Grone Brian P, Maruska Karen P
Department of Neurological Surgery, University of California, San Francisco San Francisco, CA, USA.
Department of Biological Sciences, Louisiana State University Baton Rouge, LA, USA.
Front Neurosci. 2015 Oct 13;9:365. doi: 10.3389/fnins.2015.00365. eCollection 2015.
Genome duplication, thought to have happened twice early in vertebrate evolution and a third time in teleost fishes, gives rise to gene paralogs that can evolve subfunctions or neofunctions via sequence and regulatory changes. To explore the evolution and functions of corticotropin-releasing hormone (CRH), we searched sequenced teleost genomes for CRH paralogs. Our phylogenetic and synteny analyses indicate that two CRH genes, crha and crhb, evolved via duplication of crh1 early in the teleost lineage. We examined the expression of crha and crhb in two teleost species from different orders: an African cichlid, Burton's mouthbrooder, (Astatotilapia burtoni; Order Perciformes) and zebrafish (Danio rerio; Order Cypriniformes). Furthermore, we compared expression of the teleost crha and crhb genes with the crh1 gene of an outgroup to the teleost clade: the spotted gar (Lepisosteus oculatus). In situ hybridization for crha and crhb mRNA in brains and eyes revealed distinct expression patterns for crha in different teleost species. In the cichlid, crha mRNA was found in the retina but not in the brain. In zebrafish, however, crha mRNA was not found in the retina, but was detected in the brain, restricted to the ventral hypothalamus. Spotted gar crh1 was found in the retina as well as the brain, suggesting that the ancestor of teleost fishes likely had a crh1 gene expressed in both retina and brain. Thus, genome duplication may have freed crha from constraints, allowing it to evolve distinct sequences, expression patterns, and likely unique functions in different lineages.
基因组复制被认为在脊椎动物进化早期发生过两次，在硬骨鱼中又发生了第三次，这产生了基因旁系同源物，它们可以通过序列和调控变化进化出亚功能或新功能。为了探究促肾上腺皮质激素释放激素（CRH）的进化和功能，我们在已测序的硬骨鱼基因组中搜索CRH旁系同源物。我们的系统发育和共线性分析表明，两个CRH基因，crha和crhb，是在硬骨鱼谱系早期通过crh1的复制进化而来的。我们检测了来自不同目（非洲慈鲷伯顿氏口孵非鲫（Astatotilapia burtoni；鲈形目）和斑马鱼（Danio rerio；鲤形目））的两种硬骨鱼中crha和crhb的表达。此外，我们将硬骨鱼crha和crhb基因的表达与硬骨鱼分支外类群的crh1基因（雀鳝（Lepisosteus oculatus））进行了比较。对大脑和眼睛中crha和crhb mRNA进行原位杂交，揭示了不同硬骨鱼物种中crha的独特表达模式。在慈鲷中，在视网膜中发现了crha mRNA，但在大脑中未发现。然而，在斑马鱼中，视网膜中未发现crha mRNA，但在大脑中检测到了，且仅限于腹侧下丘脑。在雀鳝的视网膜和大脑中都发现了crh1，这表明硬骨鱼的祖先可能有一个在视网膜和大脑中都表达的crh1基因。因此，基因组复制可能使crha摆脱了限制，使其能够在不同谱系中进化出不同的序列、表达模式以及可能独特的功能。
