On a matter of seminal importance

Abstract

Egg and sperm have, understandably, been the "stars" of mammalian fertilization biology, particularly because artificial reproductive technologies allow for fertilization to occur outside of the female reproductive tract without other apparent contributions from either sex. Yet, recent research, including an exciting new paper, reveals unexpected and important contributions of seminal plasma to fertility. For example, seminal plasma proteins play critical roles in modulating female reproductive physiology, and a new study in mice demonstrates that effects of some of these proteins on the female can even affect the health of her progeny. Furthermore, although several actions of seminal plasma have been conserved across taxa, male accessory glands and their products are diverse - even among mammals. Taken together, these studies suggest that the actions of seminal plasma components are important to understand, and also to consider in future development of assisted reproductive technologies (ART) for humans, farm species and endangered species of mammals.

Keywords: accessory sex glands; insect fertility; mammalian fertility; offspring health; reproduction; reproductive tract physiology; seminal proteins.

Figure 1

A: A diagrammatic frontal view the male reproductive tract of man and a dorsal view of three additional mammals, illustrating the variations in glands that contribute to the seminal plasma (yellow, ampullary glands; red, seminal vesicles; green, prostate glands; magenta, bulbourethral glands; orange, preputial gland). The epididymis (blue) also contributes to the seminal plasma. The testes are shown in black, the bladder in dark gray, and the vas deferens and penis in lighter shades of gray. B: Diagrammatic view of the male reproductive tract of four insect species (modified from images in [–64]). Unlike the situation in mammals, the accessory glands of the distantly-related insects are not homologous to the same extent as are the glands in mammals, so they are all indicated in dark blue (black, testes; gray, ducts and intromittent organ).