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

Abstract

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. Movement is the principle expressive output of the central nervous system. Locomotor movements are initiated in the brain either cortically or subcortically, but are expressed by channeling activity to locomotor networks, located primarily in the ventral part of the spinal cord, that include rhythm-generating circuits called Central Pattern Generators (CPGs). The spinal locomotor networks ensure the integration of the multiple inputs that regulate motor activity and control the rhythm, speed, and coordination of the locomotor movements. CPGs are composed of interconnected spinal interneurons (INs) of diverse types that generate patterned activity that is then imposed on the motor neurons (MNs) that innervate skeletal muscles. Although many regulatory genes that direct the differentiation of these spinal neuron populations have been identified and the role of some of these genes has been extensively studied 1 , the complete genetic programs underlying the specification of the various neuron types within locomotor networks are far from fully deciphered.

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

“…Members of the Onecut family of TFs have so far been identified as critical for the development of hepatocytes, endocrine cells of the pancreas and the gastrointestinal tract, and the spinal cord 13–20 . Nevertheless, their localization in the brain remains incomplete particularly because of the lack of genetic tools to faithfully chart the distribution of neurons expressing Onecut paralogs, and to interrogate their connectivity to infer functions.…”

Cracking the Code of Neuronal Cell Fate

“…Onecut2 encodes a member of a family of transcription factors that function as transcriptional activators controlling cell differentiation and survival, as well as oxidative defense signaling, and that have only been recently proposed as regulators of neuronal differentiation [ 177 , 178 , 179 , 180 , 181 , 182 , 183 , 184 ]. Showing a consistent increased expression of this TF in CGNs during NF-mediated rescue, our results support the importance of Onecut2 for neuronal survival ( Figure 1 and Figure 3 ) [ 43 ].…”

“…According with the anti-apoptotic, anti-oxidative and anti-inflammatory effects of this TF, we observed its increased expression following NF-induced neuronal apoptotic rescue ( Figure 1 and Figure 3 ) [ 43 ]. From a clinical point of view, Twist2 is upregulated in a variety of cancers, including glioma and neuroblastoma [ 181 ]. In addition, Twist2 dysfunctions are associated with human pathological conditions characterized by oxidative stress-induced neuronal death, supporting its potential role as therapeutical target for cancer and neurological diseases [ 199 , 200 , 200 , 201 , 202 , 203 ].…”

Modeling Movement Disorders via Generation of hiPSC-Derived Motor Neurons

“…In mice, overexpression of miR-9 induces neuronal differentiation by inhibiting the nuclear receptor [ 134 , 135 ], suggesting that miR-9 plays a role in fine-tuning the process of specification of MN subtype identity. Other studies showed that ISL1 expression by Onecut transcription factors (OC1) was important to generate LMC MNs [ 133 , 156 , 157 ]. Studies showed that miR-9 and OC1 are in mutually exclusive patterns in the embryonic spinal cord and miR-9 efficiently represses OC1 expression, demonstrating that regulation of OC1 by miR-9 is a crucial step in the specification of spinal MNs.…”