Germ cell biology--from generation to generation

Germ cells hold a unique place in the life cycle of animal species in that they are the cells that will carry the genome on to the next generation. In order to do this they must retain their DNA in a state in which it can be used to recapitulate embryonic development. In the normal life cycle, the germ cells are the only cells that retain this ability to recapitulate development, referred to as developmental totipotency. The molecular mechanisms regulating developmental potency are poorly understood. Recently its has been shown that germ cells can be turned into pluripotent stem cells when cultured in specific polypeptide growth factors that affect their survival and proliferation. The ability to manipulate developmental potency in germ cells with growth factors allows the underlying mechanisms to be dissected. Germ cells are also the only cells that undergo the unique reductive division of meiosis. This too is essential for the ability of germ cells to form the gametes that will carry the genome into the next generation. Arguably meiosis is the most important division in the life of a nascent organism. Defects in meiosis can result in embryonic or fetal loss or, if the animal survives, in the birth of an individual with chromosomal abnormalities. Recent advances in our understanding of meiosis have come from knockout mice and studies on genes identified through studies of human infertility. This review will focus on these two key aspects of germ cell biology, developmental potency and meiosis.