Dipartimento di Biologia Animale ed Ecologia, Università di Cagliari, via T. Fiorelli, 1, 09126 Cagliari, Italy.
Eur J Histochem. 2011 May 27;55(2):e12. doi: 10.4081/ejh.2011.e12.
Muraenidae is a species-rich family, with relationships among genera and species and taxonomy that have not been completely clarified. Few cytogenetic studies have been conducted on this family, and all of them showed the same diploid chromosome number (2n=42) but with conspicuous karyotypic variation among species. The Mediterranean moray eel Gymnothorax unicolor was previously cytogenetically studied using classical techniques that allowed the characterization of its karyotype structure and the constitutive heterochromatin and argyrophilic nucleolar organizer regions (Ag-NORs) distribution pattern. In the present study, we describe two new repetitive elements (called GuMboI and GuDdeI) obtained from restricted genomic DNA of G. unicolor that were characterized by Southern blot and physically localized by in situ hybridization on metaphase chromosomes. As they are highly repetitive DNA sequences, they map in heterochromatic regions. However, while GuDdeI was localized in the centromeric regions, the GuMboI fraction was distributed on some centromeres and was co-localized with the nucleolus organizer region (NOR). Comparative analysis with other Mediterranean species such as Muraena helena pointed out that these DNA fractions are species-specific and could potentially be used for species discrimination. As a new contribution to the karyotype of this species, we found that the major ribosomal genes are localized on acrocentric chromosome 9 and that the telomeres of each chromosome are composed of a tandem repeat derived from a poly-TTAGGG DNA sequence, as it occurs in most vertebrate species. The results obtained add new information useful in comparative genomics at the chromosomal level and contribute to the cytogenetic knowledge regarding this fish family, which has not been extensively studied.
海鳝科是一个物种丰富的科，属种之间的关系和分类尚未完全阐明。对该科进行的细胞遗传学研究很少，所有这些研究都显示出相同的二倍体染色体数（2n=42），但种间的核型变异显著。地中海海鳝 Gymnothorax unicolor 以前曾使用经典技术进行细胞遗传学研究，这些技术允许对其染色体组结构和组成型异染色质以及银染核仁组织区域（Ag-NORs）的分布模式进行特征描述。在本研究中，我们描述了从 G. unicolor 的受限基因组 DNA 中获得的两个新的重复元件（称为 GuMboI 和 GuDdeI），通过 Southern blot 进行了特征描述，并通过原位杂交在中期染色体上进行了物理定位。由于它们是高度重复的 DNA 序列，因此它们位于异染色质区域。然而，虽然 GuDdeI 定位于着丝粒区域，但 GuMboI 部分分布在一些着丝粒上，并与核仁组织区（NOR）共定位。与其他地中海物种（如 Muraena helena）的比较分析表明，这些 DNA 片段是物种特异性的，可能可用于物种鉴别。作为对该物种染色体组的新贡献，我们发现主要核糖体基因定位于近端着丝粒染色体 9 上，并且每条染色体的端粒由来自多-TTAGGG DNA 序列的串联重复组成，如大多数脊椎动物物种中一样。所获得的结果提供了在染色体水平上进行比较基因组学的有用信息，并为对该鱼类科的细胞遗传学知识做出了贡献，该鱼类科尚未得到广泛研究。
