小蝙蝠和某些鲸（包含海豚）各自独立进化出回声定位能力，关于它们回声定位分子机制的研究一直是热点，之前主要集中在耳蜗对高频声音的感知。沈永义副研究员和博士生梁璐在张亚平院士的指导下，注意到回声定位能力的形成，不单单依赖耳蜗对超声的感知，还依赖大脑对声音信号的处理，这才是比较完整的回声定位通路。
他们对耳蜗的Cadherin 23 (Cdh23) 基因和它的配体Protocadherin 15 (Pcdh15)基因，以及神经信号传导的Otoferlin (Otof)基因进行分析，发现这三个基因在有回声定位的物种里面都发生了显著的趋同进化，而且Cdh23和Pcdh15基因在有回声定位的物种里发生了正选择。进一步对不同大脑皮层的Otof基因表达丰度分析表明，该基因的表达丰度在有回声定位的蝙蝠的听皮层里面最高，远远高于其他皮层，以及高于该种蝙蝠胚胎期的听皮层和其他没回声定位蝙蝠的各种皮层。
因此，该研究从声音感知到神经信号传导，以及分子序列进化到基因表达丰度变化，受体和配体相互作用等方面比较系统地研究回声定位的进化，并第一次从分子水平揭示了大脑以及基因表达丰度的改变在回声定位起源上的重要作用。
该研究发表于国际知名学术期刊PLoS Genetics，并受到审稿人的好评。（生物谷Bioon.com）
doi:10.1371/journal.pgen.1002788
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Parallel Evolution of Auditory Genes for Echolocation in Bats and Toothed Whales
Yong-Yi Shen1#, Lu Liang1,2#, Gui-Sheng Li1, Robert W. Murphy1,3, Ya-Ping Zhang1,4*
The ability of bats and toothed whales to echolocate is a remarkable case of convergent evolution. Previous genetic studies have documented parallel evolution of nucleotide sequences in Prestin and KCNQ4, both of which are associated with voltage motility during the cochlear amplification of signals. Echolocation involves complex mechanisms. The most important factors include cochlear amplification, nerve transmission, and signal re-coding. Herein, we screen three genes that play different roles in this auditory system. Cadherin 23 (Cdh23) and its ligand, protocadherin 15 (Pcdh15), are essential for bundling motility in the sensory hair. Otoferlin (Otof) responds to nerve signal transmission in the auditory inner hair cell. Signals of parallel evolution occur in all three genes in the three groups of echolocators—two groups of bats (Yangochiroptera and Rhinolophoidea) plus the dolphin. Significant signals of positive selection also occur in Cdh23 in the Rhinolophoidea and dolphin, and Pcdh15 in Yangochiroptera. In addition, adult echolocating bats have higher levels of Otof expression in the auditory cortex than do their embryos and non-echolocation bats. Cdh23 and Pcdh15 encode the upper and lower parts of tip-links, and both genes show signals of convergent evolution and positive selection in echolocators, implying that they may co-evolve to optimize cochlear amplification. Convergent evolution and expression patterns of Otof suggest the potential role of nerve and brain in echolocation. Our synthesis of gene sequence and gene expression analyses reveals that positive selection, parallel evolution, and perhaps co-evolution and gene expression affect multiple hearing genes that play different roles in audition, including voltage and bundle motility in cochlear amplification, nerve transmission, and brain function.
