Neural specification is regulated by one or many transcription factors that control expression of effector genes that mediate function and determine neuronal type. Here we identify a novel role for one conserved proneural factor, the bHLH protein HLH-3, implicated in the specification of sex-specific ventral cord motor neurons in C. elegans. Proneural genes act in early stages of neurogenesis in early progenitors, but here, we demonstrate a later role for hlh-3. First, we document that differentiation of the ventral cord type C motor neuron class (VC) within their neuron class, is dynamic in time and space. Expression of VC class-specific and subclass-specific identity genes is distinct through development and is dependent on the VC position along the A-P axis and their proximity to the vulva. Our characterization of the expression of VC class and VC subclass-specific differentiation markers in the absence of hlh-3 function reveals that VC fate specification, differentiation, and morphology requires hlh-3 function. Finally, we conclude that hlh-3 cell-autonomously specifies VC cell fate.

神经规格受一个或多个转录因子调控，这些转录因子控制介导功能并决定神经元类型的效应基因的表达。在这里，我们确定了一个保守的proneural因素，bHLH蛋白HLH-3，在秀丽隐杆线虫的性别特异性腹侧运动神经元的规范中涉及一种新的作用。proneural基因在早期祖细胞的神经发生的早期阶段起作用，但是在这里，我们证明了hlh-3。首先，我们证明在其神经元类别内腹型C型运动神经元类别（VC）的分化在时间和空间上是动态的。VC类特异性和亚类特异性同一性基因的表达在发育过程中是不同的，并且取决于VC沿AP轴的位置及其与外阴的接近程度。我们在没有VC的情况下表征VC类和VC子类特异性分化标记的表达hlh-3 功能揭示了VC命运的规格，差异和形态要求 hlh-3功能。最后，我们得出结论hlh-3单元自主指定VC单元的命运。