Avani Dave, Jai Hind College
Chromosomes exchange large chunks of DNA when sex cells are formed through a unique cell division termed meiosis. This ensures that each new cell has its own genetic composition, which explains why no two siblings are ever genetically similar, except for identical twins. Crossovers, or DNA exchanges, are necessary for producing genetic variety, which is the driving force behind evolution, and their frequency and location along chromosomes are closely regulated. The relevance of this phenomenon of crossover positioning on evolution, fertility, and selective breeding is explained in a recent study conducted by Morgan, C., et al.
The course of the study:
According to Chris (co-first author of the study), we are more likely to discover techniques to adjust crossover positioning to improve present plant and animal breeding technologies if we understand the factors that influence crossover positioning. Despite more than a century of research, the biological mechanism that determines where and how many crossovers arise remains mostly unknown, a riddle that has both enthralled and tormented many famous scientists. In 1915, the term “crossover interference” was coined to explain the fact that when a crossover occurs at one site on a chromosome, it prevents further crossings from forming nearby.
A team of researchers from John Innes Centre have solved this century-old mystery by identifying a mechanism that ensures crossover numbers and positions are ‘just right’: not too many, not too few, and not too close together, using a cutting-edge combination of mathematical modelling and ‘3D-SIM’ super-resolution microscopy.
During the course of the study, the researchers focused on the behaviour of a protein called HEI10, which showed involvement in crossover creation during the time of meiosis. HEI10 proteins cluster along chromosomes, producing lots of tiny clusters at first, according to super-resolution microscopy. However, as time passes, the HEI10 proteins condense into a few considerably bigger clusters, which can activate crossover formation if they reach a critical quantity.
These results were then compared to a mathematical model that simulates this clustering and is based on HEI10 molecule diffusion and basic clustering principles. Many experimental findings were explained and predicted by the mathematical model, including the fact that crossover frequency could be reliably changed by merely changing the amount of HEI10.
“Our study indicates that data from super-resolution photographs of sex cells in Arabidopsis is congruent with a mathematical ‘diffusion-mediated coarsening’ model,” said Dr. John Fozard (co-first author of the study). He further added how this concept aids our understanding of crossover patterning on meiotic chromosomes.
The future prospects:
The research follows suit on the John Innes Centre’s tradition of studying conserved and fundamental parts of genetics using plants as model organisms. Professor Martin Howard (corresponding author) claims that this work is a remarkable example of interdisciplinary research, where cutting-edge experimentation and mathematical modelling were both needed to unlock the heart of the mechanism.
These findings will be especially useful for cereal crops like wheat, since crossovers are mainly limited to specific areas of the chromosomes, prohibiting plant breeders from accessing the whole genetic potential of these plants. Assessing whether this integrative approach can properly explain crossover patterning in other different organisms poses a fascinating future avenue.
Also read: New Structural Model of the DNA-Protein Complex
Reference: Morgan, C., Fozard, J. A., Hartley, M., Henderson, I. R., Bomblies, K., & Howard, M. (2021). Diffusion-mediated HEI10 coarsening can explain meiotic crossover positioning in Arabidopsis. Nature Communications, 12(1), 4674. https://doi.org/10.1038/s41467-021-24827-w
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Author’s Info: Avani Dave is currently in the final year of her bachelor’s degree, majoring in Life Sciences. Holding a good academic and extra-curricular record, she is on a constant journey of acquiring exposure in her field of interest while simultaneously not limiting herself to just that. Avani likes studying Diseases and Syndromes and everything under this umbrella! That being said, she is adept at working across departments and promises to deliver.
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