Prdm12 represses the expression of the visceral neuron determinants Phox2a/b in developing somatosensory ganglia

Temporal refinement of Dach1 expression contributes to the development of somatosensory neurons

During somatosensory neurogenesis, neurons are born in an unspecialized transcriptional state. Several transcription factors in these cells follow a broad-to-restricted expression trajectory as development proceeds, giving rise to neuron subtypes with different identities. The relevance of this temporal refinement of transcription factor expression remains unclear as the functions of transcription factors with broad-to-restricted expression patterns have been mostly studied in those neuron subtypes in which they remain active. Here we show that Dach1 encodes a bona fide transcription factor with a broad-to-restricted expression pattern retained and required in tactile somatosensory neurons. In developing nociceptors, Prdm12 contributes to Dach1 silencing. Using genetic approaches to prevent its temporal restriction during mouse somatosensory development, we reveal that Dach1 expression refinement is a prerequisite for the acquisition of an appropriate transcriptional profile in those somatosensory neuron subtypes in which it becomes ultimately silenced. These findings highlight the essential role played by Dach1 during somatosensory neuron development and demonstrate that the temporal pattern of broad-to-restricted expression followed by several transcription factors is physiologically important for the development of somatosensory neurons.

Loss of G9a does not phenocopy the requirement for Prdm12 in the development of the nociceptive neuron lineage

Prdm12 is an epigenetic regulator expressed in developing and mature nociceptive neurons, playing a key role in their specification during neurogenesis and modulating pain sensation at adulthood. In vitro studies suggested that Prdm12 recruits the methyltransferase G9a through its zinc finger domains to regulate target gene expression, but how Prdm12 interacts with G9a and whether G9a plays a role in Prdm12's functional properties in sensory ganglia remain unknown. Here we report that Prdm12-G9a interaction is likely direct and that it involves the SET domain of G9a. We show that both proteins are largely co-expressed in dorsal root ganglia during early murine development, opening the possibility that G9a plays a role in DRG and may act as a mediator of Prdm12's function in the development of nociceptive sensory neurons. To test this hypothesis, we conditionally inactivated G9a in neural crest using a Wnt1-Cre transgenic mouse line. We found that the specific loss of G9a in the neural crest lineage does not lead to dorsal root ganglia hypoplasia due to the loss of somatic nociceptive neurons nor to the ectopic expression of the visceral determinant Phox2b as observed upon Prdm12 ablation. These findings suggest that Prdm12 function in the initiation of the nociceptive lineage does not critically involves its interaction with G9a.