CBP and p300 coactivators contribute to the maintenance of Isl1 expression by the Onecut transcription factors in embryonic spinal motor neurons

Brain-wide mapping of efferent projections of glutamatergic (Onecut3+ ) neurons in the lateral mouse hypothalamus

AIM

This study mapped the spatiotemporal positions and connectivity of Onecut3+ neuronal populations in the developing and adult mouse brain.

METHODS

We generated fluorescent reporter mice to chart Onecut3+ neurons for brain-wide analysis. Moreover, we crossed Onecut3-iCre and Mapt-mGFP (Tau-mGFP) mice to visualize axonal projections. A dual Cre/Flp-dependent AAV construct in Onecut3-iCre cross-bred with Slc17a6-FLPo mice was used in an intersectional strategy to map the connectivity of glutamatergic lateral hypothalamic neurons in the adult mouse.

RESULTS

We first found that Onecut3 marks a hitherto undescribed Slc17a6+ /Vglut2+ neuronal cohort in the lateral hypothalamus, with the majority expressing thyrotropin-releasing hormone. In the adult, Onecut3+ /Vglut2+ neurons of the lateral hypothalamus had both intra- and extrahypothalamic efferents, particularly to the septal complex and habenula, where they targeted other cohorts of Onecut3+ neurons and additionally to the neocortex and hippocampus. This arrangement suggests that intrinsic reinforcement loops could exist for Onecut3+ neurons to coordinate their activity along the brain's midline axis.

CONCLUSION

We present both a toolbox to manipulate novel subtypes of hypothalamic neurons and an anatomical arrangement by which extrahypothalamic targets can be simultaneously entrained.

Histone modifications in neurodifferentiation of embryonic stem cells

Post-translational modifications of histone proteins regulate a long cascade of downstream cellular activities, including transcription and replication. Cellular lineage differentiation involves large-scale intracellular signaling and extracellular context. In particular, histone modifications play instructive and programmatic roles in central nervous system development. Deciphering functions of histone could offer feasible molecular strategies for neural diseases caused by histone modifications. Here, we review recent advances of in vitro and in vivo studies on histone modifications in neural differentiation.

In vitro characterization of human bone marrow mesenchymal stem cell-derived motor neurons induced by epigenetic modifiers

Background

Motor neurons (MNs) are distinct types of cells in the dorso-ventral axis of the spinal cord. These cells are developed in the presence of two main morphogens, including Sonic hedgehog (Shh) and retinoic acid (RA). On the other hand, human bone marrow mesenchymal stem cells (hBM-MSCs) are known as a multipotent type of cells with neural differentiation capacity. In this regard, the aim of this study was to quantitatively evaluate the expression of MN-related genes and the potent epigenetic regulatory genes involved in neurogenesis, including Enhancer of zeste homolog 2 (EZH-2) and P300, during hBM-MSC differentiation into MN-like cells, using RA and Shh. After isolating and inducing the cells with Shh and RA, the results were evaluated using immunocytochemistry and qRT-PCR.

Results

Our findings showed that the treated cells could express choline acetyltransferase (ChAT) and insulin gene enhancer binding protein-1 (Islet-1) antigens at the protein level, 2 weeks after induction. Moreover, at the second week after induction, the induced cells expressed MN-related genes (ChAT and ISLET-1) and epigenetic regulatory genes (EZH-2 and P300) at significant levels compared to the control (non-treated BM-MSCs) and to the induced cells at the first week (day 7). In addition, the expression of EZH-2, as a histone-modifying gene, was also significantly upregulated at the first week compared to the control. No significant upregulation was detected in the expression of motor neuron and pancreas homeobox 1 (MNX-1) in the treated groups compared to the control group.

Conclusion

We concluded that epigenetic modifiers, P300 and EZH-2, are important mediators for regulating the process of motor neuron differentiation induced by RA and Shh.

Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits

In the developing spinal cord, Onecut transcription factors control the diversification of motor neurons into distinct neuronal subsets by ensuring the maintenance of Isl1 expression during differentiation. However, other genes downstream of the Onecut proteins and involved in motor neuron diversification have remained unidentified. In the present study, we generated conditional mutant embryos carrying specific inactivation of Onecut genes in the developing motor neurons, performed RNA-sequencing to identify factors downstream of Onecut proteins in this neuron population, and employed additional transgenic mouse models to assess the role of one specific Onecut-downstream target, the transcription factor Nkx6.2. Nkx6.2 expression was up-regulated in Onecut-deficient motor neurons, but strongly downregulated in Onecut-deficient V2a interneurons, indicating an opposite regulation of Nkx6.2 by Onecut factors in distinct spinal neuron populations. Nkx6.2-null embryos, neonates and adult mice exhibited alterations of locomotor pattern and spinal locomotor network activity, likely resulting from defective survival of a subset of limb-innervating motor neurons and abnormal migration of V2a interneurons. Taken together, our results indicate that Nkx6.2 regulates the development of spinal neuronal populations and the formation of the spinal locomotor circuits downstream of the Onecut transcription factors.