A microRNA cluster downstream of Fezf2 coordinates projection identity and dendritic morphology in cortical projection neurons

Cortical projection neurons comprise classes of neurons connecting the cerebral cortex to distant targets in the nervous system. Each projection neuron class acquires a distinct molecular identity and develops characteristic patterns of axonal projection and dendritic arborization that determine their inputs, outputs, and distinct functions. How different aspects of neuron identity, including axonal and dendritic morphology, are coordinated appropriately in each specific neuron type is not known. A network of transcription factors, including the selector gene Fezf2, is central to specifying cortical projection neuron fates. However, regulation down-stream of these fate-determinant transcription factors to control different aspects of neuron identity is not understood, particularly as it relates to the development of distinct dendritic arbors that determine the inputs to each projection neuron class. Here we show that the miR-193b~365 microRNA cluster downstream of Fezf2 cooperatively represses the signaling molecule Mapk8 to regulate dendritic development in a neuron subtype-specific manner. Corticospinal motor neuron (CSMN) and callosal projection neurons (CPN) samples were isolated by FACS, then suspended in a transposition mix to generate DNA fragments. The fragments generated in the CSMN and CPN samples were dependent on the chromatin state of the nuclei. The DNA fragments were amplified using indexing primers, and purified to give the final ATAC-seq library.