Intestinal development in amniotes is driven by interactions between progenitor cells derived from the three primary germ layers. Genetic analyses and gene targeting experiments in zebrafish offer a novel approach to dissect such interactions at a molecular level. Here we show that intestinal anatomy and architecture in zebrafish closely resembles the anatomy and architecture of the mammalian small intestine. The zebrafish intestine is regionalized and the various segments can be identified by epithelial markers whose expression is already segregated at the onset of intestinal differentiation. Differentiation of cells derived from the three primary germ layers begins more or less contemporaneously, and is preceded by a stage in which there is rapid cell proliferation and maturation of epithelial cell polarization. Analysis of zebrafish mutants with altered epithelial survival reveals that seemingly related single gene defects have different effects on epithelial differentiation and smooth muscle and enteric nervous system development.

(2) and London mutation(s) (3) alter APP processing, causing increased production of the A␤ peptide of 42 amino acids (4), hypothesized to be pivotal in AD pathology (1, 5). Early onset familial AD caused by mutations in the presenilin genes supports this hypothesis, because they increase production of A␤ (42) peptide (6, 7) due to the gain of an unknown function (8). The extensive cell biological definition of the metabolic effects of the different mutations in APP in vitro requires matching analysis of their physiological impact in vivo. Transgenic mice with wild type and different mutant forms of APP have been generated and the original, most wanted end point, i.e. AD-like amyloid plaques in mouse brain, was obtained (9, 10), accompanied by cognitive deficits (11) and by hyperphosphorylation of protein tau (12). In other transgenic mouse strains overexpression of APP caused behavioral, synaptotrophic, and neurodegenerative effects, accelerated senescence, and premature death, in the absence of amyloid deposits (13-16). Intracellular expression of the A␤ peptide yielded mice with extensive neuronal loss but no amyloidosis (17). Overexpression of the C-terminal domain of APP caused neuronal degeneration (18), whereas in another model, pre-amyloid deposits, hippocampal cell loss, and cognitive deficits were documented (19).We have generated additional transgenic mouse strains, expressing human APP, either wild type or the London or Swedish clinical mutations, from the neuron-specific mouse thy-1 gene promoter. Their phenotype was analyzed by biochemical, histochemical, behavioral, electrophysiological, and pharmacological methods. Measurements of different APP metabolites in brain demonstrated that increased A␤(42) levels correlated with the formation of amyloid plaques in the brain of old APP/London transgenic mice. The plaques were extensively characterized immunohistochemically and displayed many aspects typically observed in the brain of AD patients. As opposed to plaques that developed only after at least 12 months of age, other deficits were observed from 3 months onwards and included cognitive impairment, decreased long term potentiation, differential glutamatergic responses, aggression, and neophobia, among others. These signs were largely independent of the actual isoform or mutant of APP that was expressed, were not correlated with a single APP metabolite, and are dissociated in time from plaque formation. These mice will be good models to study both early and late, neuropathological, and clinical aspects related to Alzheimer's disease. EXPERIMENTAL PROCEDURESGeneration of Transgenic Mice-cDNA coding for human wild type APP (695 isoform), the Swedish (K670N,M671L) mutant (770 isoform), and the London (V642I) mutant (695 isoform) were cloned in the pTSC vector in the mouse thy-1 gene (16). The purified, linearized minigenes were microinjected into prenuclear embryos from superovulated FVB/N females.Antibodies-Rabbit antisera B11/4 and B12/4, generated against a *

The Alagille Syndrome (AGS) is a heritable disorder affecting the liver and other organs. Causative dominant mutations in human Jagged 1 have been identified in most AGS patients. Related organ defects occur in mice that carry jagged 1 and notch 2 mutations. Multiple jagged and notch genes are expressed in the developing zebrafish liver. Compound jagged and notch gene knockdowns alter zebrafish biliary, kidney, pancreatic, cardiac and craniofacial development in a manner compatible with an AGS phenocopy. These data confirm an evolutionarily conserved role for Notch signaling in vertebrate liver development, and support the zebrafish as a model system for diseases of the human biliary system.

Biliary atresia (BA) is a rapidly progressive and destructive fibrotic disorder of unknown etiology affecting the extrahepatic biliary tree of neonates. Epidemiological studies suggest that an environmental factor, such as a virus or toxin, is the cause of the disease, although none have been definitively established. Several naturally occurring outbreaks of BA in Australian livestock have been associated with the ingestion of unusual plants by pregnant animals during drought conditions. We used a biliary secretion assay in zebrafish to isolate a previously undescribed isoflavonoid, biliatresone, from Dysphania species implicated in a recent BA outbreak. This compound caused selective destruction of the extrahepatic, but not intrahepatic, biliary system of larval zebrafish. A mutation that enhanced biliatresone toxicity mapped to a region of the zebrafish genome that has conserved synteny with an established human BA susceptibility locus. The toxin also caused loss of cilia in neonatal mouse extrahepatic cholangiocytes in culture and disrupted cell polarity and monolayer integrity in cholangiocyte spheroids. Together, these findings provide direct evidence that BA could be initiated by perinatal exposure to an environmental toxin.