title: A set of stage-specific gene transcripts identified in EK stage X and HH stage 3 chick embryos.
abstract: BACKGROUND
  The embryonic developmental process in avian species is quite different from that in mammals. The first cleavage begins 4 h after fertilization, but the first differentiation does not occur until laying of the egg (Eyal-Giladi and Kochav (EK) stage X). After 12 to 13 h of incubation (Hamburger and Hamilton (HH) stage 3), the three germ layers form and germ cell segregation in the early chick embryo are completed. Thus, to identify genes associated with early embryonic development, we compared transcript expression patterns between undifferentiated (stage X) and differentiated (HH stage 3) embryos.
  
  
  RESULTS
  Microarray analysis primarily showed 40 genes indicating the significant changes in expression levels between stage X and HH stage 3, and 80% of the genes (32/40) were differentially expressed with more than a twofold change. Among those, 72% (23/32) were relatively up-regulated at stage X compared to HH stage 3, while 28% (9/32) were relatively up-regulated at HH stage 3 compared to stage X. Verification and gene expression profiling of these GeneChip expression data were performed using quantitative RT-PCR for 32 genes at developmental four points; stage X (0 h), HH stage 3 (12 h), HH stage 6 (24 h), and HH stage 9 (30 h). Additionally, we further analyzed four genes with less than twofold expression increase at HH stage 3. As a result, we identified a set of stage-specific genes during the early chick embryo development; 21 genes were relatively up-regulated in the stage X embryo and 12 genes were relatively up-regulated in the HH stage 3 embryo based on both results of microarray and quantitative RT-PCR.
  
  
  CONCLUSIONS
  We identified a set of genes with stage-specific expression from microarray Genechip and quantitative RT-PCR. Discovering stage-specific genes will aid in uncovering the molecular mechanisms involved the formation of the three germ layers and germ cell segregation in the early chick embryos.
authors.affiliation: Department of Food and Animal Biotechnology, Seoul National University, Seoul, Korea. mir88@snu.ac.kr <mir88@snu.ac.kr>
authors.forename: Bo Ram
authors.initials: BR
authors.lastname: Lee
authors.forename: Heebal
authors.initials: H
authors.lastname: Kim
authors.forename: Tae Sub
authors.initials: TS
authors.lastname: Park
authors.forename: Sunjin
authors.initials: S
authors.lastname: Moon
authors.forename: Seoae
authors.initials: S
authors.lastname: Cho
authors.forename: Taesung
authors.initials: T
authors.lastname: Park
authors.forename: Jeong Mook
authors.initials: JM
authors.lastname: Lim
authors.forename: Jae Yong
authors.initials: JY
authors.lastname: Han
mesh_terms: D000818:Animals; D002642:Chick Embryo / Q000196:embryology*; D047108:Embryonic Development / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D046228:Microarray Analysis; D005810:Multigene Family; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D015854:Up-Regulation