Generation of motor neurons requires spatiotemporal coordination between retinoic acid and Mib-mediated Notch signaling

Hee Jeong Kong,Jae-Ho Ryu,Julan Kim,Ju-Won Kim,Bomi Seong,Ilson Whang,Jung Youn Park,Sang-Yeob Yeo

doi:10.1080/19768354.2018.1443494

Abstract

ABSTRACTMind bomb (Mib) is an E3 ubiquitin ligase that activates the Notch signaling pathway. A previous study demonstrated that the generation of late-born GABAergic neurons may be regulated by the interplay between Mib and retinoic acid (RA). However, the relationship between Mib function and the retinoid pathway during the generation of late-born motor neurons remains unclear. We investigated the differentiation of neural progenitors into motor neurons by inhibition of Notch signaling and administration of RA to Tg[hsp70-Mib:EGFP] embryos. The number of motor neurons in the ventral spinal cord increased or decreased depending on the temporal inhibition of Mib-mediated Notch signaling. Inhibition of the retinoid pathway by citral treatment had a synergistic effect with overexpression of Mib:EGFP on the generation of ectopic motor neurons. Additionally, the proteolytic fragment of Mib was detected in differentiated P19 cells following treatment with RA. Our observations imply that the function of Mib may be attenuated by the retinoid pathway, and that Mib-mediated Notch signaling and the retinoid pathway play critical roles in the spatiotemporal differentiation of motor neurons.

Highlights

In zebrafish embryos, primary neurogenesis gives rise to elavr3-positive differentiated primary motor neurons, interneurons and Rohon-Beard neurons, which populate the medial, intermediate and lateral domains on each side of the dorsal midline, respectively (Kim et al 1996)
Our observations implicated that overexpression of Mind bomb (Mib):EGFP has a lesser effect on the generation of ectopic motor neurons than those of sensory neurons and interneurons during late gastrulation (Ryu et al 2015)
The primary neurogenesis starts at 8.5 hpf known as a lategastrulation stage by expressing ngn1 as a proneural gene, and elavr3 as a neuronal marker is first expressed at 11 hpf in zebrafish embryos (Kim et al 1997)

Summary

Introduction

Primary neurogenesis gives rise to elavr3-positive differentiated primary motor neurons, interneurons and Rohon-Beard neurons, which populate the medial, intermediate and lateral domains on each side of the dorsal midline, respectively (Kim et al 1996). It is unclear whether the neurogenic phenotype can be observed within the motor neuron domain of Tg[hsp70-mib:EGFP] embryos heat-shocked before gastrulation (5.5 hpf), and whether overexpression of Mib:EGFP effectively inhibits the Notch signaling pathway.

Results

Conclusion