Genome and evolvability: clear evidence of common descent (Introduction)

by David Turell , Thursday, May 27, 2021, 20:39 (1275 days ago) @ David Turell

The control over chromosome architecture is very old:

https://science.sciencemag.org/content/372/6545/984?utm_campaign=toc_sci-mag_2021-05-27...

"The conformation of chromosomes within the nucleus can reflect a cell's type or state. However, studies of the conservation and evolutionary history of the mechanisms regulating genome structure across species are lacking. Hoencamp et al. mapped three-dimensional (3D) genome organization in 24 eukaryote species, including animals, fungi, and plants. At interphase, species' telomeres and centromeres either clustered across chromosomes or oriented in a polarized state maintaining individual chromosomal territories within the cell, a difference attributed to condensin II. An experimental loss of condensin II in human cells promotes the formation of centromere clusters but has no effect on loop or compartment formation. Whether the structure of the 3D genome varies across species may thus depend on whether they carry a functional condensin II gene.

"Abstract
We investigated genome folding across the eukaryotic tree of life. We find two types of three-dimensional (3D) genome architectures at the chromosome scale. Each type appears and disappears repeatedly during eukaryotic evolution. The type of genome architecture that an organism exhibits correlates with the absence of condensin II subunits. Moreover, condensin II depletion converts the architecture of the human genome to a state resembling that seen in organisms such as fungi or mosquitoes. In this state, centromeres cluster together at nucleoli, and heterochromatin domains merge. We propose a physical model in which lengthwise compaction of chromosomes by condensin II during mitosis determines chromosome-scale genome architecture, with effects that are retained during the subsequent interphase. This mechanism likely has been conserved since the last common ancestor of all eukaryotes. (my bold)"

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"Taken together, a model emerges in which condensin II establishes interphase 3D genome architecture at the scale of whole chromosomes. We hypothesize that (i) centromeres tend to adhere to one another, a process that is facilitated by proximity during and shortly after mitosis; (ii) the shortening of chromosomes interferes with this adhesion, enabling the centromeres to spread out over the newly formed nuclei; and (iii) chromosome territories emerge as a by-product of the resulting chromosomal separation.

"The role of condensin II in establishing the overall architecture of the genome appears to be among the most ancient capabilities defining genome folding in the eukaryotic lineage. Changes in condensin II have likely contributed to notable shifts from chromosome territories to Rabl-like features throughout the tree of life. As our exploration of the tree of life continues, one of the many fruits will be a deeper knowledge of our own cellular machinery."

Comment: That evolution is a continuum from start to now is clearly shown by studies of the evolution of the genome controls. God, as designer, makes it easy for Himself in creating common descent.