Lack of melanopsin in ganglion cells and its impact on retinal clock
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1
Faculty of Sciences Semlalia, Department of Biology, Pharmacology, Neurobiology and Behaviour laboratory, Morocco
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2
INSERM U846, Department of Chronobiology, France
The primary circadian pacemaker, in the suprachiasmatic nucleus of the mammalian brain, is photoentrained by light signals from the eyes through the retinohypothalamic tract. Evidence suggests that the entraining photoreceptors are retinal ganglion cells that project to the suprachiasmatic nucleus. The visual pigment for this photoreceptor may be melanopsin, an opsin-like protein whose coding messenger RNA is found in a subset of mammalian retinal ganglion cells.
Circadian clocks generate endogenous circadian rhythms throughout autoregulatory transcriptional-translational feedback loops comprised of a well defined set of clock genes.
The PER2 gene is a member of the Period family of genes and is expressed in a circadian pattern in the suprachiasmatic nucleus, the primary circadian pacemaker in the mammalian brain. The specific function of this gene is yet, unknown.
Our aim, in this study, was to investigate the localization and circadian rhythmic pattern of the protein expression of the PER2 clock gene in the retina of wild type (C57BL6) and transgenic melanopsin knockout mice.
Animals were housed at a constant temperature of 21°C under 12h light/12h dark condition (LD 12:12) at least two week before experiments. Just before enucleation, mice were housed under constant darkness (DD) for 2 days. Eyes were then enucleated at 0, 6 and 12 hours of subjective day and 2 hours of subjective night. Tissues were fixed in 4% paraformaldehyde, sucrose infiltrated and cryopreserved. Cryosections were examined by immunohistochemical procedure for PER2 protein.
In wild type mice, immunostraining of the ganglion cell layer and inner nuclear layers showed strong expression of PER2 protein. Levels of expression varied in line with circadian rhythm, with high levels at 0, 6 and 12 hours of subjective day and lower levels at 2 hours of subjective night under DD. The maximum level of expression appeared at 12 hours of subjective day under DD. In knockout mice, by contrast, PER2 was expressed only at 0 hour of subjective day and only in ganglion cells. Levels of expression were lower than in wild type mice.
In conclusion: mouse retina contains PER2, a representative clock gene. The time dynamic of PER2 expression reflects a circadian rhythm. This expression appeared however linked to the presence of melanopsin photopigment, since the deletion of this later abolishes the expression of PER2 in all retinal layers.
Conference:
2nd NEUROMED Workshop, Fez, Morocco, 10 Jun - 12 Jun, 2010.
Presentation Type:
Poster Presentation
Topic:
Poster Session 2: Neuroplasticity
Citation:
Lahouaoui
H,
Dkhissi-Benyahya
O and
Bennis
M
(2010). Lack of melanopsin in ganglion cells and its impact on retinal clock.
Front. Neurosci.
Conference Abstract:
2nd NEUROMED Workshop.
doi: 10.3389/conf.fnins.2010.12.00015
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Received:
03 Jun 2010;
Published Online:
03 Jun 2010.
*
Correspondence:
H. Lahouaoui, Faculty of Sciences Semlalia, Department of Biology, Pharmacology, Neurobiology and Behaviour laboratory, Marrakech, Morocco, mbennis@ucam.ac.ma