Classical photoreceptors regulate melanopsin mRNA levels in the rat retina - PubMed (original) (raw)

Classical photoreceptors regulate melanopsin mRNA levels in the rat retina

Katsuhiko Sakamoto et al. J Neurosci. 2004.

Abstract

Recent studies have demonstrated that melanopsin is a key photopigment in the mammalian circadian system. This novel opsin is exclusively expressed in retinal ganglion cells that are intrinsically sensitive to light, perhaps responding via a melanopsin-based signaling pathway. Previous investigations using transgenic mice have also demonstrated that ablation of the classical photoreceptors and of melanopsin prevents entrainment of several circadian rhythms, thus demonstrating that these photoreceptors are necessary and sufficient for circadian photoreception. In this study, we investigated the effect of photoreceptor degeneration on melanopsin mRNA regulation in RCS/N-rdy rats (Royal College of Surgeons rats with a defect in the retinal dystrophy gene). We used animals at postnatal day 21 (P21), P33, P45, and P60. At P60 degeneration of the retina in RCS/N-rdy has advanced to the point where the majority of the photoreceptors have degenerated. Our data indicate that melanopsin mRNA levels were rhythmic in light/dark cycle and in constant darkness in congenic controls (RCS/N-rdy+) and in RCS/N-rdy at P21 (i.e., before the degeneration of the photoreceptors). On the other hand, in RCS/N-rdy at P60, melanopsin mRNA levels were greatly reduced (<90%) and not rhythmic. Photoreceptor degeneration did not affect the expression of pituitary adenylate cyclase-activating polypeptide mRNA (a marker for melanopsin-containing ganglion cells). Our results suggest that classical photoreceptors (rods and cones) regulate the expression of melanopsin mRNA in the rat. Because RCS/N-rdy rats are a model for studies on retinitis pigmentosa in human, our data may provide an important insight on melanopsin function in patients affected by retinitis pigmentosa.

PubMed Disclaimer

Figures

Figure 1.

Figure 1.

A, Melanopsin mRNA levels in RCS/N-rdy and RCS/N-rdy+ retina at P60. Melanopsin mRNA levels were measured using real-time quantitative RT-PCR. mRNA levels were rhythmic in LD and DD (ANOVA; p < 0.001) in RCS/N-_rdy_+ animals but not in RCS/N-_rdy_ (ANOVA; _p_ > 0.1). Data are expressed as mean ± SEM (n ≥4 retinas). All values were normalized with respect to the values obtained in RCS/N-rdy+ animals at ZT14. The white bar at the top of the graph represents the period of light (ZT0-ZT12), and the black bar represents the period of darkness (ZT12-ZT24) when the rats were exposed to LD cycles. Photomicrographs showing the expression pattern of melanopsin-immunoreactive cells (arrow) in a 60-d-old RCS/N-rdy+ rat with a normal retina (B) and in a 60-d-old RCS/N-rdy (C). Scale bars, 20 μm. ONL, Outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer. In the dystrophic retina, the photoreceptor layer is absent. D, Western blot of protein extracts from pooled retinas probed with the melanopsin antibody. Immunoreactivity (as a 50 kDa band, arrow) was present in RCS/N-rdy+ at ZT14, and a weaker band was also present at ZT2. No immunoreactivity was detected in RCS/N-rdy rats.

Figure 2.

Figure 2.

Melanopsin mRNA levels in RCS/N-rdy at P21. All values were normalized with respect to the values obtained at ZT14 in RCS/N-rdy+. The white bar at the top of the graph represents the period of light (ZT0-ZT12), and the black bar represents the period of darkness (ZT12-ZT24) when the rats were exposed to LD cycles. Data are expressed as mean ± SEM (n ≥4 retinas).

Figure 3.

Figure 3.

PACAP mRNA levels in RCS/N-rdy+ (white bars) and RCS/N-rdy (black bars) retinas at P60 at ZT2 and ZT14. Data are expressed as mean ± SEM (n ≥4 retinas). PACAP mRNA levels did not differ between RCS/N-rdy+ and RCS/N-rdy at both time points (p > 0.05 in all cases).

Figure 4.

Figure 4.

Changes in photopigments mRNA in RCS/N-rdy rats at P21, P33, P45, and P60. A, Melanopsin; B, rhodopsin; C, green cone opsin; and D, blue cone opsin. mRNA levels were measured at ZT2 (white bars) and ZT14 (black bars). These time points correspond to the trough and the peak of the rhythm for melanopsin, rhodopsin, and green cone opsin transcripts, whereas blue cone opsin mRNA was found not rhythmic (K. Sakamoto and G. Tosini, unpublished observations). Data are expressed as mean ± SEM (n ≥3 retinas). *p < 0.05; ***p < 0.001. PN, Postnatal day.

Similar articles

Cited by

References

    1. Barnstable CJ, Drager UC (1984) Thy-1 antigen: a ganglion cell specific marker in rodent retina. Neuroscience 11: 847-855. - PubMed
    1. Belenky MA, Smeraski CA, Provencio I, Sollars PJ, Pickard GE (2003) Melanopsin retinal ganglion cells receive bipolar and amacrine cell synapses. J Comp Neurol 460: 380-393. - PubMed
    1. Berson DM, Dunn FA, Takao M (2002) Phototransduction by ganglion cells innervating the circadian pacemaker. Science 295: 1070-1073. - PubMed
    1. Czeisler CA, Shanahan TL, Klerman EB, Martens H, Brotman DJ, Emens JS, Klein T, Rizzo III JF (1995) Suppression of melatonin secretion in some blind patients by exposure to bright light. N Engl J Med 332: 6-11. - PubMed
    1. D'Cruz PM, Yasumura D, Weir J, Matthes MT, Adberrahim H, LaVail MM, Vollrath D (2000) Mutation of the receptor tyrosine kinase gene Mertk in the retinal dystrophic RCS rat. Hum Mol Genet 9: 645-651. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources