Evolutionary breakpoint regions and chromosomal remodeling in Harttia (Siluriformes: Loricariidae) species diversification

Abstract The Neotropical armored catfish genus Harttia presents a wide variation of chromosomal rearrangements among its representatives. Studies indicate that translocation and Robertsonian rearrangements have triggered the karyotype evolution in the genus, including differentiation of sex chromosome systems. However, few studies used powerful tools, such as comparative whole chromosome painting, to clarify this highly diversified scenario. Here, we isolated probes from the X1 (a 5S rDNA carrier) and the X2 (a 45S rDNA carrier) chromosomes of Harttia punctata, which displays an X1X1X2X2/X1X2Y multiple sex chromosome system. Those probes were applied in other Harttia species to evidence homeologous chromosome blocks. The resulting data reinforce that translocation events played a role in the origin of the X1X2Y sex chromosome system in H. punctata. The repositioning of homologous chromosomal blocks carrying rDNA sites among ten Harttia species has also been demonstrated. Anchored to phylogenetic data it was possible to evidence some events of the karyotype diversification of the studied species and to prove an independent origin for the two types of multiple sex chromosomes, XX/XY1Y2 and X1X1X2X2/X1X2Y, that occur in Harttia species. The results point to evolutionary breakpoint regions in the genomes within or adjacent to rDNA sites that were widely reused in Harttia chromosome remodeling.

摘要 新热带区甲鲶属（Harttia）类群的染色体组型存在广泛的染色体重排变异。已有研究显示，易位与罗伯逊重排推动了该属的核型进化，其中亦包含性染色体系统的分化。不过，目前鲜有研究借助全染色体比较涂染（comparative whole chromosome painting）这类高分辨率细胞遗传学技术，来厘清这一高度多样化的演化格局。本研究从携带X1X1X2X2/X1X2Y多重性染色体系统的斑哈特鲶（Harttia punctata）的X1染色体（携带5S核糖体DNA（5S rDNA））与X2染色体（携带45S核糖体DNA（45S rDNA））中分离得到特异性探针，并将其应用于其他哈特鲶属物种，以检测异源同源染色体区段。所得实验数据证实，易位事件在斑哈特鲶X1X2Y性染色体系统的起源过程中扮演了关键角色。同时，研究还明确了10个哈特鲶属物种中携带核糖体DNA位点的同源染色体区段发生了重定位。结合系统发育数据，本研究得以揭示部分研究物种的核型分化事件，并证实哈特鲶属中存在的两类多重性染色体系统——XX/XY1Y2与X1X1X2X2/X1X2Y——具有独立起源。研究结果表明，基因组中位于核糖体DNA位点内部或邻近区域的进化断点区域，在哈特鲶属的染色体重塑过程中被广泛复用。