2002 West Coast Worm Meeting abstract 50
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| 1 | Caltech Biology and HHMI, Pasadena, CA 91125 |
| 2 | Department of Molecular Genetics. The Ohio State University. Columbus OH 43210 |
We are interested in patterning of the 2° (secondary) vulval lineages P5.p and P7.p. In the wild-type, P5.p and P7.p produce stereotyped ABCD and DCBA patterns respectively. In lin-17 and lin-18 mutants, the polarity of the P7.p lineage becomes altered. We examined the P7.p lineage in lin-17 (encoding Frizzled Wnt receptor), lin-18 (encoding RYK receptor tyrosine kinase-related protein; W. Katz and P.W.S.), and double mutant using POP-1 (TCF/LEF) antibody staining and cell fate markers ceh-2::yfp and cdh-3::cfp.
In the wild-type, POP-1 is expressed in an asymmetric pattern with posterior daughters of P7.p and P7.px expressing a higher level than their respective sisters. In the lin-17 mutant, the asymmetry among P7.p daughters is often reversed but the asymmetry among P7.px daughters is not strongly affected (R. Hill and J.R. Priess, pers. comm.). We found that in the lin-18 mutant, as in the lin-17 mutant, the asymmetry is often reversed among P7.p daughters but not P7.px daughters. We also found that in the double mutant, the asymmetry is reversed in both P7.p daughters and P7.px daughters.
In the mid-L4 stage, ceh-2::yfp labels vulB cells (P7.ppax) and cdh-3::cfp labels vulC and vulD (P7.paxx). vulA cells of the 2° lineage can be distinguished by non-expression of either markers and adherence to the ventral cuticle in the mid-L4 stage. We found that in lin-17 and lin-18 mutants, P7.pap (presumptive vulC) cells were transformed to the vulA fate. In the double mutant, P7.paa (presumptive vulD) cells were transformed to the vulA fate. These results are consistent with reversals of POP-1 expression patterns, and indicate that the lineage that had high POP-1 levels in both P7.px and P7.pxx stages correlate with the cells that adopt the vulA fate.
The mechanism by which Ryk receptor signals is not known. The extracellular domain of LIN-18 and Ryk shows homology to Wnt binding protein WIF-1, suggesting a possible mechanism as an alternative Wnt receptor or a Wnt co-receptor. Since a probable lin-17 null mutation is enhanced by the lin-18 mutation, LIN-18 can signal independent of LIN-17. Furthermore, a lin-18::gfp fusion construct lacking the kinase domain can rescue the lin-18 mutant, suggesting that LIN-18 functions differently than receptor tyrosine kinases activated by phosphorylation. It is also possible that lin-18 functions in a separate non-Wnt pathway also involved in P7.p polarity.