Identification and characterization of putative protein phosphatase-1c[gamma]2 regulatory subunits in mouse testis.
Published: 2004
Language: eng
Number of pages: 170
Description: Lack of interaction between PP1cgamma2 and the available pool of isoform-specific regulatory subunits in the testis has the potential to best explain the sterility PP1cgamma -/- mutants.Type 1 protein phosphatases are holoenzymes composed of a single catalytic subunit (PP1c) in complex with one or more regulatory subunits. In mice, three genes encoding four PP1c isoforms have been identified---PP1calpha, PP1cbeta, PP1cgamma1 and PP1cgamma2, the latter two being derived from alternative splicing of a single PP1cgamma gene. Although the highly conserved nature of the isoforms suggests some functional overlap between them, a unique role for the PP1cgamma2 splice variant has been suggested in the mammalian testis. Specifically, the process of spermatogenesis was shown to be impaired in male mice bearing a targeted mutation in the PP1cgamma gene, ultimately resulting in infertility. A lack of functional PP1cgamma2 seems the most likely cause of the mutant phenotype, as PP1cgamma2 is the predominant PP1cgamma isoform expressed in wild type testis.Spz1 and TIPP1 (amino acids 227--534) were shown to interact specifically with PP1cgamma2 in both yeast and mammalian cells, but did not show an interaction with PP1calpha or with a truncated version of PP1cgamma2 lacking 18 amino acids from the C-terminus. Both were expressed in a stage-specific manner during spermatogenesis, and appeared abnormally expressed in the testes of PP1cgamma mutant mice. Increasing concentrations of chimeric Spz1 or TIPP1 (amino acids 227--534) were able to inhibit the activity of recombinant PP1cgamma2 in a phosphatase assay using phosphorylase a, while having little effect on the activity of recombinant PP1calpha. The interaction between PP1calpha2 and Spz1 was also shown to prevent binding of the latter to the consensus E-box promoter sequence.I have hypothesized the presence of one more regulatory subunits in the testis that interact specifically with PP1cgamma2, allowing it to mediate a function required for proper spermatogenesis. Yeast two-hybrid screening has identified at least five testis proteins that have the potential to act as PP1cgamma2-specific regulatory subunits, including the spermatogenic zip protein Spz1, a variant of endophilin B1a, a protein designated TIPP1 for t&barbelow;estis i&barbelow;nteractor of p&barbelow;rotein p&barbelow;hosphatase-1&barbelow;, and two uncharacterized testis proteins.
Notes: Adviser:  Susannah Varmuza.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 4991.