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The cellular distribution of angiotensin II type 1 (AT1) and type 2 (AT2) receptor mRNA was examined in mouse kidneys at several embryonic stages (12 to 18 days; 19 days = full term) and up to three weeks after birth by in situ hybridization. The expression of both AT1 and AT2 mRNAs appeared simultaneously at 14 days of gestation. However, their distributions were contrasting: AT1 mRNA was expressed in mature glomeruli and maturing S-shaped bodies throughout the stages examined. AT1 expression was also detected at 16 days of gestation in the proximal and distal tubules and peaked at the end of gestation. Both the temporal and spatial expression of AT1 coincide with the differentiation and proliferation of glomerular mesangial and tubular cells during nephrogenesis. In contrast, AT2 mRNA was present only in the mesenchymal cells adjacent to the stalk of the ureter bud at early developmental stages, and, later, extended to the mesenchymal cells located near, but outside, the nephrogenic area of superficial cortex and also the cells between collecting ducts. AT2 expression in these regions decreased markedly within three weeks after birth. Temporally and spatially, AT2 mRNA expression coincides with the epithelial-mesenchymal interactions that take place during early phases of nephrogenesis. The site of AT2 expression also overlaps closely with that of a specific group of cells which undergo apoptosis following nephrogenesis. Thus, contrary to current belief, the activation of AT1 and AT2 genes takes place in different cell types of the kidney during embryonic development, and thereby conceivably contributes to the ontogeny of those specific renal cells.