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Kick-off abstract :
miR-128, a brain-enriched microRNA, has been implicated in the control of neurogenesis and synaptogenesis but its potential roles in intervening processes have not been addressed. We show that post-transcriptional mechanisms restrict miR-128 accumulation to post-mitotic neurons during mouse corticogenesis and in adult stem cell niches. Premature miR-128 expression in the progenitors for upper layer neurons leads to impaired neuronal migration and inappropriate branching. Those neurons that reach their correct cortical position display a reduction in the complexity of dendritic arborization, associated with altered electrophysiological properties. We show that Phf6, a gene mutated in the cognitive disorder Börjeson-Forssman-Lehmann syndrome, is an important regulatory target for miR-128. Restoring PHF6 expression counteracts the deleterious effect of miR-128 on neuronal migration, outgrowth and intrinsic physiological properties. Our results place miR-128 upstream of PHF6 in a pathway vital for cortical lamination as well as for the development of neuronal morphology and intrinsic excitability.
Project abstract :
The anatomic and functional construction of the mammalian cortex requires the coordination of stem cell proliferation, neurogenesis, migration, specification, outgrowth and synaptogenesis. Failures at any level in this temporal progression are associated with functional disturbances ranging from microcephaly or epileptic heterotopias to neurodevelopmental aspects of intellectual disability or autism. Individual miRNAs are rapidly being assigned coordinating functions for each of the steps required for CNS morphogenesis; our efforts are focused on the functional analysis of one of the most abundant miRNAs in the cortex, miR-128. We have found that biogenesis of miR-128 in development is restricted to neurons in the cortical plate by a post-transcriptional mechanism. We are studying the nature and the significance of this timing mechanism for cortical morphogenesis. By manipulating miR-128 expression in upper layer progenitors, we have begun to reveal a regulatory circuit controlling correct upper layer lamination and connectivity. To determine downstream genes and pathways targeted by miR-128, we have extensively verified potential miR-128 target mRNAs by microarrays and sensor assays. This collection of validated candidate genes (>20 to date) includes a number of genes implicated in human developmental disturbances and a cluster of genes involved in BDNF signaling.
Upstream of miR-128, we are currently investigating the factors responsible for the developmental timing of miR-128 expression. Downstream of miR-128, we have identified Phf6, a gene as an important regulatory target for miR-128. PHF6 mediates many of the effects of miR-128 misexpression on neuronal migration, dendritic outgrowth and intrinsic excitability. Going forward, we will extend these observations to additional cortical neuronal subtypes and investigate differential activity of miR-128 and its targets genes in individual cortical layers.
Some key technologies for internal use:
We would be happy to help with :
- miRNA in situs, including co-labeling
- morphometric analysis
- in utero electroporation
- stem cell culture/differentiation
- live cell imaging
- target gene validation
- Franzoni, E., Booker, S.A., Parthasarathy, S., Rehfeld, F., Grosser, S., Srivatsa, S., Fuchs, H.R., Tarabykin, V., Vida, I., and Wulczyn, F.G. (2015). miR-128 regulates neuronal migration, outgrowth and intrinsic excitability via the intellectual disability gene Phf6. Elife 4, DOI 10.7554/eLife.04263.
- Rehfeld, F., Rohde, A.M., Nguyen, D.T.T. and Wulczyn, F.G. (2014) Lin-28 and let-7: ancient milestones on the road from pluripotency to neurogenesis. Cell Tissue Res. 359, 145–160.
- Lehmann, S.M., Krüger, C., Park, B., Derkow, K., Rosenberger, K., Baumgart, J., Trimbuch, T., Eom, G., Hinz, M., Kaul, D., Habbel, P., Kälin, R., Franzoni, E., Rybak, A., Nguyen, D. Veh, R., Ninnemann, O., Peters, O., Nitsch, R., Heppner, F.L., Golenbock, D., Schott, E., Ploegh, H.L., Wulczyn, F.G. and Lehnardt, S. (2012a). An unconventional role for miRNA: let-7 activates Toll-like receptor 7 and causes neurodegeneration. Nature Neuroscience 15, 827–835.
- Rybak,A., Fuchs,H., Hadian,K., Smirnova,L., Wulczyn,E.A., Michel,G., Nitsch,R., Krappmann,K. and Wulczyn, F.G. (2009) The let-7 target gene mouse Lin-41 is a stem cell specific E3 ubiquitin ligase for the miRNA pathway protein Ago2. Nature Cell Biology 11 1411-1420.
- Rybak,A., Fuchs,H., Smirnova,L., Brandt,C., Pohl,E.E., Nitsch,R., and Wulczyn,F.G. (2008). A feedback loop comprising lin-28 and let-7 controls pre-let-7 maturation during neural stem-cell commitment. Nature Cell Biology 10, 987-993.