Autosomal recessive polycystic kidney disease (ARPKD) is a severe form of polycystic kidney disease that presents primarily in infancy and childhood and that is characterized by enlarged kidneys and congenital hepatic fibrosis. We have identified PKHD1, the gene mutated in ARPKD. PKHD1 extends over > or =469 kb, is primarily expressed in human fetal and adult kidney, and includes a minimum of 86 exons that are variably assembled into a number of alternatively spliced transcripts. The longest continuous open reading frame encodes a 4,074-amino-acid protein, polyductin, that is predicted to have a single transmembrane (TM)-spanning domain near its carboxyl terminus, immunoglobulin-like plexin-transcription-factor domains, and parallel beta-helix 1 repeats in its amino terminus. Several transcripts encode truncated products that lack the TM and that may be secreted if translated. The PKHD1-gene products are members of a novel class of proteins that share structural features with hepatocyte growth-factor receptor and plexins and that belong to a superfamily of proteins involved in regulation of cell proliferation and of cellular adhesion and repulsion.

Abstract. PKHD1, the gene mutated in human autosomal recessive polycystic kidney disease has recently been identified. Its translation products are predicted to belong to a superfamily of proteins involved in the regulation of cellular adhesion and repulsion. One notable aspect of the gene is its unusually complex pattern of splicing. This study shows that mouse Pkhd1 and its translation products have very similar properties to its human orthologue. Mouse Pkhd1 extends over approximately 500 kb of genomic DNA, includes a minimum of 68 nonoverlapping exons, and exhibits a complex pattern of splicing. The longest ORF encodes a protein of 4059aa predicted to have an N-terminal signal peptide, multiple IPTs and PbH1 repeats, a single transmembrane span (TM), and a short cytoplasmic C-terminus. Although the protein sequence is generally well conserved (approximately 73% average identity), the C-termini share only 55% identity. The pattern of Pkhd1 expression by in situ hybridization was also examined in developing and adult mouse tissues over a range of ages (E12.5 to 3 mo postnatal). High levels of expression were present in renal and biliary tubular structures at all time points examined. Prominent Pkhd1 signals were also found in a number of other organs and tissues. Tissue-specific differences in transcript expression were revealed through the use of single exon probes. These data show that key features of human PKHD1 are highly conserved in the mouse and suggest that the complicated pattern of splicing is likely to be functionally important.

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Abstract:We present our experiments on refractometric sensing with ultrahigh-Q, crystalline, birefringent magnesium fluoride (MgF 2 ) whispering gallery mode resonators. The difference to fused silica which is most commonly used for sensing experiments is the small refractive index of MgF 2 which is very close to that of water. Compared to fused silica this leads to more than 50% longer evanescent fields and a 4.25 times larger sensitivity. Moreover the birefringence amplifies the sensitivity difference between TM and TE type modes which will enhance sensing experiments based on difference frequency measurements. We estimate the performance of our resonators and compare them with fused silica theoretically and present experimental data showing the interferometrically measured evanescent field decay and the sensitivity of mm-sized MgF 2 whispering gallery mode resonators immersed in water. These data show reasonable agreement with the developed theory. Furthermore, we observe stable Q factors in water well above 1 × 10 8 .

Mutations in PKD1 and PKD2, the genes that encode polycystin-1 and polycystin-2 respectively, account for almost all cases of autosomal dominant polycystic kidney disease. Although the polycystins are believed to interact in vivo, the two proteins often display dissimilar patterns and gradients of expression during development. In an effort to understand this apparent discrepancy, we investigated how changes in polycystin-2 expression can affect the subcellular localization of polycystin-1. We show that, when polycystin-1 is expressed alone in a PKD2 null cell line, it localizes to the cell surface, as well as to the endoplasmic reticulum. When co-expressed with polycystin-2, however, polycystin-1 is not seen at the cell surface and co-localizes completely with polycystin-2 in the endoplasmic reticulum. The localization of a polycystin-1 fusion protein was similarly affected by changes in its level of expression relative to that of polycystin-2. This phenomenon was observed in populations as well as in individual COS-7 cells. Our data suggest that the localization of polycystin-1 can be regulated via the relative expression level of polycystin-2 in mammalian cells. This mechanism may help to explain the divergent patterns and levels of expression observed for the polycystins, and may provide clues as to how the function of these two proteins are regulated during development.