(
qm37) mutants die as embryos. Moreover, at 20C,
clk-2(
qm37) mutants can be fully rescued both zygotically and maternally, while at 25C there is a strict-maternal effect. We believe that
clk-2(
qm37) is a temperature-sensitive mutation that behaves as a hypomorph at 20C and as a null at 25C. As we have found that
clk-2 is not required for the development of the germline per se at 25C, we have explored the origin of the embryonic lethality at 25C by carrying out temperature shift experiments. We have shown that
clk-2 is required before the two-cell stage of embryogenesis. The temporal and spatial expression pattern of
clk-2 deduced from northern and western analyses, and from the use of
clk-2::gfp reporter fusions, is consistent with a maternal role of
clk-2 early in development and throughout the life of the worm.