MicroRNA regulation during mouse brain development

Stem cells are capable of producing daughter cells that either retain the ability of self-renewal and keep stem cell characteristics or that can undergo lineage-specific differentiation. Asymmetric segregation of cell fate determinants into the daughter cell is believed to play fundamental roles in regulation of the fate of the daughter cells (Betschinger and Knoblich, 2004; Knoblich, 2008). The recently identified cell fate determinants from the Knoblich lab, tripartite motif (TRIM)-NHL proteins, Brain tumor (Brat) and Mei-P26 in Drosophila have been implicated in the regulation of tumorigenesis. Loss of Brat and Mei-P26 in neuroblasts and ovarian stem cells, respectively, causes daughter cell overproliferation, and subsequently the formation of brain tumor and ovarian tumor (Betschinger et al., 2006; Neumueller et al., 2008). Differential segregation of different fate determinants to generate diverse cell types is conserved in the vertebrate central nervous system (Gotz and Huttner, 2005; Yu et al., 2006). The Brat homolog, TRIM32 has been shown to localize asymmetrically at the basal side of progenitors in the ventricular zone in the developing mouse brain, where it inhibits progenitor proliferation (Schwamborn J et al., under revesion). Preliminary data from the Knoblich lab demonstrated that TRIM32 interacts with Agonaute1, a core component of the RISC complex, an interaction which has also been observed in Brat and Mei-P26 in Drosophila. Furthermore, microRNAs (miRNAs) have been identified in the TRIM32 complex. These data suggest an exciting mechanism that TRIM32 might regulate progenitor self-renewal and differentiation via the miRNA pathway. This proposal aims to examine the potential roles of miRNAs and evaluate their significance in the regulation of neural progenitor development. We propose to identify differentially regulated TRIM32-associated miRNAs and study their role in the molecular mechanisms involved in regulation of progenitor proliferation and differentiation in the developing brain. The functions of the identified miRNAs will be characterized in developing brain progenitors by using the in utero electroporation technique. Furthermore, the functions of potential targets of these miRNAs in the regulation of progenitor proliferation and differentiation will also be investigated. We anticipate that these studies will greatly advance our understanding of how cell fate determinants and miRNAs coordinately regulate neural progenitor proliferation and differentiation in developing mammalian brain.