The two most speciose families of marsupials have very different rates of chromosomal evolution. All dasyurids (carnivorous/insectivorous marsupials) examined to date have almost identical karyotypes, though this has not prevented speciation in the family (over 70 species recognised). In contrast, macropods (wallabies and kangaroos) are typified by a high level of karyotype divergence. In particular, the genus Petrogale (rock wallabies) shows remarkable levels of chromosome rearrangement, most often involving Robertsonian fusions; throughout the 22 recognised species of rock-wallabies, only two share a similar karyotype. Our previous work had demonstrated marked differences in the DNA methylation patterns between a representative of each family, the Tasmanian devil and tammar wallaby. Devil chromosomes are characterised by hypermethylation of the terminal region of chromosomes, with low levels of methylation throughout the chromosomes. In contrast tammar wallabies have extremely hypermethylated centromeres, and moderate to high levels of methylation throughout the chromosome bodies; some chromosomes had signs of elevated methylation at terminal regions. One notable chromosomal difference between these marsupial families is an unusual telomere length dimorphism in dasyurids. Since cytosine methylation of subtelomeric regions has been shown to regulate telomere length and stability, we posited that the hypermethylation of telomere regions and the telomere length dimorphism on devil chromosomes contribute to the stability of the dasyurid karyotype. To test this hypothesis, we examined broad patterns of DNA methylation and telomeric staining in three dasyurid species, and four Petrogale species, at the chromosome level. All species tested share a common pattern of chromosome terminal region hypermethylation, with generally low levels of DNA methylation throughout the rest of the chromosome body. This pattern is in spite of chromosomal rearrangements in the Petrogale species. Hypermethylation of telomeric regions is therefore not associated with telomere length dimorphism, but is a more common feature of marsupial chromosomes.
The two most speciose families of marsupials have very different rates of chromosomal evolution. All dasyurids (carnivorous/insectivorous marsupials) examined to date have almost identical karyotypes, though this has not prevented speciation in the family (over 70 species recognised). In contrast, macropods (wallabies and kangaroos) are typified by a high level of karyotype divergence. In particular, the genus Petrogale (rock wallabies) shows remarkable levels of chromosome rearrangement, most often involving Robertsonian fusions; throughout the 22 recognised species of rock-wallabies, only two share a similar karyotype. Our previous work had demonstrated marked differences in the DNA methylation patterns between a representative of each family, the Tasmanian devil and tammar wallaby. Devil chromosomes are characterised by hypermethylation of the terminal region of chromosomes, with low levels of methylation throughout the chromosomes. In contrast tammar wallabies have extremely hypermethylated centromeres, and moderate to high levels of methylation throughout the chromosome bodies; some chromosomes had signs of elevated methylation at terminal regions. One notable chromosomal difference between these marsupial families is an unusual telomere length dimorphism in dasyurids. Since cytosine methylation of subtelomeric regions has been shown to regulate telomere length and stability, we posited that the hypermethylation of telomere regions and the telomere length dimorphism on devil chromosomes contribute to the stability of the dasyurid karyotype. To test this hypothesis, we examined broad patterns of DNA methylation and telomeric staining in three dasyurid species, and four Petrogale species, at the chromosome level. All species tested share a common pattern of chromo ...
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