Expression of the B56delta subunit of protein phosphatase 2A and Mea1 in mouse spermatogenesis. Identification of a new B56gamma subunit (B56gamma4) specifically expressed in testis.

Protein phosphatase 2A (PP2A) is a critical serine/threonine phosphatase involved in the control of multiple cellular functions. Distinct regulatory subunits of this holoenzyme govern its intracellular localisation and substrate specificity. The regulatory B subunits target PP2A to the substrate. The B56delta subunit encoded by Pp2r5d is expressed in different tissues including testis. Its genomic structure shows a 3' end region of 114 bp in reverse orientation complementary to the 3' region of Mea1. In mouse seminiferous epithelium Mea1 is highly expressed in pachytene spermatocytes through to spermatid cells, while Pp2r5d shows under-expression. The potential co-regulation of both these genes was analysed. However, no potential transcriptional or post-transcriptional interference between them could be fully defined. A previously unreported subunit with testis-specific expression, B56gamma-4, was characterised. This new subunit of the B56 family has no genomic structure related to Mea1, and might replace the functions of B56delta if B56delta expression were compromised by high expression of Mea1 during spermatogenesis.

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