Initiation and Maintenance of Spermatogonial Mitotic Divisions

精子发生是一个产生精子的生殖过程，精子是一种独特的细胞，能够使卵子受精，从而开始一个新个体的生命。在动物中，精子的发生是通过雄性生殖细胞的形状和行为的一系列渐进变化发生的。在这些变化中有两种细胞分裂。第一个是产生大量被称为精原细胞的干细胞的简单过程。第二种是一种独特的分裂，称为减数分裂，它分两个阶段发生，产生4个精子，每个精子的染色体数量减少。当前项目的目标是发现告诉精原细胞改变其行为并开始细胞分裂的化学信使(1)，以及指示细胞分裂应该持续多长时间的化学信使(2)。因此，这些化学物质在(1)产生精子和(2)决定产生多少精子方面很重要。在包括哺乳动物在内的所有动物系统中，精原细胞分裂的开始和维持都是鲜为人知的过程。沃克计划使用北大西洋海星或海星来研究精子发生的基本生物学过程，因为每种动物在5个月的时间内可以产生数万亿的精子，因为精子发生的过程可以同时研究，使用完整的、活的海星或使用从这些动物的试验中获得的培养细胞。在精原细胞开始细胞分裂的重要时期，没有其他动物的生精系统允许如此近距离地观察精子的发生。这项工作的重要性在于，它应该识别出动物体内开始和维持精子产生的化学信使。到目前为止，还没有发现任何动物有这样的信使。雌激素，而不是雄激素（如睾丸激素）提供导致精原细胞开始分裂的初始信号，多胺是由精原细胞或相关细胞产生的化学物质，然后导致精原细胞继续分裂。两种化学信使（也许还有其他）参与了精子产生的过程。PI最终可能会提出在哺乳动物等更复杂的动物中外部控制精子产生的方法。

Spermatogenesis is a reproductive process that yields sperm, which are unique cells capable of fertilizing eggs and thus beginning the life of a new individual. In animals, spermatogenesis occurs via a number of progressive changes in the shape and behavior of male sex cells. Among these changes are two kinds of cell division. The first is a simple process producing large numbers of stem cells called spermatogonia. The second is a unique division, called meiosis, which occurs in two stages and which results in 4 sperm, each with a reduced number of chromosomes. The objective of the current project is to discover the chemical messenger (1) that tells spermatogonia to change their behavior and to begin cell division and also the one (2) that indicates the amount of time such cell division should continue. Therefore, these chemicals are important (1) in causing sperm to be produced and (2) in determining how many sperm are produced. The beginning and maintenance of cell division in spermatogonia are poorly understood processes in all animal systems, including mammals. Walker plans to use the Common North Atlantic sea star or starfish in studies of the basic biological process of spermatogenesis because each animal can produce trillions of sperm in a 5 month period and because the spermatogenic process can be studied simultaneously using entire, living sea stars or using cells in culture which are derived from the tests of these animals. No other animal spermatogenic system permits such close observation of spermatogenesis during the important period when spermatogonia are beginning cell division. The importance of this work is that it should identify chemical messengers that begin and maintain sperm production in an animal. No such messengers have as yet been identified for any animal. Estrogens, not androgens (like testosterone) provide the initial signal that causes spermatogonia to begin to divide and that polyamines, which are chemicals produced by spermatogonia or associated cells, then cause spermatogonia to continue to divide. Two chemical messengers (and perhaps others) are involved in the process of sperm production. The PI may ultimately be in a position to suggest means for external control of sperm production in more sophisticated animals like mammals.