Chromosome diversity in Buthidae and Chactidae scorpions from Brazilian fauna: Diploid number and distribution of repetitive DNA sequences

Abstract In this work, we analyzed cytogenetically eight Chactidae and Buthidae, including the localization of repetitive DNA sequences. The chactids possess monocentric chromosomes and the highest diploid numbers (2n=50 in Brotheas amazonicus, 2n=36 in Chactopsis amazonica, 2n=30 in Neochactas sp.) when compared with buthids (2n=10 in Tityus bahiensis, 2n=14 in Tityus apiacas and Tityus metuendus, 2n=18 in Tityus aba, 2n=26 in Ischnotelson peruassu). The localization of rDNA genes and (TTAGG)n sequences exhibited a conserved pattern of two terminal/subterminal ribosomal cistrons and terminal telomere signals. However, the comparison between the data of C-banding, DAPI after FISH and Cot-DNA fraction indicated a variable quantity and distribution of these regions, as follow: (i) positive heterochromatin and Cot-DNA signals (B. amazonicus and I. peruassu), (ii) small blocks of heterochromatin with large Cot-DNA signals (T. metuendus), (iii) positive heterochromatic regions and absence of Cot-DNA signals (T. aba and T. apiacas), and (iv) negative heterochromatin and Cot-DNA signals (T. bahiensis). Therefore, our results revealed that there still is not a clear relation between quantity of heterochromatin and presence of monocentric or holocentric chromosomes and occurrence of chromosomal rearrangements, indicating that repetitive regions in scorpions must be analyzed using different cytogenetic approaches.摘要 本研究对8种查科蝎科（Chactidae）和钳蝎科（Buthidae）物种开展了细胞遗传学分析，涵盖重复DNA序列的定位。相较于钳蝎科类群（巴西蒂泰蝎Tityus bahiensis的二倍体数目为2n=10、阿皮亚卡斯蒂泰蝎Tityus apiacas与梅图恩蒂泰蝎Tityus metuendus的二倍体数目为2n=14、阿巴蒂泰蝎Tityus aba的二倍体数目为2n=18、秘鲁伊斯奇诺蝎Ischnotelson peruassu的二倍体数目为2n=26），查科蝎科物种具备单着丝粒染色体及更高的二倍体染色体数目：亚马逊布罗泰蝎Brotheas amazonicus为2n=50、亚马逊查塔蝎Chactopsis amazonica为2n=36、新查塔蝎Neochactas sp.为2n=30。对核糖体DNA（rDNA）基因及(TTAGG)n序列的定位结果显示，其呈现保守模式：存在2个末端/亚末端核糖体顺反子，以及末端端粒信号。然而，通过C带染色、荧光原位杂交（FISH）后DAPI染色与Cot-DNA组分的对比分析表明，此类区域的数量与分布存在差异，具体可分为四类：(i) 异染色质阳性且存在Cot-DNA信号（亚马逊布罗泰蝎与秘鲁伊斯奇诺蝎）；(ii) 异染色质小片段但存在强Cot-DNA信号（梅图恩蒂泰蝎）；(iii) 异染色质阳性但无Cot-DNA信号（阿巴蒂泰蝎与阿皮亚卡斯蒂泰蝎）；(iv) 异染色质阴性但存在Cot-DNA信号（巴西蒂泰蝎）。综上，本研究结果显示，异染色质数量与单着丝粒/全着丝粒染色体（holocentric chromosomes）的存在及染色体重排的发生之间尚未存在明确关联，表明蝎类的重复区域需通过多种细胞遗传学方法开展分析。