Integration of Leptin with Other Signals Regulating the Timing of Puberty

Overview

How puberty is timed remains a major unanswered question in reproductive biology. Perhaps there is no single answer because there are many factors that time puberty. Leptin may be one of these answers, but the challenge is to fit this metabolic cue into our overall understanding of how sexual maturity is timed during the life of the individual. There are a variety of considerations, among which are the definition of puberty, level of inquiry, internal versus external influences, and differences between sexes and species. This chapter attempts to place leptin into the constellation of common and unique mechanisms that have been proposed to time the irreversible transition into adulthood. Studies using sheep as an experimental model have strongly influenced the formulation of our overall view of how puberty is timed in a large mammal living in a natural environment. As will become evident, in this species, the immediate cue timing puberty is different in males and females. Therefore, while we have been historically interested in how puberty is timed in the female, the mechanisms are more complex than for the male. Thus, our investigations into the importance of leptin as a pubertal signal in the sheep have been in the male. As a prelude to discussing the role of leptin in puberty, it is essential to lay the groundwork for what constitutes puberty. A backdrop to this discussion is a consideration of the level at which the investigations are being conducted. Although it is obvious that there is no gene for puberty, the level of investigation can range from integrative biology to molecular biology. Finally, the development of animal models and approaches even within a single species, is fraught with pitfalls, and the interpretation of data depends on the model from which they are obtained.