Ontogeny of central rhythm generation in chicks and rodents.
Recent studies help in understanding how the basic organization of brainstem neuronal circuits along the anterior-posterior (AP) axis is set by the Hox-dependent segmentation of the neural tube in vertebrate embryos. Neonatal respiratory abnormalities in Krox20(-/-), Hoxa1(-/-) and kreisler mutant mice indicate the vital role of a para-facial (Krox20-dependent, rhombomere 4-derived) respiratory group, that is distinct from the more caudal rhythm generator called Pre-Bötzinger complex. Embryological studies in the chick suggest homology and conservation of this Krox20-dependent induction of parafacial rhythms in birds and mammals. Calcium imaging in embryo indicate that rhythm generators may derive from different cell lineages within rhombomeres. In mice, the Pre-Bötzinger complex is found to be distinct from oscillators producing the earliest neuronal activity, a primordial low-frequency rhythm. In contrast, in chicks, maturation of the parafacial generator is tightly linked to the evolution of this primordial rhythm. It seems therefore that ontogeny of brainstem rhythm generation involves conserved processes specifying distinct AP domains in the neural tube, followed by diverse, lineage-specific regulations allowing the emergence of organized rhythm generators at a given AP level.
Chatonnet
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F
UPR 2216, Neurobiologie Génétique et Integrative, Institut fédératif de Neurobiologie Alfred Fessard, C.N.R.S. 1, Avenue de la terrasse, Gif sur Yvette, 91198 Cedex, France.
Borday
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C
Wrobel
L
L
Thoby-Brisson
M
M
Fortin
G
G
McLean
H
H
Champagnat
J
J
D000818:Animals; D005075:Biological Evolution; D002645:Chickens / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D051767:Early Growth Response Protein 2 / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018398:Homeodomain Proteins / Q000378:metabolism; D012125:Respiratory Center / Q000254:growth & development / Q000502:physiology*; D012377:Rodentia / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D000099261:Homeobox A1 Protein
D051767:Early Growth Response Protein 2; D018398:Homeodomain Proteins; D014157:Transcription Factors; D000099261:Homeobox A1 Protein