Dynamic miRNA expression patterns during retinal regeneration in zebrafish: reduced dicer or miRNA expression suppresses proliferation of Müller glia-derived neuronal progenitor cells.

BACKGROUND: Adult zebrafish spontaneously regenerate their retinas after damage. Although a number of genes and signaling pathways involved in regeneration have been identified, the exact mechanisms regulating various aspects of regeneration are unclear. microRNAs (miRNAs) were examined for their potential roles in regulating zebrafish retinal regeneration. RESULTS: To investigate the requirement of miRNAs during zebrafish retinal regeneration, we knocked down the expression of Dicer in retinas prior to light-induced damage. Reduced Dicer expression significantly decreased the number of proliferating Müller glia-derived neuronal progenitor cells during regeneration. To identify individual miRNAs with roles in neuronal progenitor cell proliferation, we collected retinas at different stages of light damage and performed small RNA high-throughput sequencing. We identified subsets of miRNAs that were differentially expressed during active regeneration but returned to basal levels once regeneration was completed. We then knocked down five different miRNAs that increased in expression and assessed the effects on retinal regeneration. Reduction of miR-142b and miR-146a expression significantly reduced INL proliferation at 51 h of light treatment, while knockdown of miR-7a, miR-27c, and miR-31 expression significantly reduced INL proliferation at 72 h of constant light. CONCLUSIONS: miRNAs exhibit dynamic expression profiles during retinal regeneration and are necessary for neuronal progenitor cell proliferation.