Lagman David, Franzén Ilkin E, Eggert Joel, Larhammar Dan, Abalo Xesús M
Department of Neuroscience, Science for Life Laboratory, Uppsala University, Box 593, SE-75124, Uppsala, Sweden.
BMC Evol Biol. 2016 Jun 13;16(1):124. doi: 10.1186/s12862-016-0695-z.
Phosphodiesterase 6 (PDE6) is a protein complex that hydrolyses cGMP and acts as the effector of the vertebrate phototransduction cascade. The PDE6 holoenzyme consists of catalytic and inhibitory subunits belonging to two unrelated gene families. Rods and cones express distinct genes from both families: PDE6A and PDE6B code for the catalytic and PDE6G the inhibitory subunits in rods while PDE6C codes for the catalytic and PDE6H the inhibitory subunits in cones. We performed phylogenetic and comparative synteny analyses for both gene families in genomes from a broad range of animals. Furthermore, gene expression was investigated in zebrafish.
We found that both gene families expanded from one to three members in the two rounds of genome doubling (2R) that occurred at the base of vertebrate evolution. The PDE6 inhibitory subunit gene family appears to be unique to vertebrates and expanded further after the teleost-specific genome doubling (3R). We also describe a new family member that originated in 2R and has been lost in amniotes, which we have named pde6i. Zebrafish has retained two additional copies of the PDE6 inhibitory subunit genes after 3R that are highly conserved, have high amino acid sequence identity, are coexpressed in the same photoreceptor type as their amniote orthologs and, interestingly, show strikingly different daily oscillation in gene expression levels.
Together, these data suggest specialisation related to the adaptation to different light intensities during the day-night cycle, most likely maintaining the regulatory function of the PDE inhibitory subunits in the phototransduction cascade.
磷酸二酯酶6（PDE6）是一种蛋白质复合物，可水解环磷酸鸟苷（cGMP），并作为脊椎动物光转导级联反应的效应器。PDE6全酶由属于两个不相关基因家族的催化亚基和抑制亚基组成。视杆细胞和视锥细胞表达这两个家族的不同基因：PDE6A和PDE6B编码视杆细胞中的催化亚基，PDE6G编码视杆细胞中的抑制亚基，而PDE6C编码视锥细胞中的催化亚基，PDE6H编码视锥细胞中的抑制亚基。我们对广泛动物基因组中的这两个基因家族进行了系统发育和比较同线性分析。此外，还研究了斑马鱼中的基因表达。
我们发现，在脊椎动物进化基础上发生的两轮基因组加倍（2R）过程中，这两个基因家族都从一个成员扩展到了三个成员。PDE6抑制亚基基因家族似乎是脊椎动物特有的，并且在硬骨鱼特异性基因组加倍（3R）后进一步扩展。我们还描述了一个起源于2R且在羊膜动物中已丢失的新家族成员，我们将其命名为pde6i。斑马鱼在3R后保留了PDE6抑制亚基基因的另外两个拷贝，它们高度保守，具有高氨基酸序列同一性，与其羊膜动物直系同源基因在同一光感受器类型中共表达，有趣的是，它们在基因表达水平上表现出明显不同的每日振荡。
总之，这些数据表明与昼夜循环中适应不同光照强度相关的特化，很可能维持了PDE抑制亚基在光转导级联反应中的调节功能。
