Comparison of neuroglobin expression in the retina of Tibetan sheep (Ovis ammon or argali) and domestic sheep (Ovis aries)

Neuroglobin (Ngb) is a member of the globin member that is mainly expressed in the brain and retina. The expression in the retina is greater than it is in the brain because of the high demand for oxygen by the retina. This protein reversibly binds oxygen and is involved in oxygen transport or protection against oxidative stress. The study aims to explore the pattern of Ngb expression in Tibetan sheep (Ovis ammon or argali) living in a plateau region and domestic sheep (Ovis aries) dwelling on low land. The study also provides detailed insight into the morphological characteristics of Ngb distribution closely related to oxygen metabolism in the retina of Tibetan and domestic sheep. Immunohistochemical staining procedures were performed to detect the Ngb protein expression in the retinae of both sheep, while the Inter's integrated performance primitives (IPP) semi-quantitative analysis was employed to compare the quantities of Ngb expressed in the retinae of the two types of sheep. The outer nuclear layer and the outer segment of the photoreceptor showed a negative Ngb expression, while a weak positive expression was observed in the inner core layer and ganglion cell layer, while a strong positive expression was found in the other layers. The independent T-test revealed that the expression intensity in the nerve fiber layer, inner and outer plexus layers, inner segment of the photoreceptor, and superior pigment cortex were significantly higher in the Tibetan sheep as compared to the domestic sheep. The overall Ngb expression in the Tibetan sheep was higher than the domestic sheep. The study emphasized that the different Ngb expression in the Tibetan and domestic sheep may influence their adaptation to the respective environments. The stronger Ngb expression in the retina of Tibetan sheep may indicate that Ngb is closely related to the oxygen metabolism of these animals and has a function during oxygen transport.