The regulation of human fetal gonadal development in the second trimester

Abstract

Fetal gonadal development is a complex process dependent on maturation and differentiation of several cell types with different functions. Adequate development is important for normal sexual development and fertility potential. However, to date the factors that are involved in the regulation of gonadal growth and differentiation are not well understood. The aim ofthis thesis was to investigate the role of survival and proliferative factors, namely the c-kit proto-oncogene receptor and ligand and the family of neurotrophins in human gonadal development during mid-trimester. The involvement of metalloproteinases (MMPs) and their inhibitors (TIMPs) in tissue remodelling in both human fetal testes and ovaries was also considered. C-kit and its ligand have been demonstrated to be essential to the processes of germ cell migration, proliferation and survival in the rodent and their expression was investigated in human fetal gonads. Expression of c-kit mRNA and the protein was demonstrated in both ovary and testis throughout mid-trimester. Testicular germ cellspecific expression of c-kit mRNA was confirmed using laser capture microscopy and c-kit protein was localised to the germ cells in both ovaries and testes. These data demonstrate that the expression of c-kit mRNA and protein is germ cell specific in human fetal gonads and are consistent with an important role for the c-kit/kit ligand signalling system in germ cell proliferation and survival in the developing human gonad.Neurotrophins are survival and differentiation factors in the nervous system. The presence of neurotrophins and their receptors and their role in germ cell survival was investigated in the human fetal gonads. Expression and localisation of neurotrophins 7 and their receptors was detected throughout mid-trimester in both ovaries and testes. The effects of the tyrosine kinase receptor inhibitor K252a were studied in organ cultures. In the ovary, treatment with K252a resulted in a significant fall in germ cell number and proliferation. In the testis, cell-specific marked decrease in both gonocyte and peritubular cell number and proliferation was seen after treatment with K252a, with little effect on Sertoli cells. These findings therefore demonstrate the expression of neurotrophins and their receptors in human fetal gonads during the second trimester and indicate possible roles in the regulation of proliferation/survival of germ cells and peritubular cellsMMPs and TIMPs are major regulators of tissue remodelling of the extracellular matrix (ECM) and may also be involved in the control of growth factor availability. Their production and localisation was investigated in the human fetal gonad. Tissue was collected and analysed for the presence of MMP-2 and -9 and for TIMP activities using zymographic techniques. These MMPs and in addition, MMP-I and TIMPs were localised using immunohistochemistry. The secretion of MMP-2, -9 and all four TIMPs was demonstrated from both testis and ovary, the predominant gelatinase produced being MMP-2. In both gonads, MMP-I, -2, -9 and all TIMP family members were localised to specific cell types. This therefore indicates that MMPs and TIMPs are likely to play a role in ECM remodelling during fetal gonadal development and also in the cell and matrix interactions that control a range of cellular functions