Evaluation of metanephric maturation in a human fetal kidney explant model.

We have developed a unique human fetal kidney explant model to study the role of the insulin-like growth factor (IGF) system in metanephric development. Kidneys from 10-18 wk gestation human abortuses were maintained in serum-free conditions and defined medium, which was shown to support the induction and differentiation of the viable metanephric blastema. Histologically the tissue remained viable to 192 h of serum-free culture, while metanephric differentiation, reflected by a shrinking nephrogenic zone and the formation of maturing S-shape and glomerular forms, was accelerated and occurred between 48 and 96 h. In the nephrogenic zone, a significant decrease in IGF-II gene expression occurred, which reflected the differentiation of the metanephric blastema cell mass, IGF-II expression persisted, however, in the expanded interstitial 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 Western ligand blot demonstrated an increase in the rate of IGF binding protein (IGFBP)-2 peptide production by the differentiating explant, consistent with an increase in IGFBP-2 gene expression and with metanephric differentiation. This pattern of temporal and spatial gene expression closely approximates that of normal in vivo fetal renal development and of glomerular epithelial cell differentiation.