Worm Breeder's Gazette 14(5): 75 (February 1, 1997)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
University of Colorado-Boulder Campus Box 347 Boulder, CO 80309-0347The unc-62 gene is currently defined by the embryonic lethal allele s472, two alleles that show partial maternal-effect embryonic or L1 lethality, ct344 and t2012, and the canonical weaker allele, e644, which results in an Unc phenotype. The nonviable animals display severe morphological disorganization, most notably in the posterior. We used the anti-LIN-26 antibody (which stains all hypodermal nuclei) and the MH27 antibody (which outlines tight junctions between cells) to examine the distribution and number of hypodermal cells at various stages of embryogenesis, particularly at the start of morphogenesis. Self-progeny embryos from mothers homozygous for either ct344 or t2012 have ~30 fewer hypodermal cells than wild type and mislocalize the P, V, and C-derived hypodermal cells. Antibodies against body wall muscle myosin show that these embryos do not correctly assemble the body wall muscle quadrants.
We previously reported rescue of ct344 with a 15 kb region of genomic DNA on chromosome V. A 6.9 kb region including two related pairs of nearly identical genes contains all the sequences necessary for rescue (see Fig. 1). The chromosomal organization of these four genes suggests that two inversion duplication events gave rise to this gene cluster. A 2.8 kb region including genes Ia and IIa is sufficient for rescue and we hypothesize that a fragment containing genes Ib and IIb will also rescue. The predicted products of these genes display significant similarity to a growing family of proteins that have members in yeast, slime mold, guinea pig, and human. The human homolog (p19Skp1) is directly involved in regulating the activity of CycA-CDK2 kinase and thereby controls entry into S phase (ref. 1). The yeast homolog, SKP1, also controls cell cycle progression by targeting SIC1 to a degradation pathway (ref. 2). Northern analysis shows that the C.elegans genes are expressed strongly in early embryogenesis and less strongly in adult somatic tissues. Genetic analysis of unc-62 reveals that it contributes maternally and embryonically to development. To reconcile this result with its expression pattern, we hypothesize that unc-62 RNA or gene product is imported into the developing oocytes.
So far, no molecular lesions were found in the 6.9 kb region of animals homozygous for either e644, ct344, or t2012. We currently are investigating two hypotheses that would explain all our results. 1) Southern analysis of YACs covering the unc-62 physical region reveals another class I Skp-1-like gene. This could be the authentic unc-62 gene, and the 6.9 kb fragment "rescue" could result from high copy suppression. We have isolated this additional copy and are sequencing it from mutant animals. 2) A nearby transposon is transcribed in a developmentally regulated fashion similar to that of the Skp-1-like genes. This observation is consistent with a regional regulatory element that controls the expression of all four Skp-1-like genes in the 6.9 kb region as well as the adjacent transposon. Experiments to examine the transcript levels of these genes in mutant animals are underway.
1. Zhang, H. et al. Cell 82: 915-925 (1995).
2. Bai, C. et al. Cell 86: 263-2274 (1996).