Spatial and temporal expression of kallikrein and its mRNA during nephron maturation

To determine the relationships between nephron maturation and the ontogeny of intrarenal kallikrein, the expression and distribution of kallikrein and its mRNA were examined in fetal, neonatal, and adult Sprague-Dawley rats. Kallikrein-like immunoreactivity was first expressed 1 day before birth in the upper limb of S-shaped bodies. Immediately after birth, kallikrein immunostaining was present along the apical membranes of inner cortical distal tubules, whereas subcapsular less mature comma-shaped vesicles did not express kallikrein. After completion of nephrogenesis, kallikrein was also seen in the distal and connecting tubules of the outer cortex. In situ hybridization localized the kallikrein message in the distal tubules of inner cortical nephrons in newborns and outer cortex in adults. The transition from newborn to adult life was associated with six- and fourfold increase in renal kallikrein content and mRNA accumulation, respectively. We conclude that immature distal tubules have the transcriptional and translational capacity to express the kallikrein gene and protein and that the renal kallikrein gene is developmentally regulated. The spatial and temporal changes in intrarenal kallikrein expression during ontogeny are consistent with the hypothesis that the kallikrein-kinin system plays a role in the maturation of renal functions.