Molecular cytogenetic analysis and the establishment of a cell culture in the fish species Hollandichthys multifasciatus (Eigenmann & Norris, 1900) (Characiformes, Characidae)

Abstract Hollandichthys is a fish genus of the family Characidae that was until recently considered to be monotypic, with cytogenetic, morphological, and molecular data being restricted to a few local populations. In the present study, the karyotype of a population of Hollandichthys multifasciatus was analyzed using classical and molecular cytogenetic approaches for the investigation of potential markers that could provide new perspectives on the cytotaxonomy. H. multifasciatus presented a diploid number of 2n=50 chromosomes and a karyotype formula of 8m+10sm+32st. A single pair of chromosomes presented Ag-NORs signals, which coincided with the 18S rDNA sites visualized by FISH, whilst the 5S rDNA sequences were mapped in two chromosome pairs. The distribution of the U snRNA genes was mapped on the Hollandichthys chromosomes for the first time, with the probes revealing the presence of the U1 snDNA on the chromosomes of pair 20, U2 on pairs 6 and 19, U4 on pair 16, and U6 on the chromosomes of pair 11. The results of the present study indicated karyotypic differences in comparison with the other populations of H. multifasciatus studied previously, reinforcing the need for further research to identify isolated populations or the potential existence of cryptic Hollandichthys species.

摘要 霍氏脂鲤属（Hollandichthys）是脂鲤科（Characidae）的鱼类属，直至近期仍被视为单型属，其相关细胞遗传学、形态学及分子生物学数据仅局限于少数局域种群。本研究采用经典细胞遗传学与分子细胞遗传学方法，对多带霍氏脂鲤（Hollandichthys multifasciatus）的一个种群的核型进行分析，旨在发掘可用于细胞分类学研究的潜在分子标记，以期为该类群的细胞分类学研究提供新视角。多带霍氏脂鲤的二倍体染色体数为2n=50，核型公式为8m+10sm+32st。仅1对染色体携带银染核仁组织区（Ag-NORs）信号，该位点与通过荧光原位杂交（FISH）检测到的18S rDNA位点完全重合；而5S rDNA序列则被定位在2对染色体上。本研究首次在霍氏脂鲤的染色体上定位了U型小核RNA（U snRNA）基因的分布，所用探针显示：U1 snDNA位于第20号染色体对，U2 snDNA位于第6和19号染色体对，U4 snDNA位于第16号染色体对，U6 snDNA位于第11号染色体对。本研究结果显示，该种群与此前已报道的其他多带霍氏脂鲤种群存在核型差异，这进一步强化了开展后续研究的必要性，以厘清其孤立种群的划分，或是发掘霍氏脂鲤属内隐存物种的潜在可能。