EXPRESSION OF THE HELIX-LOOP-HELIX PROTEIN, ID, DURING BRANCHING MORPHOGENESIS IN THE KIDNEY

Id, a member of the helix-loop-helix protein family, is an inhibitor o f transcriptional activation by basic-helix-loop-helix proteins. In th e developing mouse kidney, Id mRNA was observed as early as 12.5 days post-coitum (dpc) specifically in the condensed mesenchyme surrounding the ureteric buds by in situ hybridization. At 14.5 dpc, Id mRNA was localized to the collecting tubules and developing glomeruli while the surrounding mesenchyme lacked Id hybridization. From birth to day 10 postnatal, Id mRNA is localized to the collecting tubules, immature gl omeruli and renal pelvis. In the adult kidney, Id mRNA was detectable by Northern blot analysis but no cell type-specific localization was n oted by in situ hybridization. These results indicate a role for HLH-b HLH proteins in the differentiation of the epithelial structures of th e kidney.