The molecular mechanisms of cell-cell fusion are largely unknown. The fusion of the anchor cell (AC) with eight cell progeny during C. elegans gonadogenesis and vulval development is an excellent model for studying cell-cell fusion. The
ty10 mutant has been obtained and shown to be defective in this fusion process. Recently, we have shown that the H15N14 fosmid, which contains the
nsf-1 and
adr-1 genes, rescues the
ty10 mutant defect. In addition,
ty10 was shown to be an allele of C.elegans
nsf-1, which encodes N-ethylmaleimide-sensitive factor (NSF-1) and is required for intracellular membrane fusion. To determine whether
nsf-1 alone can rescue the
ty10 mutant defect, we subcloned this fosmid and made the constructs cNSF-BN1, which contains full-length
nsf-1 genomic DNA plus 1.7 kb upstream region, and cNSF-BN2, which contains an additional 3.3 kb of upstream DNA. Transformation of
ty10 mutant worms with the cNSF-BN2 construct rescues the AC fusion defect, suggesting that C. elegans NSF plays a critical role in cell-cell fusion. We are also attempting to define the
nsf-1 promoter region using cNSF-BN1. Another mutant (called
ty4) has been obtained which has a phenotype similar to that of
ty10. Interestingly,
ty4 maps to chromosome II, while
ty10 maps to chromosome I. Therefore, it is critical to map
ty4 and clone it since
ty4 may also play a role in cell-cell fusion in the same pathway with
ty10 or in other pathways that are essential for cell-cell fusion. Currently, I have been using three-factor mapping strategies as well as deficiency mapping approaches and have positioned
ty4 into a more precise genetic interval which corresponds to around 0.23 map unit (~ 300kb).