Long-Term Cultures of Mammalian Spermatogonia

This chapter discusses the long-term cultures of mammalian spermatogonia. In mammals, all premeiotic male germ cells including the stem cells are called spermatogonia. Two models of spermatogonial development have been proposed for adult rodents. In the first model, the Asingle (As) spermatogonia are considered the stem cells of spermatogenesis. They can renew themselves or can differentiate into Apaired (Apr) spermatogonia that remain connected by an intercellular bridge. The Apr spermatogonia further divide to form chains of 4, 8, or 16 Aaligned (Aal) spermatogonia. The Aal cells will then differentiate into type A1 spermatogonia. The A1 spermatogonia resume division to form A2 to A4 spermatogonia. Next, A4 cells divide to form intermediate (In) spermatogonia and In spermatogonia divide to produce type B spermatogonia. Finally, type B spermatogonia divide to form primary spermatocytes that will enter the process of meiosis. The second model considers type As spermatogonia as reserve stem cells is known as A0. These cells are believed to remain quiescent, or at the most divide very slowly, unless an excessive loss of germ cells stimulates their proliferation, for example, after injury or irradiation. In this model, the A1 through A4 spermatogonia (renewing stem cells) retain their stem cell properties and the A4 spermatogonia are able either to produce an A1 spermatogonia (dedifferentiation) or go forward and form In and type B spermatogonia.