The role of protein phosphatase 2A catalytic subunit Calpha in embryogenesis: evidence from sequence analysis and localization studies.

Protein phosphatase 2A (PP2A) constitutes one of the major families of protein serine/threonine phosphatases found in all eukaryotic cells. PP2A holoenzymes are composed of a catalytic subunit complexed with a structural regulatory subunit of 65 kDa. These core subunits associate with regulatory subunits of various sizes to form different heterotrimers which have been purified and evaluated with regard to substrate specificity. In fully differentiated tissues PP2A expression levels are highest in the brain, however, relatively little is known about expression in the developing embryo. In order to determine the composition of PP2A catalytic subunits in the mouse, cDNAs were cloned and the genomic organization of PP2A Calpha was determined. By a gene targeting approach in the mouse, we have previously shown that the absence of the major catalytic subunit of PP2A, Calpha, resulted in embryonic lethality around embryonic day E6.5. No mesoderm was formed which implied that PP2A plays a crucial role in gastrulation. Here, we extended our studies and analyzed wildtype embryos for Calpha expression at subsequent stages of development. After gastrulation is completed, we find high expression of Calpha restricted to the neural folds, which suggests that PP2A plays an additional pivotal role in neurulation.