Discovery Unveils Key Process in Chromosome Inheritance

A significant breakthrough in genetics has been reported by researchers at the University of California, Davis, revealing critical processes involved in how chromosomes are inherited from one generation to the next. Published on September 24, 2023 in the journal Nature, the study sheds light on the intricate mechanisms that safeguard the correct distribution of chromosomes in developing egg and sperm cells.

During the development of egg cells in a woman’s fetal ovaries, the quality of the chromosomes is vital for the future pregnancy. According to Neil Hunter, a professor in the Department of Microbiology and Molecular Genetics at UC Davis, the failure of chromosome pairing can lead to infertility, miscarriages, or genetic disorders in offspring. “If that goes wrong, then you end up with the wrong number of chromosomes in the eggs or sperm,” he stated.

Understanding Chromosome Pairing

Human cells contain 46 chromosomes, organized into 23 pairs inherited from each parent. As egg and sperm cells develop, these chromosome pairs align, and a process called “crossing over” occurs, where the parental chromosomes exchange segments. This mechanism not only ensures genetic diversity but also maintains the necessary connections between chromosome pairs during cell division.

Maintaining these crossover connections is particularly critical for females, especially since immature egg cells can remain in a dormant state for years. “Maintaining the crossover connections over many years is a major challenge for immature egg cells,” Hunter noted. If chromosome pairs lack these connections, they risk separating incorrectly during division, which can lead to conditions such as Down syndrome, characterized by an extra copy of chromosome 21.

Innovative Research Techniques

The research team utilized advanced genetic engineering techniques in the model organism *Saccharomyces cerevisiae*, commonly known as budding yeast, to observe the molecular events of chromosome recombination. Hunter emphasized that the chromosome structures studied have remained largely unchanged throughout evolution, with every protein examined in yeast having a direct counterpart in humans.

This study identified numerous proteins responsible for binding and processing the critical structures formed during crossover events, known as double Holliday junctions. Using a method called “real-time genetics,” the researchers were able to manipulate certain proteins to observe their effects on the formation and resolution of these junctions.

Hunter and his team discovered that proteins such as cohesin play a pivotal role in preventing the premature dismantling of these junctions by an enzyme complex known as STR in yeast, or Bloom complex in humans. This protective function is crucial for ensuring successful crossover formation, which is vital for proper chromosome segregation.

Collaborative Efforts and Funding

The research was a collaborative effort, with contributions from seven undergraduate students from UC Davis, including Jennifer Koo and Mohammad Pourhosseinzadeh. Additionally, co-authors Sara Hariri, Regina Bohn, and John E. McCarthy are all affiliated with Hunter’s lab.

The study received funding from several prestigious organizations, including the National Institutes of Health and the Howard Hughes Medical Institute. Hunter also acknowledged support from the UC Davis Comprehensive Cancer Center and the American Cancer Society, illustrating the broad relevance of this research to human health and reproduction.

In conclusion, the findings from this study not only enhance our understanding of genetic inheritance but also have important implications for addressing fertility issues and genetic diseases in humans. As the research continues to unfold, it paves the way for potential advancements in reproductive health and genetic counseling.