Using a RNAi screen, we found three genes in C. elegans of which knocking down expression resulted in aberrant oocyte development. Oocytes failed to extrude their polar bodies and displayed no pseudocleavage and cytokinesis. In addition, egg shells failed to be formed. Two of these genes (R12E2.10 and T21E3.1) show 99% similarity at the DNA level, suggesting that they originate from a duplicated ancestor. The third gene (F44F4.2) shows limited homology the other two within putative protein tyrosine phosphatase domains. Within these domains, however, amino acid residues critical for phosphatase activity appear to be missing, suggesting that these proteins may act either as scaffolding proteins or anti-phosphatases. The phenotype of a null allele mutant of F44F4.2,
tm1191, is identical to that of the RNAi knock down. MSP is a sperm cell derived protein, which when in contact with oocytes triggers a MAPK signalling pathway, resulting in oocyte maturation and ovulation. In this way, only the two most proximal oocytes are activated. Within the mutant
tm1191 and the corresponding RNAi knock-down worms, MAPK in oocytes of the proximal germ line was prematurely activated. Relative high amounts of diphospho-MAPK was observed up to the -5 oocyte by fluorescence microscopy. In addition, Western blot analysis revealed elevated levels of the phosphorylated, germline specific 55 kD MPK-1. Collectively, these data suggest a role for pseudo-tyrosine phosphatase domain containing proteins in the timely regulation of MAPK activation, which is essential for a correct oocyte maturation program.