Genomic Organization of Microsatellites and LINE-1- like Retrotransposons: Evolutionary Implications for Ctenomys minutus (Rodentia: Ctenomyidae) Cytotypes

Simple Summary In animals, several species contain substantial chromosomal and genomic variation among their populations, but as to what could have driven such diversification is still a puzzle for most cases. Here, we used molecular cytogenetic analysis to expose the main genomic elements involved in the population variation observed in the Neotropical underground rodents of the genus Ctenomys (Rodentia: Ctenomyidae), which harbor the most significant chromosomal variation among mammals (2n = 10 to 2n = 70). These data provide evidence for a correlation between repetitive genomic content and localization of evolutionary breakpoint regions (EBRs) and highlight their direct impact in promoting chromosomal rearrangements. Abstract The Neotropical underground rodents of the genus Ctenomys (Rodentia: Ctenomyidae) comprise about 65 species, which harbor the most significant chromosomal variation among mammals (2n = 10 to 2n = 70). Among them, C. minutus stands out with 45 different cytotypes already identified, among which, seven parental ones, named A to G, are parapatrically distributed in the coastal plains of Southern Brazil. Looking for possible causes that led to such extensive karyotype diversification, we performed chromosomal mapping of different repetitive DNAs, including microsatellites and long interspersed element-1 ( LINE-1 ) retrotransposons in the seven parental cytotypes. Although microsatellites were found mainly in the centromeric and telomeric regions of the chromosomes, different patterns occur for each cytotype, thus revealing specific features. Likewise, the LINE-1 -like retrotransposons also showed a differential distribution for each cytotype, which may be linked to stochastic loss of LINE-1 in some populations. Here, microsatellite motifs (A) 30 , (C) 30 , (CA) 15 , (CAC) 10 , (CAG) 10 , (CGG) 10 , (GA) 15 , and (GAG) 10 could be mapped to fusion of chromosomes 20/17, fission and inversion in the short arm of chromosome 2, fusion of chromosomes 23/19, and different combinations of centric and tandem fusions of chromosomes 22/24/16. These data provide evidence for a correlation between repetitive genomic content and localization of evolutionary breakpoints and highlight their direct impact in promoting chromosomal rearrangements

Genomic Organization of Repetitive DNA in Woodpeckers (Aves, Piciformes): Implications for Karyotype and ZW Sex Chromosome Differentiation.

Birds are characterized by a low proportion of repetitive DNA in their genome when compared to other vertebrates. Among birds, species belonging to Piciformes order, such as woodpeckers, show a relatively higher amount of these sequences. The aim of this study was to analyze the distribution of different classes of repetitive DNA-including microsatellites, telomere sequences and 18S rDNA-in the karyotype of three Picidae species (Aves, Piciformes)-Colaptes melanochloros (2n = 84), Colaptes campestris (2n = 84) and Melanerpes candidus (2n = 64)-by means of fluorescence in situ hybridization. Clusters of 18S rDNA were found in one microchromosome pair in each of the three species, coinciding to a region of (CGG)10 sequence accumulation. Interstitial telomeric sequences were found in some macrochromosomes pairs, indicating possible regions of fusions, which can be related to variation of diploid number in the family. Only one, from the 11 different microsatellite sequences used, did not produce any signals. Both species of genus Colaptes showed a similar distribution of microsatellite sequences, with some difference when compared to M. candidus. Microsatellites were found preferentially in the centromeric and telomeric regions of micro and macrochromosomes. However, some sequences produced patterns of interstitial bands in the Z chromosome, which corresponds to the largest element of the karyotype in all three species. This was not observed in the W chromosome of Colaptes melanochloros, which is heterochromatic in most of its length, but was not hybridized by any of the sequences used. These results highlight the importance of microsatellite sequences in differentiation of sex chromosomes, and the accumulation of these sequences is probably responsible for the enlargement of the Z chromosome

Partial karyotypes of a female <i>Colaptes campestris</i> (A), a female <i>Colaptes melanochloros</i> (B) and a male <i>Melanerpes candidus</i> (C).

<p>Bar = 5μm.</p

Diploid number of Picidae species.

<p>Diploid number of Picidae species.</p

Specimen information and number of samples used in this study.

<p>Specimen information and number of samples used in this study.</p

Metaphase chromosomes of a male <i>Melanerpes candidus</i> hybridized with: 18S rDNA (A), telomeric DNA (B) and microsatellites DNA (C-G).

<p>Chromosomes were counterstained with DAPI (blue) and microsatellite probes were labeled directly during synthesis with Cy3 (red). Probes used are indicated in the lower left corner of the images. Sex chromosomes are indicated in each metaphase. Bar = 5μm.</p

Hybridization of repetitive sequences in Picidae.

<p>Hybridization of repetitive sequences in Picidae.</p

Chromosomal morphology of Picidae species included in this study.

<p>Chromosomal morphology of Picidae species included in this study.</p

Metaphase chromosomes of a female <i>Colaptes melanochloros</i> hybridized with: 18S rDNA (A), telomeric DNA (B) and microsatellites DNA (C-G).

<p>Chromosomes were counterstained with DAPI (blue), and microsatellite probes were labeled directly during synthesis with Cy3 (red). Probes used are indicated in the lower left corner of the images. Sex chromosomes are indicated in each metaphase. Bar = 5μm.</p

Distribution and localization of microsatellite sequences in chromosomes 1–5 and Z in <i>Colaptes</i> (A) and <i>M</i>. <i>candidus</i> (B).

<p>Distribution and localization of microsatellite sequences in chromosomes 1–5 and Z in <i>Colaptes</i> (A) and <i>M</i>. <i>candidus</i> (B).</p