Different combinations of Notch ligands and receptors regulate V2 interneuron progenitor proliferation and V2a/V2b cell fate determination

Abstract

The broad diversity of neurons is vital to neuronal functions. During vertebrate development, the spinal cord is a site of sensory and motor tasks coordinated by interneurons and the ongoing neurogenesis. In the spinal cord, V2-interneuron (V2-IN) progenitors (p2) develop into excitatory V2a-INs and inhibitory V2b-INs. The balance of these two types of interneurons requires precise control in the number and timing of their production. Here, using zebrafish embryos with altered Notch signaling, we show that different combinations of Notch ligands and receptors regulate two functions: the maintenance of p2 progenitor cells and the V2a/V2b cell fate decision in V2-IN development. Two ligands, DeltaA and DeltaD, and three receptors, Notch1a, Notch1b, and Notch3 redundantly contribute to p2 progenitor maintenance. On the other hand, DeltaA, DeltaC, and Notch1a mainly contribute to the V2a/V2b cell fate determination. A ubiquitin ligase Mib, which activates Notch ligands, acts in both functions through its activation of DeltaA, DeltaC, and DeltaD. Moreover, p2 progenitor maintenance and V2a/V2b fate determination are not distinct temporal processes, but occur within the same time frame during development. In conclusion, V2-IN cell progenitor proliferation and V2a/V2b cell fate determination involve signaling through different sets of Notch ligand-receptor combinations that occur concurrently during development in zebrafish.

Regeneration of Sensory Hair Cells Requires Localized Interactions between the Notch and Wnt Pathways

“…The heterogeneous expression patterns of notch receptors and ligands suggest that different combinations may regulate progenitor proliferation or cell fate determination (Alunni et al, 2013; Okigawa et al, 2014). To determine in which cells Notch signaling is active, we analyzed the expression pattern of the Notch reporter Tg(Tp1bglob:eEGFP) crossed with Tg(atoh1a:dTomato) that labels hair cells.…”

“…For example, deltaa is strongly expressed in NM poles, where no hair cell differentiation occurs (Figures 2I-2J). Recent studies showed that different ligand/ receptor combinations regulate either progenitor proliferation or cell fate determination in the CNS and spinal cord (Alunni et al, 2013; Okigawa et al, 2014). As a result, the expression pattern of Notch pathway members is not sufficient to deduce in which cells Notch signaling is active (Perdigoto and Bardin, 2013; Petrovic et al, 2014).…”

Molecular and cellular development of spinal cord locomotor circuitry

“…Mice models with abnormal Mib1 resulted in unclear spinal progenitors, premature or unbalanced differentiation or loss of astrocytes and oligodendrocytes (Kang et al, 2013). In zebrafish embryos two ligands, DeltaA and DeltaD, and three receptors, Notch1a, Notch1b, and Notch3 redundantly contribute to p2 progenitor maintenance; on the other hand, DeltaA, DeltaC, and Notch1a mainly contribute to the V2a/V2b cell fate determination (Okigawa et al, 2014). Misra et al (2009) showed Foxn4 and proneural factors may serve as the trigger to initiate asymmetric Dll4-Notch and subsequent BMP/TGFβ signaling events required for neuronal diversity in the V2 domain (Okigawa et al, 2014).…”

“…In zebrafish embryos two ligands, DeltaA and DeltaD, and three receptors, Notch1a, Notch1b, and Notch3 redundantly contribute to p2 progenitor maintenance; on the other hand, DeltaA, DeltaC, and Notch1a mainly contribute to the V2a/V2b cell fate determination (Okigawa et al, 2014). Misra et al (2009) showed Foxn4 and proneural factors may serve as the trigger to initiate asymmetric Dll4-Notch and subsequent BMP/TGFβ signaling events required for neuronal diversity in the V2 domain (Okigawa et al, 2014). V2b fate is specified by active Notch1, Foxn4, Mash1 , and Scl Notch-binding protein MAML is also required for this specification (Peng et al, 2007).…”

From classical to current: Analyzing peripheral nervous system and spinal cord lineage and fate

“…A number of modes of diversification have been identified including different migration paths (Sockanathan and Jessell, 1998), being derived from distinct subpopulations of neural progenitors within a domain (Agalliu et al, 2009), or through intercellular interactions as the neurons differentiate. For example, the division of the V2 INs, into the V2 a and V2 b subclasses, occurs through differential activation of the Notch signaling pathway (Del Barrio et al, 2007; Okigawa et al, 2014; Peng et al, 2007; Rocha et al, 2009). …”