||A cell identity determining gene, mab-21, has been studied in our lab to understand its role in guiding sensory organ patterning of C. elegans. In mab-21 mutant, ray 6 precursor cell adopts a fate similar to that of ray 4 and subsequently fuses with it. The function of mab-21 is to maintain the ray 6 cell identity. In order to identify new components worked for this particular process, a genome-wide RNA interference (RNAi) screen was performed and a novel C2H2 type zinc-finger encoding gene, mab-30, was identified. mab-30 mutant animals showed developmental defects on the specification of ray 6, which is similar to those observed in mab-21 mutants. The temporal and spatial expression of mab-30 overlaps with that of mab-21 in the ray 6 structural cell. I hypothesize that mab-30 acts in the ray 6 structural cell in concert with other mab-21 pathway components to determine the ray 6 identity. Using different genetic approaches, I demonstrated that mab-30 interacts with several components in MAB-21/SIN3/HDAC (MSH) complex. The results implicate that the function of mab-30 in the patterning of rays might involve chromatin modification to regulate downstream target components. Since the zinc-finger domains in MAB-30 may confer DNA binding ability and thus target specificity for gene regulation, a thorough analysis of MAB-30 direct target genes and their regulation is essential for expanding our characterization of mab-21 pathway and its executory machinery. From a genome-wide chromatin immunoprecipitation (ChIP) on chip analysis, I have successfully identified and mapped a large number of novel targets. A robo receptor encoding gene, sax-3, was shown to be the direct downstream target of mab-30. The genetic interaction between sax-3 and mab-21 further suggested that the mab-21 pathway may cross-talk with sax-3/slt-1 signaling pathway through mab-30. The results from my study provide a more elaborate picture outlining the execution of a patterning process via direct control of cell recognition and cell-cell signaling events through well-characterized guidance molecules.