Diversity and Evolution of Highly Repetitive DNA Sequences Constituting Chromosome Site-Specific Heterochromatin in Two Gerbillinae Species

Constitutive heterochromatin, consisting of repetitive sequences, diverges very rapidly; therefore, its nucleotide sequences and chromosomal distributions are often largely different, even between closely related species. The chromosome C-banding patterns of two Gerbillinae species, <i>Meriones unguiculatus</i> and <i>Gerbillus perpallidus</i>, vary greatly, even though they belong to the same subfamily. To understand the evolution of C-positive heterochromatin in these species, we isolated highly repetitive sequences, determined their nucleotide sequences, and characterized them using chromosomal and filter hybridization. We obtained a centromeric repeat (MUN-<i>Hae</i>III) and a chromosome 13-specific repeat (MUN-<i>Eco</i>RI) from <i>M. unguiculatus</i>. We also isolated a centromeric/pericentromeric repeat (GPE-MBD) and an interspersed-type repeat that was predominantly amplified in the X and Y chromosomes (GPE-<i>Eco</i>RI) from <i>G. perpallidus</i>. GPE-MBD was found to contain a 17-bp motif that is essential for binding to the centromere-associated protein CENP-B. This indicates that it may play a role in the formation of a specified structure and/or function of centromeres. The nucleotide sequences of the three sequence families, except GPE-<i>Eco</i>RI, were conserved only in Gerbillinae. GPE-<i>Eco</i>RI was derived from the long interspersed nuclear elements 1 retrotransposon and showed sequence homology throughout Muridae and Cricetidae species, indicating that the repeat sequence occurred at least in the common ancestor of Muridae and Cricetidae. Due to a lack of assembly data of highly repetitive sequences constituting heterochromatin in whole-genome sequences of vertebrate species published to date, the knowledge obtained in this study provides useful information for a deep understanding of the evolution of repetitive sequences in not only rodents but also in mammals.