A centromere-specific retroviral element associated with breaks of synteny in macropodine marsupials

Abstract

Studies of chromosome evolution have focused heavily on the evolution of conserved syntenic, gene-rich domains. It is obvious, however, that the centromere plays an equally important role in chromosome evolution, through its involvement in fissions, centric fusions, translocations, inversions and centric shifts. It is unclear how the centromere, either as a functioning unit of the chromosome or as a DNA sequence motif, has been involved in these processes. Marsupials of the family Macropodidae (kangaroos, wallabies, rat kangaroos and potoroos) offer unique insights into current theories expositing centromere emergence during karyotypic diversification and speciation. Tracing the genomic distribution of centromeric sequences in a model macropodine (subfamily Macropodinae: kangaroos and wallabies) species, Macropus eugenii (tammar wallaby), indicates these sequences have played an important role in chromosome evolution through possible segmental duplications associated with phylogenetically conserved breaks of synteny, pericentromeric and subtelomeric regions. Hybrids between different kangaroo species provide evidence that the centromere is unstable within this group of mammals and is involved in a large number of chromosome aberrations. A better understanding of the genetic and epigenetic factors that define centromeres and how centromeres may mediate changes in chromosome architecture are critical not only to our understanding of basic cellular functioning but also to our understanding of the process of speciation.

Recent Amplification of the Kangaroo Endogenous Retrovirus, KERV, Limited to the Centromere

“…KERV could participate in chromatin structure reorganization such that the chromatin configuration is no longer optimal for LINE insertions. Conversely, KERV's sequence conservation, continued expression, localization to centromeres, breaks of synteny, and nearly ubiquitous distribution in the marsupial clade set it apart from previously observed ERVs (23,24). Thus, KERV's relationship with the host may vary from the relationship observed by Cantrell et al (13) due to the different evolutionary forces under which the Macropus and Oryzomys genomes and associated TEs have evolved.…”

“…In the mammalian genome, these retroposition events are associated with mutations, diseases, and epigenetic modifications (20). Alternatively, TEs may be exapted by the host genome; for example, retroelements are implicated in centromere demarcation (24,35), telomere function (6), host defense (5,44,45), DNA repair (8), and placental development (55). Since TEs can impact the evolution of both gene regulation and function, an understanding of the complex interplay between genomes and their resident TEs is needed.…”

“…KERV was originally found as an amplified sequence at the centromeres in an interspecific hybrid between the two closely related wallaby species Macropus rufogriseus and M. eugenii (52). More recent hybridization experiments have proven that KERV is present in all extant marsupials at active and latent centromeres (23,24). The sister taxa M. eugenii and M. rufogriseus diverged within the last 1 million to 2 million years (29) and represent taxa with a rich evolutionary history in their resident retroelement populations.…”

Genomic Instability Within Centromeres of Interspecific Marsupial Hybrids

“…The second, KERV-1, is a retrovirus that is found in the genomes of a wide range of marsupials (Ferreri et al 2005). It is found at higher copy number at the active centromere (O'Neill et al 1998;Ferreri et al 2004) as well as in low copy number at breaks of synteny between the conserved chromosome segments within marsupials (Ferreri et al 2004).…”

Centromere Evolution: Digging into Mammalian Primary Constriction

“…1). It is considered thereof a major constituent of Macropus active and latent centromeres since it has undergone amplification at this locus (Ferreri et al, 2011;Ferreri et al, 2005;Ferreri et al, 2004;O'Neill et al, 1998). Particularly, in M. rufogriseus KERV is localized at the centromere of all autosomes, but it is absent or present in low copy number at the centromere of the sex chromosomes (Ferreri et al, 2011;Ferreri et al, 2004).…”