Genome complexity: handling replication (Introduction)

by David Turell , Tuesday, December 06, 2022, 17:09 (508 days ago) @ David Turell

Precise control of chromosome size and shape:

https://phys.org/news/2022-12-unwinding-chromosomes-unique-perspective-chromosomal.html

"Mitosis, chromosomes ensure that genetic material is equally divided among the daughter cells. Interestingly, the dimensions and degree of DNA condensation in mitotic chromosomes vary from organism to organism. How this is regulated—i.e., what factor governs mitotic chromosomal formation and dimensions—remains a mystery.

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"During mitosis, DNA undergoes significant compaction to form chromosomes. A large protein ring complex called condensin plays a key role in the compaction process. It binds at specific sites on DNA and compresses it by forming loops. So, scientists know that condensin is crucial for DNA compaction, which is closely related to chromosomal dimensions—with thicker chromosomes being more compacted. They also know that the pattern of condensin-binding sites is species-specific. But the exact role of condensin and chromatin contacts in determining chromosomal dimensions is, as yet, unclear.

"The researchers explored various facets of condensin and chromatin contacts to address the questions at hand. They employed Hi-C and super-resolution microscopy to analyze the correlation between mitotic chromatin contacts and chromosomal arm length in both budding and fission yeasts, S. cerevisiae and S. pombe, respectively.

"Conclusive evidence was found indicating that the distance between chromatin contacts is directly proportional to arm length in both interphase and mitosis. Hence, shorter arms have short range contacts and longer arms have long range contacts. This was found to be species-specific. (my bold)

"Now, longer distances of chromatin contacts lead to larger chromatin loops, both of which are indicators of wider chromosomal arms. The authors thus investigated both budding and fission yeasts to conclude that within a species, longer chromosomal arms were always wider. Motivated by the successful observation in the yeasts, they extended their study to human cells, to find the same correlations.

"'We made the unexpected discovery that longer chromosomal arms are always thicker throughout eukaryotic species, which helps us understand how mitotic chromosomes form during cell divisions," explains Kakui. Their study would be the first to conclusively establish that chromosomal arm length determines mitotic chromosome width."

Comment: these precise requirements in all species require design. How this is controlled is yet to be found.