Chicken transcription factor AP-2: cloning, expression and its role in outgrowth of facial prominences and limb buds.
Embryonic facial development in chick embryos involves a sequential activation of genes that control differential growth and patterning of the beak. In the present study we isolate one such gene, the transcription factor, AP-2, that is known to be expressed in the face of mouse embryos. The protein sequence of chick AP-2alpha is 94% homologous to human and mouse AP-2. Wholemount in situ hybridization with a probe for chick AP-2 identifies expression from primitive streak stages up to stage 28. The most striking expression patterns in the head are during neural crest cell migration when AP-2 transcripts follow closely the tracts previously mapped for neural crest cells. Later, expression in the facial mesenchyme is strongest in the frontonasal mass and lateral nasal prominences and is downregulated in the maxillary and mandibular prominences. Once limb buds are visible, high expression is seen in the distal mesenchyme but not in the apical ectodermal ridge. The expression patterns of AP-2 in stage 20 embryos suggested that the gene may be important in "budding out" of facial prominences and limb buds. We implanted beads soaked in retinoic acid in the right nasal pit of stage 20 embryos resulting in a specific inhibition of outgrowth of the frontonasal mass and lateral nasal prominences. AP-2 expression was completely down-regulated in the lateral nasal within 8 hr of bead application. In addition, the normal up-regulation of AP-2 in the frontonasal mass did not occur following retinoic-acid treatment. There was an increase in programmed cell death around the right nasal pit that accompanied the down-regulation of AP-2. Prominences whose morphogenesis were not affected by retinoic acid did not have altered expression patterns. We removed the apical ectodermal ridge in stage 20 limb buds and found that AP-2 expression was partially downregulated 4 hr following ridge removal and completely downregulated 8 hr following stripping. Application of an FGF-4 soaked bead to the apex of the limb bud maintained AP-2 expression. Thus AP-2 is involved in outgrowth and could be regulated by factors such as FGFs that are present in the ectoderm of both the face and limb.
Shen
H
H
Faculty of Dentistry, University of British Columbia, 2199 Wesbrook Mall, Vancouver, British Columbia, V6T 1Z3, Canada.
Wilke
T
T
Ashique
A M
AM
Narvey
M
M
Zerucha
T
T
Savino
E
E
Williams
T
T
Richman
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D002642:Chick Embryo; D002645:Chickens; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000502:physiology; D004627:Embryonic Induction; D005145:Face / Q000196:embryology*; D005147:Facial Bones / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D006801:Humans; D018878:Limb Buds / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D009420:Nervous System / Q000196:embryology; D011994:Recombinant Proteins / Q000096:biosynthesis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000096:biosynthesis* / Q000737:chemistry / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects; D014212:Tretinoin / Q000494:pharmacology; D014981:Xenopus; D029867:Xenopus Proteins
D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; C493673:TFAP2A protein, human; C493668:Tfap2a protein, mouse; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D029867:Xenopus Proteins; C493675:tfap2a protein, Xenopus; D014212:Tretinoin