Nuclear pre-mRNA 3'-end processing regulates synapse and axon development in C. elegans.

Nuclear pre-mRNA 3'-end processing is vital for the production of mature mRNA and the generation of the 3' untranslated region (UTR). However, the roles and regulation of this event in cellular development remain poorly understood. Here, we report the function of a nuclear pre-mRNA 3'-end processing pathway in synapse and axon formation in C. elegans. In a genetic enhancer screen for synaptogenesis mutants, we identified a novel polyproline-rich protein, Synaptic defective enhancer-1 (SYDN-1). Loss of function of sydn-1 causes abnormal synapse and axon development, and displays striking synergistic interactions with several genes that regulate specific aspects of synapses. SYDN-1 is required in neurons and localizes to distinct regions of the nucleus. Through a genetic suppressor screen, we found that the neuronal defects of sydn-1 mutants are suppressed by loss of function in Polyadenylation factor subunit-2 (PFS-2), a conserved WD40-repeat protein that interacts with multiple subcomplexes of the pre-mRNA 3'-end processing machinery. PFS-2 partially colocalizes with SYDN-1, and SYDN-1 influences the nuclear abundance of PFS-2. Inactivation of several members of the nuclear 3'-end processing complex suppresses sydn-1 mutants. Furthermore, lack of sydn-1 can increase the activity of 3'-end processing. Our studies provide in vivo evidence for pre-mRNA 3'-end processing in synapse and axon development and identify SYDN-1 as a negative regulator of this cellular event in neurons.