ABSTRACT
Corticogenesis consists of a series of synchronised events, including fate transition of cortical progenitors, neuronal migration, specification and connectivity. NeuroD1, a basic helix-loop-helix (bHLH) transcription factor (TF), contributes to all of these events, but how it coordinates these independently is still unknown. Here, we demonstrate that NeuroD1 expression is accompanied by a gain of active chromatin at a large number of genomic loci. Interestingly, transcriptional activation of these loci relied on a high local density of adjacent bHLH TFs motifs, including, predominantly, Tcf12. We found that activity and expression levels of Tcf12 were high in cells with induced levels of NeuroD1 that spanned the transition of cortical progenitors from proliferative to neurogenic divisions. Moreover, Tcf12 forms a complex with NeuroD1 and co-occupies a subset of NeuroD1 target loci. This Tcf12-NeuroD1 cooperativity is essential for gaining active chromatin and targeted expression of genes involved in cell migration. By functional manipulation in vivo, we further show that Tcf12 is essential during cortical development for the correct migration of newborn neurons and, hence, for proper cortical lamination.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/metabolism , Cerebral Cortex/growth & development , Animals , Basic Helix-Loop-Helix Transcription Factors/antagonists & inhibitors , Basic Helix-Loop-Helix Transcription Factors/genetics , Cell Movement , Cerebral Cortex/metabolism , Chromatin/metabolism , Embryonic Development/genetics , Female , Histones/metabolism , Mice , Mice, Inbred C57BL , Mouse Embryonic Stem Cells/cytology , Mouse Embryonic Stem Cells/metabolism , Neurogenesis , Neurons/cytology , Neurons/metabolism , RNA Interference , RNA, Small Interfering/metabolismABSTRACT
Smad anchor for receptor activation (SARA, zfyve9) has been classically observed in early endosomes of different cells types where it regulates vesicular transport of proteins and membrane components. Very few other members of the zinc finger FYVE domain-containing family (zfyve) have different functions other than controlling membrane trafficking. By analyzing SARA localization throughout mouse embryonic brain development, we detected that besides the endosomal localization it also targets neuronal nuclei, specifically of the cortical layers V/VI. These findings were confirmed in human brain organoids. When evaluating neuronal cell lines, we found that SARA accumulates in nuclei of PC-12 cells, but not Neuro-2a, highlighting its specificity. SARA functions as a specific marker of the deep cortical layers until the first postnatal week. This temporal regulation corresponds with the final phases of neuron differentiation, such as soma ventral translocation and axonal targeting. In sum, here we report that SARA localization during brain development is temporarily regulated, and layer specific. This defined pattern helps in the identification of early born cortical neurons. We further show that other zfyve family members (FYCO1, WDFY3, Hrs) also distribute to nuclei of different cells in the brain cortex, which raises the possibility that this might be an extended feature within the protein family.
