A recent study by researchers at the University of Hawaiʻi at Mānoa and Washington State University shows how fathers pass on traits influenced by their environment to their children. The research provided new data refining the mechanistic basis of paternal epigenetic inheritance.
The team was spearheaded by Monika Ward of the John A. Burns School of Medicine (JABSOM) and Wei Yan of Washington State University, whose work offers new insight into how these hereditary signals function.
Published June 10 in PNAS , the study challenges the idea that sperm pick up this vital environmental information while maturing in a specific part of the male reproductive system called the epididymis. Instead, researchers found that mature sperm lack the specific mitochondrial DNA (genetic material for cell energy) required to facilitate this process, suggesting the information is set earlier while the sperm is still in the testes.
How testes help pass on traits
To test this, researchers fed male mice a high-fat diet. They then used a specialized fertilization technique to create offspring using both early-stage sperm from the testes and fully mature sperm. They discovered that the early sperm passed on traits from the father's diet just as effectively as the mature sperm did.
"This work is a perfect example of how assisted reproduction technologies can be used to advance understanding of key processes in male reproduction," said Ward, a researcher in the Yanagimachi Institute for Biogenesis Research and professor of anatomy, biochemistry and physiology.
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By using a direct injection technique with early-stage sperm, the team proved that sperm do not need to mature in the epididymis to pass on environmental information.
The study also clarified the amount of mitochondrial DNA in sperm. By testing sperm at various stages, the team confirmed that this material is progressively removed during development, leaving mature sperm almost entirely without it. They also found that small RNA, which carries genetic information, is primarily set during development in the testes.
The findings support a framework in which environmentally responsive molecular information is programmed during sperm development in the testes and later delivered to the egg by mature sperm depleted of mitochondrial DNA.
"The founder of our institute, Ryuzo Yanagimachi, was a pioneer who first developed many of the techniques used in modern IVF," said Ward. "This study is a great example of how his legacy and our expertise continue to lead to new scientific discoveries."
