Mutations in the C. elegans gene lin-44 lead to reversals in the polarity of certain asymmetric cell divisions. We have discovered that lin-44 is a member of the Wnt family of genes, which encode secretory glycoproteins implicated in intercellular signaling. Both in situ hybridization experiments using lin-44 transcripts and experiments using reporter constructs designed to mimic patterns of lin-44 expression indicate that lin-44 is expressed in hypodermal cells at the tip of the tail and posterior to the cells with polarities affected by lin-44 mutations. Our mosaic analysis indicates that lin-44 acts cell nonautonomously. We propose that LIN-44 protein is secreted by tail hypodermal cells and affects the polarity of asymmetric cell divisions that occur more anteriorly in the tail.
Bibliographical noteFunding Information:
We thank members of the Herman, Shaw, and Rougvie laboratories for advice and discussion. We are grateful to L. Miller and S. Kim for advice on the generation of the YAC derivatives, H. Browning for the unamplified genomic library, R. Barstead for the cDNA library, M. Chal-fie for the GFP expression vector, and A. Fire for the heat shock and laczexpression vectors. Some strains used in this work were provided by the Caenorhabditis Genetics Center. This work was supported by National Institutes of Health grants GM22387 to R. K. H., HD22163 to J. E. S., and GM24943 to H. R. H.; M. A. H. was supported in part by National Institutes of Health training grant GM07287. H. R. H. is an Investigator of the Howard Hughes Medical Institute.