FUNCTIONAL ROLE OF MICRORNA-7 IN NEURAL DEVELOPMENT

Abstract

In the developing central nervous system (CNS) neurons and glia are sequentially produced from the ventricular neural progenitor cells. The progenitors restrict their differentiation potential by developmental stage-specific temporal specification. An important question in developmental neurobiology is to understand the role of signaling networks and factors that control switch from neurogenesis to gliogenesis. Recently microRNAs have found their importance in fine tuning key signaling factors in various developmental events. MicroRNAs are short non-coding RNAs that selectively repress translation of specific mRNA transcripts. These post-transcriptional regulators orchestrate various important cellular events including self renewal, differentiation and cell type specification. We characterized miRNA expression changes during the differentiation of a human neuroblastoma cell line SH-SY5Y through miRNA profiling. microRNA-7 was highly upregulated during neuronal differentiation in vitro, suggesting an analogous potential role for miR-7 during neural development in vivo. Ectopic expression of this microRNA in both human neural cell lines and zebrafish resulted in a more glial cell phenotype particularly giving rise to more number of oligodendrocytes and less neurons. Loss of function resulted in an increase in the production of mature neurons specifically dopaminergic neurons in the ventral part of the forebrain region. To identify potential target genes regulated by miR-7, we profiled the global changes in gene expression following miR-7 ectopic expression in ReNVM and neural progenitor cells derived from human ES cells. miR-7 represses around 143 targets that contain the seed match sequence of the microRNA and are predicted targets of miR-7 by conventional methods. The key targets repressed by microRNA-7 were TCF/LEF family members which act as downstream effectors of canonical Wnt/ß-catenin signaling pathway. Using transgenic Wnt TCF reporter lines in zebrafish we have shown this microRNA negatively regulates the Wnt signaling pathway in-vivo. Ectopic expression of miR-7 resulted in an increase in the sonic hedgehog pathway which is antagonistic to the Wnt pathway. Together, we report the role of a microRNA in maintaining a pool of neural progenitor cells by negatively regulating the canonical Wnt-ß catenin pathway and controlling the timing and production of both the glial and neuronal subtypes in the central nervous system.