Laboratory for Early Embryogenesis, RIKEN Center for Developmental Biology, Kobe, Japan.
Dev Dyn. 2011 Jan;240(1):162-75. doi: 10.1002/dvdy.22520.
The chick, Gallus gallus, is the traditional model in avian developmental studies. Data on other bird species are scarce. Here, we present a comparative study of the embryonic development of the chick and the emu Dromaius novaehollandiae, a member of Paleognathae, which also includes the ostrich, rhea, tinamou, kiwi, and cassowary. Emu embryos ranging from Hamburger and Hamilton (HH) equivalent stages 1 to 43 were collected and their gross morphology analyzed. Its early development was studied in detail with time-lapse imaging and molecular techniques. Emu embryos in general take 2-3 times longer incubation time to reach equivalent chicken stages, requiring 1 day for HH2, 2.5 days for HH4, 7 days for limb bud initiation, 23 days for feather germ appearance, and approximately 50-56 days for hatching. Chordin gene expression is similar in emu and chick embryos, and emu Brachyury is not expressed until HH3. Circulation is established at approximately the 27- to 30-somite stage. Forelimb buds are formed and patterned initially, but their growth is severely retarded. The size difference between an emu and a chick embryo only becomes apparent after limb bud formation. Overall, emu and chick embryogenesis proceeds through similar stages, but developmental heterochrony between these two species is widely observed.
鸡（Gallus gallus）是禽类发育研究中的传统模式动物。其他鸟类的数据则较为匮乏。本研究比较了鸡和鸸鹋（Dromaius novaehollandiae）的胚胎发育。鸸鹋属于古颚总目，包括鸵鸟、美洲鸵、鹤鸵、几维鸟和食火鸡。我们收集了处于 Hamburger 和 Hamilton（HH）分期 1 到 43 期的鸸鹋胚胎并分析其大体形态，利用延时成像和分子技术详细研究了其早期发育过程。总体而言，鸸鹋胚胎孵化所需的时间比鸡长 2-3 倍，达到 HH2 期需要 1 天，HH4 期需要 2.5 天，肢芽起始需要 7 天，羽芽出现需要 23 天，孵化则需要 50-56 天。鸸鹋和鸡胚胎的 Chordin 基因表达相似，而 Brachyury 基因在 HH3 期才开始表达。血液循环大约在 27-30 体节阶段建立。前肢芽最初形成并开始模式化，但生长严重滞后。只有在肢芽形成后，鸸鹋和鸡胚胎的大小差异才变得明显。总体而言，鸸鹋和鸡的胚胎发生经历相似的阶段，但这两个物种的发育时程存在广泛的差异。
