Somatic and ventral motoneurons (sMNs and vMNs, respectively) are both required for the central control of vertebrate body movement and homeostasis. But although much is known about how the differentiation of sMNs is controlled, less is known about vMN specification in the developing hindbrain. On p. 4149, Pattyn and his colleagues describe how the Nkx6 and Nkx2 classes of homeodomain proteins have complementary roles in vMN specification in mice and chicks. While Nkx2.2 is sufficient to induce vMNs, Nkx6 proteins are not needed for vMN generation but instead prevent these cells from differentiating into interneurons and direct later aspects of their differentiation. The authors also show that Nkx6 proteins and the motoneuron determinant Olig2 act in parallel in sMN differentiation, a result that leads them to conclude that sMN and vMN cell fate specification requires a combination of transcription factors rather than a single master regulator.

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