Chromosome Banding in Amphibia. XXXIV. Intrachromosomal Telomeric DNA Sequences in Anura

Abstract

The mitotic chromosomes of 4 anuran species were examined by various classical banding techniques and by fluorescence in situ hybridization using a (TTAGGG)_n repeat. Large intrachromosomal telomeric sequences (ITSs) were demonstrated in differing numbers and chromosome locations. A detailed comparison of the present results with numerous published and unpublished data allowed a consistent classification of the various categories of large ITSs present in the genomes of anurans and other vertebrates. The classification takes into consideration the total numbers of large ITSs in the karyotypes, their chromosomal locations and their specific distribution patterns. A new category of large ITSs was recognized to exist in anuran species. It consists of large clusters of ITSs located in euchromatic chromosome segments, which is in clear contrast to the large ITSs in heterochromatic chromosome regions known in vertebrates. The origin of the different categories of large ITSs in heterochromatic and euchromatic chromosome regions, their mode of distribution in the karyotypes and evolutionary fixation in the genomes, as well as their cytological detection are discussed.

Non-random distribution of microsatellite motifs and (TTAGGG)n repeats in the monkey frog Pithecopus rusticus (Anura, Phyllomedusidae) karyotype

“…However, the clear conservation of the chromosome structure in this group, the origin of the ITSs detected in the present study probably cannot be explained by rearrangements, but may be a result of the amplification of (TTAGGG)n repeats, which occurred independently during the chromosomal evolution of these species. Interestingly, these ITSs are associated with heterochromatin, given that they were detected in pericentromeric regions, coinciding with the C-band positive blocks reported by Bruschi et al (2014a), and a similar pattern has been ob-served in the Phyllomedusa species (Bruschi et al, 2014b), and in other anuran species (Schmid and Steinlein, 2016). As observed in P. rusticus, intense hybridization signals were also detected in the homologs of pair 13 in Phyllomedusa vaillantii, indicating that the (TTAGGG)n sequence is an important component of the repetitive DNA of these chromosomes in the phyllomedusids (Bruschi et al, 2014b).…”

Distribution of Interstitial Telomeric Sequences in Primates and the Pygmy Tree Shrew (Scandentia)

“…Telomere sequence probes have recently been mapped in order to clarify the location, role, and origin of ITSs in many animal karyotypes, including fish [Schneider et al, 2013], reptiles [Rovatsos et al, 2015;Altmanová et al, 2016], amphibians [Bruschi et al, 2014;Schmid and Steinlein, 2016], and many mammalian groups: Chiroptera [Calixto et al, 2014], Perissodactyla [Danielak-Czech et al, 2013], and Rodentia [Rovatsos et al, 2011;Nagamachi et al, 2013;Lanzone et al, 2015]. ITSs have also been analyzed in primates, and 3 principal classes have been identified, het-ITSs, s-ITSs, and subtelo-ITSs [Ruiz-Herrera et al, 2008]: (1) het-ITSs are large telomeric repeats that mainly correspond to heterochromatic segments, such as in centromeric or pericentromeric regions or within chromosomal arms; they are possibly remnants of chromosomal rearrangements such as fusions or inversions [Ijdo et al, 1991;Ventura et al, 2012]; (2) short ITSs (s-ITSs) are very small repeated sequences at an internal chromosomal position, not located at evolutionary breakpoints [Farré et al, 2009]; they are considered to be the result of double-strand breakage repair linked to retrotransposons and are identifiable through a molecular approach; (3) subtelo-ITSs are another kind of ITSs described in subtelomeric positions, as a possible result of recombination or amplification processes.…”

Comparative cytogenetics of tree frogs of the Dendropsophus marmoratus (Laurenti, 1768) group: conserved karyotypes and interstitial telomeric sequences

“…In the hylid Itapotihyla langsdorffii (Duméril & Bibron, 1841), ITSs were also observed in several centromeres (Gruber et al 2012b), but in this case the het-ITSs are not as large as those previously mentioned. In addition to the aforementioned hylids, other fifteen hylid species showed ITSs in their karyotypes (Meyne et al 1990, Wiley et al 1992, Suárez et al 2013, Mattos et al 2014, Bruschi et al 2014, Schmid and Steinlein 2016), which suggests that the appearance of this type of sequence is recurrent in the Hylidae family. Only the centromeric ITS found in chromosome 3 of Scarthyla goinorum (Bokermann, 1962) was clearly interpreted as a remnant of a chromosomal fusion that in that case could respond to the reduced chromosome number observed in this species (Suárez et al 2013).…”

“…Chromosomal sites composed of telomeric repeats localized apart from the telomeres, also known as interstitial or intrachromosomal telomeric sequences (ITSs) or repeats (ITRs), have been detected in several animals (Meyne et al 1990, Nanda et al 2002, Rovatsos et al 2015, Schmid and Steinlein 2016) and plants (Tek and Jiang 2004, He et al 2013). Based on the genomic location and sequence organization, especially in the number of telomeric repeats, Ruiz-Herrera et al (2008) classified the ITSs in short ITSs (s-ITSs) and heterochromatic ITS (het-ITS).…”

“…On the other hand, the het-ITSs have been widely considered to be remnants of ancestral chromosomal rearrangements as fusions (e.g., Lee et al 1993, Slijepcevic 1998, Ropiquet et al 2010, Paço et al 2013, Young et al 2013) and inversions (e.g., Farré et al 2009, Ocalewicz et al 2013, Paço et al 2013). Recently, Schmid and Steinlein (2016) proposed an additional category of ITS, named euchromatic-ITSs (eu-ITSs), to accommodate the large ITSs that are not revealed as heterochromatic sites by C-banding or staining with base-specific fluorochromes.…”