For many years, it was thought that sperm do not retain any histone packaging and therefore could not transmit histone-based epigenetic information to offspring. Recent studies, however, have shown that about 10 percent of histone packaging is retained in both human and mouse sperm.
“Furthermore, where the chromosomes retain histone packaging of DNA is in developmentally important regions, so those findings raised awareness of the possibility that sperm may transmit important epigenetic information to embryos,” Strome said.
When her lab looked at C. elegans sperm, they found the sperm genome fully retains histone packaging. Other researchers had found the same is true for another commonly studied organism, the zebrafish.
“Like zebrafish, worms represent an extreme form of histone retention by sperm, which makes them a great system to see if this packaging really matters,” Strome said.
Her lab focused on a particular epigenetic mark (designated H3K27me3) that has been well established as a mark of repressed gene expression in a wide range of organisms. The researchers found that removing this mark from sperm chromosomes causes the majority of the offspring to be sterile. Having established that the mark is important, they wanted to see if it is sufficient to guide normal germline development.
The researchers addressed this by analyzing a mutant worm in which the chromosomes from sperm and egg are separated in the first cell division after fertilization, so that one cell of the embryo inherits only sperm chromosomes and the other cell inherits only egg chromosomes (normally, each cell of an embryo inherits chromosomes from both egg and sperm). This unusual chromosome segregation pattern allowed the researchers to generate worms whose germ line inherited only sperm chromosomes and therefore only sperm epigenetic marks. Those worms turned out to be fertile and to have normal gene expression patterns.
“These findings show that the DNA packaging in sperm is important, because offspring that did not inherit normal sperm epigenetic marks were sterile, and it is sufficient for normal germline development,” Strome said.
While the study shows that epigenetic information transmitted by sperm is important for normal development, it does not directly address how the life experience of a father can affect the health of his descendants. Strome’s lab is investigating this question with experiments in which worms are treated with alcohol or starved before reproducing. Paper. (open access) – Tomoko M. Tabuchi, Andreas Rechtsteiner, Tess E. Jeffers, Thea A. Egelhofer, Coleen T. Murphy, Susan Strome. Caenorhabditis elegans sperm carry a histone-based epigenetic memory of both spermatogenesis and oogenesis. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-06236-8 More.
The epigenetics effect appears to lie in the fact that the packaging matters, not just the DNA.
As noted earlier, epigenetics is bad news for Darwinism. It turns out that genes can change during a life form’s lifetime and those changes can be passed on. Natural selection acting on random mutations in the genome (Darwinism) simply cannot be the driving force claimed, any more than Freud or Jung could really explain history on a single principle. They could only explain some things and Darwin can only explain some things. That makes evolution a rather messy history (like all true histories), and not at all welcome to propagandists.
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See also: Study: Nicotine effects persist through several generations of mice, via sperm Researcher: “Not much had been known about the effects of paternal smoking on their children and grandchildren. Our study shows that paternal nicotine exposure can be deleterious for the offspring in multiple generations.”
Epigenetics is involved in strengthening memory
Anthropologist John Hawks is cool to epigenetics shedding light on evolution. Responses like this from a usually level-headed thinker mainly demonstrate that epigenetics is likely to upset quite a few applecarts.
Peter Ward: Epigenetics explains why there are fewer “species” than we think
Epigenetic change: Lamarck, wake up, you’re wanted in the conference room!