AbstractBackgroundTheretinoblastomatumor suppressor (Rb) acts in a conserved pathway that is deregulated in most human cancers. Inactivation of the single Rb-related gene inCaenorhabditis elegans, lin-35, has only limited effects on viability and fertility, yet causes changes in cell-fate and cell-cycle regulation when combined with inactivation of specific other genes. For instance,lin-35Rb is a synthetic multivulva (synMuv) class B gene, which causes a multivulva phenotype when inactivated simultaneously with a class A or C synMuv gene.ResultsWe used the ORFeome RNAi library to identify genes that interact withC. elegans lin-35Rb and identified 57 genes that showed synthetic or enhanced RNAi phenotypes inlin-35mutants as compared torrf-3anderi-1RNAi hypersensitive mutants. Based on characterizations of a deletion allele, the syntheticlin-35interactorzfp-2was found to suppress RNAi and to cooperate withlin-35Rb in somatic gonad development. Interestingly, ten splicing-related genes were found to function similar tolin-35Rb, as synMuv B genes that prevent inappropriate vulval induction. Partial inactivation of specific spliceosome components revealed further similarities withlin-35Rb functions in cell-cycle control, transgene expression and restricted expression of germline granules.ConclusionWe identified an extensive series of candidatelin-35Rb interacting genes and validatedzfp-2as a novellin-35synthetic lethal gene. In addition, we observed a novel role for a subset of splicing components inlin-35Rb-controlled processes. Our data support novel hypotheses about possibilities for anti-cancer therapies and multilevel regulation of gene expression.