Comparative Analyses Reveal Conserved and Modified Steps in the Testis Descent and Scrotum Development in Mouse and...

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Developmental biology

Background:

• Mammalian testes descend into a scrotum, but its position relative to the phallus differs between marsupials (cranial) and placental mammals (caudal).
• Previous studies suggest common ancestry for testis descent mechanisms, prompting investigation into independent evolution of scrotal positioning.

Purpose of the Study:

• To compare the histological and molecular processes of testis descent and scrotum development in a metatherian (opossum) and a eutherian (mouse).
• To elucidate the evolutionary path of scrotal testis development.

Main Methods:

• Histological and molecular comparisons of testis descent and scrotum development.
• Utilized gray short-tailed opossum (Monodelphis domestica) as the metatherian model and mouse as the eutherian model.
• Employed cell-labeling analyses and dynamic expression studies of Gsc1.

Main Results:

• The transabdominal phase of testis descent is similar between opossum and mouse.
• The scrotal phase differs due to distinct scrotum positions, with extensive cell/tissue rearrangements observed in mouse development.
• Gsc1 expression was detected in murine scrotal development but absent in the developing opossum genitalia and scrotum.

Conclusions:

• Scrotum development and the scrotal phase of testis descent likely involved the recruitment of new regulatory pathways during eutherian evolution.
• Suggests distinct evolutionary trajectories for scrotal morphology and function between metatherians and eutherians.