Biological complexity: how sperm prepares for fertilization (Introduction)

by David Turell , Friday, August 20, 2021, 21:05 (1191 days ago) @ David Turell

Two necessary molecular steps:

https://phys.org/news/2021-08-givgirdin-spatiotemporal-sperm-capacitation.html

"Mammalian sperm cannot fertilize an egg from the get-go. It's an ability acquired only after insemination, during passage through the female reproductive tract, and requires two consecutive, time-sensitive processes to provide sperm with the physical and biochemical traits necessary to complete their fundamental job.

"The first process is called capacitation, which alters the physiology of each spermatozoa, changing the membrane of the head to help it penetrate the hard, outer layer of an egg—the zona pellucida—and chemistry in the tail to generate greater motility, the ability to move and swim.

"The second process is acrosome reaction (AR), a chemical action that involves releasing enzymes in the spermatozoa's head that further boost penetration of the zona pellucida.

"Both processes are essential to successful fertilization of an egg, and AR is time-dependent: It cannot take place too early or too late. Indeed, premature AR has been associated with idiopathic (spontaneous) male infertility.

***

"Specifically, the research team, led by senior author Pradipta Ghosh, MD, professor in the departments of Medicine and Cellular and Molecular Medicine at UC San Diego School of Medicine, found that GIV—a member of the G protein family that serve as molecular switches inside cells, transmitting and fine-tuning signals—regulates the activity of enzymes that turn on and turn off the processes of capacitation and AR.

"'The findings demonstrate how GIV orchestrates distinct signaling programs in sperm that separated by space and time, effectively supporting capacitation while inhibiting premature AR," said Ghosh. "As a result, GIV plays an essential role in male fertility.'"

Comment: this process which requires two coordinated timed steps demonstrates irreducible complexity which means it had to be designed all at once before being put in place