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UBC Theses and Dissertations

Epithelium is required for maintaining FGFR-2 expression levels in facial Mesenchyme of the developing chick embryo Matovinovic, Elizabeth


In the developing chick embryo, FGFR-2 expression patterns correlate with outgrowth of facial prominences: frontonasal mass prominences which form the prenasal cartilage and upper beak express high levels of FGFR-2 receptor while maxillary prominences which form the flattened corners of the beak and palatal shelves express low FGFR-2 transcript levels. Facial epithelium is an abundant source of FGFs and is required to support outgrowth of mesenchymal tissue including cartilage rod formation. Since FGFR-2 is highly expressed in regions of facial outgrowth and epithelium is required for outgrowth of facial prominences, epithelium could be required to maintain FGFR-2 transcripts in facial mesenchyme. To test this hypothesis, we removed epithelium to inhibit outgrowth of regions of the embryonic face, grafted frontonasal mass and maxillary prominences into a host limb bud and then examined changes in FGFR-2 expression using in situ hybridization. We also hybridized adjacent sections with collagen II probe to identify regions undergoing chondrogenesis. Our results indicate that removal of epithelium from frontonasal mass lead to a decrease in FGFR-2 and collagen II expression 24 hours after grafting to host and that neither FGFR-2 nor collagen II expression increased to expected levels at 48 hours. These results suggest that there are signals in the epithelium required for increasing FGFR-2 and collagen II gene transcription and the expression of these genes are linked to outgrowth of facial prominences. We localized FGF8 transcripts in the developing chick face to determine whether FGF8 is a putative epithelial signal required for FGFR-2 expression. Our results indicate that FGF8 ectodermal expression does not overlap FGFR-2 expression in mesenchymal tissue and therefore is not a signal required for the expression of this receptor.

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