Shen H, Wilke T, Ashique A M, Narvey M, Zerucha T, Savino E, Williams T, Richman J M
Faculty of Dentistry, University of British Columbia, 2199 Wesbrook Mall, Vancouver, British Columbia, V6T 1Z3, Canada.
Dev Biol. 1997 Aug 15;188(2):248-66. doi: 10.1006/dbio.1997.8617.
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.
鸡胚的胚胎面部发育涉及一系列基因的激活，这些基因控制着喙的差异生长和形态形成。在本研究中，我们分离出了一个这样的基因，即转录因子AP - 2，已知它在小鼠胚胎的面部表达。鸡AP - 2α的蛋白质序列与人类和小鼠的AP - 2有94%的同源性。用鸡AP - 2探针进行全胚胎原位杂交，可鉴定出从原条期到第28期的表达情况。头部最显著的表达模式出现在神经嵴细胞迁移期间，此时AP - 2转录本紧密跟随先前为神经嵴细胞绘制的路径。后来，面部间充质中的表达在额鼻突和外侧鼻突中最强，在上颌突和下颌突中表达下调。一旦肢芽可见，在远端间充质中可见高表达，但在顶端外胚层嵴中未见表达。第20期胚胎中AP - 2的表达模式表明，该基因可能在面部突起和肢芽的“萌芽”过程中起重要作用。我们将浸泡在视黄酸中的珠子植入第20期胚胎的右侧鼻凹，导致额鼻突和外侧鼻突的生长受到特异性抑制。在应用珠子后8小时内，外侧鼻中AP - 2的表达完全下调。此外，视黄酸处理后，额鼻突中AP - 2的正常上调并未发生。在右侧鼻凹周围，程序性细胞死亡增加，同时伴随着AP - 2的下调。形态发生不受视黄酸影响的突起，其表达模式没有改变。我们切除了第20期肢芽的顶端外胚层嵴，发现切除嵴后4小时，AP - 2表达部分下调，切除8小时后完全下调。将浸泡有FGF - 4的珠子应用于肢芽顶端可维持AP - 2的表达。因此，AP - 2参与生长，并且可能受面部和肢体外胚层中存在的FGF等因子的调节。
