Circadian Expression of Bmal1 and Serotonin-N-Acetyltransferase mRNAs in Chicken Retina Cells and Pinealocytes In Vivo and In Vitro

May 9, 2006Journal of molecular neuroscience : MN

Daily rhythms of key clock and serotonin-related genes in chicken eye and pineal gland cells, studied inside the body and in the lab

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Abstract

cBmal1 mRNA peaks during the light phase between Zeitgeber time (ZT) 8 and 10.

In chicken retinal cells, cBmal1 and cAANAT mRNA levels were analyzed under a 14/10-h light/dark cycle and in vitro over 4 light/dark cycles.
cBmal1 mRNA shows a peak before the nocturnal increase of cAANAT expression at ZT 16-17.
Retinal cBmal1 and cAANAT mRNAs demonstrate less pronounced rhythmic patterns compared to their counterparts in the pineal gland.
cClock mRNA did not display a detectable rhythmic expression in the analyzed retinal cells.
The observed phase relationship between retinal cBmal1 and cAANAT suggests a potential regulatory link similar to that in the pineal gland.

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Unlike mammals, rhythmic changes in serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) transcripts in chicken pineal cells are controlled by an oscillator located in the pinealocytes themselves, which is comprised of clock genes. Asimilar clock-dependent pathway has been postulated to regulate the retinal melatonin rhythm. In chicken retinal photoreceptor cells and pinealocytes, the chicken AANAT gene (cAANAT) is coexpressed with clock genes, including cBmal1 and cClock, which might regulate cAANAT transcription. Here, we have studied the temporal profile of cBmal1, cClock, and cAANAT mRNAexpressions in retinal cells in vivo with chickens housed in a 14/10-h light/dark (LD) cycle for 2 wk and in vitro cultured in a superfusion system for 4 LD cycles. mRNA levels of these genes were analyzed by RT-PCR and compared with their corresponding pineal transcripts. cBmal1 mRNA showed a peak during the light phase between Zeitgeber time (ZT) 8 and 10, preceding the amplitude of the nocturnal increase in cAANAT expression at ZT 16-17. Retinal cBmal1 and cAANAT mRNAs exhibited less robust cycling than their corresponding pineal transcripts in the same animal. cClock mRNAlevels failed to exhibit a well-detectable rhythm. The phase of the rhythms of retinal cBmal1 and cAANAT mRNAs suggests a link between retinal cBmal1 and cAANAT expressions similar to the regulation of pineal cAANAT transcription. Based on the highly conserved nature of the clockwork, it is reasonable to consider that chicken retina and pineal gland might serve as a useful tool for the development of drugs that could influence clock function in man.

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Circadian Expression of Bmal1 and Serotonin-N-Acetyltransferase mRNAs in Chicken Retina Cells and Pinealocytes In Vivo and In Vitro

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