The LIM homeodomain protein MEC-3 controls the differentiation of ten neurons: the six touch cells, the two FLP cells and the two PVD cells. Several genes(
mec-2,4,6,7,9,10,14,18), all needed for the function of touch cells, are expressed in a
mec-3 dependent fashion. These genes are likely to be a subset of the
mec-3-dependent genes for several reasons: 1)these genes were identified by mutations that cause touch insensitivity, genes that mutate to supersensitivity have not been sought; 2) genes with redundant functions would not have been identified in past screens; 3) genes that are needed for touch cell development or function but do not affect touch sensitivity (e.g., genes needed for chemical synaptic transmission or exclusively for AVM and PVM function) would not be identified in past screen; and 4)genes required for FLP or PVD functions have not been identified. To identify these other genes, we used the Representational Difference Analysis (RDA) modified for cDNA by Chuck Ma ( 10th International Worm Meeting, P.9), Hubank and Schatz,( Nuc.Acid Res. 22:5640-5648,1994) and O!Neill and Sinclair(Nuc.Acid Res. 25:2681-1682, 1997). We further improved the method by using different tester and driver ratios to identify which conditions enrich for
mec-7 and
mec-18 cDNAs. Of 95 cDNA clones initially isolated, 6% of clones were
mec-7 and 10% were
mec-18. About 80% of the clones contained the same cDNA; unfortunately no RNA was detected by northern blotting, so we have been unable to confirm whether this cDNA is
mec-3 dependent. The remaining clones identified 5 new candidates for
mec-3-dependent cDNAs. Three cDNAs show a 2, 6 or 10 fold decrease, respectively, in
mec-3 mRNA compared to N2 mRNA on northern blots. The expression of the other two cDNAs is being investigated. None of these cDNAs map to positions near previous known touch genes. We intend to look at the expression patterns of these cDNAs and to enlarge our screen to identify more genes of this type.