Developmental expression pattern of phototransduction components in mammalian pineal implies a light-sensing function

Abstract

Whereas the pineal organs of lower vertebrates have been shown to be photosensitive, photic regulation of pineal function in adult mammals is thought be mediated entirely by retinal photoreceptors. Extraretinal regulation of pineal function has been reported in neonatal rodents, although both the site and molecular basis of extraretinal photoreception have remained obscure. In this study we examine the developmental expression pattern of all of the principal components of retinal phototransduction in rat pineal via cRNA in situ hybridization. All of the components needed to reconstitute a functional phototransduction pathway are expressed in the majority of neonatal pinealocytes, although the expression levels of many of these genes decline dramatically during development. These findings strongly support the theory that the neonatal rat pineal itself is photosensitive. In addition, we observe in neonatal pinealocytes the expression of both rod-specific and cone-specific phototransduction components, implying the existence of functionally different subtypes of pinealocytes that express varying combinations of phototransduction enzymes.

Fig. 1.

Expression of visual pigment mRNA in rodent pineal at different ages. A, Rhodopsin. Rat rhodopsin is used as a probe. All magnifications are at 100× except P2 rat pineal, adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×. Exposure times for adult rat and mouse retina are 30 min, whereas exposure times for pineals are 2 d. Exposure times for both sense controls are 2 d.B, Blue cone pigment. Mouse blue cone pigment is used as a probe. All magnifications are at 100× except P2 rat pineal, adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×. The dark band above the photoreceptor layer of the mouse retina in this and all subsequent figures is the retina pigmented epithelium, which is unpigmented in the albino rat retinas tested. The final panel, showing P200, is taken at 400× magnification. C, Red cone pigment. Mouse red/green cone pigment is used as a probe. All magnifications are at 100× except P2 rat pineal, adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×.

Fig. 2.

Transducin expression in rodent pineal at different ages. A, Rod transducin. Mouse rod transducin is used as a probe. All magnifications are at 100× except adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×. The final panel, showing P12 rat pineal, is taken at 400× magnification. Black arrows indicate selected rod transducin-expressing cells in the P12 pineal. B, Cone transducin. Mouse cone transducin is used as a probe. All magnifications are at 100× except adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×. The final panel, showing P200 rat pineal, is taken at 400× magnification. Note the nonexpressing meninginal tissue that surrounds the P2–P8 pineals.

Fig. 3.

Expression of phosphodiesterase in rodent pineal at different ages. A, Rod phosphodiesterase. Mouse rod phosphodiesterase is used as a probe. All magnifications are at 100× except adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×. The final panel, showing P12 rat pineal, is taken at 400× magnification. Black arrows indicate selected rod phosphodiesterase-expressing cells in the P12 pineal.B, Cone phosphodiesterase. Human cone phosphodiesterase is used as a probe. All magnifications are at 100× except adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×. Note the nonexpressing meninginal tissue that surrounds the P2–P12 pineals. The arrow points out selected, weakly hybridizing cone photoreceptor cells.

Fig. 4.

Phototransduction desensitization elements expressed in rodent pineal at different ages. A, Rhodopsin kinase. Rat rhodopsin kinase is used as a probe. All magnifications are at 100× except adult rat retina, which is at 200×. Note the nonexpressing meninginal tissue adjacent to the P12 pineal.B, Expression of recoverin. Mouse recoverin is used as a probe. All magnifications are at 100× except adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×.C, Rod arrestin. Rat rod arrestin is used as a probe. All magnifications are at 100× except adult rat retina, which is at 200×. Note the nonexpressing meninginal tissue adjacent to the P12 pineal. D, Cone arrestin. Rat cone arrestin is used as a probe. All magnifications are at 100× except adult rat retina, which is at 200×. Arrows indicate selected cone arrestin-expressing cells.

Fig. 5.

Expression of interphotoreceptor retinol-binding protein (IRBP) in rodent pineal at different ages. Mouse IRBP is used as a probe. All magnifications are at 100× except P2 rat pineal, adult mouse pineal, adult rat retina, and adult mouse retina, which are at 200×.

Fig. 6.

Potential mechanisms of phototransduction in neonatal rodent pineal. Shaded phototransduction components are expressed in the majority of neonatal rat pinealocytes and together can form a complete phototransduction cascade. Membrane-linked and soluble NO-activated guanylate cyclase, shown as potential sources of cGMP, have been shown to be expressed in rat pinealocytes by numerous studies (Spessert, 1993; Lin et al., 1994; Maronde, 1995; Yang et al., 1995).