MOLECULAR-CLONING AND DEVELOPMENTAL REGULATION EXPRESSION OF 2 ISOFORMS OF THE CATALYTIC SUBUNIT OF PROTEIN PHOSPHATASE 2A FROM XENOPUS-LAEVIS

Two types of PP2A catalytic subunit cDNA clones were isolated from a X enopus oocyte library. One type corresponds to the Xenopus C36 alpha ( XC36 alpha) isoform as published by Cormier et al. (1991) and another type encodes for a novel isoform of PP2A(C36) (XC36 beta), more homolo gous to the C36 beta isoform cloned from Mammalia. Northern blot analy sis with isoform specific probes showed that the XC36 alpha mRNA trans cript of 2 kb is more abundant than the XC36 beta mRNA of 1.9 kb durin g embryogenesis and in adult tissues. Both transcripts are highly expr essed in ovary and heart relative to the other adult tissues examined. The high expression levels of both XC36 alpha and XC36 beta transcrip ts in the ovary decrease during the first mitotic embryonic divisions. Resumption of zygotic expression starts at about the same time for bo th mRNAs, during the tailbud stage, but the XC36 beta transcript shows only a moderate and transient increase and declines again during the tadpole stage whereas expression of XC36 alpha increases further durin g the same period until the onset of metamorphosis. (C) 1995 Academic Press, Inc.