The evolutionary dynamics of ribosomal genes, histone H3, and transposable Rex elements in the genome of Atlantic snappers

Lutjanidae is a family of primarily marine and carnivorous fishes distributed in the Atlantic, Indian, and Pacific oceans, with enormous economic and ecological importance. In order to better clarify the conservative chromosomal evolution of Lutjanidae, we analyzed the evolutionary dynamics of 5 repetitive DNA classes in 5 Lutjanus and in 1 Ocyurus species from the Western Atlantic. The ribosomal 18S sites were generally located in a single chromosome pair, except for L. jocu and L. alexandrei where they are found in 2 pairs. In turn, the 5S rDNA sites are unique, terminal and nonsyntenic with the 18S rDNA sites. In 3 species analyzed, H3 hisDNA genes were found in 1 chromosomal pair. However, while L. jocu presented 2 H3 sites, O. chrysurus showed a noteworthy dispersion of this gene in almost all chromosomes of the karyotype. Retrotransposons Rex1 and Rex3 do not exhibit any association with the explosive distribution of H3 sequences in O. chrysurus. The low compartmentalization of Rex elements, in addition to the general nondynamic distribution of ribosomal and H3 genes, corroborate the karyotype conservatism in Lutjanidae species, also at the microstructural level. However, some “disturbing evolutionary waves” can break down this conservative scenario, as evidenced by the massive random dispersion of H3 hisDNA in the genome of O. chrysurus. The implication of the genomic expansion of H3 histone genes and their functionality remain unknown, although suggesting that they have higher evolutionary dynamics than previously thought.

笛鲷科（Lutjanidae）是一类主要分布于大西洋、印度洋及太平洋海域的海洋肉食性鱼类，具备极高的经济与生态价值。为更清晰阐明笛鲷科的保守染色体演化历程，本研究对西大西洋海域的5种笛鲷属（Lutjanus）鱼类及1种锥齿鲷属（Ocyurus）鱼类的5类重复DNA序列的演化动态展开分析。18S核糖体RNA基因（18S rDNA）位点通常仅定位于1对染色体，唯有约库笛鲷（Lutjanus jocu，即原文L. jocu）与亚历山大笛鲷（Lutjanus alexandrei，即原文L. alexandrei）的该类位点分布于2对染色体上。与之相对，5S核糖体RNA基因（5S rDNA）位点为单一位点、端粒定位且与18S rDNA位点不存在同线性关联。在所分析的3个物种中，H3组蛋白基因（H3 hisDNA）均定位于1对染色体上。然而，约库笛鲷仅存在2个H3基因位点，而黄尾锥齿鲷（Ocyurus chrysurus，即原文O. chrysurus）的该基因则呈现出显著的分散式分布，几乎覆盖核型的全部染色体。反转录转座子（Retrotransposons）Rex1与Rex3与黄尾锥齿鲷的H3序列爆发式分布不存在任何关联。Rex元件的低区室化特征，加之核糖体基因与H3基因整体上的非动态分布模式，进一步证实了笛鲷科物种在微观结构层面同样存在核型保守性。但部分"扰动性演化浪潮"可打破这一保守格局，黄尾锥齿鲷的H3组蛋白基因在其基因组中的大规模随机分散分布即为典型例证。尽管H3组蛋白基因的基因组扩张现象暗示其演化动态性远超此前学界的认知，但其基因组扩张的生物学意义与具体功能仍未明晰。