REGULATION OF LEYDIG CELL MITOSIS AND DIFFERENTIATION

成年男性产生睾丸激素的能力来自于 青春期睾丸间质细胞数量增加。睾丸间质细胞增加 在数量上通过一个渐进的事件序列，其中Leydig细胞 前体最初增殖，而不是降低它们的有丝分裂率， 它们开始表达成年睾丸间质细胞特有的蛋白质 细胞，尤其是类固醇生成酶。纯化Leydig的研究 由PI和其他人进行的细胞，已经定义了离散阶段 在进行性间质细胞分化的连续体中：纺锤体 未成熟间质细胞 细胞，虽然增殖性较低，但仍处于细胞周期中， 含有类固醇细胞器，合成类固醇，但分泌 5 α-减少雄激素而不是睾酮;成年Leydig细胞， 它们不分裂，主要分泌睾丸激素。 促黄体生成激素（LH）通过LH控制Leydig细胞功能 在成年阶段大量存在的受体。 然而，Leydig细胞祖细胞的LH受体数量可以忽略不计， 对这种激素的反应比较迟钝。这些考虑 使我们假设睾丸间质细胞发育的开始是 由其他因子如类固醇生成因子-1（SF-1）调节。LH是 据报道，增加睾丸间质细胞的数量， 睾丸激素的分泌此应用程序侧重于两个过程， LH不太可能是控制刺激： 从祖细胞到未成熟Leydig过渡期间的有丝分裂率 细胞;和刺激雄激素代谢酶5 α- 还原酶和3 α-羟基类固醇脱氢酶， 由祖细胞和未成熟间质细胞分泌睾酮。 将研究苗勒管抑制物质（MIS），因为 MIS基因的靶向缺失导致Leydig细胞增生， 表明该因子通常是生长抑制剂。在 计划为具体目标1进行的实验，我们将确定 间质细胞有丝分裂减少，这是观察到之间 大鼠产后14天和21天，由MIS引起;确定是否 睾丸激素诱导的未成熟间质细胞有丝分裂增加， 终末分化所需的;调查参与 雌激素对睾丸间质细胞的生长抑制，因为MIS是 观察到调节芳香酶，催化雌二醇的酶 合成.为“具体目标II”计划的实验将分别 评估睾酮生物合成和雄激素的调节- 通过LH、睾酮、SF-1和MIS代谢酶活性; 确定辅因子对这些酶的控制程度 可用性;并确定类固醇生成酶 活性由新的Leydig细胞同种型催化。

The capacity for testosterone production in the adult male results from increases in Leydig cell numbers during puberty. Leydig cells increase in number through a gradual sequence of events in which Leydig cell precursors initially proliferate, than lower their rate of mitosis as they begin to express proteins that are characteristic of adult Leydig cells, most notably, steroidogenic enzymes. Studies of purified Leydig cells conducted by the PI and others, have defined discrete stages within the continuum of progressive Leydig cell differentiation: spindle shaped, highly proliferative progenitor Leydig cells; immature Leydig cells, which, though less proliferative, remain in the cell cycle, contain steroidogenic organelles, synthesize steroids, but secrete 5alpha-reduced androgens rather than testosterone; adult Leydig cells, which do not divide and which secrete primarily testosterone. Luteinizing hormone (LH) controls Leydig cell function through LH receptors that are present in abundant numbers that the adult stage. However, Leydig cell progenitors have negligible numbers of LH receptors and are comparatively unresponsive to this hormone. These considerations led us to hypothesize that the beginning of Leydig cell development is regulated by other factors such as steroidogenic factor-1 (SF-1). LH is reported to increase Leydig cell numbers and is known to increase levels of testosterone production. This application focuses on two processes in which LH is unlikely to be the controlling stimulus: the decrease in mitotic rate during the transition from progenitor to immature Leydig cell; and stimulation of the androgen-metabolizing enzymes 5alpha- reductase and 3alpha-hydroxysteroid dehydrogenase, which lower testosterone secretion by progenitor and immature Leydig cells. Mullerian inhibiting substance (MIS) will be investigated because targeted deletion of the MIS gene causes Leydig cell hyperplasia, indicating that this factor is normally a growth inhibitor. In experiments planned for Specific Aim 1, we will determine if the reduction in progenitor Leydig cell mitosis, that is observed between days 14 and 21 postpartum in the rat, caused by MIS; establish whether testosterone-induced increases in mitosis of immature Leydig cells are required for terminal differentiation; investigate the involvement of estrogen in growth inhibition of the Leydig cells, because MIS is observed to regulate aromatase, the enzyme that catalyzes estradiol synthesis. The experiments planned for Specific Aim II will individually evaluate the regulation of testosterone biosynthetic and androgen- metabolizing enzyme activities by LH, testosterone, SF-1, and MIS; determine the extent of control of these enzymes by co-factor availability; and identify instances where steroidogenic enzyme activities are catalyzed by novel Leydig cell isoforms.