Milani Diogo, Ramos Érica, Loreto Vilma, Martí Dardo Andrea, Cardoso Adauto Lima, de Moraes Karen Cristiane Martinez, Martins Cesar, Cabral-de-Mello Diogo Cavalcanti
Departamento de Biologia, UNESP - Univ Estadual Paulista, Instituto de Biociências/IB, Rio Claro, São Paulo, CEP 13506-900, Brazil.
Departamento de Morfologia, UNESP - Univ Estadual Paulista, Instituto de Biociências/IB, Botucatu, São Paulo, Brazil.
BMC Genet. 2017 Aug 29;18(1):81. doi: 10.1186/s12863-017-0548-9.
Satellite DNAs (satDNAs) are organized in repetitions directly contiguous to one another, forming long arrays and composing a large portion of eukaryote genomes. These sequences evolve according to the concerted evolution model, and homogenization of repeats is observed at the intragenomic level. Satellite DNAs are the primary component of heterochromatin, located primarily in centromeres and telomeres. Moreover, satDNA enrichment in specific chromosomes has been observed, such as in B chromosomes, that can provide clues about composition, origin and evolution of this chromosome. In this study, we isolated and characterized a satDNA in A and B chromosomes of Abracris flavolineata by integrating cytogenetic, molecular and genomics approaches at intra- and inter-population levels, with the aim to understand the evolution of satDNA and composition of B chromosomes.
AflaSAT-1 satDNA was shared with other species and in A. flavolineata, was associated with another satDNA, AflaSAT-2. Chromosomal mapping revealed centromeric blocks variable in size in almost all chromosomes (except pair 11) of A complement for both satDNAs, whereas for B chromosome, only a small centromeric signal occurred. In distinct populations, variable number of AflaSAT-1 chromosomal sites correlated with variability in copy number. Instead of such variability, low sequence diversity was observed in A complement, but monomers from B chromosome were more variable, presenting also exclusive mutations. AflaSAT-1 was transcribed in five tissues of adults in distinct life cycle phases.
The sharing of AflaSAT-1 with other species is consistent with the library hypothesis and indicates common origin in a common ancestor; however, AflaSAT-1 was highly amplified in the genome of A. flavolineata. At the population level, homogenization of repeats in distinct populations was documented, but dynamic expansion or elimination of repeats was also observed. Concerning the B chromosome, our data provided new information on the composition in A. flavolineata. Together with previous results, the sequences of heterochromatic nature were not likely highly amplified in the entire B chromosome. Finally, the constitutive transcriptional activity suggests a possible unknown functional role, which should be further investigated.
卫星DNA（satDNA）以彼此直接相邻的重复序列形式组织，形成长阵列并构成真核生物基因组的很大一部分。这些序列根据协同进化模型进化，并且在基因组水平上观察到重复序列的同质化。卫星DNA是异染色质的主要成分，主要位于着丝粒和端粒中。此外，已观察到特定染色体中存在satDNA富集现象，例如在B染色体中，这可以为该染色体的组成、起源和进化提供线索。在本研究中，我们通过在种群内和种群间水平整合细胞遗传学、分子和基因组学方法，分离并鉴定了黄褐阿布拉蟋A和B染色体中的一种satDNA，旨在了解satDNA的进化和B染色体的组成。
AflaSAT - 1 satDNA与其他物种共有，并且在黄褐阿布拉蟋中，它与另一种satDNA，即AflaSAT - 2相关联。染色体定位显示，对于这两种satDNA，A染色体组几乎所有染色体（除第11对染色体外）中着丝粒区域大小可变，而对于B染色体，仅出现一个小的着丝粒信号。在不同种群中，AflaSAT - 1染色体位点数量可变，与拷贝数的变异性相关。与这种变异性不同的是，在A染色体组中观察到低序列多样性，但B染色体的单体更具变异性，也存在独特的突变。AflaSAT - 1在成虫不同生命周期阶段的五种组织中都有转录。
AflaSAT - 1与其他物种共有，这与文库假说一致，并表明在共同祖先中具有共同起源；然而，AflaSAT - 1在黄褐阿布拉蟋基因组中高度扩增。在种群水平上，记录了不同种群中重复序列的同质化，但也观察到重复序列的动态扩增或消除。关于B染色体，我们的数据提供了有关黄褐阿布拉蟋组成的新信息。与先前的结果一起，异染色质性质的序列在整个B染色体中不太可能高度扩增。最后，其组成型转录活性表明可能存在未知的功能作用，应进一步研究。
