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Samuel D Cross, Benjamin J Gilles, Lori A Bachman, Alan D Marmorstein, Lihua Y Marmorstein; Control of maintenance and regeneration of planarian eyes by ovo. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):440.
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© ARVO (1962-2015); The Authors (2016-present)
More than 2 million traumatic eye injuries occur in the U.S. each year with bilateral blindness occurring at a rate as high as 75 per 100,000 cases. The planarian Schmidtea mediterranea has the ability to regenerate its eyes. In this study we sought to determine whether eye regeneration in S. mediterranea could occur in the absence of the wound healing response typically associated with regeneration in many organisms.
A previous study (Lapan & Reddien, Cell Rep. 2(2):294-307,2012) demonstrated that maintenance of eyes in S. mediterranea requires the gene ovo. 240 S. mediterranea were treated with ovo RNAi or control (unc-22) RNAi by feeding liver paste containing dsRNA. Following loss of eyes, ovo RNAi treatment was halted and replaced with control RNAi treatment. Quantitative real-time PCR was used to monitor changes in ovo expression during ovo RNAi knock-down and following the switch to control RNAi. Fluorescent in situ hybridization was used to localize ovo expression in control and ovo RNAi treated worms. Eye functionality was monitored via a phototaxis assay.
In the ovo RNAi treated group, the eyes were observed to gradually shrink until they were completely absent. 100% of the planarians receiving ovo RNAi lost both eyes within 120 days of the onset of treatment. Functional loss of eyes was validated using a phototaxis assay. Ovo RNAi treated planarians were unable to regenerate eyes in response to wounding. Upon switching from ovo RNAi to control RNAi, eyes becamevisible as small pigmented spots in the head within 25 days. The eyes slowly developed, gaining pigmented cells first and more slowly developing the non-pigmented photoreceptors.
S. mediterranea have the ability to generate whole eyes in the absence of a wound healing response. This ability requires expression of ovo. Understanding how S. mediterranea control eye maintenance and regeneration could help to provide clues to genetic programs necessary to coax human stem cells to differentiate into various eye tissues.
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