Effect of microinjection of rap 2A point mutant proteins on maturation and mottling in Xenopus oocytes.

We have analyzed the morphological alterations induced in Xenopus oocytes as a consequence of the microinjection of rap 2A proteins with point mutations at critical positions in the functional domains defined for members of the ras superfamily. Ala 35 rap 2A, a point mutation in the "effector" domain, is able to induce the rearrangement of the pigments in the animal hemisphere termed "mottling". This characteristic phenotype is delayed in asn 17 rap 2A and wild-type rap 2A proteins. A completely different phenotype appears as a consequence of the microinjection of Val 12-rap 2A. This mutant is able to trigger oocyte maturation and is less efficient inducing mottling than Ala 35 or wild-type rap 2A proteins. Neither of these rap 2A mutant proteins is able to counteract ras-induced maturation. However there is a striking interference with progesterone-induced maturation, since wild-type or val 12 rap 2A microinjection reduced the viability of progesterone-treated oocytes. These findings suggest that rap2A proteins are regulatory elements in distinct signal transduction pathways that either lead to the morphological changes associated with the phenotype "mottling" or to oocyte maturation.