Our in vivo experiment delivers CO2 in a physiological context, and indicates that proper localization of the RTN to the highly vascularized ventral brainstem surface (where chemosensitive Dabrafenib concentration astrocytes reside) ( Gourine et al., 2010) is critical for adult chemoresponsiveness. Whether the blunted chemosensitivity in the adult mouse is due to cell-autonomous deficits in RTN neurons and/or their displacement away from the ventral surface vascular bed and chemosensitive astrocytes is unknown. Furthermore, it is interesting to note that adult mice conditionally expressing the CCHS-causing PHOX2B mutation in the Egr-2 domain also show a partially impaired

hypercapnic response and hypersensitivity to hypoxia due to increased synaptic input from the carotid bodies ( Ramanantsoa et al., 2011). This crosstalk between central and peripheral chemosensory systems warrants further investigation, as disturbance in blood gas homeostasis and failure to arouse from sleep are serious detriments to health. Several bHLH transcription factors have emerged as disease-defining genes or genetic modifiers for neonatal respiratory disorders. Mutations in the transcription factor 4 (TCF4, an Atoh1-interacting bHLH factor) cause Pitt-Hopkins syndrome, which manifests SCH-900776 with infantile-onset hyperventilation ( Amiel et al., 2007). Heterozygous nucleotide substitutions

in human achaete-scute homolog-1 of CCHS patients have been uncovered and might impair noradrenergic neural development Cytidine deaminase ( de Pontual et al., 2003). Both TCF4 and achaete-scute homolog-1 null mice die during the newborn period because of unknown breathing and feeding defects ( Guillemot et al., 1993; Zhuang et al., 1996). In light of these dramatic phenotypes, studying conditional mutants of these bHLH factors will facilitate the identification of additional neuronal structures that ensure proper respiratory activity in the

early postnatal life. In sum, we provide direct evidence that the expression of Atoh1 in the postmitotic RTN neurons during fetal hindbrain development serves as an intrinsic signal that guides proper neuronal migration and projection, which is a critical step to stimulate inspiratory rhythm at birth. Selective loss of paramotor Atoh1 expression compromises neonatal breathing and adult hypercapnic response. These findings provide an example of how transient expression of a bHLH transcription factor shapes the physiological function of postmitotic neurons and provide insights into the developmental assembly of respiratory network that might be altered in neonatal respiratory disorders. Moreover, these data suggest that early developmental abnormalities, if survived, have an impact on physiological responses and respiratory health in adults. Animal housing, husbandry, and euthanasia were conducted under the guidelines of the Center for Comparative Medicine, Baylor College of Medicine.