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

含有Lhx基因的LIM-homeobox构成转录调控因子，在模式形成和细胞类型规范的控制中起关键作用。我们鉴定出鸡Lhx基因的两个基因，分别命名为Lhx6和L3/Lhx8，它们广泛表达于颅面区。全载原位杂交显示Lhx6和L3/Lhx8在14期至31期在上颌和下颌突的限制区域表达，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质。为了确定Lhx6和L3/Lhx8在上颌和下颌骨原基中的表达是否需要来自上覆口腔上皮的信号，我们将25期鸡胚胎上颌/下颌骨突移植到肢体芽中，在有或没有口腔上皮的情况下生长间充质。上颌和下颌骨间充质与上皮移植后，Lhx6和L3/Lhx8表达水平显著。Lhx6和L3/Lhx8在无上皮间质移植物中未见表达。为了进一步研究口腔上皮信号分子的分布，我们将Fgf-8或Tgf-β3浸泡过的头植入去上皮的上颌间充质移植物中。Tgf-β3微珠和Fgf-8诱导移植物中L3/Lhx8的表达。总的来说，我们的数据表明，Lhx6和L3/Lhx8在面部原基中的表达需要上皮-间质相互作用。Fgf-8和Tgf-β3可能调控上颌突的表达。

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.