A principal challenge currently facing biologists is how to connect the complete DNA sequence of an organism to its development and behaviour. Large-scale targeted-deletions have been successful in defining gene functions in the single-celled yeast Saccharomyces cerevisiae, but comparable analyses have yet to be performed in an animal. Here we describe the use of RNA interference to inhibit the function of approximately 86% of the 19,427 predicted genes of C. elegans. We identified mutant phenotypes for 1,722 genes, about two-thirds of which were not previously associated with a phenotype. We find that genes of similar functions are clustered in distinct, multi-megabase regions of individual chromosomes; genes in these regions tend to share transcriptional profiles. Our resulting data set and reusable RNAi library of 16,757 bacterial clones will facilitate systematic analyses of the connections among gene sequence, chromosomal location and gene function in C. elegans.

NeuroD1/␤2 is a basic helix-loop-helix (bHLH) factor expressed in the endocrine cells of the pancreas and in a subset of neurons as they undergo terminal differentiation. We now show that NeuroD1 is expressed in corticotroph cells of the pituitary gland and that it is involved in cell-specific transcription of the proopiomelanocortin (POMC) gene. It was previously shown that corticotroph-specific POMC transcription depends in part on the action of cell-restricted bHLH factors that were characterized as the CUTE (corticotroph upstream transcription element) (M. Therrien and J. Drouin, Mol. Cell. Biol. 13:2342-2353, 1993) complexes. We now demonstrate that these complexes contain NeuroD1 in association with various ubiquitous bHLH dimerization partners. The NeuroD1-containing heterodimers specifically recognize and activate transcription from the POMC promoter E box that confers transcriptional specificity. Interestingly, the NeuroD1 heterodimers activate transcription in synergy with Ptx1, a Bicoid-related homeodomain protein, which also contributes to corticotroph specificity of POMC transcription. In the adult pituitary gland, NeuroD1 transcripts are detected in POMC-expressing corticotroph cells. Taken together with the restricted pattern of Ptx1 expression, these results suggest that these two factors establish the basis of a combinatorial code for the program of corticotroph-specific gene expression.Families of cell-restricted basic helix-loop-helix (bHLH) transcription factors control differentiation in many cell lineages. For example, the myogenic bHLH factors are involved in various steps of myogenesis, and they do so as musclespecific transcription factors (16,40,44,46,53,55). Similarly, Tal-1/SCL is required for differentiation of the hematopoietic lineage (3, 48), and a growing family of neurogenic bHLH factors has been identified in neural tissues. The Mash-1 and HES-1 bHLH factors that were originally cloned by homology to the Drosophila genes achaete-scute, and Hairy and Enhancer of Split behave as positive and negative regulators, respectively, of neurogenesis (15,18,19). The functions of other neural tissue-specific bHLH factors are not yet known (22,32,34). One member of this group, NeuroD1, was recently shown to be associated with late neuronal differentiation in Xenopus laevis (30). The same factor was also isolated as ␤2, a cell-specific transcription factor of the insulin gene (41). Thus, this socalled neural tissue-specific bHLH factor is also expressed in a small subset of endocrine cells of the pancreas. We now report on the expression and transcriptional role of NeuroD1/␤2 in specific endocrine cells of the anterior pituitary gland that express the proopiomelanocortin (POMC) gene.The development of the neuroendocrine system is highly integrated; indeed, pituitary development and hypothalamic development are intimately associated, as disruption of one affects the other (24-26). The pituitary gland develops from a placodal invagination of the stomodeum starting at embryonic day 8.5 (E8.5) i...

In Caenorhabditis elegans, numerous 'synMuv' (synthetic multivulval) genes encode for chromatin-associated proteins involved in transcriptional repression, including an orthologue of Rb and components of the NuRD histone deacetylase complex. These genes antagonize Ras signalling to prevent erroneous adoption of vulval fate. To identify new components of this mechanism, we performed a genome-wide RNA interference (RNAi) screen. After RNAi of 16 757 genes, we found nine new synMuv genes. Based on predicted functions and genetic epistasis experiments, we propose that at least four post-translational modifications converge to inhibit Ras-stimulated vulval development: sumoylation, histone tail deacetylation, methylation, and acetylation. In addition, we demonstrate a novel role for sumoylation in inhibiting LIN-12/ Notch signalling in the vulva. We further show that many of the synMuv genes are involved in gene regulation outside the vulva, negatively regulating the expression of the Delta homologue lag-2. As most of the genes identified in this screen are conserved in humans, we suggest that similar interactions may be relevant in mammals for control of Ras and Notch signalling, crosstalk between these pathways, and cell proliferation.