We now have the sperm proteome of a primate. In a paper in Molecular & Cellular Proteomics, researchers describe the sperm proteome of the rhesus macaque, the first primate to have its sperm proteome analyzed.
Sperm proteomes from nonprimate species, such as rats, mice and fruit flies, already have been determined. “For comparative evolutionary and functional genomics studies, a primate sperm proteome was highly desirable to include in this growing list of sperm proteomes,” explains Tim Karr at Arizona State University.
Rhesus monkeys bear many genetic and physiological similarities to humans, so they are used regularly as a nonhuman primate model system in biomedical research, including human reproduction research. “Knowing the rhesus sperm proteome will greatly expand the possibility for targeted molecular studies of spermatogenesis and fertilization in a commonly used model species for human infertility,” explains Karr. (See ASBMB Today story from May bout sperm and male infertility.)
In their study, Karr and colleagues collected epididymis tissues from male monkeys that contained sperm cells. (The epididymis is a long tubular lumen through which sperm travel after they leave the testis, an essential part of sperm maturation and fertility.) The investigators separated the sperm from the tissue and then proceeded to extract all the proteins from the sperm. The investigators next carried out gel electrophoresis, protein digestion and high-throughput mass spectrometry to identify all the proteins in the rhesus sperm.
From their analysis, Karr and colleagues identified, among other things, new ADAM proteins, ADAMs 3, 4 and 6, in the rhesus macaque that have been lost or are nonfunctional in humans. This gives a glimpse of how the two species evolutionarily diverged.
The investigators also identified almost all components of the 20S proteasome core, including known activators of the proteasome. “This suggests there exists an active form of the proteasome in mature sperm,” says Karr.
Karr says he and his colleagues are now “very excited about our developmental work on sperm maturation in the mouse and macaque.” Based on what is known about the two animal sperm proteomes, the investigators now are analyzing the process of sperm maturation during epididymal transport.