Regulation of miR-34 Family in Neuronal Development.

Differentiation of neural stem cells (NSC's) to mature and functional neurons requires coordinated expression of mRNA, microRNAs (miRNAs) and regulatory proteins. Our earlier unbiased miRNA profiling studies have identified miR-200, miR-34 and miR-221/222 as maximally up-regulated miRNA families in differentiating PC12 cells and demonstrated the capability of miR-200 family in inducing neuronal differentiation (J. Neurochem, 2015, 133, 640-652). In present study, we have investigated role of miR-34 family in neuronal differentiation and identified P53 as mediator of nerve growth factor (NGF) induced miR-34a expression in differentiating PC12 cells. Our studies have shown that NGF induced miR-34a, arrests proliferating PC12 cells to G1 phase, which is pre-requisite for neuronal differentiation. Our studies have also shown that increased expression of miR-34a controls the P53 level in differentiated PC12 cells in feedback inhibition manner, which probably prevents differentiated cells from P53 induced apoptosis. Expression profiling of miR-34 family in different neuronal, non-neuronal and developing cells have identified differentiated and aged brain cells as richest source of miR-34, which also indicates that higher expression of miR-34 family helps in maintaining the mature neurons in non-proliferative stage. In conclusion, our studies have shown that miR-34 is brain enriched miRNA family, which up-regulates with neuronal maturation and brain ageing and co-operative regulation of P53 and miR-34a helps in neuronal differentiation by arresting cells in G1 phase.