Disease relevance of Opn4

• Perinatally the melanopsin positive cells increase in number and migrate towards the ganglion cell layer [1].
• Melanopsin-expressing retinal ganglion cells are more injury-resistant in a chronic ocular hypertension model [2].

High impact information on Opn4

• Here we show that most retinal ganglion cells (RGCs) that project to the SCN express the photopigment melanopsin [3].
• A rare type of mammalian retinal ganglion cell (RGC) expresses the photopigment melanopsin and is a photoreceptor [4].
• Dopamine regulates melanopsin mRNA expression in intrinsically photosensitive retinal ganglion cells [5].
• Dopamine synthesis and release in the retina are regulated by the rod and the cone photoreceptors via retinal circuitry; our new data indicate that DA controls melanopsin expression, indicating that classical photoreceptors may modulate the transcription of this new photopigment [5].
• Melanopsin is exclusively expressed in PACAP-containing cells which in adults become the retinal ganglion cells constituting the retinohypothalamic tract [1].

Biological context of Opn4

• 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 [6].
• Even though solid evidence regarding the function of melanopsin exists, little is known about the regulation of melanopsin gene expression [7].

Anatomical context of Opn4

• The early expression of melanopsin argues for a photoreceptor role in the developing retinohypothalamic tract which is functional as early as the first day after birth [1].
• Furthermore, melanopsin-containing RGCs do not depend on inputs from rods and cones to transmit light signals to the SCN [8].
• Constant light decreased melanopsin immunostaining time dependently, beginning in the distal dendrites and progressing to the proximal dendrites and the soma [9].
• Melanopsin was expressed in the majority of RGCs that project to the SCN, vSPZ, and VLPO and in a subpopulation of RGCs that innervate the PTA and the IGL but not in RGCs projecting to the dorsal LGN or superior colliculus [10].
• The photopigment melanopsin has recently been identified in intrinsically photosensitive retinal ganglion cells (RGCs) that project to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and olivary pretectal nucleus, suggesting that melanopsin might influence a variety of irradiance-driven responses [10].

Other interactions of Opn4

• Photoreceptor degeneration did not affect the expression of pituitary adenylate cyclase-activating polypeptide mRNA (a marker for melanopsin-containing ganglion cells) [6].

Analytical, diagnostic and therapeutic context of Opn4

• Here we report using immunohistochemistry and in situ hybridisation that melanopsin during rat retinal development is expressed already at prenatal day 18 in cells of the inner neuroblast layer [1].

References