Kinetic analysis of npBAF to nBAF switching reveals exchange of SS18 with CREST and integration with neural developmental pathways.
During the development of the vertebrate nervous system, neural progenitors divide, generate progeny that exit mitosis, and then migrate to sites where they elaborate specific morphologies and synaptic connections. Mitotic exit in neurons is accompanied by an essential switch in ATP-dependent chromatin regulatory complexes from the neural progenitor Brg/Brm-associated factor (npBAF) to neuron-specific nBAF complexes that is in part driven by miR-9/9* and miR-124. Recapitulating this microRNA/chromatin switch in fibroblasts leads to their direct conversion to neurons. We have defined the kinetics of neuron-specific BAF complex assembly in the formation of induced neurons from mouse embryonic stem cells, human fibroblasts, and normal mouse neural differentiation and, using proteomic analysis, found that this switch also includes the removal of SS18 and its replacement by CREST at mitotic exit. We found that switching of chromatin remodeling mechanisms is highly correlated with a broad switch in the use of neurogenic transcription factors. Knock-down of SS18 in neural stem cells causes cell-cycle exit and failure to self-renew, whereas continued expression of SS18 in neurons blocks dendritic outgrowth, underlining the importance of subunit switching. Because dominant mutations in BAF subunits underlie widely different human neurologic diseases arising in different neuronal types, our studies suggest that the characteristics of these diseases must be interpreted in the context of the different BAF assemblies in neurons rather than a singular mammalian SWItch/sucrose nonfermentable (mSWI/SNF) complex.
PubMed ID: 23785148
PMC ID: PMC3685834
Article link: J Neurosci.
Grant support: CA163915 NCI NIH HHS , NS046789 NINDS NIH HHS , T32 HD007249 NICHD NIH HHS , Howard Hughes Medical Institute , R01 CA163915 NCI NIH HHS , R01 NS046789 NINDS NIH HHS , R37 NS046789 NINDS NIH HHS
Genes referenced: banf1 ss18 ss18l1