Figure 1.

miRNA regulation of cerebral cortical neurogenesis. Scheme representing a part of the cortical wall corresponding to the area boxed in half brain coronal section (upper left). Before onset of neurogenesis (E10.5), symmetrical divisions increase the pool of NEPCs (light gray). Neurogenesis in the Cx starts at E11.5, when some Pax6-positive radial glial cells (blue) divide asymmetrically in the VZ. These cells self-renew (dark blue) and generate neurons in the SVZ either directly (orange) or indirectly through Tbr2-positive basal progenitors (pink). These concurrent steps are regulated by a set of miRNAs: Let-7b, miR-9, miR-124 and miR-134 (1, 2). Basal progenitors can sometime divide asymmetrically to self-renew but also divide symmetrically to give birth to two neurons. Differentiation of projection neurons that migrate through the intermediate zone (IZ) and integrate the CP requires Let-7b, miR-9, miR-34a and miR-137 (3). Terminal differentiation, including dendritogenesis and synapse formation, involves the expression of miR-34a, mir-132, mir-125b and miR-134 (4). The inset (right) shows the inside-out organization of cortical layers. Successive waves of postmitotic neurons are generated (graded orange), and these neurons migrate along radial glial cells (blue) through the IZ to reach the CP. Migration of neurons into the CP is regulated by miR-134 and miR-137 (6). The CP is builded in an inside-out manner and neurons stop their migration under the MZ where Cajal–Retzius cells (CR) (blue turquoise) are located. The generation of CR is controlled by miR-9 (5). MGE, medial ganglionic eminence, LGE, lateral ganglionic eminence, LV, lateral ventricle