Worm Breeder's Gazette 13(2): 31 (February 1, 1994)
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.
The let-23 gene encodes a receptor type tyrosine kinase(1) and is necessary for vulval induction, survival past the L1 stage, hermaphrodite fertility and for male spicule development. For the vulval induction, it was proposed that Let-23 acts in vulval precursor cells(VPCs) to receive and transduce an inductive signal from the anchor cell(1). Genetic mosaic analysis of the let-23 gene function supports this proposal(2).
We have analyzed] the 5' regulatory regions of the let-23 gene to understand the mechanism of the expression. We cloned a let-23 homologue from Caenorhabditis vulgaris (formerly called C. vulgarensis ) to find evolutionary conservations in the upstream sequences. The gene in C. vulgaris probably encodes a protein of 1332 amino acids, 76% of which are shared with Let-23 of 1323 amino acids in C. elegans. The exon 15 for the tyrosine kinase domain in C. elegans is split into two exons in C. vulgaris, and a total of 19 exons is found in the C. vulgaris gene. The 12kb EcoRI-SalI fragment carrying the C. vulgaris gene rescued the lethal phenotype in the germline transformation of let-23 ( mn23 )mutant. Therefore, the gene cloned from C. vulgaris is homologous to the C. elegans let-23 gene structurally and functionally. We have found sixteen 5' upstream sequences that are conserved between C. elegans and C. vulgaris (Fig. 1, a~p).
We have also examined rescue activities of various let-23 5' deletion constructs. A construct which has 2984bp upstream of the initiation codon ATG rescued let-23 ( mn23 )lethal mutation. However, constructs carrying 2656bp, 2279bp or 2055bp did not rescue the mutation. The region from -2984bp to -2656bp includes two conserved sequences(Fig. 1, c and d). One of them (d) has a sequence AATCTTCA/CT which is similar to a consensus AATATNCAT for Pit-l/GHF-l binding sites(3). Constructs which has 2055bp, 1926bp,1672bp or 1487bp upstream of the ATG rescued let-23 ( sy97 )vulvaless mutation, but one with 1074bp did not. The region from -1487bp to -1074bp includes a conserved sequence(l in Fig. l) .
These results indicate that the regions between -2984 and -2656 and that between -1487 and -1074 are required for the rescue of a lethal or vulvaless mutation, respectively. Two conserved sequences in the former (c and d) may be activating elements for the transcription of the let-23 gene in the cells important for the larval survival. The conserved sequence in the latter (l) may be a cis-acting element required for the expression in VPCs.
(1) Aroian, Koga, Mendel, Ohshima & Sternberg, Nature 348, 693-699(1990)
(2) Koga & Ohshima, Abstracts of C. elegans Meeting, 248(1993)
(3) Ingraham, Flynn, Voss, Albert, Kapiloff, Wilson & Rosenfeld, Cell 61,1021-1033(1990)
