Department of Anatomy and Neuroscience, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
Division of Ecological Genetics, National Institute of Genetics, Shizuoka, Japan.
Comp Biochem Physiol Part D Genomics Proteomics. 2018 Dec;28:99-106. doi: 10.1016/j.cbd.2018.07.002. Epub 2018 Jul 7.
Variation in the laterality often exists within species and can be maintained by frequency-dependent selection. Although the molecular developmental mechanisms underlying the left-right axis formation have been investigated, the genomic mechanisms underlying variation in laterality remain largely unknown. The scale-eating cichlid Perissodus microlepis in Lake Tanganyika exhibit lateralized predation; lefty individuals with the mouth opening toward the right preferentially attack on the prey's left trunk, while righty individuals with the opposite opening attacks on the right trunk. Here, we performed RNA-sequencing and subsequent confirmation with quantitative-PCR in the telencephalon, optic tectum, and hindbrain of the cichlid and identified five genes (pkd1b, ntn1b, ansn, pde6g, and rbp4l1) that were differentially expressed between the hemispheres regardless of the laterality. Surprisingly, pkd1b and ntn1b are involved in nodal and netrin signalling, respectively, which are important for left-right asymmetry formation during early embryogenesis. This result indicates that nodal- and netrin-related signals may also play important roles in the maintenance of asymmetry in adult brain. By contrast, no genes showed reversal of lateral differences between lefty and righty individuals in any brain regions examined, suggesting that laterality in the scale-eating cichlid does not simply result from inversion of the left-right asymmetry of gene expression.
种内通常存在偏侧性变异，并可通过频率依赖选择得以维持。虽然已研究了导致左右轴形成的分子发育机制，但偏侧性变异的基因组机制在很大程度上仍然未知。坦噶尼喀湖中的食藻鲷鱼 Perissodus microlepis 表现出偏侧性捕食行为；口向右开口的左利个体更倾向于攻击猎物的左侧躯干，而口向左开口的右利个体则攻击右侧躯干。在这里，我们对食藻鲷的大脑皮层、视顶盖和后脑进行了 RNA 测序，并通过定量 PCR 进行了后续验证，鉴定出了五个无论偏侧性如何在半球间均有差异表达的基因（pkd1b、ntn1b、ansn、pde6g 和 rbp4l1）。令人惊讶的是，pkd1b 和 ntn1b 分别参与了 nodal 和 netrin 信号通路，这对早期胚胎发育过程中的左右不对称形成很重要。这一结果表明，nodal 和 netrin 相关信号也可能在成年大脑的不对称性维持中发挥重要作用。相比之下，在任何检查的脑区中，没有基因显示左利和右利个体之间的偏侧性差异出现反转，这表明食藻鲷的偏侧性并不简单地源于基因表达左右不对称的反转。
