The role of UCH-L1 in mammalian spermatogonia

睾丸中的干细胞是成人中最重要的干细胞系统之一，因为它们产生的精子可以跨代传递遗传信息。干细胞可以以两种不同的方式分裂：它们可以自我更新以产生更多的干细胞，或者分化成一种能够增殖并最终产生精子的固定细胞类型。这一过程被称为干细胞命运决定，对哺乳动物的繁殖至关重要。如果这种微妙的平衡倾向于自我更新，精子最终会消失。但是，如果分化过多，睾丸的干细胞就会全部流失，精子就会停止产生。在任何一种情况下，不孕症都会随之而来。考虑到干细胞命运决定的重要性，可能令人惊讶的是，控制它的机制在很大程度上是未知的。我们之前发现了一种叫做UCH-L1的蛋白质，它在许多物种的神经系统和未分化的睾丸生殖细胞中特异性表达。当生殖细胞开始向精子分化时，UCH-L1不再存在。然而，虽然UCH-L1的表达仅限于未分化的生殖细胞，但其在这些细胞中的功能尚不清楚。我们设计了一系列实验来帮助描述UCH-L1影响生殖细胞命运决定的分子和细胞途径。首先，我们将使用具有特定UCH-L1缺失的小鼠模型来确定其缺失如何影响精子发生的进展。然后，我们将确定UCH-L1在生殖细胞中与哪些蛋白质结合，以及它如何参与控制生殖细胞分化。对其他细胞类型如神经元或癌细胞的研究表明，UCH-L1与mTORC1通路相互作用，控制细胞代谢。我们将调查这是否也发生在睾丸。我们还将监测UCH-L1存在或不存在时基因表达的差异。一个细胞是否是一个真正的干细胞的决定性测试是它的整个细胞谱系的重建能力。就睾丸而言，真正的干细胞可以在生殖细胞耗尽的受体动物的睾丸上定植，并产生精子。我们假设，在没有UCH-L1的干细胞中，重建精子发生的能力受到损害，我们将使用移植试验来验证这一假设。最后，我们将把我们在小鼠模型中的发现转化为作为农业重要物种的猪。我们将使用一种特定的抑制剂或抑制基因表达来阻断猪生殖细胞中UCH-L1的功能，并将研究是否与小鼠模型中相同的途径受到影响。然后，我们将使用我们之前开发的移植试验来进一步确定UCH-L1在猪生殖细胞分化中的作用。了解是什么调控了干细胞的维持和分化，将使我们能够开发出在体外繁殖睾丸干细胞的系统，并有助于设计生育调控策略。

Stem cells in the testis are one of the most important stem cell systems in the adult because they produce sperm that transmit genetic information across generations. Stem cells can divide in two distinct ways: they can self-renew to generate more stem cells or differentiate to a committed cell type that will proliferate and ultimately produce sperm. This process, known as stem cell fate decision, is essential for mammalian reproduction. If this delicate balance is skewed toward self-renewal, sperm cells will eventually disappear. If there is too much differentiation, however, the testis will lose all of its stem cells and consequently, sperm production will cease. In either case infertility will ensue. Given the importance of stem cell fate decision, it is perhaps surprising that the mechanisms that govern it are largely unknown. We previously identified a protein, called UCH-L1 that is specifically expressed in the nervous system and in the undifferentiated germ cells of the testis in many species. As germ cells begin to differentiate toward sperm, UCH-L1 is no longer present. Yet, while the expression of UCH-L1 is restricted to undifferentiated germ cells, its function in these cells is unknown. We have designed a series of experiments that help characterize the molecular and cellular pathways by which UCH-L1 influences germ cell fate decision. First, we will use a mouse model with a specific deletion of UCH-L1 to identify how its absence affects progression of spermatogenesis. We will then identify which proteins UCH-L1 binds to in germ cells and how it is involved in controlling germ cell differentiation. Studies in other cell types such as neurons or cancer cells show that UCH-L1 interacts with the mTORC1 pathway in the control of cell metabolism. We will investigate if this also occurs in the testis. We will also monitor differences in gene expression in the presence or absence of UCH-L1. The definitive test as to whether a cell is a true stem cell is the ability to recreate its entire cell lineage. In case of the testis, a true stem cell can colonize the testis of a recipient animal depleted of germ cells, and produce sperm. We hypothesis that the ability to reconstitute spermatogenesis is impaired in stem cells without UCH-L1 and we will use transplantation assays to test this hypothesis. Finally, we will translate our findings in the mouse model to the pig as an agriculturally important species. We will block the function of UCH-L1 in pig germ cells using a specific inhibitor or suppression of gene expression and will investigate whether the same pathways are affected as in the mouse model. We will then use transplantation assays previously developed by us to further define the role of UCH-L1 in pig germ cell differentiation. Knowing what regulates stem cell maintenance versus differentiation will allow us to develop systems to propagate testis stem cells in vitro and help design strategies for fertility regulation.