The role of retinoid exposure in specification of the foundational SSC pool

项目摘要/摘要 新生小鼠睾丸开始精子发生时，精原细胞被分离成 不同的未分化和分化的种群。未分化的精原细胞比例 保留干细胞潜能(作为基础精原干细胞，或SSCs)，其余 对维甲酸(RA)作出反应，成为增殖和分化的前体精原细胞。 这一最初的命运决定是至关重要的，因为不平衡会导致精子生成缺陷，从而导致人类 睾丸癌或不育症。目前尚不清楚精原细胞命运的决定是如何调控的。 我们最近有了一个令人兴奋的发现，新生男性生殖细胞在它们的 在体内和体外对RA的反应性(在缺乏利基环境的情况下)。最早的时候 出生后第1天，我们可以识别出两个不同的成熟原细胞亚群：1-那些 在体外或体内都不能对RA(RA-无反应)有反应，以及2-能有反应的 但还没有在体内(‘RA反应’)。这项提案的目标是确定是否 基础SSC池由本质上预先编程的繁荣原细胞形成 (预先决定)或来自那些恰好占据有限数量的干细胞壁龛(选择)。 我们的数据有力地表明，一些成熟原细胞是预先决定保持未分化的 并成为SSCs，而这种命运表现为无法应对核扩散和 分化信号由RA提供。在拟议的目标中，我们将探讨这一RA是否不敏感 是固有的(生殖细胞自主的)还是由体细胞(生殖细胞非自主的)决定的，定义 在出生后发育期间，出现不同的RA反应性，并确定是否 基本的SSC池仅由这些RA不敏感的生殖细胞形成。在目标1中，我们将 评估与新生儿生殖细胞类风湿反应相关的基因表达异质性。 通过种系或体细胞异质性表达涉及RA反应性的基因可能 解释哪一舱决定了SSC前体的命运。在目标2中，我们将定义RA的角色 类风湿关节炎反应性中的接受和分解代谢。我们预测RA不敏感本质上是 预先编程、持久，并定义了基本的SSC群体。在目标3中，我们将确定 RA不敏感的精原细胞是否优先产生基础SSCs。我们会 在体内调节RA水平，并检测随后对基础SSC形成的影响 游泳池。总而言之，这些目标的结果将定义RA响应如何有助于 新生儿睾丸中的基础SSC池。

PROJECT SUMMARY/ABSTRACT Spermatogenesis begins in the neonatal mouse testis with the segregation of prospermatogonia into distinct undifferentiated and differentiating populations. A proportion of undifferentiated spermatogonia retain stem cell potential (as foundational spermatogonial stem cells, or SSCs), and the remainder becomes progenitor spermatogonia that proliferate and differentiate in response to retinoic acid (RA). This initial fate decision is critical, as imbalances cause spermatogenic defects that can lead to human testicular cancer or infertility. It is currently unknown how spermatogonial fate decisions are regulated. We have recently made the exciting discovery that neonatal male germ cells differ in their responsiveness to RA both in vivo and in vitro (in the absence of the niche environment). As early as postnatal day (P) 1, we can identify two distinct subpopulations of prospermatogonia: 1 – those that cannot respond to RA (‘RA-non-responsive’) either in vitro or in vivo, and 2 – those that can respond but do not yet in vivo (‘RA-responsive’). The objective of this proposal is to determine whether the foundational SSC pool forms from prospermatogonia that are intrinsically preprogrammed (predetermination) or from those that happen to occupy a limited number of stem cell niches (selection). Our data strongly suggest that some prospermatogonia are predetermined to remain undifferentiated and become SSCs, and that this fate is manifest by an inability to respond to the proliferation and differentiation signal provided by RA. In the proposed aims, we will explore whether this RA insensitivity is intrinsic (germ cell autonomous) or determined by somatic cells (germ cell non-autonomous), define when during postnatal development differential RA responsiveness appears, and determine whether the foundational SSC pool is formed solely from these RA-insensitive germ cells. In Aim 1, we will assess gene expression heterogeneity associated with neonatal germ cell RA responsiveness. Heterogeneous expression of genes involving RA responsiveness by either the germline or soma could explain which compartment dictates the fate of SSC precursors. In Aim 2, we will define the roles of RA reception and catabolism in RA responsiveness. We predict that RA insensitivity is intrinsically preprogrammed, long lasting, and defines the foundational SSC population. In Aim 3, we will determine whether RA-insensitive prospermatogonia preferentially give rise to foundational SSCs. We will modulate RA levels in vivo and examine the subsequent effect on formation of the foundational SSC pool. Together, the results of these aims will define how RA responsiveness contributes to formation of the foundational SSC pool in the neonatal testis.