Laminin α1 chain G domain peptide, RKRLQVQLSIRT, inhibits epithelial branching morphogenesis of cultured embryonic mouse submandibular gland

Active sequences from the laminin α1 and α2 chain carboxyl-terminal globular domains (G domain) have been identified by screening overlapping synthetic peptides in a number of biological assays (Nomizu et al. [1995] J. Biol. Chem. 270:20583–20590; Nomizu et al. [1996] FEBS Lett. 396:37–42). We have tested the activity of these peptides in submandibular gland explants of embryonic day 13 mice to determine the functional sites involved in organ development. The laminin α1 chain peptide, RKRLQVQLSIRT (residues 2719–2730 and designated AG-73), significantly inhibited epithelial branching morphogenesis. In contrast, other cell adhesive laminin α1 chain peptides including the AASIKVAVSADR and NRWHSIYITRFG failed to inhibit the branching. MG-73, a homologue of AG-73 from the laminin α2 chain, did not inhibit the branching. The α2 chain peptide had no effect, which may be due to the low levels of this laminin chain in day 13 mice. Laminin α2 chain-specific monoclonal antibodies strongly reacted with the basement membranes of developed acini but only weakly stained embryonic day 13 submandibular epithelium. The expression of E-cadherin and α6 integrin, as detected by immunofluorescence, were unchanged in both AG-73 and control scramble peptide-treated epithelial cells of the explants. In contrast, immunostaining of nidogen/entactin showed that explants treated with AG-73 for 3 days had a discontinuous basement membrane. Explants treated for 3 days with control peptide showed a normal basement membrane. These results suggest that the region containing the AG-73 sequence of the laminin α1 chain is crucial for development of submandibular gland at early embryonic stages. The discontinuous basement membrane in AG-73-treated explants may indicate an important role for this region in basement membrane assembly. Dev. Dyn. 1998;212:394–402. © 1998 Wiley-Liss, Inc.