Work that sheds light on how human gametes develop is reported in a paper published in Nature Cell Biology this week. The findings may help to understand oocyte development in the ovarian reserve in women, and stem cell development in the testes of men, as well as providing a road map for future attempts to develop gametes in a dish.
Human infertility affects about ten per cent of the reproductive-aged population, and most causes of human infertility are unexplained. Although humans usually reproduce at between fifteen and forty-five years of age, the cells that give rise to human gametes appear much earlier. It has therefore been suggested that reproductive problems as an adult may be caused by problems with gamete precursor formation during fetal life.
Amander Clark and colleagues isolated the precursor cells of human gametes - oocytes and sperm - from fetuses six to twenty weeks after fertilization and characterized the early events leading to their appearance. Until now, most of the information available on the early stages of gamete formation came from studies in mice. By isolating human gamete precursors based on expression of a cell surface protein, and analysing global changes to their DNA, RNA and proteins, the authors identified two major developmental phases, whereas only one has been so far been recognized in mice.