Differential expression of the laminin A and B chains in chimeric kidneys.

The expression of laminin in embryonic kidneys growing in ovo is followed with mouse-specific, affinity-purified antibodies against the laminin A and B chains. In mouse kidneys growing on the chicken chorioallantoic membrane, the epithelium and nephrogenic mesenchyme are derived from mouse and the vasculature from chicken chorioallantoic vessels. Hence, with the mouse-specific antibodies, it is possible to analyze the deposition of laminin chains by the nephrogenic tissue, because laminin derived from the chicken vasculature remains unstained. In these chimeras, only the laminin B chain, but not the A chain, is expressed in the undifferentiated nephrogenic mesenchyme. The basement membrane around the ureter bud is labeled by the antibodies against both laminin A and B chains. In the mesenchyme, the laminin A chain appears when the mesenchyme converts into tubules. The results suggest that the laminin A and B chains are synthesized differentially in the embryonic nephrogenic tissue.