University of Cambridge > > Evolution and Development Seminar Series > The development and evolution of vertebrate oxygen-sensing cells

The development and evolution of vertebrate oxygen-sensing cells

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When oxygen levels in the blood or surrounding air/water drop below a set point (hypoxia), oxygen-sensing cells release neurotransmitters to stimulate afferent glossopharyngeal and/or vagal nerve endings, triggering increased ventilation via the respiratory reflex. In amniotes, these comprise carotid body glomus cells and ‘pulmonary neuroendocrine cells’ in the lung airway epithelium. In anamniotes, they comprise ‘neuroepithelial cells’ (NECs) in the gill and orobranchial epithelia (including the lung epithelium of air-breathing ray-finned fishes, lobe-finned lungfishes and amphibians), plus the carotid labyrinth of amphibians. It is currently assumed that carotid body glomus cells, which are neural crest-derived and develop in association with the third pharyngeal arch artery, evolved from gill NECs, which also develop in association with pharyngeal arch arteries. However, this has never been tested. Using vital dye labelling, neural fold grafts, genetic lineage-tracing and analysis of zebrafish mutants lacking all neural crest cells, I show that the serotonergic NECs in the gill and orobranchial epithelia of zebrafish, frog and lamprey are not neural crest-derived, hence cannot be homologous to carotid body glomus cells. Instead, NECs are most likely homologous to pulmonary neuroendocrine cells, which are endoderm-derived. In neonatal mammals, neural crest-derived adrenal chromaffin cells are sensitive to hypoxia, and at least some hypoxia-responsive chromaffin cells persist in the adult. I propose that carotid body glomus cells evolved from scattered chromaffin cells associated with the large blood vessels of the pharyngeal arches, first reported a century ago in lamprey, whose existence we have confirmed by tyrosine hydroxylase expression.

This talk is part of the Evolution and Development Seminar Series series.

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