Biologists observe molecular ‘transfer’ that plays a key role in reproduction
Everyone considers that sperm is made exclusively by men. Well, it turns out that females also contribute to what makes a sperm a sperm.
Nearly 20% of couples in the United States fail to conceive naturally after a year of trying, according to the Centers for Disease Control and Prevention. In internally fertilized species, such as humans, a female’s ability to become pregnant and carry a pregnancy to term depends on effective interactions between sperm and the female reproductive tract (FRT). When these interactions are faulty, the result can be a failed pregnancy. Therefore, it is crucial to understand the factors that contribute to sperm viability between copulation and fertilization.
A research team from the Department of Biology in the College of Arts and Sciences at Syracuse University and Cornell University, led by Steve Dorus, associate professor of biology at Syracuse University, studied the history of fruit fly (Drosophila melanogaster) sperm life to better understand molecular continuity between male and female genitalia, in other words, how the male and female genitalia provide support to keep sperm viable before fertilization . Their results, published on March 7, 2022 in the journal Proceedings of the National Academy of Sciences (PNAS), shed light on important events that may play a role in infertility so far poorly understood.
The team, which includes members of Syracuse University’s Center for Reproductive Evolution, explored changes in the composition of fruit fly sperm, beginning shortly after they emerge from the testis, after insemination, and finally after prolonged storage in the FRT. Fruit flies are powerful model organisms for investigations like this because they are easy to grow in the lab, have short generation times, and their genetics are well understood. In their study, the group found that the proteome, or protein composition, of sperm undergoes substantial changes after being transferred to FRT.
For internally fertilized species, a sperm’s developmental “journey”—on its way to its final destination of fertilizing an egg and starting a new life—transcends the male and female reproductive pathways. After leaving the testicle, the sperm pass through the seminal vesicles of the male and down into the ejaculatory duct, where they mix with proteins in the seminal fluid. The team found that many of these seminal proteins are gradually lost after sperm migrate past the insemination site within the FRT.
Conversely, proteins of female origin that can help sperm with functions such as energy metabolism, begin to associate with sperm immediately after mating, signifying a changing of the custody of the proteins. After several days of storage in the FRT, the research team was surprised to discover that almost 20% of the proteins in the sperm had been replaced by proteins of female origin. Female contributions support sperm viability during the extended period between copulation and fertilization. This “transfer” in maintaining sperm viability from males to females means that sperm are materially the product of both sexes, and this can be a crucial aspect of reproduction in all internally fertilized species, including humans. .
By studying the intimate pathways through which sperm interact with FRT during the later stages of functional maturation, the team’s research advances understanding of animal fertility and the contributions of each sex to reproductive success.
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Erin L. McCullough et al, Drosophila sperm life history involves molecular continuity between the male and female reproductive tracts, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2119899119
Quote: Biologists observe molecular ‘handover’ that plays key role in reproduction (March 8, 2022) Retrieved March 8, 2022 from https://phys.org/news/2022-03-biologists-molecular-hand-off- key-role.html
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