The implications of satellite DNA instability on cellular function and evolution

[Heterochromatin and epigenetic control of repeat sequences]

L’hétérochromatine est une structure décrite comme restrictive et répressive. On la retrouve notamment au niveau des séquences répétées qui représentent près de la moitié du génome humain. Ces séquences, dont l’origine reste incertaine, peuvent jouer un rôle structural, protecteur ou régulateur. Cependant, leur homologie de séquence ou leur capacité à transposer pour certaines, peuvent compromettre la stabilité du génome, et la formation d’hétérochromatine au niveau de ces régions permet de les réguler. Souvent imaginée comme une structure dont la composition est stable, l’hétérochromatine est en réalité bien plus hétérogène, en fonction du locus et du type cellulaire où elle est établie.

Evolution of Repetitive Elements, Their Roles in Homeostasis and Human Disease, and Potential Therapeutic Applications

Repeating sequences of DNA, or repetitive elements (REs), are common features across both prokaryotic and eukaryotic genomes. Unlike many of their protein-coding counterparts, the functions of REs in host cells remained largely unknown and have often been overlooked. While there is still more to learn about their functions, REs are now recognized to play significant roles in both beneficial and pathological processes in their hosts at the cellular and organismal levels. Therefore, in this review, we discuss the various types of REs and review what is known about their evolution. In addition, we aim to classify general mechanisms by which REs promote processes that are variously beneficial and harmful to host cells/organisms. Finally, we address the emerging role of REs in cancer, aging, and neurological disorders and provide insights into how RE modulation could provide new therapeutic benefits for these specific conditions.

Dynamic interplay between human alpha-satellite DNA structure and centromere functions

Maintenance of genome stability relies on functional centromeres for correct chromosome segregation and faithful inheritance of the genetic information. The human centromere is the primary constriction within mitotic chromosomes made up of repetitive alpha-satellite DNA hierarchically organized in megabase-long arrays of near-identical higher order repeats (HORs). Centromeres are epigenetically specified by the presence of the centromere-specific histone H3 variant, CENP-A, which enables the assembly of the kinetochore for microtubule attachment. Notably, centromeric DNA is faithfully inherited as intact haplotypes from the parents to the offspring without intervening recombination, yet, outside of meiosis, centromeres are akin to common fragile sites (CFSs), manifesting crossing-overs and ongoing sequence instability. Consequences of DNA changes within the centromere are just starting to emerge, with unclear effects on intra- and inter-generational inheritance driven by centromere's essential role in kinetochore assembly. Here, we review evidence of meiotic selection operating to mitigate centromere drive, as well as recent reports on centromere damage, recombination and repair during the mitotic cell division. We propose an antagonistic pleiotropy interpretation to reconcile centromere DNA instability as both driver of aneuploidy that underlies degenerative diseases, while also potentially necessary for the maintenance of homogenized HORs for centromere function. We attempt to provide a framework for this conceptual leap taking into consideration the structural interface of centromere-kinetochore interaction and present case scenarios for its malfunctioning. Finally, we offer an integrated working model to connect DNA instability, chromatin, and structural changes with functional consequences on chromosome integrity.