The WT1 gene, located on chromosome 11p13, is mutated in a low number of Wilms tumors (WTs). Germ-line mutations in the WT1 gene are found in patients with bilateral WT and͞or associated genital tract malformations (GU). We have identified 19 hemizygous WT1 gene mutations͞deletions in 64 patient samples. The histology of the tumors with mutations was stromal-predominant in 13, triphasic in 3, blastemal-predominant in 1, and unknown in 2 cases. Thirteen of 21 patients with stromal-predominant tumors had WT1 mutations and 10 of these were present in the germ line. Of the patients with germ-line alterations, six had GU and a unilateral tumor, two had a bilateral tumor and normal GU tracts, and two had a unilateral tumor and normal GU. Three mutations were tumor-specific and were found in patients with unilateral tumors without GU. These data demonstrate a correlation of WT1 mutations with stromalpredominant histology, suggesting that a germ-line mutation in WT1 predisposes to the development of tumors with this histology. Twelve mutations are nonsense mutations resulting in truncations at different positions in the WT1 protein and only two are missense mutations. Of the stromal-predominant tumors, 67% showed loss of heterozygosity, and in one tumor a different somatic mutation in addition to the germline mutation was identified. These data show that in a large proportion of a histopathologically distinct subset of WTs the classical two-hit inactivation model, with loss of a functional WT1 protein, is the underlying cause of tumor development.The WT1 gene was isolated by positional cloning from chromosome 11p13 (1, 2) and encodes a transcription factor of the zinc finger (ZF) family. Loss of heterozygosity (LOH) studies showed that tumors frequently have lost markers from chromosome 11p. Subsequently, it was found that this loss is often limited to the region 11p15, where a second locus, WT2, involved in the development of Wilms tumor (WT) has been assumed to exist. Further LOH studies revealed loss of chromosome 16q in about 20% of WTs, suggesting that a third locus is located at this site. Susceptibility for the rare form of familial WT in several generations does not show linkage to either of these regions; therefore, another WT locus must exist in these cases (3-5). The WT1 gene encodes four transcripts produced by alternative splicing (6, 7) and encodes a protein with a predicted size of 45-49 kDa. DNA binding to a GC-rich motif identical to the early growth response-binding site was demonstrated for the WT1 protein lacking splice II in the ZF (WT͞ϪKTS), whereas the WT1 protein containing these amino acids (WT͞ϩKTS) does not bind to this sequence (8). Recently it was shown that WT1͞ϩKTS can also bind to a similar GC-rich DNA motif (9). More recent studies have established that the proline-glutamine rich amino terminus has transcriptional regulatory properties. It was shown that WT1 containing splice I (WT͞ϩ17aa) is a repressor, whereas WT1͞Ϫ17aa can be either a repressor or activator depending on the ar...

Abcb11 encodes for the liver bile salt export pump, which is rate-limiting for hepatobiliary bile salt secretion. We employed transthyretin-Abcb11 and BACAbcb11 transgenes to develop mice overexpressing the bile salt export pump in the liver. The mice manifest increases in bile flow and biliary secretion of bile salts, phosphatidylcholine, and cholesterol. Hepatic gene expression of cholesterol 7␣-hydroxylase and ileal expression of the apical sodium bile salt transporter are markedly reduced, whereas gene expression of targets of the nuclear bile salt receptor FXR (ileal lipid-binding protein, short heterodimer partner (SHP) is increased. Because these changes in gene expression are associated with an increased overall hydrophobicity of the bile salt pool and a 4-fold increase of the FXR ligand taurodeoxycholate, they reflect bile salt-mediated regulation of FXR and SHP target genes. Despite the increased biliary secretion of bile salts, fecal bile salt excretion is unchanged, suggestive of an enhanced enterohepatic cycling of bile salts. Abcb11 transgenic mice fed a lithogenic (high cholesterol/fat/cholic acid) diet display markedly reduced hepatic steatosis compared with wild-type controls. We conclude that mice overexpressing Abcb11 display an increase in biliary bile salt secretion and taurodeoxycholate content, which is associated with FXR/SHP-mediated changes in hepatic and ileal gene expression. Because these mice are resistant to hepatic lipid accumulation, regulation of Abcb11 may be important for the pathogenesis and treatment of steatohepatitis.

Cholesterol cholelithiasis is one of the most common gastroenterological diseases in Western countries. It is a polygenic disease resulting from disturbed biliary cholesterol homeostasis. Association studies identified six human gallstone candidate genes. Polymorphisms in the genes encoding the apolipoproteins B and E, phospholipid flippase ( ABCB4), cholesterol ester transfer protein ( CETP), cholesterol-7alpha-hydroxylase ( CYP7A1) and ileal bile acid transporter ( SLC10A2) are correlated with gallstone prevalence. Quantitative Trait Locus (QTL) analysis localises additional unknown gallstone genes in inbred mice. Based on the natural variation of cholesterol gallstone susceptibility among different inbred strains, 5 lithogenic ( Lith) loci have been identified. Hepatobiliary transporters (e. g. bile salt export pump Abcb11) and key proteins of the lipoprotein metabolism (e. g. hepatic lipase Lipc) could be established as creedal candidate genes for Lith loci. The rapid progress of mouse and human genome projects provides the basis for the analysis of orthologous human LITH genes in gallstone patients, which might offer new prospects for individual risk assessment and molecular targets for stone prevention.

Zusammenfassung An 3 Schafen (60–70 kg Lebendmasse) mit Umleitungskanülen im proximalen Colon wurden insgesamt 76 3‐stündige Perfusionsversuche durchgeführt, um die Nettoresorption von Calcium und von anorganischem Phosphat aus diesem Darmabschnitt zu bestimmen. Die Perfusionslösungen entsprachen in ihrer Zusammensetzung der Flüssigkeitsphase des Coloninhaltes, wiesen aber für Calcium einen Konzentrationsbereich von 0–6,56 mmol. l−1, für anorganisches Phosphat von 0–6,53 mmol. l−1 auf. Für Ca wurde bei Konzentrationen unter 1,20 mmol. l−1 eine Nettosekretion, bei höheren Konzentrationen eine Nettoresorption gemessen. Es bestand eine enge Korrelation zwischen Konzentrationen der Perfusionslösungen und dem Ca‐Nettofluß, und die Ergebnisse legen eine Diffusion nahe. Für anorganisches Phosphat ergab sich außer bei Verwendung einer phosphatfreien Perfusionslösung immer eine Nettoresorption aus dem Lumen, die zum Teil als Diffusion gedeutet werden kann. Daneben bestanden Anzeichen für einen weiteren Transportmechanismus im Bereich niedriger Phosphatkonzentration in der Perfusionsflüssigkeit. Unterschiede in der Flüssigkeits‐Nettoresorption hatten keinen erkennbaren Einfluß auf die Nettoflüsse von Calcium und von anorganischem Phosphat.

New Molecular Mechanisms of Gallstone Pathogenesis Cholelithiasis is a common gastrointestinal disease that results from the precipitation of cholesterol crystals or amorphous calcium bilirubinates in the gallbladder and the biliary tree. More than 10% of the German population develop gallstones, most of which are cholesterol stones and result from altered hepatic bile formation. During the past decades, research has focused on molecular mechanisms of bile secretion and cholesterol crystallization and led to the development of oral litholysis. More recently, new concepts in bile pigment physiology and mapping of lithogenic genes in inbred mice have identified new targets for early diagnosis and prevention of gallstone disease.