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.
Proc Biol Sci. 2010 Nov 22;277(1699):3469-75. doi: 10.1098/rspb.2010.0811. Epub 2010 Jun 9.
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.
鸡的大脑在成年后比鹌鹑的大脑大两倍多。为了确定这种物种间大脑大小的差异是如何在发育过程中出现的，我们研究了神经发生时间或细胞周期率的差异是否解释了鸡和鹌鹑之间大脑大小的差异。具体来说，我们检查了用尼氏染色的鸡和鹌鹑胚胎切片中神经事件（如神经发生起始）的时间。我们使用累积溴脱氧尿苷标记法在鸡和鹌鹑的胚胎发育第 2 天（ED2）和第 5 天（ED5）来估计脑细胞周期率。我们报告说，一旦时间表示为整个孵育期的百分比，鸡和鹌鹑之间的神经事件时间高度保守。在绝对时间上，鸡的神经发生比鹌鹑更早开始。因此，神经事件的时间不能解释鸡脑相对于鹌鹑脑的扩张。在 ED5 时，两种物种的细胞周期率也相似。然而，在 ED2，神经发生开始之前，鸡的脑细胞比鹌鹑的脑细胞周期更快。这些数据表明，鸡的大脑比鹌鹑的大脑大，主要是因为在胚胎发育的早期阶段，鸡和鹌鹑之间的细胞周期率存在物种差异。
