UNESP-Univ Estadual Paulista, Instituto de Biociências/IB, Depto, de Biologia, Rio Claro/SP, Brazil.
BMC Evol Biol. 2013 Aug 9;13:167. doi: 10.1186/1471-2148-13-167.
The accumulation of repetitive DNA during sex chromosome differentiation is a common feature of many eukaryotes and becomes more evident after recombination has been restricted or abolished. The accumulated repetitive sequences include multigene families, microsatellites, satellite DNAs and mobile elements, all of which are important for the structural remodeling of heterochromatin. In grasshoppers, derived sex chromosome systems, such as neo-XY♂/XX♀ and neo-X1X2Y♂/X1X1X2X2♀, are frequently observed in the Melanoplinae subfamily. However, no studies concerning the evolution of sex chromosomes in Melanoplinae have addressed the role of the repetitive DNA sequences. To further investigate the evolution of sex chromosomes in grasshoppers, we used classical cytogenetic and FISH analyses to examine the repetitive DNA sequences in six phylogenetically related Melanoplinae species with X0♂/XX♀, neo-XY♂/XX♀ and neo-X1X2Y♂/X1X1X2X2♀ sex chromosome systems.
Our data indicate a non-spreading of heterochromatic blocks and pool of repetitive DNAs (C0t-1 DNA) in the sex chromosomes; however, the spreading of multigene families among the neo-sex chromosomes of Eurotettix and Dichromatos was remarkable, particularly for 5S rDNA. In autosomes, FISH mapping of multigene families revealed distinct patterns of chromosomal organization at the intra- and intergenomic levels.
These results suggest a common origin and subsequent differential accumulation of repetitive DNAs in the sex chromosomes of Dichromatos and an independent origin of the sex chromosomes of the neo-XY and neo-X1X2Y systems. Our data indicate a possible role for repetitive DNAs in the diversification of sex chromosome systems in grasshoppers.
在性染色体分化过程中，重复 DNA 的积累是许多真核生物的共同特征，在重组受到限制或废除后，这种积累变得更加明显。积累的重复序列包括多基因家族、微卫星、卫星 DNA 和移动元件，它们都是异染色质结构重塑的重要组成部分。在直翅目昆虫中，衍生的性染色体系统，如 neo-XY♂/XX♀和 neo-X1X2Y♂/X1X1X2X2♀，在 Melanoplinae 亚科中经常观察到。然而，关于 Melanoplinae 性染色体进化的研究尚未涉及重复 DNA 序列的作用。为了进一步研究直翅目昆虫性染色体的进化，我们使用经典细胞遗传学和 FISH 分析方法，研究了六个系统发育相关的 Melanoplinae 物种的 X0♂/XX♀、neo-XY♂/XX♀和 neo-X1X2Y♂/X1X1X2X2♀性染色体系统中的重复 DNA 序列。
我们的数据表明，异染色质块和重复 DNA 库（C0t-1 DNA）在性染色体中没有扩散；然而，多基因家族在 Eurotettix 和 Dichromatos 的新性染色体中的扩散非常显著，特别是 5S rDNA。在常染色体中，多基因家族的 FISH 定位揭示了基因组内和基因组间染色体组织的明显模式。
这些结果表明，Dichromatos 的性染色体中重复 DNA 具有共同的起源和随后的差异积累，而 neo-XY 和 neo-X1X2Y 系统的性染色体则具有独立的起源。我们的数据表明，重复 DNA 可能在直翅目昆虫性染色体系统的多样化中发挥作用。
