title: Embryonic development of the emu, Dromaius novaehollandiae.
abstract: 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.
authors.affiliation: Laboratory for Early Embryogenesis, RIKEN Center for Developmental Biology, Kobe, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nagai
authors.forename: Siu-Shan
authors.initials: SS
authors.lastname: Mak
authors.forename: Wei
authors.initials: W
authors.lastname: Weng
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Nakaya
authors.forename: Raj
authors.initials: R
authors.lastname: Ladher
authors.forename: Guojun
authors.initials: G
authors.lastname: Sheng
mesh_terms: D000818:Animals; D048429:Cell Size; D002642:Chick Embryo; D003001:Cloning, Molecular; D020312:Dromaiidae / Q000196:embryology* / Q000235:genetics; D004625:Embryo, Nonmammalian; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology*; D005326:Fetal Proteins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D050437:Genes, Developmental; D006023:Glycoproteins / Q000235:genetics; D053823:Hedgehog Proteins / Q000235:genetics; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D019170:Somites / Q000196:embryology / Q000254:growth & development; D020825:T-Box Domain Proteins / Q000235:genetics; D059008:Time-Lapse Imaging; D015053:Zygote / Q000166:cytology / Q000254:growth & development; D000098908:Brachyury Protein
chemical_list: D005326:Fetal Proteins; D006023:Glycoproteins; D053823:Hedgehog Proteins; D036341:Intercellular Signaling Peptides and Proteins; D020825:T-Box Domain Proteins; D000098908:Brachyury Protein; C054234:chordin