Neonatal Apneic Phenotype In A Murine Congenital Central Hypoventilation Syndrome Model Is Induced Through Non-Cell Autonomous Developmental Mechanisms

Congenital central hypoventilation syndrome (CCHS) represents a rare genetic disorder usually caused by mutations in the homeodomain transcription factorPHOX2B. Some CCHS patients suffer mainly from deficiencies in CO(2)and/or O(2)respiratory chemoreflex, whereas other patients present with full apnea shortly after birth. Our goal was to identify the neuropathological mechanisms of apneic presentations in CCHS. In the developing murine neuroepithelium,Phox2bis expressed in three discrete progenitor domains across the dorsal-ventral axis, with different domains responsible for producing unique autonomic or visceral motor neurons. Restricting the expression of mutantPhox2bto the ventral visceral motor neuron domain induces marked newborn apnea together with a significant loss of visceral motor neurons, RTN ablation, andpreBotzingercomplex dysfunction. This finding suggests that the observed apnea develops through non-cell autonomous developmental mechanisms. MutantPhox2bexpression in dorsal rhombencephalic neurons did not generate significant respiratory dysfunction, but did result in subtle metabolic thermoregulatory deficiencies. We confirm the expression of a novel murinePhox2bsplice variant which shares exons 1 and 2 with the more widely studiedPhox2bsplice variant, but which differs in exon 3 where most CCHS mutations occur. We also show that mutantPhox2bexpression in the visceral motor neuron progenitor domain increases cell proliferation at the expense of visceral motor neuron development. We propose that visceral motor neurons may function as organizers of brainstem respiratory neuron development, and that disruptions in their development result in secondary/non-cell autonomous maldevelopment of key brainstem respiratory neurons.