Initiation and Maintenance of Spermatogonial Mitotic Divisions

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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.