MicroRNA-15b promotes neurogenesis and inhibits neural progenitor proliferation by directly repressing TET3 during early neocortical development

MicroRNAs (miRNAs) are important regulators of mouse brain development. However, their precise roles in this context remain to be elucidated. Through screening of expression profiles from a miRNA microarray and experimental analysis, we show here that miR‐15b controls several aspects of cortical neurogenesis. miR‐15b inhibits cortical neural progenitor cell (NPC) proliferation and promotes cell‐cycle exit and neuronal differentiation. Additionally, miR‐15b expression decreases the number of apical progenitors and increases basal progenitors in the VZ/SVZ. We also show that miR‐15b binds to the 3′ UTR of TET3, which plays crucial roles during embryonic development by enhancing DNA demethylation. TET3 promotes cyclin D1 expression, and miR‐15b reduces TET3 expression and 5hmC levels. Notably, TET3 expression rescues miR‐15b‐induced impaired NPC proliferation and increased cell‐cycle exit in vivo . Our results not only reveal a link between miRNAs, TET, and DNA demethylation but also demonstrate critical roles for miR‐15b and TET3 in maintaining the NPC pool during early neocortical development. Synopsis This study shows that miR‐15b targets TET3 and that miR‐15b and TET3 contribute to maintain the NPC pool during early neocortical development. miR‐15b is expressed in neural progenitors, represses NPC proliferation, increases the number of basal progenitors, and promotes neurogenesis. miR‐15b directly targets TET3 to epigenetically repress cyclin D1 expression and NPC proliferation. Graphical Abstract This study shows that miR‐15b targets TET3 and that miR‐15b and TET3 contribute to maintain the NPC pool during early neocortical development.