Modulação dos genes de relógio Per1, Cry1b, Clock e da melanopsina por endotelina-1 em células embrionárias de Danio rerio / Modulation of clock genes Per1, Cry1b, Clock and of melanopsin by endothelin-1 in Danio rerio embryonic cells

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Biological clocks are endogenous timekeepers that are present both in eukaryotic as in prokaryotic organisms. Different clocks have different periods, and those that have about 24h of oscillation are called circadian clocks. In mammals, the first identified circadian clock is located in the suprachiasmatic nucleus, in the hipothalamus. It is now well known that clocks are present in brain regions other than the suprachiasmatic nucleus and in many peripheral tissues. In Drosophila and Danio rerio, peripheral oscillators can be synchronized directly by light, while in mammals the reset of the phase seems to be controlled by signals regulated by the suprachiasmatic timekeepers. The maintenance of the circadian clock is governed by positive and negative feedback loops, in general starting with the activation of Per and Cry genes by CLOCK and BMAL1. A new opsin called melanopsin, was recently discovered in the retina of all studied vertebrates, in a subset of intrinsically photosensitive ganglion cells. This photopigment is responsible for capturing light and sending this information to the suprachiasmatic nucleus. Endothelin (ET) is a 21-amino acid residue vasoconstrictor peptide. There are three endogenous isoforms of ETs, ET1, ET2 and ET3. Three subtypes of endothelin receptors have already been cloned: ETA, ETB and ETC, all members of the family of G protein -coupled receptors. Organs, tissues and cells of Danio rerio constitute an excellent model for the study of clock genes and rhythms in vitro. In ZEM 2S embryonic cells of this teleost, we demonstrated the presence of melanopsin, the endothelin receptor ETA, and the six Cry genes by PCR. The presence of melanopsin was also confirmed by immunohistochemistry. ZEM 2S cells previously kept for five days in 14L:10D (lights on 9:00am) were transferred in the sixth day to the following conditions: constant darkness, 14L:10D, 10L:14D and constant light, and growth curves were determined. ZEM 2S showed inhibition of proliferation by light. The temporal expression pattern of the genes Per1, Cry1b, Clock and of melanopsin and their modulation by ET-1 were studied. ZEM 2S cells were kept in 12D:12L photoperiod (lights on 9:00am) for five days, and then treated with 10-11M, 10-10M, 10-9M and 10-8M ET-1, for 24h. RNA extracted every 3 hours was submitted to RT-PCR for subsequent analysis by Real Time-PCR. 18S ribosomal RNA was used to normalize the results. Melanopsin did not show rhythmicity of expression in 12D:12L photoperiod. ET-1 exhibited a biphasic effect, increasing the expression in the lower concentrations, and reducing at the higher concentrations. At 10-10M, ET-1 apparently established an oscillation along the 24h-period, with increasing expression in the dark phase, reaching a peak at ZT2, and decreasing during the light phase, with the minimum at ZT6 and 9. The expression of Clock gene was rhythmic in 12D:12L photoperiod, with significant higher values in ZT12 to ZT21 than ZT0, ZT3 e ZT9, indicating an increase of expression coincident with the dark period. A peak of expression was observed at ZT6, during the light phase. At 10-11 and 10-10M, ET-1 abolished the rhythm of expression of Clock, and inhibited the peak of expression at ZT6. Expression of Clock remained high only at ZT18. At the higher concentrations (10-9M e 10-8M), the inhibition occurred at all ZTs, completely abolishing the rhythm and attenuating any variation previously observed among ZTs. The expression of Per1 gene was rhythmic in 12D:12L photoperiod, with significant higher values at ZTs 21, 0, 3, 6 and 9 than at ZTs 12, 15 and 18, indicating an increase of expression in the light phase. It is important to mention that at ZT21 there was already a significant increase, anticipatory of the light phase. At 10-11 e 10-10M, ET-1 did not alter neither the period nor the amplitude of this rhythm. The evident action of ET-1 was the inhibition of Per1 expression in the light phase (ZT0, ZT3, ZT6 e ZT9), and also at ZT21 (dark phase), at the higher concentrations (10-9M e 10-8M), with no change in the oscillation period, but markedly reducing its amplitude. The expression of Cry1b was rhythimic during the light:dark cycle, with increase in the light phase and reduction in the dark phase. Again, ET-1 showed a biphasic effect on this gene expression, increasing it during the light phase at the concentration of 10-11M, and at ZT6 and 9 at 10-10M. However, the hormone did not affect either the period or the amplitude of the rhythm. On the other hand, along the light phase, there was inhibition of Cry1b in the presence of ET-1 10-9 and 10-8M, reducing the amplitude observed in the control cells.

ASSUNTO(S)

ritmos biológicos células embrionárias endothelin biological rhythms endotelina danio rerio embryonic cells danio rerio

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