Oliveira S G, Cabral-de-Mello D C, Arcanjo A P, Xavier C, Souza M J, Martins C, Moura R C
Departamento de Morfologia, Instituto de Biociências, Universidade Estadual Paulista/UNESP, Botucatu, Brazil.
Cytogenet Genome Res. 2012;138(1):46-55. doi: 10.1159/000339648. Epub 2012 Jul 11.
Repetitive DNA sequences constitute a high fraction of eukaryotic genomes and are considered a key component for the chromosome and karyotype evolution. For a better understanding of their evolutionary role in beetles, we examined the chromosomes of 5 species of the genus Coprophanaeus by C-banding, fluorochrome staining CMA₃/DA/DAPI, and fluorescence in situ hybridization (FISH) with probes for 18S and 5S rRNA genes. The Coprophanaeus species have identical chromosome numbers and a conserved chromosome morphology. However, they show different sex chromosome forms, XY, Xy, XY(p), and heterochromatin seems to be involved in the origin and diversification of these forms. C-banding showed primarily the presence of diphasic chromosomes in all species examined. After CMA₃/DA/DAPI staining, 1-9 autosomal pairs showed CMA₃-positive blocks depending on the species, while DAPI-positive blocks were detected only in Coprophanaeusdardanus. FISH mapping revealed 5S rDNA signals in one autosomal pair in each species, whereas the number of pairs with 18S rDNA signals varied from 1-8 between the Coprophanaeus species. Our results suggest that distinct genetic mechanisms had been involved in the karyotype evolution of Coprophanaeus species, i.e. mechanisms maintaining the conserved number of 5S rDNA clusters and those generating variability in the amount of heterochromatin, sex chromosome forms, and distribution of 18S rDNA clusters.
重复DNA序列在真核生物基因组中占比很高，被认为是染色体和核型进化的关键组成部分。为了更好地理解它们在甲虫中的进化作用，我们通过C带、荧光染料染色CMA₃/DA/DAPI以及用18S和5S rRNA基因探针进行荧光原位杂交（FISH），研究了粪金龟属5个物种的染色体。粪金龟属物种具有相同的染色体数目和保守的染色体形态。然而，它们表现出不同的性染色体形式，XY、Xy、XY(p)，异染色质似乎参与了这些形式的起源和多样化。C带显示在所研究的所有物种中主要存在双相染色体。CMA₃/DA/DAPI染色后，根据物种不同，1 - 9对常染色体显示CMA₃阳性块，而仅在粪金龟中检测到DAPI阳性块。FISH定位显示每个物种的一对常染色体上有5S rDNA信号，而粪金龟属物种中具有18S rDNA信号的染色体对数在1 - 8之间变化。我们的结果表明，不同的遗传机制参与了粪金龟属物种的核型进化，即维持5S rDNA簇保守数量的机制以及导致异染色质数量、性染色体形式和18S rDNA簇分布产生变异的机制。
