Immunity: selecting best egg & sperm immunity (Introduction)

by David Turell , Monday, October 01, 2018, 18:22 (2246 days ago) @ David Turell

Contribution to immunity of the new embryo after egg and sperm meet involves sperm selection by the egg by a currently unknown mechanism in the egg which picks a compatible immunity gene selection by a currently unknown process:

https://phys.org/news/2018-10-female-gametes-sperm-immune-genes.html

"Through clever partner selection, animals can increase the future success of their offspring. With some species, this process continues even after the sex act. Researchers at the Max Planck Institute for Evolutionary Biology in Plön have discovered that among sticklebacks, the egg cells of the fish are involved in the decision regarding fertilisation. An accumulation of genes in the genetic material of the male gamete's cells determines which sperm is allowed in to the egg cell. Since vertebrates are highly similar in terms of their immune system, including with regard to the gene complex in question, the researchers assume that egg cells of other vertebrates – perhaps even those of humans – are able to control their fertilisation.

***

"Without a powerful immune system, no animal can survive for long, let alone produce offspring. Since half of the immune genes of both parents respectively are passed on in combination to the offspring, it is worth selecting a sex partner who best supplements one's own immune genes. (my bold)

***

"Here, a decisive role is played by the genes of the "Major Histocompatibility Complex (MHC)", an accumulation of extremely variable immune genes on chromosome 6. "We already discovered some time ago how the gene complex impacts the smell of a human body, and identified our body's own perfume. This plays an important role when we select a partner," Milinski explains. "With such immune genes, which complement your own genes, the immune system of your offspring is particularly diverse, and can fend off a large number of pathogens."

***

"Every human and most animals have two – often different – varieties of every individual gene. An egg or sperm cell only receives one of the two gene variants in each case. Some of the cells therefore have immune gene variants that match each other better than others. During fertilisation, an egg cell can therefore in fact merge with a sperm that has been given an MHC variant that does not match so well – despite prior partner selection and what appeared to be the matching immune genes.

***

"The egg – not the woman – must therefore select its own partner, namely the sperm with the complementary MHC variant. According to the researcher team in Plön, this is precisely what the egg cells of sticklebacks do. The scientists presented egg cells with sperm with different MHC variants and observed which of the male gametes was successful. "Our experiments show that the sperm with the highest chance of fertilisation is the sperm whose MHC may differ from that of the egg, but which still shows certain similarities," explains Tobias Lenz, who heads the Evolutionary Immunogenomics research group at the Max Planck Institute in Plön.

***

"Researchers do not yet know how the egg selects the sperm. "Our experiments show that the selection process continues even after the sex act. Since it is impossible to tell on the basis of scent which immune gene variants will finally be successful, the selection by the egg cells is an extremely important supplement to partner selection. The offspring are more resistant to pathogens as a result, and therefore have an evolutionary advantage," Milinski explains. Additionally, egg cells can in this way avoid fertilisation by the sperm of unwanted males."

Comment: Note my bold. Immunity is vital for survival. Mammals pass generalized antibodies to newborns through colostrum in milk, to help the infant survive until its own immunity begins to build an appropriate library of antibodies. The 'MHC' complex is similar to the HLA complex which is studied by implant surgeons to find compatible donors for organ transplants, except that HLA looks for compatibility and MHC is opposite and looks to fight invaders. I think research will find that the egg has receptors which can recognize the right genes in sperm, all an automatic process that had to be designed to allow sexual reproduction to be a safe way to reproduce. Sexual reproduction allows for more manipulation of genes to develop more complex organisms beyond the groups of individual cells with slight variation in function, as in bacterial mats.