School of Life Sciences, East China Normal University, Shanghai, China.
Curr Biol. 2010 Oct 26;20(20):1834-9. doi: 10.1016/j.cub.2010.09.008. Epub 2010 Oct 7.
The early radiation of cetaceans coincides with the origin of their defining ecological and sensory differences [1, 2]. Toothed whales (Odontoceti) evolved echolocation for hunting 36-34 million years ago, whereas baleen whales (Mysticeti) evolved filter feeding and do not echolocate [2]. Echolocation in toothed whales demands exceptional high-frequency hearing [3], and both echolocation and ultrasonic hearing have also evolved independently in bats [4, 5]. The motor protein Prestin that drives the electromotility of the outer hair cells (OHCs) is likely to be especially important in ultrasonic hearing, because it is the vibratory response of OHC to incoming sound waves that confers the enhanced sensitivity and selectivity of the mammalian auditory system [6, 7]. Prestin underwent adaptive change early in mammal evolution [8] and also shows sequence convergence between bats and dolphins [9, 10], as well as within bats [11]. Focusing on whales, we show for the first time that the extent of protein evolution in Prestin can be linked directly to the evolution of high-frequency hearing. Moreover, we find that independent cases of sequence convergence in mammals have involved numerous identical amino acid site replacements. Our findings shed new light on the importance of Prestin in the evolution of mammalian hearing.
鲸类的早期辐射与它们在生态和感官上的决定性差异的起源相一致 [1, 2]。齿鲸（齿鲸目）在 3600 万至 3400 万年前进化出回声定位来捕猎，而须鲸（须鲸目）则进化出滤食方式且不进行回声定位 [2]。齿鲸的回声定位需要异常高的高频听力 [3]，蝙蝠也独立进化出回声定位和超声听力 [4, 5]。驱动外毛细胞（OHC）电动力的运动蛋白 Prestin 可能在超声听力中尤为重要，因为正是 OHC 对传入声波的振动反应赋予了哺乳动物听觉系统增强的敏感性和选择性 [6, 7]。Prestin 在哺乳动物进化的早期就经历了适应性变化 [8]，并且在蝙蝠和海豚之间以及在蝙蝠内部也表现出序列趋同 [9, 10]。我们专注于鲸鱼，首次表明 Prestin 中蛋白质进化的程度可以直接与高频听力的进化联系起来。此外，我们发现哺乳动物中独立的序列趋同案例涉及到许多相同的氨基酸位点替换。我们的研究结果为 Prestin 在哺乳动物听觉进化中的重要性提供了新的认识。
