L3/Lhx8 Expression on Upper Lip Development in Chick Embryo

Objectives: L3/Lhx8, a member of LIM-homeobox domain family of transcription factors, is implicated in the control of pattern formation and cell type specification. We have ever identified a chicken L3/Lhx8 gene, which was widely expressed in the craniofacial region. The purpose of this study was to investigate the L3/Lhx8 expression during upper lip development. Methods: Maxillary mesenchyme of chick embryo was dissected and the total RNA was analyzed with RT-PCR. To explore signaling molecules responsible for L3/Lhx8 induction, the dissected mesenchyme was transplanted into the host limb buds in the presence or absence of oral epithelium. We applied Affi-gel beads soaked in Fgf-8b or TGF-β3 to the graft. The embryos were processed for in situ hybridization of whole-mount and the frozen tissue sections. Results: Whole-mount in situ hybridization showed that L3/Lhx8 mRNA was expressed from Stage 15 to 31 in overlapping domains of the maxillary and mandibular processes but not in the frontonasal mass. These signals were detected in the mesenchyme underneath the oral epithelium. Significant level of the expression gradually increased from Stage 27 to 31. Application of Fgf-8b and TGF-β3 induced expression of L3/Lhx8 in the epithelium-free mesenchymal grafts which showed no expression of L3/Lhx8. Conclusions: Our data suggested that the L3/Lhx8 gene contributes to epithelial mesenchymal interaction during upper lip formation and that Fgf-8b and TGF-β3 were, in part, responsible for the L3/Lhx8 expression in the maxillary process. This study was supported by Grants-in-Aid from JSPS #17592143 and Scientific Research on Priority Areas-Advanced Brain Science Project.