Project Summary The molecular characterization of sex-specific piRNA transcription and snRNA transcription in C. elegans. PIWI-interacting RNAs (piRNAs) play key roles in repressing transposons in the germline. Loss of transposon- targeting piRNAs can have sex-specific consequences leading to genomic instability and infertility. However, the mechanisms of sex-specific piRNA expression remain largely unknown. Recent studies have revealed that SNPC-4, a core factor required for snRNA transcription, is also essential for piRNA transcription in C. elegans and suggests that the snRNA transcriptional machinery may have been co-opted to transcribe piRNAs. Therefore, identifying the transcription factors and characterizing the specific protein domains that dictate sex- specific piRNA and snRNA transcriptional specificity will address this critical knowledge gap. The small nuclear RNA activating protein complex (SNAPc) is a conserved heterotrimeric complex consisting of SNAPC1, SNAPC3, and SNAPC4 that facilitates snRNA transcription in mammals. Unlike mammals, C. elegans have several orthologs of SNAPC1 that have sexually dimorphic roles in piRNA biogenesis. My preliminary data show that SNPC-1.2 promotes female piRNA transcription while SNPC-1.3 is a known male piRNA transcription factor. Furthermore, my initial data show the C. elegans SNAPC3 ortholog, SNPC-3.4, facilitates snRNA biogenesis, while SNPC-3.1 and SNPC-3.2 act redundantly to drive both male and female piRNA expression. I will investigate my hypothesis that SNPC-1.2 is a bona fide female piRNA transcription factor and harbors unique protein motifs conferring female piRNA expression, while distinct domains in SNPC-1.3 specify male piRNA expression (Aim 1). Additionally, I predict SNPC-3.4 is a snRNA biogenesis factor, while SNPC-3.1 and SNPC-3.2 act redundantly to drive piRNA transcription. Analogous to the SNPC1 family, I predict that distinct domains within SNPC-3.4 and SNPC-3.1/3.2 specify their recruitment and transcription at snRNA and piRNA genomic loci, respectively (Aim 2). Collectively, these data will elucidate the snRNA and female and male piRNA transcriptional complexes and identify the protein motifs that engender snRNA and sex-specific piRNA transcription. This work may have implications in treating fertility defects that are due to abnormal piRNA expression as well as different neuronal diseases associated with snRNA misregulation such as ALS.