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：转座因子（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、适应性演化和物种形成密切相关。本研究旨在对双齿蜣螂属（Dichotomius）卢德沃特蜣螂亚属（Luederwaldtinia）丝质物种复合群（Dichotomius (Luederwaldtinia) sericeus complex）的4个系统发育亲缘关系较近的物种种群中的类Mariner转座子（Mariner-like element）进行特征分析，并明确其染色体定位与基因组累积特征。研究通过荧光原位杂交（fluorescent in situ hybridization）技术，对分离得到的该转座因子在各分析物种的不同种群中进行定位。对该分离因子的特征鉴定结果显示，其为一段退化转座子，命名为DgmarMITE。该转座子全长496 bp，AT碱基占比达57%，并携带24 bp的末端反向重复序列（terminal inverted repeats）。原位杂交结果表明，该因子仅存在于所分析的四个物种中的两个物种内。在不同种群的吉尔莱双齿蜣螂（D. (L.) gilletti）与瓜里本西斯双齿蜣螂（D. (L.) guaribensis）的染色体核型中，DgmarMITE的位点分布于异染色质区与常染色质区，且其在染色体上的位置与拷贝数量均存在种群间差异。本研究结果证实，DgmarMITE在上述物种的基因组中存在差异化累积现象，这一过程可能由异位重组（ectopic recombination）以及由近缘或无关转座因子的转座酶（transposase）介导的该因子跨转座活动所导致。