EPIDERMAL GROWTH-FACTOR SYSTEM IS A PHYSIOLOGICAL REGULATOR OF DEVELOPMENT OF THE MOUSE FETAL SUBMANDIBULAR-GLAND AND REGULATES EXPRESSION OF THE ALPHA-6-INTEGRIN SUBUNIT

Epidermal growth factor (EGF) and transforming growth factor-alpha (TG F-alpha) regulate branching morphogenesis of fetal mouse submandibular gland (SMG) rudiments in vitro, The EGF system (EGF, TGF-alpha, and t heir shared receptor, EGFR) also regulates expression of integrins and their ligands in the extracellular matrix, We show here that inhibiti on of EGFR tyrosine-kinase activity by a tyrphostin retards in vitro d evelopment of SMGs. Using total RNA isolated from pooled SMGs taken fr om intact mouse fetuses, mRNA transcripts for EGF, TGF-alpha, and EGFR were detected by reverse transcription-polymerase chain reaction (RT- PCR), and age-dependent variations in the levels of these mRNA were qu antitatively determined by nuclease protection assays, These findings suggest that the EGF system is operative in the in vivo development of this gland, alpha 6-Integrin subunit was localized by immunofluoresce nce at the basal surface of epithelial cells, Branching morphogenesis of cultured SMG rudiments was inhibited by anti-alpha 6 antibodies, Sy nthesis of alpha 6-subunit in cultured SMGs, detected by metabolic lab eling and immunoprecipitation, was increased by EGF and drastically re duced by tyrphostin, RT-PCR revealed that mRNAs for alpha 6- and beta 1- and beta 4-integrin subunits are expressed at all ages between embr yonic day 13 and postnatal day 7, These findings suggest that 1) the E GF system is a physiologic regulator of development of fetal mouse SMG , and 2) one mechanism by which it acts may be by regulating expressio n of integrins, which in turn control interaction of epithelial cells with the extracellular matrix. (C) 1997 Wiley-Liss, Inc.