From in vitro culture to in vivo models to study testis development and spermatogenesis.

The testis is a complex organ playing host to one of the most intricate mass cell divisions occurring in postnatal life. Since the beginning of the 20th century, great efforts have been made to recapitulate spermatogenesis and elucidate spermatogonial stem cell function. These efforts have resulted in the development of a variety of model systems that provide invaluable knowledge regarding testis organogenesis, key cell types and their interactions, and signaling pathways controlling testis function. The goal of this review is to elaborate on the evolution of the techniques available from in vitro culture systems to in vivo bioassays by providing up to date information and weighing their particular strengths and weaknesses. Each technique offers a different approach to the elucidation of male reproduction, the enhancement of germ-lineage genetic manipulation, the preservation of gametes, the restoration of fertility, and the improvement in our understanding of stem cell biology.