Regulation of Expression of Sprouty Isoforms by EGF, FGF7 or FGF10 in Fetal Mouse Submandibular Glands

Abstract

Branching morphogenesis of the fetal mouse submandibular gland (SMG) is regulated by signaling through the ErbB and FGF families of tyrosine kinase receptors, whose members activate the ERK-1/2 pathway. The four Sprouty (Spry) proteins are inhibitory modulators of ERK-1/2. There is little information on their expression during pre- and postnatal development of the SMG. Qualitative RT-PCR detected mRNAs for Spry1, 2, and 4 from embryonic day 13 (E13) through postnatal day 7 (P7), but only trace amounts of Spry1 and 2 in adult SMGs. More sensitive quantitative RT-PCR revealed that transcripts for all four Spry isoforms are expressed, and each shows individual patterns of variation across fetal and early postnatal stages, and that there are very low levels of Spry1 and 2, but no Spry3 and 4, in adult glands. EGF, FGF7 and FGF10 upregulate expression of mRNA for Spry1, but only FGF7 upregulates Spry2 mRNA. EGF strongly induces an activating phosphorylation of all four Spry isoforms, but both FGFs do so only minimally. Quantitative RT-PCR of samples collected by laser capture microdissection showed that transcripts for Spry1 are confined to the epithelium of E13 SMG rudiments. The isoform-specific temporal variation in the patterns of expression of Spry1, 2, 3 and 4 suggests a potentially important role for these negative modulators of growth-factor driven ras/ERK-1/2 signaling at stages when the SMG is most actively undergoing branching morphogenesis.