Role of LIM homeobox genes, Lhx6 and L3/Lhx8 in maxillary and mandibular development in chick embryo

含LIM同源框（Lhx）基因构成转录调节因子，在控制模式形成和细胞类型特化中起关键作用。我们已经确定了两个基因的鸡Lhx基因，命名为Lhx 6和L3/Lhx 8，这是广泛表达的颅面区域。整体原位杂交显示Lhx 6和L3/Lhx 8在第14 - 31期的上颌和下颌突的限制性区域表达，而在额鼻肿块中不表达。冷冻切片显示这些信号在上皮下的间充质中。为了确定Lhx 6和L3/Lhx 8在上颌骨和下颌骨原基中的表达是否需要来自覆盖的口腔上皮的信号，进行了将第25阶段鸡胚上颌骨/下颌骨突移植到肢芽中，其中间充质在口腔上皮存在或不存在的情况下生长。Lhx 6和L3/Lhx 8在上颌骨和下颌骨间充质与上皮移植物中表达显著。无上皮间充质移植物中Lhx 6和L3/Lhx 8仍无表达。为了进一步研究口腔上皮细胞中信号分子的分布，将浸泡有Fgf-8或TGF-β3的磁珠植入去除上皮的上颌间充质移植物中。TGF-β3珠以及Fgf-8诱导移植物中L3/Lhx 8的表达。总之，我们的数据表明，Lhx 6和L3/Lhx 8在面部原基的表达需要上皮间质相互作用。FGF-8和TGF-β3可能参与调控上颌骨突起的表达。

LIM-homeobox containing (Lhx) genes constitute transcriptional regulators that play critical roles in the control of pattern formation and cell type specification. We have identified two genes of chicken Lhx genes, designated Lhx6 and L3/Lhx8, which were widely expressed in the craniofacial region. Whole-mount in situ hybridization showed Lhx6 and L3/Lhx8 were expressed from Stage 14 to 31 in restrict domains of the maxillary and mandibular processes but not in the frontonasal mass. Frozen sections revealed these signals in the mesenchyme underneath the epithelium. To determine whether the expression of Lhx6 and L3/Lhx8 in the maxilla and mandibular primordia requires signals from the overlying oral epithelium, transplant of Stage 25 chick embryo maxilla/mandibular process into the limb bud was performed in which the mesenchyme was grown in the presence or absence of oral epithelium. The grafts of maxilla and mandibular mesenchyme with the epithelium resulted in significant levels of Lhx6 and L3/Lhx8 expressions. No expression of Lhx6 and L3/Lhx8 was still shown in those grafts of epithelium-free mesenchyme. In order to further examine the distribution of signaling molecules from oral epithelium, soaked bead in Fgf-8 or Tgf-β3 was implanted into either maxillary mesenchymal graft from which the epithelium had been removed. Tgf-β3 beads as well as Fgf-8 induced expressions of L3/Lhx8 in the grafts. Overall our data suggested that expression of Lhx6 and L3/Lhx8 in the facial primordia required the epithelial-mesenchymal interactions. Fgf-8 and Tgf-β3 may be capable of regulating the expression in the maxillary processes.