Vittorazzi Stenio Eder, Lourenço Luciana Bolsoni, Recco-Pimentel Shirlei Maria
Departamento de Biologia Estrutural e Funcional, Instituto de Biologia, Universidade Estadual de Campinas, 13083-863 Campinas, São Paulo, Brazil.
BMC Genet. 2014 Oct 15;15:111. doi: 10.1186/s12863-014-0111-x.
Satellite DNA sequences are the most abundant components of heterochromatin and are repeated in tandem hundreds to thousands of times in the genome. However, the number of repeats of a specific satellite family can vary even between the genomes of related species or populations. The PcP190 satellite DNA family was identified in the genome of the leptodactylid frog Physalaemus cuvieri, which showed to be derived most likely from the 5S rDNA in an ancestral species. In this study, we investigate the presence of the PcP190 satellite DNA in several P. cuvieri populations and in four closely related species at the chromosomal and molecular level. Furthermore, we investigate the occurrence of this satellite DNA in the genomes of P. marmoratus as well as in representative species of the leptodactylid genus Leptodactylus (L. latrans) and the hylodid family (Crossodactylus gaudichaudii), all with the aim of investigating if the PcP190 satellite DNA presents or not a restricted distribution.
The PcP190 satellite DNA was detected in all the analyzed species. Some of them exhibited particular sequence differences, allowing the identification of species-specific groups of sequences, but in other species, the sequences were more conserved. However, in a general analysis, conserved and variable domains have been recognized within the PcP190 monomer. The chromosomal analysis performed on P. cuvieri populations and closely related species revealed high variability of the satellite DNA amount and its chromosomal location, which has always been coincident with regions of centromeric/pericentromeric heterochromatin.
The PcP190 satellite DNA was found in representatives of two families, Leptodactylidae and Hylodidae, indicating that these sequences are widely distributed and conserved in these frogs. There is a pattern of non-random variation within the repeating units, indicating interplay between stochastic events and selective pressure along the PcP190 sequences. Karyotypic differences involving the PcP190 satellite DNA prove to be highly dynamic on the chromosomes of the Physalaemus and its differential accumulation has contributed to the differentiation process of the Z and W sex chromosomes in P. ephippifer.
卫星DNA序列是异染色质中最丰富的成分，在基因组中以串联形式重复数百到数千次。然而，即使在相关物种或种群的基因组之间，特定卫星家族的重复次数也可能有所不同。PcP190卫星DNA家族是在细趾蟾科蛙类库维耶氏细趾蟾（Physalaemus cuvieri）的基因组中鉴定出来的，它很可能起源于一个祖先物种中的5S rDNA。在本研究中，我们在染色体和分子水平上研究了PcP190卫星DNA在几个库维耶氏细趾蟾种群以及四个近缘物种中的存在情况。此外，我们还研究了这种卫星DNA在大理石纹细趾蟾（P. marmoratus）以及细趾蟾属（Leptodactylus）的代表性物种（拉氏细趾蟾，L. latrans）和雨蛙科（Crossodactylus gaudichaudii）基因组中的出现情况，所有这些研究都是为了探究PcP190卫星DNA是否呈现出受限的分布。
在所有分析的物种中都检测到了PcP190卫星DNA。其中一些物种表现出特定的序列差异，从而能够鉴定出物种特异性的序列组，但在其他物种中，序列更为保守。然而，在总体分析中，已在PcP190单体中识别出保守和可变结构域。对库维耶氏细趾蟾种群和近缘物种进行的染色体分析显示，卫星DNA的数量及其染色体定位具有高度变异性，并且始终与着丝粒/近着丝粒异染色质区域一致。
在细趾蟾科和雨蛙科的代表物种中发现了PcP190卫星DNA，这表明这些序列在这些蛙类中广泛分布且保守。重复单元内存在非随机变异模式，表明随机事件与PcP190序列上的选择压力之间存在相互作用。涉及PcP190卫星DNA的核型差异在库维耶氏细趾蟾的染色体上被证明是高度动态的，其差异积累促成了斑背细趾蟾（P. ephippifer）Z和W性染色体的分化过程。
