Small Regulatory RNAs in Development
Tuesday, February 20, 2007
Presented by the RNAi Discussion Group
Organizer: Oliver Hobert, Columbia University
miRNA Regulation of Synaptic Development and Plasticity
Brian McCabe, PhD
Learning, memory and behavior are thought to be possible through the plastic ability of synaptic connections to alter their function, shape and complexity in response to changes in development, activity or experience. We are interested in defining the molecular pathways that regulate synapse architectural growth and change in a Drosophila model system. Regulation of RNA translation has been shown to be important for synapse function in a number contexts and model systems. We will present data that a discrete subset of miRNAs in Drosophila are integral to the regulation of synapse structural plasticity and discuss likely synaptic RNA targets.
RNAi biology in C. elegans
Massachusetts Institute of Technology
RNA interference in C. elegans was discovered as a biological response to exogenously introduced double-stranded RNA. dsRNA commonly induces sequence-specific gene silencing at the post-transcriptional level. Additional responses of C. elegans to dsRNA introduced with bacterial food and likely occurring in the nucleus will be presented. Also, a role for RNAi-response genes in chromatin regulation during C. elegans development will be discussed.
MicroRNAs miR-290-295 in Blastocyst-Derived Stem Cells and the Early Mouse Embryo
At the molecular level, stem cell maintenance and differentiation depend on a complex network of mechanisms that control gene expression. While transcription factors that govern key aspects of stem cell biology (e.g., Oct-4 and Nanog in embryonic stem (ES) cells) have been identified, very little is known about the role of microRNA (miRNA) dependent post-transcriptional control. Direct short RNA cloning led to the identification of miR-290-295 as the most abundant miRNAs in mouse ES cells. These miRNAs are encoded by a cluster of six pre-miRNA hairpins with related sequences and appear to be ES cell and pre-implantation embryo-specific by the following criteria: (1) their sequences are unrelated to any previously described miRNAs, including the extensive collection of miRNAs cloned from adult mouse organs; (2) they can not be detected in adult mouse organs with northern blots; (3) they are repressed during ES cell differentiation in vitro; and (4) all ESTs that map within the miR-290-295 cluster are derived from ES cells and pre-implantation embryos. Sequence analysis shows that this Early Embryonic miRNA Cluster (EEmiRC) is remarkably variable in different mammalian orders and can only be identified bioinformatically in placental (eutherian) mammals. This result fits nicely with the fact that pre-implantation development is a uniquely eutherian feature and suggests that EEmiRC may be involved in the differentiation and/or maintenance of the extraembryonic lineages. Consistent with eutherian specific function we have detected the EEmiRC miRNAs in trophoblastic stem (TS) cells. However, preliminary data indicate that EEmiRC is not expressed in mature placenta. Thus, EEmiRC is likely to play a role very early in development, perhaps as early as pre- or peri- implantation. Since ES and TS cells are derived from the blastocyst inner cell mass and trophoblast, respectively, it is tempting to speculate that EEmiRC controls the initial differentiation of these lineages or of cell types directly derived from them.