Microanatomy of the Monodelphis Domestica Prostate

Science Center, Bent Corridor

The mammalian prostate gland secretes fluids that, along with sperm from the testes and fluids from other glands, comprise semen. In metatherian mammals, prostate microanatomy is poorly known. We designed a project comparing the histology of the metatherian prostate (using Monodelphis domestica, the lab opossum) to the better known eutherian prostate (using Rattus norvegicus, the lab rat) using paraffin histology and probasin immunohistochemistry. Because probasin is a well-known and highly conserved prostate-specific protein, in eutherians, we hypothesized that it would be a useful reference protein. While the microanatomy of the rat prostate differed considerably from that of the opossum, both prostates clearly synthesized probasin. The rat prostate consists of 3 lobes (each ~3-5 mm) arranged around the base of the urethra along with the urinary bladder. In contrast, the opossum prostate, an elongated cylinder (~25 mm x 6 mm), connects the urinary bladder to the base of the penis. The opossum prostate is divided into a light-colored anterior portion and a dark-colored posterior portion, both of which are traversed by a central channel, the urethra. Another important difference is that probasin-positive cells are restricted to the posterior portion of the opossum prostate, while in the rat, all of the lobes contain probasin. Our results demonstrate that probasin is one of probably numerous secretory products synthesized in the metatherian prostate. These secretions await identification, but our work establishes that the probasin gene is conserved and functional in these two groups of mammals.