On 22 January, we published online the paper by Marmigère et al. about the transcription factor Runx1’s role in specifying TrkA-positive nociceptive sensory neurons. Then the Feb. 2 issue of Neuron came out with two papers also describing the function of Runx1 in nociceptor development (Chen et al. and Kramer et al.). Neuron also ran a third paper, on Runx3, and interestingly, although the three Neuron papers come from three different groups at Harvard, Basel and Columbia, they all share two co-authors.

I guess I shouldn’t be too surprised at the sudden avalanche of Runx1 papers. We’ve known for a while that the related Runx3 is crucial to the development of TrkC-positive proprioceptive sensory neurons (Levanon et al., Inoue et al., both published in 2002), so together with the known expression patterns of the Runx’s, the idea that Runx1 would be ‘responsible’ for the nociceptive subpopulation wasn’t very far-fetched; of course several groups would be looking into this. Nevertheless I’m amazed that the three groups managed to published their Runx1 work in top-level journals near-simultaneously.

There are some very interesting differences among the Runx1 papers’ conclusions. Marmigère et al., using electroporation of wildtype and inhibitory Runx1 constructs, or siRNA, into developing chick embryos, found that Runx is necessary and sufficient for TrkA expression, and thus survival, of young nociceptors. Chen et al. made a conditional knockout of Runx1 and conclude that it is not required for TrkA expression or survival, but instead for the postnatal switch of many nociceptive neurons from TrkA to Ret expression (as well as other mature characteristics of these neurons).

Maybe these contradictory results can be explained by differences in timing of the experiments? Marmigère et al. electroporated at stage HH13, about 2.5 days old embryos, which is long before Runx expression sets in, while Chen et al. show loss of Runx1 at embryonic day 13.5, which is a bit later than its expression begins in mouse DRG. Or maybe one method is superior to the other, or maybe we’re wrestling with species differences?