Biology researchers from the University of Southampton have brought us a step closer to fully understanding how we inherit our chromosomes from our parents and grandparents.
In a study, published in the journal Nature Communications, Professor Keith Jones and colleagues from the School of Biological Sciences have observed, for the very first time, a power struggle for survival in eggs when chromosomes are passed from one generation to the next.
In every egg, there are two copies of each chromosome, one inherited from our mother and one from our father. In order to produce a mature egg only one of these survives and gets passed on to the embryo. The dogma in biology is that which one survives is chosen randomly and dates back to work done by the father of modern genetics Gregor Mendel in the 1800s. However, Professor Jones and colleagues, using eggs from mice where the maternal and paternal chromosomes could be visualised, showed that they do compete for survival. They have found chromosomes carrying a particularly large centromere, which is a distinct region of the chromosome, can ‘cheat’ this competition and stand a better chance of surviving than its partner chromosome with a smaller centromere.
Professor Jones explains “We used mice that were bred from different parent strains, and as such, their eggs contained chromosomes which we could attribute to one parent or the other. By following the chromosomes during the process of cell division, in which only one of the chromosomes will survive, we were able to watch the chromosome with the larger centromere position itself in the egg so as to survive. We then went onto examine some of the key egg proteins involved in how this struggle plays out.
“It gives us an interesting take on how chromosomes are behaving in eggs,” Professor Jones concludes. “We’d like to feel we’re individuals where all our chromosomes pull together to work for the common good, but actually it may not be like that. In eggs, when only some chromosomes survive the creation of a new egg, we may have to think about the process as a struggle for survival and suddenly, at the level of the chromosome, whoever is suited to win that battle will win out overall.
For Professor Jones and his team, the results of this study give them an interesting take on a well-known problem in egg quality to do with their poor ability to produce embryos with the correct number of chromosomes. “Our expertise is in imaging chromosomes in eggs, which is difficult to perform because it’s a process that lasts several hours and needs molecular using tools that make the chromosomes visible to us,” says Professor Jones. “Historically, we’ve been investigating this area because we’re interested in why chromosome division in eggs is so poor, leading to genetic disorders like Down’s Syndrome, which is where the embryo inherits an extra maternal copy of chromosome 21. We are speculating here, but maybe there is a connection between the ability of chromosomes to fight for survival in the egg and the fact that embryos do end up with the wrong number of chromosomes so often.”
Source: University of Southmapton