PRDM12 Is Transcriptionally Active and Required for Nociceptor Function Throughout Life

PR domain-containing member 12 (PRDM12) is a key developmental transcription factor in sensory neuronal specification and survival. Patients with rare deleterious variants in PRDM12 are born with congenital insensitivity to pain (CIP) due to the complete absence of a subtype of peripheral neurons that detect pain. In this paper, we report two additional CIP cases with a novel homozygous PRDM12 variant. To elucidate the function of PRDM12 during mammalian development and adulthood, we generated temporal and spatial conditional mouse models. We find that PRDM12 is expressed throughout the adult nervous system. We observed that loss of PRDM12 during mid-sensory neurogenesis but not in the adult leads to reduced survival. Comparing cellular biophysical nociceptive properties in developmental and adult-onset PRDM12 deletion mouse models, we find that PRDM12 is necessary for proper nociceptive responses throughout life. However, we find that PRDM12 regulates distinct age-dependent transcriptional programs. Together, our results implicate PRDM12 as a viable therapeutic target for specific pain therapies even in adults.

Nociceptor subtypes are born continuously over DRG development peaking at E10.5 - E11.5.

Sensory neurogenesis in the dorsal root ganglion (DRG) occurs in two waves of differentiation with larger, myelinated proprioceptive and low-threshold mechanoreceptor (LTMR) neurons differentiating before smaller, unmyelinated (C) nociceptive neurons. This temporal difference was established from early birthdating studies based on DRG soma cell size. However, distinctions in birthdates between molecular subtypes of sensory neurons, particularly nociceptors, is unknown. Here, we assess the birthdate of lumbar DRG neurons in mice using a thymidine analog, EdU, to label developing neurons exiting mitosis combined with co-labeling of known sensory neuron markers. We find that different nociceptor subtypes are born on similar timescales, with continuous births between E9.5 to E13.5, and peak births from E10.5 to E11.5. Notably, we find that thinly myelinated Aδ-fiber nociceptors and peptidergic C-fibers are born more broadly between E10.5 and E11.5 than previously thought and that non-peptidergic C-fibers and C-LTMRs are born with a peak birth date of E11.5. Moreover, we find that the percentages of nociceptor subtypes born at a particular timepoint are the same for any given nociceptor cell type marker, indicating that intrinsic or extrinsic influences on cell type diversity are occurring similarly across developmental time. Overall, the patterns of birth still fit within the classical ″two wave″ description, as touch and proprioceptive fibers are born primarily at E10.5, but suggest that nociceptors have a slightly broader wave of birthdates with different nociceptor subtypes continually differentiating throughout sensory neurogenesis irrespective of myelination.

Loss of Prdm12 during development, but not in mature nociceptors, causes defects in pain sensation

SummaryPrdm12 is as a key transcription factor in nociceptor neurogenesis. Mutations of Prdm12 cause Congenital Insensitivity to Pain (CIP) due to failure of nociceptor development. However, precisely how deletion of Prdm12 during development or adulthood affects nociception is unknown. Here, we employ tissue- and temporal-specific knockout mouse models to test the function of Prdm12 during development and in adulthood. We find that constitutive loss of Prdm12 causes deficiencies in proliferation during sensory neurogenesis. We also demonstrate that conditional knockout from dorsal root ganglia (DRGs) during embryogenesis causes defects in nociception. In contrast, we find that in adult DRGs, Prdm12 is dispensable for pain sensation and injury-induced hypersensitivity. Using transcriptomic analysis, we found unique changes in adult Prdm12 knockout DRGs compared to embryonic knockout, and that PRDM12 is likely a transcriptional activator in the adult. Overall, we find that the function of PRDM12 changes over developmental time.

Neuroblast sensory quiescence depends of vascular cytoneme contacts and sensory neuronal differentiation requires initiation of blood flow

SummaryIn many organs, stem cell function depends on the communication with their niche partners. Cranial sensory neurons develop in close proximity to blood vessels, however whether vasculature is an integral component of their niches is yet unknown. Here, two separate, novel roles for vasculature in cranial sensory neurogenesis in zebrafish are uncovered. The first involves precise spatiotemporal endothelial-neuroblast cytoneme contacts and Dll4-Notch signalling to restrain neuroblast proliferation. Secondly, we find that blood flow onset triggers a transcriptional response to modify neuroblast metabolic status and is required for sensory neuron differentiation. In contrast, no role of sensory neurogenesis in vascular development is found, suggesting a unidirectional signalling from vasculature to sensory neuroblasts. Altogether, we demonstrate that the cranial vasculature constitutes a hitherto unrecognized niche component of the sensory ganglia that regulates the pace of their growth and differentiation dynamics.Highlights♦ Vasculature is part of the cranial sensory ganglia niche and regulates neurogenesis.♦ Cytoneme contacts between endothelial cells and sensory neuroblasts are required for neuroblast quiescence.♦ Endothelial Dll4 and neuroblast Notch1 signal to regulate the growth of cranial sensory ganglia.♦ Initiation of blood flow triggers a transcriptional metabolic switch and sensory neuronal differentiation.