What Animal Models of Testicular Descent and Germ Cell Maturation Tell Us about the Mechanism in Humans.

Testicular descent occurs in most mammals in two main steps that have different hormonal control and anatomical processes. The evolution of testicular descent reveals the same basic processes in humans and animals, with minor differences in timing and anatomy, especially the location of the scrotum and the processus vaginalis. Animal models are useful as they reveal some embryological processes that cannot be studies easily in humans, such as the potential role of the mammary line and the role of the genitofemoral nerve. Postnatal germ cell development is very similar in animal models and humans, except for the timing of arrival of the testis into the scrotum, which is before birth in humans versus around puberty in rodents. Once all the minor differences between animal models and humans are taken into account, animal experimentation has provided amazing insights into the mechanisms of testicular descent, and recently, how the postnatal germ cell develops in normally descended and undescended testes.