A repeat DNA sequence from the Y chromosome in species of the genus Microtus

A new repeated DNA from Microtus thomasi, Mth-Alu2.2, was cloned and characterized and is presented here for the first time. Digestion of genomic DNA from M. thomasi with AluI restriction enzyme revealed a 2.2-kb repetitive DNA sequence with a high AT content (69%). This sequence consists of a tandemly repeated nonanucleotide of the consensus sequence CACAATGTA, which constitutes approximately 93-95% of the total unit length. The location of the Mth-Alu2.2 sequence in the karyotype was determined by FISH, demonstrating strong hybridization signals in the pericentromeric regions of all chromosomes and in the heterochromatin blocks of several X chromosome variants. In addition, the distribution of the 4 pericentromeric repeat sequences Msat-160, Mth-Alu900, Mth-Alu2.2, and interstitial telomeric repeats was analyzed by in situ hybridization in M. thomasi, in order to shed light on the complex composition of the chromosomal pericentromeric regions in this species. The order and organization of these sequences in the pericentromeric regions are conserved, with slight variations in both the degree of overlapping and the amount of each repeated DNA in the chromosomes. Specifically, Mth-Alu2.2 is localized in the terminal regions of the chromosomes, with Msat-160 occupying the immediately inner region, partially intermixed with Mth-Alu2.2. The sequence Mth-Alu900 is found in internal positions below Msat-160, and the interstitial telomeric repeats are located close to the long-arm euchromatin of the chromosomes.

Section: Resultsmentioning

confidence: 99%

Molecular and Physical Characterization of the Complex Pericentromeric Heterochromatin of the Vole Species Microtus thomasi

Rovatsos

Marchal

Romero-Fernández

et al. 2014

“…The repeat DNA sequence pMAHAE2, an exclusive component of the gonosomal heterochromatin present on the giant sex chromosomes from M. agrestis , has a high AT content (65%) (Kalscheuer et al, 1996). Also, the repeated DNA sequence from M. cabrerae McaY851, specific to the Y chromosome heterochromatin in most Microtus species, has an AT content of 58.3% (Marchal et al, 2004a).…”

Section: Resultsmentioning

confidence: 99%

“…Several studies have demonstrated that amplification of repetitive DNA sequences on sex chromosomes of Microtus species gives rise to blocks of constitutive heterochromatin (Kozlova et al, 2003;Marchal et al, 2004aMarchal et al, , b, 2006Acosta et al, 2008), possibly through different, independent and rapid processes in each species. For example the giant sex chromosome heterochromatin of M. agrestis and M. cabrerae must have originated recently through independent and different mechanisms in each species (Marchal et al, 2004a(Marchal et al, , b, 2006Acosta et al, 2008). …”

Section: Mth-alu900-con Actggtcaaaccggttta---------------------------mentioning

confidence: 99%

A new pericentromeric repeated DNA sequence in Microtus thomasi

Acosta

Marchal

Mitsainas

et al. 2009

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Several karyotypic forms have been previously described in populations of the vole species Microtus thomasi from Greece. In particular, the karyomorphs Microtus thomasi ‘thomasi’ and ‘atticus’ differ in X chromosome morphology, being acrocentric and subtelocentric, respectively. Furthermore, remarkable heterochromatin content variability has been described in sex chromosomes of both karyomorphs. Genomic DNA digestion with AluI allowed us to clone an 884 bp long repeated DNA sequence (Mth-Alu900) from the karyomorph M. thomasi ‘atticus’. This repeated DNA is AT rich and seems to be organized mainly as a dimer of the 884-bp unit, which presents three simple repeats (CAAAT, CAGAT and CAGAC) that constitute 80% of the total unit length. This repeated DNA is exclusive to M. thomasi, since it is absent from the genome of other studied Arvicolinae species. The chromosomal location of Mth-Alu900 was analyzed on M. thomasi ‘thomasi’ and M. thomasi ‘atticus’ karyomorphs, with different sex chromosome constitution. It was mainly located on the pericentromeric heterochromatin of most autosomes and X chromosomes on both karyomorphs. Results are also discussed in relation to karyotypic and sex chromosome variations in M. thomasi. To our knowledge, Mth-Alu900 constitutes a new – the third discovered so far – pericentromeric repeated DNA sequence described in Microtus species.

“…This may also be the case for Psittacidae species which show a higher content of repetitive DNAs evidenced by C-banding, as in Alisterus scapularis [Christidis et al, 1991] and G. brachyurus [Caparroz and Duarte, 2004], which have an accumulation of heterochromatin in their enlarged W chromosomes. Hence, although repetitive sequences represent a small percentage of avian genomes, it seems that they play an important role in the differentiation of sex chromosomes, as observed in many other groups [Marchal et al, 2004;Kejnovsky et al, 2009;Cioffi et al, 2011a ;Matsubara et al, 2016]. As an example, a recent analysis of sex chromosomes in Sauropsida (reptiles and birds) demonstrated that the amplification of microsatellite repeats was strongly associated with the process of differentiation and heterochromatinization of sex-specific chromosomes [Matsubara et al, 2016].…”

mentioning

confidence: 99%

Chromosomal Mapping of Repetitive DNAs in Myiopsitta monachus and Amazona aestiva (Psittaciformes, Psittacidae) with Emphasis on the Sex Chromosomes

Furo¹,

Kretschmer

Santos³

et al. 2017

Here, for the first time, we describe the karyotype of Myiopsitta monachus (Psittacidae, Arini). We found 2n = 48, corresponding to the lowest diploid number observed in Neotropical Psittaciformes so far, with an uncommonly large W chromosome homomorphic to the Z. In order to better understand the evolution of the sex chromosomes in this species, we applied several molecular cytogenetic approaches, including C-banding, FISH mapping of repetitive DNAs (several microsatellite repeats), and whole-chromosome painting on metaphases of M. monachus. For comparison, another species belonging to the same tribe but with a smaller W chromosome (A. aestiva) was also analyzed. The results show that the constitutive heterochromatin has a very diverse distribution pattern in these species revealing heterochromatic blocks in the centromeric region of all chromosomes and in most of the length of the W chromosome in A. aestiva, while in M. monachus they were found in interstitial and telomeric regions. Concerning the microsatellites, only the sequence (CG)_n produced signals on the W chromosome of A. aestiva, in the distal region of both arms. However, in M. monachus, (CAA)_n, (CAG)_n, and (CG)_n probes were accumulated on the W chromosome, and, in addition, the sequence (CAG)_n also hybridized to heterochromatic regions in macrochromosomes, as well as in microchromosomes. Based on these results, we suggest that the increase in length of the W chromosome in M. monachus is due to the amplification of repetitive elements, which highlights their significant role in the evolutionary process of sex chromosome differentiation.