Smith Matthew A, Waugh David A, McBurney Denise L, George John C, Suydam Robert S, Thewissen Johannes G M, Crish Samuel D
Department of Pharmaceutical Sciences, Northeast Ohio Medical University, Rootstown, Ohio, USA.
Rebecca D. Considine Research Institute, Akron Children's Hospital, Akron, Ohio, USA.
J Comp Neurol. 2021 Jun;529(9):2376-2390. doi: 10.1002/cne.25101. Epub 2021 Jan 12.
The cetacean visual system is a product of selection pressures favoring underwater vision, yet relatively little is known about it across taxa. Previous studies report several mutations in the opsin genetic sequence in cetaceans, suggesting the evolutionary complete or partial loss of retinal cone photoreceptor function in mysticete and odontocete lineages, respectively. Despite this, limited anatomical evidence suggests cone structures are partially maintained but with absent outer and inner segments in the bowhead retina. The functional consequence and anatomical distributions associated with these unique cone morphologies remain unclear. The current study further investigates the morphology and distribution of cone photoreceptors in the bowhead whale and beluga retina and evaluates the potential functional capacity of these cells' alternative to photoreception. Refined histological and advanced microscopic techniques revealed two additional cone morphologies in the bowhead and beluga retina that have not been previously described. Two proteins involved in magnetosensation were present in these cone structures suggesting the possibility for an alternative functional role in responding to changes in geomagnetic fields. These findings highlight a revised understanding of the unique evolution of cone and gross retinal anatomy in cetaceans, and provide prefatory evidence of potential functional reassignment of these cells.
鲸类视觉系统是选择压力有利于水下视觉的产物，但跨分类群对其了解相对较少。先前的研究报告了鲸类视蛋白基因序列中的几种突变，分别表明在须鲸和齿鲸谱系中视网膜锥状光感受器功能在进化上完全或部分丧失。尽管如此，有限的解剖学证据表明，在北极露脊鲸的视网膜中，锥状结构部分保留，但外段和内段缺失。与这些独特的锥状形态相关的功能后果和解剖分布仍不清楚。当前的研究进一步调查了北极露脊鲸和白鲸视网膜中锥状光感受器的形态和分布，并评估了这些细胞替代光感受的潜在功能能力。精细的组织学和先进的显微镜技术揭示了北极露脊鲸和白鲸视网膜中另外两种先前未描述过的锥状形态。参与磁感受的两种蛋白质存在于这些锥状结构中，这表明它们可能在响应地磁场变化方面具有替代功能作用。这些发现凸显了对鲸类中锥状细胞和视网膜大体解剖独特进化的重新认识，并为这些细胞潜在的功能重新分配提供了初步证据。
