Molecular Cytogenetic Characterization of the Genome Organization of the 6-Banded Armadillo <i>(Euphractus sexcinctus)</i>

Abstract

Xenarthra, as the probable earliest offshoot of the placental tree, represents a key taxon for understanding mammalian phylogeny. To gain further insight into the chromosomal evolution and genome organization of the xenarthrans, we have established the first genome-wide comparative chromosome map between human and the 6-banded armadillo (Euphractussexcinctus, 2n = 58), a basal species on the Xenarthra branch, by reciprocal cross-species chromosome painting. In total, 22 human autosomal paints revealed 41 homologous segments in the euchromatic genome of E. sexcinctus. Our results provide further support for the notion that the 2 human homologous segmental associations, i.e. HSA 2/8 and 7a/10p, could constitute the synapomorphies that unite the xenarthrans. Moreover, we propose that the putative ancestral Xenarthra karyotype closely resemble the 2n = 54 karyotype of the E. sexcinctus, consisting of the equivalents of HSA1p, 1q, 2a, 2b, 2c/8c, 3/21, 4a, 4b/8b, 5, 6a, 6b, 7a/10p, 7b/16p, 8a, 9, 10q, 11, 12a/22a, 12b/22b, 13, 14/15, 16q/19q, 17, 18, 19p, 20, and X. In addition, we have analysed the C-banding patterns of E. sexcinctus, and cloned, FISHmapped and sequenced 7 novel repetitive DNA segments, providing further information on the complexity of genome architecture of E. sexcinctus.

Chromosome Evolution in Xenarthra: New Insights from an Ancient Group

“…3 ). Some of these chromosome features correspond to previous suggestions of ancestral xenarthran arrangements made on the basis of intraordinal chromosome painting results [Dobigny et al, 2005], which reinforced the conclusions of Liu et al [2011].…”

“…In addition, based on literature data, the chromosome segments that would be homologous between human and B . tridactylus could be deduced [Svartman et al, 2006;Yang et al, 2006, Liu et al, 2011Azevedo et al, 2012]. A summary of the results of these studies is presented in table 2 .…”

“…torquatus and possibly also in B. tridactylus led to the suggestion that this would be a chromosome signature of Xenarthra [Yang et al, 2006;Liu et al, 2011;Azevedo et al, 2012]. This association was not detected in C. hoff-manni and D .…”

“…The association HSA2/8, found in C. didactylus , T. tetradactyla and E. sexcinctus has also been considered a chromosome signature of Xenarthra [Yang et al, 2006;Liu et al, 2011]. Nevertheless, its absence in all the other studied species of the group led Azevedo et al [2012] to conclude that it may be a result of convergence, instead of a Xenarthra synapomorphy.…”

“…More recently, based on the available data from 5 Xenarthra species already painted with human chromosomespecific probes and using the conserved syntenies between the sequenced genomes of human and of the marsupial to represent symplesiomorphies, Liu et al [2011] proposed an ancestral Xenarthra karyotype (AXK) with 2n = 54. This AXK would be similar to the karyotype of the 6-banded armadillo E. sexcinctus and composed of: the associations HSA2c/8c, 3/21, 4b/8b, 7a/10p, 7b/16p, 12/22 (2 !…”