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Biologists Have Discovered A Molecular “Hand-Off” That Is Critical In The Process Of Reproduction

Biologists Have Discovered A Molecular "Hand-Off" That Is Critical In The Process Of Reproduction

According to the Centers for Disease Control and Prevention, over 20 percent of couples in the United States cannot conceive naturally after one year of trying. A female’s capacity to get pregnant and bring a pregnancy to term in animals with internal fertilization, such as humans, is based on the effectiveness of interactions between sperm and the female reproductive system (FRT). When such exchanges are not functioning correctly, the consequence might be a failed pregnancy.

As a result, it is critical to understand the variables that influence sperm viability during the period between copulation and fertilization.

Dr. Steve Dorus, associate professor of biology at Syracuse University, has been working with a research team from the Department of Biology at Cornell University and the Department of Biology at Syracuse University to understand better the life history of fruit fly (Drosophila melanogaster) sperm to gain a better understanding of the molecular continuity between male and female reproductive tracts. In other words, how the male and female reproductive systems offer assistance to maintain the sperm viable before conception is examined in detail. Their findings, which will be published on March 7, 2022, in the journal Proceedings of the National Academy of Sciences USA (PNAS), shed light on critical processes that may play a role in infertility but have been poorly understood up until now, according to the researchers.

Researchers from Syracuse University’s Center for Reproductive Evolution investigated the compositional changes in fruit fly sperm starting quickly after they exit the testis, continuing during insemination and ultimately after extended storage inside the fruit fly reproductive tract (FRT). In experiments such as this one, fruit flies are excellent model organisms because they are simple to cultivate in the laboratory, have a short generation period, and have a well-understood genetic structure. The researchers discovered that the proteome, or the protein content of the sperm, undergoes significant modifications once it is transferred to the FRT during their research.

Because internal fertilization is used in animals with internal fertilization, the ‘travel’ that sperm takes on its route to its eventual goal of fertilizing an egg and initiating a new life spans both the male and female reproductive systems after exiting the testis, sperm travel via the male’s seminal vesicles and down the ejaculatory duct, where they combine with proteins found in seminal fluid. The researchers discovered that many of these seminal proteins are gradually lost when sperm move away from the insemination site inside the FRT and towards the ovary.

In contrast, female-derived proteins, which may assist the sperm with activities such as energy consumption, begin to connect with the sperm immediately after mating, indicating a shift in the protein composition of the sperm. When the sperm was examined after several days in the FRT, the researchers were astonished to find that over 20% of the sperm’s proteins had been replaced with proteins generated from females. The contributions of the females help to maintain sperm viability over the extended period between copulation and fertilization. Men and women both contribute to preserving sperm viability, which indicates that sperm are essentially the product of both sexes. This may be a critical feature of reproduction in all internally fertilizing species, including humans, as well as in other animals.

In particular, by examining the close interactions between sperm and the FRT throughout the last phases of functional maturation, the team’s research contributes to a better understanding of animal fertility and the contributions made by each sexe to successful reproduction.

Dorus and Pitnick were joined by former postdoctoral researcher Erin McCullough and doctorate graduate Emma Whittington as co-authors on the paper, published in the journal Nature Communications. Professor Mariana Wolfner and postdoctoral researcher Akanksha Singh from Cornell University were co-authors of the article. A grant from the National Science Foundation, a grant from the National Institutes of Health, and a donation from Mike and Jane Weeden to Syracuse University contributed to the team’s study.

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