Catenins: A role in spertmatogenesis and sperm maturation

外质特化是睾丸中支持细胞(基础ES)和支持细胞与生殖细胞(顶端ES)之间形成的基于肌动蛋白的黏附连接复合体。这种连接复合体的重要性可以从以下事实得到证明：在与生育潜力降低相关的病理条件下，异常或破坏的ES有助于精子细胞坍塌和少精子症，包括精索静脉曲张、高催乳素血症、糖尿病和特发性少精子症。与其他连接复合体相比，ES对睾丸微环境改变的易感性更强，这可能解释了为什么ES在生育能力受损的情况下经常被干扰。因此，识别调控ES动态的调节分子和信号通路对于了解ES易感性的机制及其在男性生育中的作用至关重要。最近，我们获得了有趣的结果，表明在生殖细胞和支持细胞中高表达的信号蛋白β-连环蛋白在调节生殖细胞-支持细胞在顶端ES的黏附中发挥重要作用。我们发现，精子细胞特异性的β-连环蛋白缺失不仅会导致精子细胞塌陷(表明顶端ES受损)，而且还会导致精子数量显著减少和生殖细胞凋亡增加。这些结果使我们假设β-连环蛋白是将支持细胞-生殖细胞黏附与生殖细胞发育和成熟所必需的信号事件结合在一起的分子纽带。我们认为，在胚胎干细胞顶端，生殖细胞β-连环蛋白复合体与支持细胞上的β-连环蛋白复合体结合，触发了调节减数分裂后生殖细胞分化的信号级联反应。我们提出了两个特定的目标来验证这些假说：(1)通过针对顶端外质特化的事件来阐明β-catenin在生殖细胞发育和成熟中的作用。在这个目标中，我们只针对顶端ES的事件，通过产生鱼精蛋白1(PRM1)启动子驱动的条件基因敲除小鼠，特异性沉默伸长精子细胞中的β-连环蛋白，从而区分发生在细胞腔的事件和发生在细胞底部的事件。(2)鉴定和鉴定在顶端ES中受β-连环蛋白调控的信号通路。为此，我们将通过进行基因芯片分析，识别和表征β-连环蛋白调控基因，以确定它们在调控心尖ES功能中可能发挥的特定作用。这项基础研究的结果将提供对ES在男性生育中的作用的洞察，并更好地理解这些关键途径中的缺陷导致不育的机制。此外，这些研究可能带来新的见解，从治疗上损害生精上皮中的生殖细胞运动，从而扰乱精子发生，作为一种可逆的男性避孕的新方法。

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.