Catenins: A role in spertmatogenesis and sperm maturation

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Ectoplasmic specializations are specialized actin-based adherens junctional complexes formed between Sertoli cells (basal ES) and between Sertoli and germ cells (apical ES) in the testis. The importance of this junctional complex is evidenced by the fact that the abnormal or disrupted ES contributes to spermatid sloughing and oligospermia in pathological conditions associated with reduced fertility potential, including varicocele, hyperprolactinemia, diabetes and idiopathic oligospermia. The greater vulnerability of ES to alterations in testis microenvironment compared to other junctional complexes, may explain why ES is frequently disrupted in cases of impaired fertility. Therefore, identification of the regulatory molecules and signaling pathways that regulate ES dynamics is vital to understand the mechanism of ES susceptibility and its role in male fertility. Recently, we have obtained interesting results that show signaling protein “β-catenin, which is highly expressed in the germ cells and Sertoli cells, to play an important role in regulating germ cell- Sertoli cell adhesion at the apical ES. We show that spermatid-specific deletion of β-catenin not only results in spermatid sloughing (indicating an impaired apical ES), but also causes significantly reduced sperm count and increased germ cell apoptosis. These results led us to hypothesize that β-catenin is the molecular link that integrates Sertoli cells-germ cells adhesion with the signaling events essential for germ cell development and maturation. We propose that binding of germ cell β-catenin-complex to β-catenin-complex on Sertoli cell at the apical ES surface triggers a signaling cascade that regulates post-meiotic germ cell differentiation. Two specific aims are proposed to test these hypotheses: (1) To elucidate the function of β-catenin in germ cell development and maturation by targeting events at the apical ectoplasmic specialization. In this aim, we are targeting events only at the apical ES by generating protamine 1 (Prm1) promoter driven conditional knockout mice that specifically silences β-catenin in elongating spermatids, thereby distinguishing the events occurring at the cell lumen from those at the base of the cell. (2) To identify and characterize signaling pathways regulated by β-catenin at the apical ES. In this aim, by performing microarray analysis, we will identify and characterize β-catenin regulated genes to determine specific roles they might play in regulating apical ES functions. The results of this basic research will provide insights into the role of ES in male fertility and a better understanding of the mechanisms by which defects in these critical pathways lead to infertility. In addition, these studies could lead to new insights for therapeutically compromising germ cell movement in the seminiferous epithelium, thereby disrupting spermatogenesis, as a novel approach to reversible male contraception.