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 <i>Spry1, 2</i>, and <i>4</i> from embryonic day 13 (E13) through postnatal day 7 (P7), but only trace amounts of <i>Spry1</i> and <i>2</i> in adult SMGs. More sensitive quantitative RT-PCR revealed that transcripts for all four <i>Spry</i> isoforms are expressed, and each shows individual patterns of variation across fetal and early postnatal stages, and that there are very low levels of <i>Spry1</i> and <i>2</i>, but no <i>Spry3</i> and <i>4</i>, in adult glands. EGF, FGF7 and FGF10 upregulate expression of mRNA for <i>Spry1</i>, but only FGF7 upregulates <i>Spry2</i> mRNA. EGF strongly induces an activating phosphorylation of all four <i>Spry</i> isoforms, but both FGFs do so only minimally. Quantitative RT-PCR of samples collected by laser capture microdissection showed that transcripts for <i>Spry1</i> are confined to the epithelium of E13 SMG rudiments. The isoform-specific temporal variation in the patterns of expression of <i>Spry1, 2, 3</i> and <i>4</i> 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.