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The polycystic kidney disease (PKD1) gene-encoded protein, polycystin-1, is developmentally regulated, with highest expression levels seen in normal developing kidneys, where it is distributed in a punctate pattern at the basal surface of ureteric bud epithelia. Overexpression in ureteric epithelial cell membranes of an inhibitory pMyr-GFP-PKD1 fusion protein via a retroviral (VVC) delivery system and microinjection into the ureteric bud lumen of embryonic day 11 mouse metanephric kidneys resulted in disrupted branching morphogenesis. Using confocal quantitative analysis, significant reductions were measured in the numbers of ureteric bud branch points and tips, as well as in the total ureteric bud length, volume and area, while significant increases were seen as dilations of the terminal branches, where significant increases in outer diameter and volumes were measured. Microinjection of an activating 5TM-GFP-PKD1 fusion protein had an opposite effect and showed significant increases in ureteric bud length and area. These are the first studies to experimentally manipulate polycystin-1 expression by transduction in the embryonic mouse kidney and suggest that polycystin-1 plays a critical role in the regulation of epithelial morphogenesis during renal development. Keywords: Polycystic kidney disease; Polycystin-1; Kidney; Development; Ureteric bud; Branching morphogenesis; Viral transduction; Epithelial cell adhesion; Migration; Focal adhesion

Research has been conducted on the retinoic acid-inducible heparin-binding protein midkine. The analysis of the purified recombinant murine midkine biophysical characteristics are presented.

Mutations in the gene encoding the cystic fibrosis transmembrane regulator (CFTR) causes cystic fibrosis, an autosomal recessive disease characterized by impaired pancreatic function. To determine the role of the CFTR protein during nephrogenesis, expression of CFTR was examined in fetal kidneys by immunohistochemistry and Western blotting. The results revealed a 165-kDa protein with a size similar to that of the CFTR protein and a 75-kDa protein. However, the latter was detected only when a COOH-terminal-specific antibody was used. Analysis showed that this protein is similar to the CFTR protein previously reported in humans.

Aquaporins (AQP) are membrane water channels in the renal collecting duct (CD) which are involved in water transport. Expression of two AQPs, AQP1 and AQP2, was investigated during pathogenesis of autosomal dominant polycystic kidney disease. During 12-wk. gestation, AQP1 was detected in developing proximal tubule epithelia while AQP2 was detected in the apical cell membranes of the ureteric bud and the CD system. AQP1 was later seen in descending thin limbs of Henle and AQP2 was restricted to CD cells.

A study to characterize the transcriptional and posttranscriptional regulation of fibroblast growth factor (FGF) receptor 1 (FGFR-1) in the embryonic rat kidney is presented. The study was conducted to improve knowledge of the role of FGF in embryogenesis and particularly in angiogenesis. The study involved FGFR-1 cDNA cloning and sequencing. The results showed that in rat kidney, FGFR-1 is expressed as alpha, beta and gamma splicing variants, with the beta isoform expressed in greater abundance than the other two. It was also discovered that FGFR-1 expression is greater in the embryonic than the mature rat kidney.

Burrow, Christopher R., Olivier Devuyst, Xiaohong Li, Laura Gatti, and Patricia D. Wilson. Expression of the [Beta]2-subunit and apical localization of [Na.sup.+]-[K.sup.+]-ATPase in metanephric kidney. Am. J. Physiol. 277 (Renal Physiol. 46): F391-F403, 1999.--During kidney organogenesis, the [Na.sup.+]-[K.sup.+]-ATPase pump is not restricted to the basolateral plasma membrane of the renal epithelial cell but is instead either localized to the apical and lateral membrane sites of the early nephron or expressed in a nonpolarized distribution in the newly formed collecting ducts. The importance of [Na.sup.+]-[K.sup.+]-ATPase [Beta]-subunit expression in the translocation of the [Na.sup.+]-[K.sup.+]-ATPase to the plasma membrane raises the question to which [Beta]-subunit isoform is expressed during kidney organogenesis. Immunocytochemical, Western analysis and RNase protection studies showed that both [Beta]2-subunit protein and [Beta]2 mRNA are expressed in the early gestation to midgestation human metanephric kidney. In contrast, although [Beta]1 mRNA abundance is equivalent to that of the [Beta]2-subunit in the metanephric kidney, the [Beta]1-subunit protein was not detected in early to midgestation metanephric kidney samples. Immunocytochemical analysis revealed that both [Alpha]1- and [Beta]2-subunits were present in the apical epithelial plasma membranes of distal nephron segments of early stage nephrons, maturing loops of Henle, and collecting ducts during kidney development. We also detected a significant increase in [Alpha]1 and [Beta]1 mRNA after birth with a marked reduction in [Beta]2 mRNA abundance associated with an increase in [Alpha]1- and [Beta]1-subunit proteins and loss of [Beta]2 protein expression. These studies support the conclusion that the expression of the [Beta]2-subunit in the fetal kidney may be an [Na.sup.+]-[K.sup.+]-ATPase pump in the epithelia of the developing nephron during kidney organogenesis. sodium-potassium adenosinetriphosphatase; renal epithelium; sodium transport; nephron

Examines the role of human protein kinase X gene (PRKX) on the activation of renal epithelial cell migration and morphogenesis. Phylogeny of the PRKX family; Use of PRKX immunoprecipitation kinase assay; Regulation of PRKX expression in human kidney.

Background: Congenital absence of alpha-galactosidase in Fabry disease leads eventually to renal failure. Fabry disease is an attractive candidate for gene therapy, but uptake mechanisms of the enzyme must be understood for it to be used in treating patients with Fabry disease., Methods: Immortalized human renal epithelial cells from three regions of the tubule were grown in culture on collagen-coated Transwell filters and were incubated with recombinant alpha-galactosidase protein placed at either the luminal or basolateral side of the cells. Uptake into cells was measured, and kinetic studies were performed. Blocking experiments were done with mannose 6-phosphate., Results: Uptake from the basolateral side of the filters predominated in all three cell types. Only in distal tubule cells was mannose 6-phosphate able to block uptake to any degree. The kinetic data reveal a high Km for both luminal and basolateral cell surfaces., Conclusions: These data suggest that to correct the renal phenotype in Fabry disease, high levels of the enzyme will be need to be delivered to kidney cells. This will likely best be achieved with local administration of a vector containing the transgene directly to the kidney.