EVALUATION OF METANEPHRIC MATURATION IN A HUMAN FETAL KIDNEY EXPLANT MODEL

We have developed a unique human fetal kidney explant model to study t he role of the insulinlike growth factor (IGF) system in metanephric d evelopment. Kidneys from 10-18 nit gestation human abortuses were main tained in serum-free conditions and defined medium, which was shown to support the induction and differentiation of the viable metanephric b lastema. Histologically the tissue remained viable to 192 h of serum-f ree culture, while metanephric differentiation, reflected by a shrinki ng nephrogenic zone and the formation of maturing S-shape and glomerul ar forms, was accelerated and occurred between 48 and 96 h. In the nep hrogenic zone, a significant decrease in IGF-II gene expression occurr ed, which reflected the differentiation of tile metanephric blastema c ell mass. ICF-IT expression persisted, however, in the expanded inters titial mesenchyme. With differentiation over 48 h an increase in IGFBP -2 and WT1 gene expression by Northern blot analysis occurred, and was localized by in situ hybridization to the differentiating glomerular epithelial cell mass. Analysis of the explant-conditioned media by Wes tern ligand blot demonstrated an increase in the rate of IGF binding p rotein (IGFBP)-2 peptide production by the differentiating explant, co nsistent with an increase in IGFBP-2 gene expression and with metaneph ric differentiation. This pattern of temporal and spatial gene express ion closely approximates that of normal in vivo fetal renal developmen t and of glomerular epithelial cell differentiation.