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R. S. Ashby, P. Megaw, R. Maleszka, I. Morgan; Changes in Retinal Expression of ZENK mRNA During the Onset of, and Recovery From, Experimentally-Induced Myopia. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5932.
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To examine the time-course of changes in ZENK and pre-pro glucagon (PPG) mRNA expression during the development of form-deprivation myopia (FDM) and lens-induced myopia (LIM), and the reduced rate of growth caused by the removal of diffusers.
Chickens had their left eye covered with either a translucent diffuser or a -10D lens for a period of 1 hr, or 1, 3 and 7 days. For recovery experiments, form-deprived chicks had the diffusers removed for either 1hr, or 1 or 3 days. Six samples were collected at each time point, with each sample containing two retinas, one from each of two animals. RT-PCR was carried out on mRNA, and the results were normalised against ß-actin. Percentage changes in mRNA expression were calculated by the formula of Pfaffl, 2000 .
ZENK mRNA levels were down-regulated during the entire 7 days of FDM. A similar pattern was seen during lens treatment, with ZENK mRNA levels significantly reduced following 1hr of lens wear, and remaining reduced for the entire 7 days of treatment. In contrast, ZENK mRNA levels showed an increase in expression within 1hr of recovery from FDM, before returning to baseline levels for the remainder of the experimental period. PPG mRNA expression was significantly down-regulated on days 1, 3, and 7 of FDM, with a similar suppression in mRNA levels seen during LIM. During recovery, PPG mRNA levels remained suppressed 1hr after diffuser removal, but became significantly elevated on days 1 and 3 of recovery.
The expression of PPG and ZENK changes bi-directionally in response to opposing growth stimuli. However, this bi-directional change is not symmetrical: FDM depresses ZENK mRNA expression for a prolonged period of time, while the removal of diffusers enhances ZENK expression for a much shorter period. The earlier appearance of ZENK downregulation, compared to PPG, suggests that changes in the expression of ZENK may ultimately control the expression of PPG in the chick retina. The effect of lens treatment on the expression of PPG and ZENK mRNA levels does not differ significantly from that of form-deprivation.1. Pfaffl, M.W., Nucleic Acids Res, 2001. 29(9): p. e45.
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