Development and regulation of growth and differentiated function in human and subhuman primate fetal gonads.

We have attempted to summarize the research on primate fetal gonadal development that has occurred over the past three decades. Many similarities exist between fetal gonadal development in human and subhuman primates; therefore, comparisons and analogies between these species can be made. Fetal gonadal development is a complex process dependent on timely maturation and differentiation of several cell types with different functions. Adequate development is important for normal sexual development and intact adult fertility potential as well as for intrauterine priming of neural centers in the central nervous system. While the fetal primate testis is active in steroidogenesis, the fetal ovary seems to be quiescent throughout most of gestation, although some ovarian steroidogenic enzymes have been demonstrated. Growth and development of both gonads are controlled during late gestation at least in part by pituitary hormones, while earlier in gestation other yet undefined regulators (placental, intragonadal) likely also are active. The main goal of this review was to demonstrate that gonadal growth and differentiation, both in males and females, is regulated by endocrine factors as well as by intragonadal, autocrine/paracrine agents. Although many parts of the puzzle are still missing it is probable that, similar to fetal development of other endocrine tissues and to events in postnatal gonads, these local regulators have important functions. Currently, primate fetal gonadal research is lacking in at least two key aspects: 1) the definition of paracrine and autocrine nonsteroidal factors that are involved in the regulation of gonadal growth and differentiation in vitro; and 2) in vivo studies in subhuman primates that might better help to clarify the biological roles of the multiple extra- and intragonadal hormones and their complex interactions. To date, the regulation of gonadal steroidogenesis has been investigated more thoroughly than the regulation of gonadal growth. Most of our knowledge stems from observations of gonadal development in anencephalics or subhuman primates after pituitary ablation. Because of the constraints of small organ size and limitation of material, studies of fetal primate gonadal development have been limited. Given such limitations, new molecular biological techniques, including polymerase chain reaction and in situ hybridization, may provide the means of addressing these questions. Further, because of these limitations, sensitive cell separation techniques need to be developed to achieve enriched primary gonadal cell cultures from individual gonads.