Abstract
In the pMN domain of the spinal cord, Notch signaling regulates the balance between motor neuron differentiation and maintenance of the progenitor state for later oligodendrocyte differentiation. Here, we sought to study the role of Notch signaling in regulation of the switch from the pMN progenitor state to differentiated motor neurons in a human model system. Human embryonic stem cells (hESCs) were directed to differentiate to pMN-like progenitor cells by the inductive action of retinoic acid and a Shh agonist, purmorphamine. We found that the expression of the Notch signaling effector Hes5 was induced in hESC-derived pMN-like progenitors and remained highly expressed when they were cultured under conditions favoring motor neuron differentiation. Inhibition of Notch signaling by a γ-secretase inhibitor in the differentiating pMN-like progenitor cells decreased Hes5 expression and enhanced the differentiation toward motor neurons. Conversely, over-expression of Hes5 in pMN-like progenitor cells during the differentiation interfered with retinoic acid- and purmorphamine-induced motor neuron differentiation and inhibited the emergence of motor neurons. Inhibition of Notch signaling had a permissive rather than an inductive effect on motor neuron differentiation. Our results indicate that Notch signaling has a regulatory role in the switch from the pMN progenitor to the differentiated motor neuron state. Inhibition of Notch signaling can be harnessed to enhance the differentiation of hESCs toward motor neurons.