Worm Breeder's Gazette 11(2): 99
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.
During post-embryonic development, C. elegans develops through four molts, synthesizing a new and morphologically distinct cuticle at each molt. Mutations in heterochronic genes lin-4, lin- 28, and lin-29 result in either precocious formation of a morphologically adult cuticle at the third (L3) molt, or retarded formation of a larva cuticle at the fourth (L4) molt. Collagens are major components of cuticle, and genes encoding collagens are temporally regulated as shown by their patterns of mRNA accumulation ( Cox and Hirsh, 1985). Thus, it is likely that heterochronic genes are involved directly or indirectly in the temporal regulation of collagen genes responsible for the stage-specific aspects of cuticle morphology. We have previously reported the identification of two collagen genes, col-10 and col-17 that are expressed at the L3 molt and are not expressed at the L4 molt in wild type (CSH meeting abstract 160, 1989). We have sequenced the col-17 gene and found that col-17 consists of one large open reading frame of 283 amino acid. Immediately preceding the translational initiator ATG is a consensus splice acceptor sequence (TTCCAG), suggesting that either cis or trans-splicing may occur utilizing this acceptor sequence. The absence of a consensus splice donor signal between the TATA sequence and the translational initiator ATG (about 220 bp) and the similarity in the position of this splicing-receptor in col-17 and trans-spliced collagen genes ( Park and Kramer, 1989; Kramer, personal communication) suggest that col-17 might be trans-spliced. The positions of Cys in the col-17 protein are identical to those of col-12, d Kramer, 1989), thus col-17 belongs to the family of col-12, s. We examined col-17 expression in various heterochronic mutants by Northern analysis using a gene-specific 20 base oligonucleotide probe for col-17. Our results showed that the precocious mutants, lin-14( ma135), 60) and lin-28(n719), appear to precociously turn off col-17 transcription at the L3 molt. Although none of these precocious mutants completely turns off col-17 transcription at the L3 molt, lin-14(ma135) and lin-28(n719) mutations, which cause more severe precocious defects than lin-14(n360), similarly caused a more severely reduced col-17 expression at the L3 molt. In contrast, the retarded mutants lin-4(e912), 36/+) and lin-29(n546) continue to express col-17 at the L4 molt to a level comparable to the wild type at the L3 molt. In contrast to col-17, ranscribed at the L3 molt but is transcribed at the L4 molt in wild type (Cox and High. 1985; Cox et al. 1989). A gene-specific 20 base oligonucleotide probe for col-7 was used to probe the same Northern filter that had been probed with col-17. Our results showed that the retarded mutants, lin-4(e912), 361+) and lin-29(n546) fail to express col-7 at the L4 molt, suggesting that lin-4 and lin-29 gene products are required for col-7 transcription and that lin-14 gene product inhibits col-7 transcription (e912, and n719 are lf; n536 is gf). To our surprise, precocious mutants homozygous for lin-14(lf) or lin-28(lf) mutations did not express col-7 precociously at the L3 molt. Thus, despite the fact that these precocious mutations cause the formation of a morphologically adult cuticle at the L3 molt, they could not cause the expression of the full set of adult-specific collagens at the L3 molt. We have not yet examined col-7 expression in the lin-14(lf); ) double mutant. Perhaps the loss of either lin-14 or lin-28 can cause precocious expression of positive regulators of col-7 such as lin-29, that are required but not sufficient to activate early col-7 expression.