In the developing central nervous system, cellular diversity depends in part on organising signals that establish regionally restricted progenitor domains, each of which produces distinct types of differentiated neurons. However, the mechanisms of neuronal subtype specification within each progenitor domain remain poorly understood. The p2 progenitor domain in the ventral spinal cord gives rise to two interneuron (IN) subtypes, V2a and V2b, which integrate into local neuronal networks that control motor activity and locomotion. Foxn4, a forkhead transcription factor, is expressed in the common progenitors of V2a and V2b INs and is required directly for V2b but not for V2a development. We show here in experiments conducted using mouse and chick that Foxn4 induces expression of delta-like 4 (Dll4) and Mash1 (Ascl1). Dll4 then signals through Notch1 to subdivide the p2 progenitor pool. Foxn4, Mash1 and activated Notch1 trigger the genetic cascade leading to V2b INs, whereas the complementary set of progenitors, without active Notch1, generates V2a INs. Thus, Foxn4 plays a dual role in V2 IN development: (1) by initiating Notch-Delta signalling, it introduces the asymmetry required for development of V2a and V2b INs from their common progenitors; (2) it simultaneously activates the V2b genetic programme.
"Analysis of mid-cervical ventral spinal cord revealed that at E10.5, which is when MNs emerge from the pMN domain, a cluster of Dll4-positive cells is located just dorsal of nascent Pou3f1+ Isl1/2+ MNs (Fig. 6A,B). Previous studies have mapped Dll4 expression to the p2 progenitor domain (Del Barrio et al., 2007; Peng et al., 2007). Furthermore, Notch1 protein is detectable on the most immature, medial MNs, and Pou3f1 expression in MNs overlaps with that of the Notch target gene Hey1 (supplementary material Fig. S11). "
[Show abstract][Hide abstract] ABSTRACT: Air breathing is an essential motor function for vertebrates living on land. The rhythm that drives breathing is generated within the central nervous system and relayed via specialised subsets of spinal motor neurons to muscles that regulate lung volume. In mammals, a key respiratory muscle is the diaphragm, which is innervated by motor neurons in the phrenic nucleus. Remarkably, relatively little is known about how this crucial subtype of motor neuron is generated during embryogenesis. Here, we used direct differentiation of motor neurons from mouse embryonic stem cells as a tool to identify genes that direct phrenic neuron identity. We find that three determinants, Pou3f1, Hoxa5 and Notch, act in combination to promote a phrenic neuron molecular identity. We show that Notch signalling induces Pou3f1 in developing motor neurons in vitro and in vivo. This suggests that the phrenic neuron lineage is established through a local source of Notch ligand at mid-cervical levels. Furthermore, we find that the cadherins Pcdh10, which is regulated by Pou3f1 and Hoxa5, and Cdh10, which is controlled by Pou3f1, are both mediators of like-like clustering of motor neuron cell bodies. This specific Pcdh10/Cdh10 activity might provide the means by which phrenic neurons are assembled into a distinct nucleus. Our study provides a framework for understanding how phrenic neuron identity is conferred and will help to generate this rare and inaccessible yet vital neuronal subtype directly from pluripotent stem cells, thus facilitating subsequent functional investigations.
Development 02/2014; 141(4):784-94. DOI:10.1242/dev.097188 · 6.46 Impact Factor
"In the developing mouse spinal cord, Notch1 and Notch3 are mainly expressed in the ventricular zone, and Notch2 in the floor plate . Interestingly, Notch1 signaling is selectively responsible for the differentiation of interneurons in the V2 domain and of motoneurons in the VMN domain , . "
[Show abstract][Hide abstract] ABSTRACT: Members of the ADAM (a disintegrin and metalloprotease) family are involved in embryogenesis and tissue formation via their proteolytic function, cell-cell and cell-matrix interactions. ADAM10 is expressed temporally and spatially in the developing chicken spinal cord, but its function remains elusive. In the present study, we address this question by electroporating ADAM10 specific morpholino antisense oligonucleotides (ADAM10-mo) or dominant-negative ADAM10 (dn-ADAM10) plasmid into the developing chicken spinal cord as well as by in vitro cell culture investigation. Our results show that downregulation of ADAM10 drives precocious differentiation of neural progenitor cells and radial glial cells, resulting in an increase of neurons in the developing spinal cord, even in the prospective ventricular zone. Remarkably, overexpression of the dn-ADAM10 plasmid mutated in the metalloprotease domain (dn-ADAM10-me) mimics the phenotype as found by the ADAM10-mo transfection. Furthermore, in vitro experiments on cultured cells demonstrate that downregulation of ADAM10 decreases the amount of the cleaved intracellular part of Notch1 receptor and its target, and increases the number of βIII-tubulin-positive cells during neural progenitor cell differentiation. Taken together, our data suggest that ADAM10 negatively regulates neuronal differentiation, possibly via its proteolytic effect on the Notch signaling during development of the spinal cord.
PLoS ONE 01/2014; 9(1):e84617. DOI:10.1371/journal.pone.0084617 · 3.23 Impact Factor
"It is also intriguing that the Gata3 gene has never been found to be expressed in any CNS progenitors but only in some differentiated neurons. In the spinal cord, Gata3 is expressed in V2b interneurons and its expression is regulated by Notch signaling (Del Barrio et al., 2007). Notch signaling plays a critical role in the ontogeny of forebrain ependymal cells (Carlen et al., 2009) but less is known about its function on the ontogeny of spinal cord ependymal cells. "
[Show abstract][Hide abstract] ABSTRACT: Spinal cord injury (SCI) is a major health burden and currently there is no effective medical intervention. Research performed over the last decade revealed that cells surrounding the central canal of the adult spinal cord and forming the ependymal layer acquire stem cell properties either in vitro or in response to injury. Following SCI activated ependymal cells generate progeny cells which migrate to the injury site but fail to produce the appropriate type of cells in sufficient number to limit the damage, rendering this physiological response mainly ineffective. Research is now focusing on the manipulation of ependymal cells to produce cells of the oligodendrocyte lineage which are primarily lost in such a situation leading to secondary neuronal degeneration. Thus, there is a need for a more focused approach to understand the molecular properties of adult ependymal cells in greater detail and develop effective strategies for guiding their response during SCI.
Frontiers in Physiology 11/2013; 4:340. DOI:10.3389/fphys.2013.00340 · 3.53 Impact Factor
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