Bigger brains cycle faster before neurogenesis begins: a comparison of brain development between chickens and bobwhite quail.
The chicken brain is more than twice as big as the bobwhite quail brain in adulthood. To determine how this species difference in brain size emerges during development, we examined whether differences in neurogenesis timing or cell cycle rates account for the disparity in brain size between chickens and quail. Specifically, we examined the timing of neural events (e.g. neurogenesis onset) from Nissl-stained sections of chicken and quail embryos. We estimated brain cell cycle rates using cumulative bromodeoxyuridine labelling in chickens and quail at embryonic day (ED) 2 and at ED5. We report that the timing of neural events is highly conserved between chickens and quail, once time is expressed as a percentage of overall incubation period. In absolute time, neurogenesis begins earlier in chickens than in quail. Therefore, neural event timing cannot account for the expansion of the chicken brain relative to the quail brain. Cell cycle rates are also similar between the two species at ED5. However, at ED2, before neurogenesis onset, brain cells cycle faster in chickens than in quail. These data indicate that chickens have a larger brain than bobwhite quail mainly because of species differences in cell cycle rates during early stages of embryonic development.
100 Qureshey Research Laboratory, Department of Neurobiology and Behavior and Center for the Neurobiology of Learning and Memory, University of California, Irvine, CA 92697, USA. charvetcj@gmail.com
Christine J
CJ
Charvet
Georg F
GF
Striedter
D000818:Animals; D015415:Biomarkers; D001921:Brain / Q000254:growth & development*; D002453:Cell Cycle; D002642:Chick Embryo; D002645:Chickens / Q000254:growth & development*; D003088:Colinus / Q000196:embryology / Q000254:growth & development*; D055495:Neurogenesis / Q000235:genetics / Q000502:physiology*; D013045:Species Specificity
D015415:Biomarkers