Expression of Flrt2 in the midface during early embryogenesis

Background: Development of the midface during embryogenesis involves differential expression of growth factors between midfacial processes or growth factor signalling from the epithelium to underlying mesenchyme of independent processes. Fibronectin-like transmembrane protein 2 (Flrt2) has been shown to be expressed differentially between the medial and lateral nasal prominences (MNP and LNP) using microarray and reverse transcriptase (RT)-PCR (Gong, unpublished). FLRT2 has also been shown in vitro to interact with FGFR2 (Gong, unpublished), a receptor for FGF, a key regulator in tissue differentiation and development. These results suggest that Flrt2 is involved in midfacial patterning. Objectives: To determine the expression pattern of Flrt2 during early embryogenesis. Methods: In situ hybridization (ISH) was used to characterize Flrt2 expression in the midfacial region in 9.5-15.5dpc mouse embryos using whole mount murine embryos and/or sections of the craniofacial region. Results: Whole mount and section ISH data demonstrated that Flrt2 was expressed in the mesenchyme of the MNP from 9.5-12.5dpc. Epithelial expression of Flrt2 was observed in a distinct region of the inner MNP at 10.5dpc, which is the site for the developing vomeronasal organ. From 13.5-15.5dpc, Flrt2 was expressed in the medial region of the midface in the developing nasal septum and secondary palate. Flrt2 was also expressed in the developing tooth buds, hair follicles, tongue, and eye. Conclusion: Microarray, RT-PCR, and ISH results suggest that Flrt2 may be essential in midfacial outgrowth and patterning. Further experimentation is required to determine the function of FLRT2 during embryogenesis.