Expression dynamics of functionally equivalent Neurog1/2 genes enable protracted neurogenesis and temporal emergence of somatosensory neuron lineages

Dorsal root ganglia (DRG) somatosensory neurons of the mechano/proprioceptive and thermo/nociceptive lineages differentiate during successive neurogenic waves defined by the complementary expression and combinatorial roles of the proneural genes Neurog2 and Neurog1. Using a gene-swapping approach, we show here that both paralogs are largely interchangeable in this structure and beyond, including for fate determination, indicating that their specific requirements primarily reflect divergent evolution of their regulatory sequences rather than protein activities. This result, combined with birth-dating data and phenotyping of complementary transgenic models, where delayed onset or premature arrest of neurogenesis predictably triggers opposite changes in DRG content, highlights that somatosensory precursors' commitment to the mechano/proprioceptive or thermo/nociceptive lineage is rapidly biased but critically depends on differentiation timing. Together, these findings support a model where the dynamic spatiotemporal expression of functionally equivalent Neurog1 and Neurog2 proteins ensures a protracted neurogenic period, allowing the sequential emergence of distinct neuronal lineages.