针对眼斑拟石首鱼Sciaenops ocellatus染色体标记匮乏的问题,利用荧光原位杂交(FISH)定位了眼斑拟石首鱼的18S r DNA、5S r DNA和端粒序列。结果显示,眼斑拟石首鱼的核型公式为2n=48t;仅有1对18S r DNA位点,位于第1对染色体的次缢痕部位;有2对5S r DNA位点,FISH信号强度不等,强信号位于第8对染色体的近着丝粒端,弱信号位于第3对染色体的臂间。端粒FISH信号出现于所有染色体的两端,但表现出染色体两端信号不平衡的特点,着丝粒端FISH信号明显强于远端信号。这一特点为判定染色体的方向提供了便利。结合其他石首鱼的核型数据可以推断,2n=48t的核型及单对近着丝粒分布的18S r DNA位点是石首鱼的共同祖征;在石首鱼进化过程中,曾发生活跃但不影响宏观核型的小规模重排。研究结果丰富了眼斑拟石首鱼染色体的辨识标记,并为研究石首鱼染色体进化提供了基础数据。
The family Sciaenidae is remarkable for its species richness and economic importance. However, the cytogenetic data available in this fish group are still limited, especially those obtained using fl uorescence in situ hybridization(FISH). In the present study, the chromosome characteristics of a sciaenid species, Argyrosomus amoyensis, were examined with several cytogenetic methods, including dual-FISH with 18 S and 5 S rDNA probes, and a self-genomic in situ hybridization procedure(Self-GISH). The karyotype of A. amoyensis comprised 2 n=48 acrocentric chromosomes. A single pair of nucleolar organizer regions(NORs) was located at the proximal position of chromosome 1, which was positive for silver nitrate impregnation(AgNO_3) staining and denaturation-propidium iodide(DPI) staining but negative for Giemsa staining and 4',6-diamidino-2-phenylindole(DAPI) staining, and was confi rmed by FISH with 18 S rDNA probes. The 5 S rDNA sites were located at the centromeric region of chromosome 3. Telomeric FISH signals were detected at all chromosome ends with dif ferent intensities, but internal telomeric sequences(ITSs) were not found. Self-GISH resulted in strong signals distributed at the centromeric regions of all chromosomes. C-banding revealed not only centromeric heterochromatin, but also heterochromatin that located on NORs, in interstitial and distal telomeric regions of specifi c chromosomes. These results suggest that the karyotype of Amoy croaker was relatively conserved and primitive. By comparison with the reported cytogenetic data of other sciaenids, it can be deduced that although the karyotypic macrostructure and chromosomal localization of 18 S rDNA are conserved, the distribution of 5 S rDNA varies dynamically among sciaenid species. Thus, the 5 S rDNA sites may have different evolutionary dynamics in relation to other chromosomal regions, and have the potential to be ef fective cytotaxonomic markers in Sciaenidae.
