Changes to the three-dimensional (3D) structure of sperm chromosomes during sperm development can affect fertility in mice, it has been revealed.

Sperm and egg development, also known as gametogenesis, involves recombination, the shuffling of genes between chromosomes. This process is affected by the 3D structure of chromosomes – the way the DNA is packed, and which chunks of the genome are connected, and can affect sperm viability according to new research.

Dr Aurora Ruiz-Hererra from the Universitat Autònoma de Barcelona and lead author of the study, published in Nature Communications, explained: 'The study shows that both the dynamics of the genome organisation during the formation of gametes and the recombination is affected by the presence of chromosomal rearrangements'.

The team compared the rate of recombination in male mice between five wild-caught populations of mice and a population of common lab mice. Two of the wild mouse populations had a high prevalence of Robertsonian (Rb) fusions, a type of recombination where stray chunks of chromosome fuse together abnormally and can result in genetic conditions in humans such as Down's syndrome. 

They found that the mouse populations with a higher prevalence of these fusions exhibited a decrease in the rate of recombination which negatively impacted gametogenesis and the viability of the sperm. Higher levels of failed sperm development and immotile sperm were seen in these mice.

'The results point to the importance of the three-dimensional genomic context in which the recombination takes place, where factors such as chromosomal reorganisations can shape the genomic makeup of a given species' said Dr Covadonga Vara, co-author of the study.

The work showed that the observed effects could be partially explained by the fact that the presence of Rb fusions affected the 3D structure of the chromosomes. This change in structure alters how chromosomes interact with each other, and the expression of genes encoded on them.

The authors suggest that the presence of these fusions could have an evolutionary role in exposing parts of the genome to different regulatory mechanisms or enabling shuffling between genome regions which would not otherwise mix.

The findings of this work may lead to a greater understanding of adaptive processes as well as shine light on the mechanisms influencing fertility and genetic condition in humans.

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Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.