Lagman David, Callado-Pérez Amalia, Franzén Ilkin E, Larhammar Dan, Abalo Xesús M
Department of Neuroscience, Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
PLoS One. 2015 Mar 25;10(3):e0121330. doi: 10.1371/journal.pone.0121330. eCollection 2015.
Gene duplications provide raw materials that can be selected for functional adaptations by evolutionary mechanisms. We describe here the results of 350 million years of evolution of three functionally related gene families: the alpha, beta and gamma subunits of transducins, the G protein involved in vision. Early vertebrate tetraploidisations resulted in separate transducin heterotrimers: gnat1/gnb1/gngt1 for rods, and gnat2/gnb3/gngt2 for cones. The teleost-specific tetraploidisation generated additional duplicates for gnb1, gnb3 and gngt2. We report here that the duplicates have undergone several types of subfunctionalisation or neofunctionalisation in the zebrafish. We have found that gnb1a and gnb1b are co-expressed at different levels in rods; gnb3a and gnb3b have undergone compartmentalisation restricting gnb3b to the dorsal and medial retina, however, gnb3a expression was detected only at very low levels in both larvae and adult retina; gngt2b expression is restricted to the dorsal and medial retina, whereas gngt2a is expressed ventrally. This dorsoventral distinction could be an adaptation to protect the lower part of the retina from intense light damage. The ontogenetic analysis shows earlier onset of expression in the pineal complex than in the retina, in accordance with its earlier maturation. Additionally, gnb1a but not gnb1b is expressed in the pineal complex, and gnb3b and gngt2b are transiently expressed in the pineal during ontogeny, thus showing partial temporal subfunctionalisation. These retina-pineal distinctions presumably reflect their distinct functional roles in vision and circadian rhythmicity. In summary, this study describes several functional differences between transducin gene duplicates resulting from the teleost-specific tetraploidisation.
基因复制提供了可通过进化机制进行功能适应性选择的原材料。我们在此描述了三个功能相关基因家族三亿五千万年的进化结果：转导素的α、β和γ亚基，转导素是参与视觉的G蛋白。早期脊椎动物的四倍体化产生了单独的转导素异源三聚体：用于视杆细胞的gnat1/gnb1/gngt1，以及用于视锥细胞的gnat2/gnb3/gngt2。硬骨鱼特有的四倍体化产生了gnb1、gnb3和gngt2的额外复制基因。我们在此报告，这些复制基因在斑马鱼中经历了几种类型的亚功能化或新功能化。我们发现，gnb1a和gnb1b在视杆细胞中以不同水平共表达；gnb3a和gnb3b发生了区域化，将gnb3b限制在视网膜的背侧和内侧，然而，在幼虫和成年视网膜中仅检测到极低水平的gnb3a表达；gngt2b的表达仅限于视网膜的背侧和内侧，而gngt2a则在腹侧表达。这种背腹差异可能是一种适应性变化，以保护视网膜下部免受强光损伤。个体发育分析表明，松果体复合体中的表达比视网膜中更早开始，这与其更早成熟相一致。此外，gnb1a而非gnb1b在松果体复合体中表达，gnb3b和gngt2b在个体发育过程中在松果体中短暂表达，因此显示出部分时间上的亚功能化。这些视网膜 - 松果体差异大概反映了它们在视觉和昼夜节律中的不同功能作用。总之，本研究描述了硬骨鱼特有的四倍体化导致的转导素基因复制之间的几种功能差异。
