This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Eggs follow a very different developmental path from sperm. Once a male hits puberty, sperm cells are produced continuously throughout his life.
Eggs, however, are all produced during the fetal stage. Once formed, eggs enter a long dormant state called the dictyate stage, in which the process of cell division (meiosis) is paused partway through. This dormant period ends only when the egg is ovulated.
During this time, the egg keeps its chromosomes properly organized due to the presence of a protein complex called REC8 cohesin. Working like a molecular glue, REC8 holds together the chromosome copies created before the cell division arrest. REC8 is never replenished during the dormant period.
Because REC8 cohesin weakens progressively with age, its decline is now thought to be a major reason why eggs from older women are more likely to end up with the wrong number of chromosomes. This condition, called aneuploidy, is a leading cause of miscarriage, infertility and chromosomal disorders such as Down syndrome. It remains unclear whether egg cells have any active mechanism to protect this irreplaceable cohesin from breaking down, or whether the protein is simply left to degrade passively over time as the egg ages.
A research team led by Professor Kei-ichiro Ishiguro from the Graduate School of Medicine, Chiba University, Japan, set out to address this question. Their paper, which was published in the journal Nature Aging, describes the discovery of a previously unknown protein that helps preserve chromosome cohesion in eggs from before birth to adulthood. Co-authors of the study included Sakie Iisaka, a doctoral student, and Dr.
Ryuki Shimada from Chiba University, as well as Dr. Shuhei Yoshida from the RIKEN Center for Biosystems Dynamics Research (BDR), Japan. The researchers first compared gene activity in fetal immature eggs (oocytes) and male germ cells, which do not undergo the same prolonged arrest, using single-cell RNA sequencing.
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