br Introduction The neocortex also called the dorsal cortex

Introduction The neocortex, also called the dorsal cortex, is an immensely complex mammalian BIRB796 manufacturer structure that controls higher cognitive functions, such as problem solving and reasoning, sensory perception, emotional processing, and attention. The developing neocortex is populated by several major types of neural progenitors (NPs) that primarily give rise to the excitatory neurons that populate the cortical wall (Florio and Huttner, 2014; Gertz et al., 2014). The mouse neocortex consists of self-renewing radial glial cells (RGCs) that reside in the ventricular zone (VZ) and give rise to postmitotic neurons as well as intermediate progenitors (IPs), which populate the subventricular zone (SVZ). These NP populations generate most of the neurons in the cortical plate (CP) (Englund et al., 2005; Franco and Muller, 2013; Sessa et al., 2008). As progenitors exit the cell cycle and terminally differentiate, early-born neurons migrate away from the VZ/SVZ to form the deeper layers of the cortex, and late-born neurons migrate past these cells to populate the outer layers, thereby forming an inside-out six-layer structure characteristic of the mammalian cortex (Kowalczyk et al., 2009; Toma et al., 2014). Regulation of proliferation in NPs must be tightly controlled, as the length of the cell cycle and the timing of cell-cycle exit determine the size of the NP and postmitotic neuron population, and the laminar positioning of mature neurons within the six layers of the cortical wall (Taverna et al., 2014). Regulators of cell-cycle progression play crucial roles in neocortical development and expansion (Chenn and Walsh, 2002, 2003; Pilaz et al., 2009). Consequently, investigating the genes and processes involved in neocortical development should provide insight into the development and remarkable evolutionary expansion of the cortex observed in higher mammals, as well as neurodevelopmental disorders that arise from abnormal NP proliferation and differentiation (Kriegstein et al., 2006; Rakic, 2009; Sun and Hevner, 2014). MicroRNAs (miRNAs) are a class of small, noncoding RNAs that have recently emerged as important regulators of neural development (Fineberg et al., 2009; Shibata et al., 2011). Previous work has demonstrated that miRNAs are essential for normal neocortical development (Bian et al., 2013; Kawase-Koga et al., 2010; Nowakowski et al., 2013; Pollock et al., 2014). Mice lacking dorsal cortical expression of the miRNA-processing molecule Dicer, and thus, expression of most miRNAs, develop abnormally small cortices (Davis et al., 2008; Kawase-Koga et al., 2009). This evidence suggests that miRNAs are required for cortical development; however, the specific miRNAs that regulate neurogenesis in the neocortex are still being uncovered. miRNA-210 (miR-210) has previously been described to regulate tissue development, tumorigenesis, and post-ischemia (Biswas et al., 2010; Huang et al., 2009). Overexpression of miR-210 in non-neural tissues impairs proliferation (He et al., 2013; Tsuchiya et al., 2011; Zhang et al., 2009). Further, gene ontology analysis of predicted and verified mRNA targets of miR-210 reveal that many are involved in regulating the cell cycle and, possibly, in neural development (Fasanaro et al., 2009). Taken together, these data suggests that miR-210 is a promising potential regulator of NP proliferation and differentiation. Here, we demonstrate that miR-210 is expressed in NPs throughout neocortical development and is an important regulator of NP proliferation. We show that altering miR-210 expression levels disrupts cell-cycle progression, ultimately altering the number and final laminar position of NP-derived postmitotic neurons. We also verify cyclin-dependent kinase 7 (Cdk7) as a target of miR-210 and an important regulating factor in the NP cell cycle. Our results suggest that proper expression levels of CDK7 and miR-210 are required for normal neocortical development.