Department of Biological Sciences, University of Bergen, Bergen, Norway.
Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Oslo, Norway.
Sci Rep. 2018 Jul 10;8(1):10404. doi: 10.1038/s41598-018-28498-4.
Sensitivity to environmental stressors largely depend on the genetic complement of the organism. Recent sequencing and assembly of teleost fish genomes enable us to trace the evolution of defense genes in the largest and most diverse group of vertebrates. Through genomic searches and in-depth analysis of gene loci in 76 teleost genomes, we show here that the xenosensor pregnane X receptor (Pxr, Nr1i2) is absent in more than half of these species. Notably, out of the 27 genome assemblies that belong to the Gadiformes order, the pxr gene was only retained in the Merluccidae family (hakes) and Pelagic cod (Melanonus zugmayeri). As an important receptor for a wide range of drugs and environmental pollutants, vertebrate PXR regulate the transcription of a number of genes involved in the biotransformation of xenobiotics, including cytochrome P450 enzymes (CYP). In the absence of Pxr, we suggest that the aryl hydrocarbon receptor (Ahr) have evolved an extended regulatory role by governing the expression of certain Pxr target genes, such as cyp3a, in Atlantic cod (Gadus morhua). However, as several independent losses of pxr have occurred during teleost evolution, other lineages and species may have adapted alternative compensating mechanisms for controlling crucial cellular defense mechanisms.
对环境应激源的敏感性在很大程度上取决于生物体的基因组成。最近对硬骨鱼类基因组的测序和组装使我们能够追踪防御基因在最大和最多样化的脊椎动物群体中的进化。通过对 76 种硬骨鱼类基因组中的基因座进行基因组搜索和深入分析，我们在此表明，超过一半的这些物种缺乏外源性传感器孕烷 X 受体 (Pxr，Nr1i2)。值得注意的是，在属于 Gadiformes 目 27 个基因组组装中，pxr 基因仅在 Merluccidae 科（无须鳕）和 Pelagic cod（Melanonus zugmayeri）中保留。作为广泛的药物和环境污染物的重要受体，脊椎动物 PXR 调节涉及外源性物质生物转化的许多基因的转录，包括细胞色素 P450 酶 (CYP)。在没有 Pxr 的情况下，我们认为芳烃受体 (Ahr) 通过调节某些 Pxr 靶基因（如 cyp3a）的表达，在大西洋鳕鱼（Gadus morhua）中进化出了扩展的调节作用。然而，由于在硬骨鱼类进化过程中发生了几次 pxr 的独立缺失，其他谱系和物种可能已经适应了替代的补偿机制，以控制关键的细胞防御机制。
