Characterization and chromosomal mapping of the DgmarMITE transposon in populations of Dichotomius (Luederwaldtinia) sericeus species complex (Coleoptera: Scarabaeidae)

Abstract Transposable elements are dispersed repetitive DNA sequences that can move within the genome and are related to genome and chromosome evolution, adaptation, and speciation. The aim of this study was to characterize and determine the chromosomal location and accumulation of a Mariner-like element in populations of four phylogenetically related species of the Dichotomius (Luederwaldtinia) sericeus complex. Mapping of the isolated element was performed by fluorescent in situ hybridization in different populations of analyzed species. Characterization of the isolated element revealed a degenerated transposon, named DgmarMITE. This transposon is 496-bp-long, AT rich (57%), and contains 24 bp terminal inverted repeats. In situ mapping revealed presence of this element only in two out of four species analyzed. DgmarMITE sites were located in heterochromatic and euchromatic regions and varied in location and number on the karyotypes of Dichotomius (L.) gilletti and D. (L.) guaribensis across different populations. These results demonstrate differential accumulation of the DgmarMITE in genomes of these species, which is probably due to the occurrence of ectopic recombination and cross-mobilization of the element mediated by the transposase of closely related or unrelated transposable elements.

摘要
转座子（Transposable elements）是一类可在基因组内移动的散在重复DNA序列，与基因组及染色体进化、适应性演化及物种形成密切相关。本研究旨在解析类Mariner转座子（Mariner-like element）的特征，并确定其在丝质双角蜣螂（Dichotomius (Luederwaldtinia) sericeus）种群复合体中4个系统发育亲缘关系较近的物种种群内的染色体定位与拷贝累积情况。研究通过荧光原位杂交（fluorescent in situ hybridization）对分离得到的该元件完成定位分析。
对该分离元件的特征解析显示，其为一段退化型转座子，命名为DgmarMITE。该转座子全长496 bp，AT碱基含量丰富（达57%），并包含24 bp的末端反向重复序列（terminal inverted repeats）。原位杂交定位结果表明，该元件仅存在于所分析的4个物种中的2个。DgmarMITE的插入位点分布于异染色质与常染色质区域，且在不同种群的吉列特双角蜣螂（D. (L.) gilletti）和瓜里本西斯双角蜣螂（D. (L.) guaribensis）的核型中，其插入位置与拷贝数均存在差异。本研究结果证实，DgmarMITE在这两个物种的基因组中存在差异性累积，该现象大概率由异位重组事件，以及由亲缘关系相近或无关转座子的转座酶介导的该元件交叉转座所导致。