Martinez Pablo Ariel, de Araujo Washington Candeia, Molina Wagner Franco
Universidade Federal do Rio Grande do Norte (UFRN), Departamento de Biologia Celular e Genética, Centro de Biociências, Lagoa Nova s/n, CEP 59078-970, Natal, Rio Grande do Norte, Brasil.
Mar Genomics. 2010 Jun;3(2):85-9. doi: 10.1016/j.margen.2010.07.001. Epub 2010 Aug 13.
The Tetraodontiformes are one of the main irradiation lineages of Teleosts representing a highly specialized group. Among its families, Tetraodontidae has the lowest DNA/cell content of the vertebrates, and for this reason has been used as a model group for genomic evolution studies. Seeking to widen the cytogenetic database of this family, we performed a chromosomal analysis of the species Canthigaster figueiredoi using conventional staining, Ag-NORs, C-banding, base-specific fluorochromes DAPI-CMA(3), and in situ hybridization with 18S rDNA probe. This species has 2n=36 (10 m+6sm+20a; FN=52). Multiple Ag-NORs (CMA(3)(+)) sites were detected on the four chromosome pairs. Heterochromatic blocks (CMA(3)(+)) were present in the centromeric regions of most of the pairs, extending on the short arm of some chromosomes. A GC-positive polymorphic heterochromatic region was identified in some of the individuals, in one or both of the homologs of the 6th pair. The presence of heteromorphic B microchromosomes was detected in the karyotype of one female, exhibiting intra-individual variation of 0-3 Bs. The occurrence of heterochromatic polymorphisms, multiple NORs, and B chromosomes in C. figueiredoi are very infrequent events in marine fish. They are probably associated to the accentuated restructuring and genomic reduction suffered by this family.
鲀形目是硬骨鱼的主要辐射谱系之一，代表了一个高度特化的类群。在其所属科中，四齿鲀科的DNA/细胞含量在脊椎动物中最低，因此被用作基因组进化研究的模式类群。为了扩大该科的细胞遗传学数据库，我们使用常规染色、银染核仁组织区（Ag-NORs）、C带、碱基特异性荧光染料DAPI-CMA(3)以及与18S rDNA探针的原位杂交技术，对费氏尖鼻鲀（Canthigaster figueiredoi）进行了染色体分析。该物种具有2n = 36（10条中着丝粒染色体 + 6条亚中着丝粒染色体 + 20条端着丝粒染色体；臂数 = 52）。在四对染色体上检测到多个Ag-NORs（CMA(3)(+)）位点。大多数染色体对的着丝粒区域存在异染色质块（CMA(3)(+)），并在一些染色体的短臂上延伸。在部分个体的第6对同源染色体中的一条或两条上，发现了一个GC阳性的多态性异染色质区域。在一条雌性个体的核型中检测到异形B微染色体的存在，其个体内B染色体数量在0至3条之间变化。费氏尖鼻鲀中异染色质多态性、多个核仁组织区以及B染色体的出现，在海洋鱼类中是非常罕见的事件。它们可能与该科所经历的显著重组和基因组缩减有关。
