Developmental changes in the carotid body transcriptome accompanying the maturation of chemosensitivity

The carotid body (CB) chemoreceptors mediate rapid cardiorespiratory reflexes to hypoxia, which mature peri-natally and are vital for fetal hypoxia tolerance and post-natal ventilatory control. This maturation is associated with an increase in the sensitivity of the CB electrophysiological response to hypoxia (chemosensitivity): a process that is incompletely understood but critical to systemic oxygen homeostasis. Hypothesizing that perinatal CB gene expression changes would reveal candidate mechanisms for oxygen chemosensitivity, we studied the CB transcriptome in sheep, where peri-natal CB physiology is well-characterised. CB-mediated cardiovascular reflexes are detectable at fetal day 120, and robust by term (day 145), while hypoxic ventilatory responses are established by post-natal day 15. We performed RNA sequencing on sheep CBs at each of these stages, and adults, along with the superior cervical ganglion (SCG) as an oxygen-insensitive control. This allowed us to define tissue-specific changes in the CB transcriptome correlating with chemosensitivity maturation. Striking, progressive CB enrichment is observed in genes implicated in murine CB chemosensitivity, including potassium channels (KCNK9), mitochondrial complex IV regulators (NDUFA4L2, HIGD1C), and HIF-2; (EPAS1). Genes with this expression pattern are also enriched for regulators of diacylglycerol (DAG), particularly the DAG kinase DGKH: one of the most abundant CB transcripts increasing in parallel with chemosensitivity. Across developmental stages, the CB also exhibits marked down-regulation of metabolic pathways and ATP/GTP consuming processes, potentially providing a state permissive to metabolic signal detection. Together, this builds a detailed picture of the CB transcriptional signature, with core features established in fetal life and conserved across species.