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

项目总结/摘要 精子发生开始于新生小鼠睾丸， 不同的未分化和分化群体。一部分未分化的精原细胞 保留干细胞潜能（作为基础精原干细胞或SSC），其余 成为响应于视黄酸（RA）而增殖和分化的祖精原细胞。 这一最初的命运决定是至关重要的，因为失衡会导致生精缺陷，从而导致人类 睾丸癌或不育目前尚不清楚精原细胞命运决定是如何调节的。 我们最近取得了令人兴奋的发现，新生男性生殖细胞在其 在体内和体外（在没有生态位环境的情况下）对RA的反应性。早在 出生后（P）1天，我们可以确定两个不同的亚种群的原丝藻：1 -那些， 在体外或体内不能对RA应答（“RA-无应答”），2 -那些可以应答的 但在体内还没有（“RA-反应性”）。本提案的目的是确定 来自于原生藻类的基本SSC库形式， （预先决定）或从那些碰巧占据有限数量的干细胞小生境（选择）。 我们的数据有力地表明，一些原核细胞是预定的，以保持未分化 并成为SSCs，这种命运表现为无法应对增殖和 分化信号由RA提供。在拟议的目标中，我们将探讨这种RA不敏感性是否 是内在的（生殖细胞自主的）或由体细胞决定的（生殖细胞非自主的）， 当在出生后发育期间出现不同的RA反应时，并确定是否 基础SSC库仅由这些RA不敏感的生殖细胞形成。在目标1中，我们 评估与新生儿生殖细胞RA反应性相关的基因表达异质性。 生殖细胞系或索马细胞中涉及RA反应性的基因的异质性表达， 解释哪个隔间决定SSC前体的命运。在目标2中，我们将定义RA的角色 RA反应性中的接收和催化作用。我们预测RA不敏感性本质上是 预编程的，持久的，并定义了基本的SSC人口。在目标3中，我们将确定 RA不敏感的原核细胞是否优先产生基础SSC。我们将 调节体内RA水平，并检查对基础SSC形成的后续影响 池总之，这些目标的结果将定义RA反应如何有助于形成 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.