Comparison of neuroglobin distribution and expression in the retina of adult yak and cattle

Abstract

The yak belongs to the genus Bos and is therefore related to cattle (Bos primigenius species). The yak may have diverged from cattle at any point between one and five million years ago, and the yak is supposed to be more closely related to cattle than to other members of its designated genus. Here, we evaluated the distribution of neuroglobin (NGB) expression in the retina of adult yak and cattle. Five healthy yaks and five cattle were used in the study. Immunohistochemical stainings were performed to assess the distribution of NGB in the retina of adult yak and cattle. The results demonstrated that NGB was expressed at high levels in the retina of adult yak and cattle in the ganglion cell layer, outer plexiform layer, photoreceptor inner segments, and pigment epithelial layer (+++). Medium NGB expression was found in the nerve fiber layer, ganglion cell layer, inner plexiform layer, and photoreceptor outer segments (++). In contrast, NGB was only weakly expressed in the inner nuclear layer (+), while no expression was found in the outer nuclear layer (–). Expression in the inner limiting membrane, outer limiting membrane, and optic nerves of the cattle was weak (+) and comparable to expression in the adult yak. No NGB expression was found in the outer nuclear layer of both yak and cattle. The level of NGB expression in the retinal ganglion cell layer, kernel layer, optic nerve, and photoreceptor inner segments was significantly higher in yak than in cattle (P < 0.05). These results suggest that NGB might play an important role in oxygen homeostasis of the retina and normal function of the optic nerve of yak and cattle under high-altitude hypoxic conditions. Nevertheless, its specific functional mechanism needs further investigation.