Gross M C, Schneider C H, Valente G T, Porto J I R, Martins C, Feldberg E
Instituto Nacional de Pesquisas da Amazônia, Universidade Federal do Amazonas, Departamento de Biologia, Manaus, Brazil.
Cytogenet Genome Res. 2009;127(1):43-53. doi: 10.1159/000279443. Epub 2010 Jan 29.
As part of a genetic screening program for wild Discus fishes, we analyzed karyotypes and cytogenetic characteristics of Symphysodon aequifasciatus, S. discus and S. haraldi using C-banding and fluorescent in situ hybridization (FISH) with the Rex3 retrotransposon and 5S rDNA probes in mitotic and meiotic chromosomes. In the 3 species, diploid chromosome number was 2n = 60 and karyotypes contained predominantly meta-submetacentric chromosomes. C-banding showed blocks of constitutive heterochromatin mainly in the pericentromeric region. Physical mapping of repetitive 5S rDNA sequences and Rex3 retrotransposons in mitotic and meiotic chromosomes showed partial colocalization of constitutive heterochromatin and repetitive elements. Correlations among the accumulation of repetitive elements, heterochromatinization and chromosome rearrangements have been hypothesized to explain the karyotype differentiation in the Symphysodon genus. The role of repetitive elements in adaptation to highly diverse habitats, as well as in the generation of the phenotypic and genetic variability found in wild Discus populations, needs to be further investigated.
作为野生七彩神仙鱼基因筛查项目的一部分，我们利用C显带技术以及有丝分裂和减数分裂染色体上的Rex3逆转座子和5S rDNA探针进行荧光原位杂交（FISH），分析了横纹神仙鱼、盘丽鱼和塔尔氏神仙鱼的核型和细胞遗传学特征。在这3个物种中，二倍体染色体数均为2n = 60，核型主要由中着丝粒 - 亚中着丝粒染色体组成。C显带显示组成型异染色质块主要位于着丝粒周围区域。有丝分裂和减数分裂染色体上重复的5S rDNA序列和Rex3逆转座子的物理图谱显示，组成型异染色质和重复元件部分共定位。重复元件的积累、异染色质化和染色体重排之间的相关性被认为可以解释七彩神仙鱼属的核型分化。重复元件在适应高度多样的栖息地以及在野生七彩神仙鱼种群中发现的表型和遗传变异产生中的作用，还有待进一步研究。
