Mapping the distribution of the telomeric sequence (T₂AG₃)_n in rock wallabies, <i>Petrogale</i> (Marsupialia: Macropodidae), by fluorescence in situ hybridization

Abstract

The distribution of the conserved vertebrate telomeric sequence (T₂AG₃)_n was examined by fluorescence in situ hybridization in the six Petrogale (rock wallabies) taxa of the lateralis complex. As expected, the (T₂AG₃)_n sequence was located at the termini of all chromosomes in all taxa. However, the sequence was also present at several nontelomeric (viz., interstitial and centromeric) sites. The signals identified were associated with either ancient rearrangements involved with the formation of the 2n = 22 plesiomorphic macropodine karyotype or more recent rearrangements associated with karyotypes derived from the 2n = 22 karyotype. Interstitial (T₂AG₃)_n signals identified on chromosomes 3 and 4 in all six species of the lateralis complex and a large centromeric signal identified on chromosome 7 in the five subspecies/races of P. lateralis appear to be related to the more ancient rearrangements. Subsequent chromosome evolution has seen these signals retained, lost, or amplified in different Petrogale lineages. Within the lateralis complex, in two submetacentric chromosome derived by recent centric fusions, the telomeric sequence was identified at or near the centromere, indicating its retention during the fusion process. In the two taxa where chromosome 3 was rearranged via a recent centromeric transposition to become an acrocentric chromosome, the telomeric signal was located interstitially.

Mapping the distribution of the telomeric sequence (T₂AG₃)_n in the Macropodoidea (Marsupialia) by fluorescence in situ hybridization. II. The ancestral 2n = 22 macropodid karyotype

“…The distribution of the telomeric sequence in these complements is consistent with ITSs as 'remnant' telomeres, i.e. it is invariably found at the site of rearrangements (Metcalfe et al, 1997(Metcalfe et al, , 1998(Metcalfe et al, , 2002(Metcalfe et al, , 2004. We have also examined three 2n = 22 ancestral macropodine karyotypes with little or no C-banding (Metcalfe et al, 1998(Metcalfe et al, , 2002.…”

“…Three Petrogale chromosomal groups are recognised (Briscoe et al, 1982;Eldridge and Close, 1993), the lateralis/penicillata group (14 taxa), xanthopus group (three species) and brachyotis group (three species). All taxa of the lateralis/ penicillata and xanthopus groups were examined (this paper and Metcalfe et al, 1997Metcalfe et al, , 2002. Species from the brachyotis group (Petrogale) show extensive C-banding and are not included (Eldridge et al, 1992).…”

“…All these complements show very little or no Cbanding (Rofe, 1979;Sharman et al, 1990). Results are compared with data presented in previous studies (Metcalfe et al, 1997(Metcalfe et al, , 1998(Metcalfe et al, , 2002(Metcalfe et al, , 2004.…”

“…it is invariably found at the site of rearrangements (Metcalfe et al, 1997(Metcalfe et al, , 1998(Metcalfe et al, , 2002(Metcalfe et al, , 2004. We have also examined three 2n = 22 ancestral macropodine karyotypes with little or no C-banding (Metcalfe et al, 1998(Metcalfe et al, , 2002. Here we examine an additional five 2n = 22 ancestral macropodine karyotypes, specifically those of the three species of the Petrogale xanthopus group (P. xanthopus , P. rothschildi and P. persephone) and two Thylogale species (T. billardierii and T. stigmatica) .…”

Localization of Telomeric Sequences in the Chromosomes of Three Species of Calomys (Rodentia, Sigmodontinae)

“…Less frequently, tracts of this telomeric sequence can be detected at additional, non-telomeric locations, mainly at pericentric regions but also at interstitial sites, and the distribution of these internal telomeric signals (ITS) can vary among closely related species (Meyne et al 1990). ITS are generally considered to be relics of chromosome rearrangements (Meyne et al 1990, Metcalfe et al 2002, Nanda et al 2002 or to correspond to repetitive DNA rich in (T 2 AG 3 ) n sequences (Garagna et al 1997, Meyne et al 1990, Multani et al 2001, Pagnozzi et al 2000. In addition, molecular studies have suggested that some short internal telomeric repeats might have been originated by the repair of doublestranded breaks (Azzalin et al 2001, Faravelli et al 2002, Nergadze et al 2004.…”