Chromosome plasticity in Ctenomys (Rodentia Octodontidae): chromosome 1 evolution and heterochromatin variation

Abstract

A chromosome 1 (Cr1) pericentric inversion is described in six of seven species in the genus Ctenomys (tuco-tucos) from Uruguay. The inversion was inferred from G-band analyses of subtelocentric Cr1 hypothesised to be derived from the ancestral metacentric condition. Cr1 varies across species in heterochromatin amount and localisation including a metacentric chromosome without positive C-bands in C. torquatus, a subtelocentric chromosome with heterochromatic short arms in C. rionegrensis, and a subtelocentric chromosome negative after C-banding in five of the species analysed here. Pachytene chromosomes from C. rionegrensis, a species with the highest heterochromatin content, and C. torquatus, one of the species with the lowest heterochromatin content, were analysed in order to assess possible mechanisms of heterochromatin evolution. This analysis revealed the presence of three heterochromatic chromocenters in C. rionegrensis where bivalents converge, while in C. torquatus only one chromocenter was observed. In both species, highly repetitive DNA was observed, localised in chromocenters after "in situ" hybridisation. Heterochromatin associated protein M31 was localised in chromocenters of both species after immuno-detection. The spread of heterochromatin in Ctenomys chromosomes could be produced by chromatin exchanges at the chromocenter level. We propose the exchange of this DNA associated proteins between non-homologous chromosomes in pachytene to be the responsible for the spread of heterochromatin through the karyotypes of species like C. rionegrensis.

Integrative lineage delimitation in rodents of the Ctenomys Corrientes group

“…These rodents have undergone enormous levels of chromosomal evolution with diploid numbers varying from 2n = 10 to 2n = 70, mainly due to Robertsonian translocations, but also heterochromatin additions/losses, pericentric inversions and/or tandem fusions had been postulated (Reig and Kiblisky 1969, Cook et al 1990, Massarini et al 1991, Freitas 2006, Novello and Villar 2006, Caraballo et al 2015. Their subterranean lifestyle has been associated to high population subdivision and low vagility which may have promoted the fixation of chromosomal novelties by genetic drift Kiblisky 1969, Ortells 1995).…”

Possible Heterochromatin Horizontal Spread through Non-Homologous Chromosome Associations in Pachytene Chromocenters of <i>Ctenomys </i>Rodents

“…6 , arrows). As described before, G-band analysis [Novello and Villar, 2006] revealed a pericentric inversion of C. torquatus metacentric chromosome no. 1 that originates the subtelocentric morphology in the remaining species of the C. pearsoni complex and C. rionegrensis ( fig.…”

“…Karyotypic differences in Ctenomys involve changes in chromosome morphology Novello and Altuna, 2002] and variations in heterochromatin amount and localization [Gallardo, 1991;Freitas, 1994;Rossi et al, 1995;Novello et al, 1996a, b;Novello and Villar, 2006]. In the populations surveyed here, 2n values and heterochromatin variation were observed, indicating a high degree of chromosome change.…”

Chromosomes and speciation in tuco-tuco (Ctenomys, Hystricognathi, Rodentia)

“…Диплоидное число хромосом в этой группе варьирует от 40 до 70. Измен-чивость кариотипа у тукотуко обусловлена фиксацией различных хромосомных перестроек: робертсоновских транслокаций, перицентрических инверсий и изменений гетерохроматина (добавления или делеции Спозитивного материала) (Reig, Kiblisky, 1969;Cook et al, 1990;Giménez et al, 2002;Novello, Villar, 2006). Более того, хромосомный полиморфизм наблюдается и внутри многих видов тукотуко (Massarini et al, 2002;Freitas, 2007;Caraballo et al, 2012;Lopes et al, 2013).…”