Phox2b mutation mediated by Atoh1 expression impaired respiratory rhythm and ventilatory responses to hypoxia and hypercapnia
Retrotrapezoid nucleus (RTN) neurons are involved in central chemoreception and respiratory control. Lineage tracing studies demonstrate RTN neurons to be derived from Phox2b and Atoh1 expressing progenitor cells in rhombere 4. Phox2b exon 3 mutations cause congenital central hypoventilation syndrome (CCHS), producing an impaired respiratory response to hypercapnia and hypoxia. Our goal was to investigate the extent to which a conditional mutation of Phox2b within Atoh1-derived cells might affect a) respiratory rhythm; b) ventilatory responses to hypercapnia and hypoxia and c) number of RTN-chemosensitive neurons. Here, we used a transgenic mouse line carrying a conditional Phox2b{Delta}8 mutation activated by cre-recombinase. We crossed them with Atoh1Cre mice. Ventilation was measured by whole body plethysmograph during neonate and adult life. In room air, experimental and control groups showed similar basal ventilation; however, Atoh1Cre/Phox2b{Delta}8 increased breath irregularity. The hypercapnia and hypoxia ventilatory responses were impaired in neonates. In contrast, adult mice recovered ventilatory response to hypercapnia, but not to hypoxia. Anatomically, we observed a reduction of the Phox2b+/TH- expressing neurons within the RTN region. Our data indicates that conditionally expression of Phox2b mutation by Atoh1 affect development of the RTN neurons and are essential for the activation of breathing under hypoxic and hypercapnia condition, providing new evidence for mechanisms related to CCHS neuropathology.