DataSheet_1_New Insights Into the Evolution of Corticotropin-Releasing Hormone Family With a Special Focus on Teleosts.pdf

Corticotropin-releasing hormone (CRH) was discovered for its role as a brain neurohormone controlling the corticotropic axis in vertebrates. An additional crh gene, crh2, paralog of crh (crh1), and likely resulting from the second round (2R) of vertebrate whole genome duplication (WGD), was identified in a holocephalan chondrichthyan, in basal mammals, various sauropsids and a non-teleost actinopterygian holostean. It was suggested that crh2 has been recurrently lost in some vertebrate groups including teleosts. We further investigated the fate of crh1 and crh2 in vertebrates with a special focus on teleosts. Phylogenetic and synteny analyses showed the presence of duplicated crh1 paralogs, crh1a and crh1b, in most teleosts, resulting from the teleost-specific WGD (3R). Crh1b is conserved in all teleosts studied, while crh1a has been lost independently in some species. Additional crh1 paralogs are present in carps and salmonids, resulting from specific WGD in these lineages. We identified crh2 gene in additional vertebrate groups such as chondrichthyan elasmobranchs, sarcopterygians including dipnoans and amphibians, and basal actinoperygians, Polypteridae and Chondrostei. We also revealed the presence of crh2 in teleosts, including elopomorphs, osteoglossomorphs, clupeiforms, and ostariophysians, while it would have been lost in Euteleostei along with some other groups. To get some insights on the functional evolution of the crh paralogs, we compared their primary and 3D structure, and by qPCR their tissue distribution, in two representative species, the European eel, which possesses three crh paralogs (crh1a, crh1b, crh2), and the Atlantic salmon, which possesses four crh paralogs of the crh1-type. All peptides conserved the structural characteristics of human CRH. Eel crh1b and both salmon crh1b genes were mainly expressed in the brain, supporting the major role of crh1b paralogs in controlling the corticotropic axis in teleosts. In contrast, crh1a paralogs were mainly expressed in peripheral tissues such as muscle and heart, in eel and salmon, reflecting a striking subfunctionalization between crh1a and b paralogs. Eel crh2 was weakly expressed in the brain and peripheral tissues. These results revisit the repertoire of crh in teleosts and highlight functional divergences that may have contributed to the differential conservation of various crh paralogs in teleosts.

促肾上腺皮质激素释放激素（Corticotropin-releasing hormone, CRH）因其作为调控脊椎动物促肾上腺皮质激素轴的脑神经激素的功能而被发现。另一类crh基因crh2是crh（即crh1）的旁系同源基因，推测由脊椎动物第二次全基因组复制（2R whole genome duplication, WGD）事件产生，该基因已在全头亚纲软骨鱼类、基底哺乳类、多种蜥形类以及非硬骨鱼的辐鳍鱼全骨类群中被鉴定到。已有研究提示，crh2在包括硬骨鱼类在内的部分脊椎动物类群中发生了多次独立丢失。本研究进一步探究了脊椎动物中crh1与crh2的演化命运，并重点聚焦于硬骨鱼类。系统发育与共线性分析显示，受硬骨鱼特异性全基因组复制（3R whole genome duplication, WGD）事件影响，大多数硬骨鱼中存在两份crh1旁系同源基因：crh1a与crh1b。crh1b在所有被研究的硬骨鱼中均得以保留，而crh1a则在部分物种中发生了独立丢失。鲤科与鲑科鱼类中存在额外的crh1旁系同源基因，这源于该类群特异性的全基因组复制事件。本研究还在更多脊椎动物类群中鉴定到crh2基因，包括软骨鱼纲板鳃类、肉鳍鱼亚纲（含肺鱼类与两栖类）以及基底辐鳍鱼类：多鳍鱼科与软骨硬鳞鱼次亚纲类群。本研究同时证实，crh2在部分硬骨鱼类类群中存在，包括海鲢总目、骨舌鱼总目、鲱形目与骨鳔总目，而在真骨下纲及其他部分类群中发生了丢失。为深入解析crh旁系同源基因的功能演化，本研究选取两类代表性物种开展分析：拥有3种crh旁系同源基因（crh1a、crh1b、crh2）的欧洲鳗鲡，以及拥有4种crh1型crh旁系同源基因的大西洋鲑。研究中比对了这些基因的一级结构与三维结构，并通过实时定量聚合酶链反应（quantitative polymerase chain reaction, qPCR）检测了它们的组织表达分布。所有肽段均保留了人类CRH的结构特征。鳗鲡的crh1b基因与大西洋鲑的两份crh1b基因均主要在脑组织中表达，这证实了crh1b旁系同源基因在硬骨鱼促肾上腺皮质激素轴调控中的核心功能。与之相反，鳗鲡与大西洋鲑中的crh1a旁系同源基因主要在外周组织（如肌肉与心脏）中表达，这反映出crh1a与crh1b旁系同源基因之间存在显著的亚功能化分化。鳗鲡的crh2基因在脑组织与外周组织中均呈低水平表达。本研究结果重新梳理了硬骨鱼中crh基因的家族组成，并揭示了可能导致硬骨鱼不同crh旁系同源基因差异化保留的功能分化现象。