DIFFERENTIAL EXPRESSION OF 5 LAMININ ALPHA-(1-5) CHAINS IN DEVELOPINGAND ADULT-MOUSE KIDNEY

The nature of the laminin a chains in the embryonic and adult kidney i s still being debated. The present study attempted to clarify this iss ue by immunofluorescence study using monoclonal antibodies against mou se alpha 1, alpha 2, and alpha 5 chains and in situ hybridization for the alpha 2, alpha 3B, alpha 4, and alpha 5 mRNAs. Novel alpha 1 chain -specific monoclonal antibodies against E8 fragment revealed a restric ted distribution of alpha 1 chain in a subset of epithelial basement m embranes in the embryo, in agreement with previous mRNA data. The alph a 2 mRNA was produced by mesenchyme, although the protein was deposite d in epithelial basement membranes. The alpha 3B mRNA was found only i n a small subset of endothelial cells. The alpha 4 mRNA was found tran siently in embryonic mesenchyme, with particularly high levels in cond ensed mesenchyme, close to the tips of the ureteric tree where tubulog enesis is initiated. The alpha 5 mRNA was strongly expressed by ureter epithelium but not expressed at early stages of tubulogenesis. Immuno fluorescence verified low levels of the alpha 5 chain in the early sta ges of tubulogenesis. However, during the capillary loop stage, the al pha 5 chain became strongly expressed in the developing glomerular bas ement membrane, which matches the in situ hybridization results. Durin g subsequent maturation of the kidney, the alpha 5 chain became ubiqui tously expressed in basement membranes. Overall, the alpha 5 chain exh ibited the broadest pattern of expression, followed by the alpha 1 cha in, particularly in the adult stage. These chains were the only ones p roduced by epithelial cells. Although some basement membranes containe d several alpha chains, we failed to detect any of the five studied ch ains in some basement membranes. Thus, the identity of the alpha chain s of many embryonic kidney blood vessels and several basement membrane s in the inner medulla in the developing and adult kidney remain uncle ar. (C) 1997 Wiley-Liss, Inc.