Wendling O, Dennefeld C, Chambon P, Mark M
Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), CNRS/INSERM/ULP/Collège de France, BP 163, CU de Strasbourg, France.
Development. 2000 Apr;127(8):1553-62. doi: 10.1242/dev.127.8.1553.
The requirement of retinoic acid (RA) in the initial formation of the pharyngeal arches was investigated by treating headfold-stage mouse embryos with a pan-RAR antagonist in vitro and in vivo. This results in a complete absence of mesenchyme, arteries, nerves and epibranchial placodes of the 3rd and 4th pharyngeal arches, complete agenesis of the 3rd and 4th pouches and consistent lack of the 6th arch artery. Mesodermally derived endothelial cells are absent from the 3rd and 4th pharyngeal arch region and the distribution domain of EphA2 transcripts in mesodermal cells is shifted caudally. In situ hybridization with CRABPI, kreisler and EphA4 probes and the pattern of expression of a Wnt1-lacZ transgene show that neural crest cells (NCC) normally destined to the 3rd and 4th arches migrate ectopically. Most interestingly, the appearance of the 3rd and 4th arches is prevented by the antagonist only during a very narrow window of time, which does not correspond to the period of post-otic NCC migration. Both the timing of appearance and the nature of the defects in RAR antagonist-treated embryos indicate that migrating NCC and mesodermal cells destined to the caudal pharyngeal arches do not represent primary targets of RA action. Alterations in the endodermal expression pattern of Hoxa1, Hoxb1, Pax1, Pax9, Fgf3 and Fgf8 in response to the antagonist-induced block in RA signal transduction demonstrate for the first time that RA signaling is indispensable for the specification of the pharyngeal endoderm and suggest that this signaling is necessary to provide a permissive environment locally for the migration of NCC and mesodermal cells. Our study also indicates that the formation of the 2nd pharyngeal arch and that of the 3rd and 4th pharyngeal arches probably involve distinct RA-dependent developmental processes.
通过在体外和体内用泛RAR拮抗剂处理头褶期小鼠胚胎，研究了视黄酸（RA）在咽弓初始形成中的需求。这导致第三和第四咽弓的间充质、动脉、神经和鳃上板完全缺失，第三和第四咽囊完全发育不全，并且第六弓动脉持续缺失。第三和第四咽弓区域中没有中胚层来源的内皮细胞，并且EphA2转录本在中胚层细胞中的分布域向尾侧移动。用CRABPI、kreisler和EphA4探针进行原位杂交以及Wnt1-lacZ转基因的表达模式表明，正常情况下注定要进入第三和第四弓的神经嵴细胞（NCC）异位迁移。最有趣的是，拮抗剂仅在非常狭窄的时间窗口内阻止第三和第四弓的出现，这与耳后NCC迁移期不对应。RAR拮抗剂处理胚胎中缺陷的出现时间和性质都表明，迁移到尾侧咽弓的NCC和中胚层细胞不是RA作用的主要靶点。Hoxa1、Hoxb1、Pax1、Pax9、Fgf3和Fgf8在内胚层表达模式的改变，以响应拮抗剂诱导的RA信号转导阻滞，首次证明RA信号对于咽内胚层的特化是不可或缺的，并表明这种信号对于为NCC和中胚层细胞的迁移局部提供允许环境是必要的。我们的研究还表明，第二咽弓的形成以及第三和第四咽弓的形成可能涉及不同的RA依赖发育过程。
