Role of the C. elegans U2 snRNP protein MOG-2 in sex determination, meiosis, and splice site selection

In Caenorhabditis elegans, germ cells develop as spermatids in the larva and as oocytes in the adult. Such fundamentally different gametes are produced through a fine-tuned balance between feminizing and masculinizing genes. For example, the switch to oogenesis requires repression of the fem-3 mRNA through the mog genes. Here we report on the cloning and characterization of the sex determination gene mog-2. MOG-2 is the worm homolog of spliceosomal protein U2A′. We found that MOG-2 is expressed in most nuclei of somatic and germ cells. In addition to its role in sex determination, mog-2 is required for meiosis. Moreover, MOG-2 binds to U2B″/RNP-3 in the absence of RNA. We also show that MOG-2 associates with the U2 snRNA in the absence of RNP-3. Therefore, we propose that MOG-2 is a bona fide component of the U2 snRNP. Albeit not being required for general pre-mRNA splicing, MOG-2 increases the splicing efficiency to a cryptic splice site that is located at the 5′ end of the exon.

Research highlights
► The nematode Caenorhabditis elegans produces both sperm and oocytes.
► mog-2 is required for the switch from spermatogenesis to oogenesis.
► mog-2 codes for the homolog of spliceosomal protein U2A′.
► MOG-2 binds to the U2 snRNA and to the RNP-3/U2B″ protein.
► mog-2 increases the splicing efficiency to a cryptic 3′ intron splice acceptor site.