Highly species-specific centromeric repetitive DNA sequences in lizards: molecular cytogenetic characterization of a novel family of satellite DNA sequences isolated from the water monitor lizard (Varanus salvator macromaculatus, Platynota).

Two novel repetitive DNA sequences, VSAREP1 and VSAREP2, were isolated from the water monitor lizard (Varanus salvator macromaculatus, Platynota) and characterized using molecular cytogenetics. The respective lengths and guanine-cytosine (GC) contents of the sequences were 190 bp and 57.5% for VSAREP1 and 185 bp and 59.7% for VSAREP2, and both elements were tandemly arrayed as satellite DNA in the genome. VSAREP1 and VSAREP2 were each located at the C-positive heterochromatin in the pericentromeric region of chromosome 2q, the centromeric region of chromosome 5, and 3 pairs of microchromosomes. This suggests that genomic compartmentalization between macro- and microchromosomes might not have occurred in the centromeric repetitive sequences of V. salvator macromaculatus. These 2 sequences did only hybridize to genomic DNA of V. salvator macromaculatus, but no signal was observed even for other squamate reptiles, including Varanus exanthematicus, which is a closely related species of V. salvator macromaculatus. These results suggest that these sequences were differentiated rapidly or were specifically amplified in the V. salvator macromaculatus genome.

Heterochromatin blocks constituting the entire short arms of acrocentric chromosomes of Azara's owl monkey: formation processes inferred from chromosomal locations.

Centromeres and telomeres of higher eukaryotes generally contain repetitive sequences, which often form pericentric or subtelomeric heterochromatin blocks. C-banding analysis of chromosomes of Azara's owl monkey, a primate species, showed that the short arms of acrocentric chromosomes consist mostly or solely of constitutive heterochromatin. The purpose of the present study was to determine which category, pericentric, or subtelomeric is most appropriate for this heterochromatin, and to infer its formation processes. We cloned and sequenced its DNA component, finding it to be a tandem repeat sequence comprising 187-bp repeat units, which we named OwlRep. Subsequent hybridization analyses revealed that OwlRep resides in the pericentric regions of a small number of metacentric chromosomes, in addition to the short arms of acrocentric chromosomes. Further, in the pericentric regions of the acrocentric chromosomes, OwlRep was observed on the short-arm side only. This distribution pattern of OwlRep among chromosomes can be simply and sufficiently explained by assuming (i) OwlRep was transferred from chromosome to chromosome by the interaction of pericentric heterochromatin, and (ii) it was amplified there as subtelomeric heterochromatin. OwlRep carries several direct and inverted repeats within its repeat units. This complex structure may lead to a higher frequency of chromosome scission and may thus be a factor in the unique distribution pattern among chromosomes. Neither OwlRep nor similar sequences were found in the genomes of the other New World monkey species we examined, suggesting that OwlRep underwent rapid amplification after the divergence of the owl monkey lineage from lineages of the other species.