CIP2A Promotes Proliferation of Spermatogonial Progenitor Cells and Spermatogenesis in Mice

Sami Ventelä,Jukka Westermarck,Juho-Antti Mäkelä,Christophe Côme,Edward K Chan,Jorma Toppari,Markku Kallajoki,Robin M Hobbs,Pier Paolo Pandolfi,Leni Mannermaa

doi:10.1371/journal.pone.0033209

Abstract

Protein phosphatase 2A (PP2A) is a critical regulator of protein serine/threonine phosphorylation. However, the physiological and developmental roles of different PP2A complexes are very poorly understood. Here, we show that a newly characterized PP2A inhibitory protein CIP2A is co-expressed with ki-67 and with self-renewal protein PLZF in the spermatogonial progenitor cell (SPC) population in the testis. CIP2A and PLZF expression was shown also to correlate Ki-67 expression in human testicular spermatogonia. Functionally, CIP2A mutant mouse testes exhibited smaller number of PLZF-positive SPCs and reduced sperm counts. Moreover, seminiferous tubuli cells isolated from CIP2A mutant mice showed reduced expression of Plzf and other renewal genes Oct-4 and Nanog at mRNA level. However, PLZF-deficient testes did not show altered CIP2A expression. Importantly, spermatogonia-specific restoration of CIP2A expression rescued PLZF expression and sperm production defects observed in CIP2A mutant mice. Taken together, these results reveal first physiological function for an emerging human oncoprotein CIP2A, and provide insights into maintenance of PLZF-positive progenitors. Moreover, demonstration that CIP2A expression can be systematically inhibited without severe consequences to normal mouse development and viability may have clinical relevance regarding targeting of oncogenic CIP2A for future cancer therapies.

Highlights

Cellular proliferation is essential for growth of any organism as well as for normal tissue development
When subsequent generations of the CIP2AHOZ mice were analyzed for cancerous inhibitor of PP2A (CIP2A) expression, we observed a progressive increase in testicular expression of both CIP2A mRNA and protein
We show that CIP2A expression correlates with the expression of spermatogonial proliferation and self-renewal markers both in human testis during ontogenesis and in mouse spermatogonia (Figure 2)

Summary

Introduction

Cellular proliferation is essential for growth of any organism as well as for normal tissue development. A special mode of cellular proliferation, the self-renewal of tissue-specific stem -and progenitor cells is required both to support the renewal of tissues and for the rapid production of sperm. The only actively proliferating and self-renewing cell types are the spermatogonial stem and progenitor cells (SPCs) that reside in the basal layer of the tubules [1]. PLZF was originally identified in two mouse studies as being essential for the maintenance of the spermatogonial progenitor population and spermatogenesis [3,4]. PLZF was shown to promote spermatogonial selfrenewal by opposing the function of mTORC1 [5].

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Conclusion