Zebrafish transgenic Enhancer TRAP line database (ZETRAP)

Background  

The zebrafish, Danio rerio, is used as a model organism to study vertebrate genetics and development. An effective enhancer trap (ET) in zebrafish using the Tol2 transposon has been demonstrated. This approach could be used to study embryogenesis of a vertebrate species in real time and with high resolution.     

Characterization and properties of pre beta-HDL particles formed by ABCA1-mediated cellular lipid efflux to apoA-I

The contribution of ABCA1-mediated efflux of cellular phospholipid (PL) and cholesterol to human apolipoprotein A-I (apoA-I) to the formation of pre beta 1-HDL (or lipid-poor apoA-I) is not well defined. To explore this issue, we characterized the nascent HDL particles formed when lipid-free apoA-I was incubated with fibroblasts in which expression of the ABCA1 was upregulated. After a 2 h incubation, the extracellular medium contained small apoA-I/PL particles (pre beta 1-HDL; diameter = 7.5 +/- 0.4 nm). The pre beta 1-HDL (or lipid-poor apoA-I) particles contained a single apoA-I molecule and three to four PL molecules and one to two cholesterol molecules. An apoA-I variant lacking the C-terminal alpha-helix did not form such particles when incubated with the cell, indicating that this helix is critical for the formation of lipid-poor apoA-I particles. These pre beta 1-HDL particles were as effective as lipid-free apoA-I molecules in mediating both the efflux of cellular lipids via ABCA1 and the formation of larger, discoidal HDL particles. In conclusion, pre beta 1-HDL is both a product and a substrate in the ABCA1-mediated reaction to efflux cellular PL and cholesterol to apoA-I. A monomeric apoA-I molecule associated with three to four PL molecules (i.e., lipid-poor apoA-I) has similar properties to the lipid-free apoA-I molecule.     

Effects of enrichment of fibroblasts with unesterified cholesterol on the efflux of cellular lipids to apolipoprotein A-I.

This study elucidates the factors underlying the enhancement in efflux of human fibroblast unesterified cholesterol and phospholipid (PL) by lipid-free apolipoprotein (apo) A-I that is induced by cholesterol enrichment of the cells. Doubling the unesterified cholesterol content of the plasma membrane by incubation for 24 h with low density lipoprotein and lipid/cholesterol dispersions increases the pools of PL and cholesterol available for removal by apoA-I from about 0.8-5%; the initial rates of mass release of cholesterol and PL are both increased about 6-fold. Expression of the ATP binding cassette transporter A1 (ABCA1) is critical for this increased efflux of lipids, and cholesterol loading of the fibroblasts over 24 h increases ABCA1 mRNA about 12-fold. The presence of more ABCA1 and cholesterol in the plasma membrane results in a 2-fold increase in the level of specific binding of apoA-I to the cells with no change in binding affinity. Characterization of the species released from either control or cholesterol-enriched cells indicates that the plasma membrane domains from which lipids are removed are cholesterol-enriched with respect to the average plasma membrane composition. Cholesterol enrichment of fibroblasts also affects PL synthesis, and this leads to enhanced release of phosphatidylcholine (PC) relative to sphingomyelin (SM); the ratios of PC to SM solubilized from control and cholesterol-enriched fibroblasts are approximately 2/1 and 5/1, respectively. Biosynthesis of PC is critical for this preferential release of PC and the enhanced cholesterol efflux because inhibition of PC synthesis by choline depletion reduces cholesterol efflux from cholesterol-enriched cells. Overall, it is clear that enrichment of fibroblasts with unesterified cholesterol enhances efflux of cholesterol and PL to apoA-I because of three effects, 1) increased PC biosynthesis, 2) increased PC transport via ABCA1, and 3) increased cholesterol in the plasma membrane.     

SEPALLATA3: the 'glue' for MADS box transcription factor complex formation

Background  

Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family. SEPALLATA3 (SEP3) has been shown to mediate complex formation and, therefore, special attention is paid to this factor in this study.     

Global transcriptional response of pig brain and lung to natural infection by Pseudorabies virus

Background  

Pseudorabies virus (PRV) is an alphaherpesviruses whose native host is pig. PRV infection mainly causes signs of central nervous system disorder in young pigs, and respiratory system diseases in the adult.     

A sensitive assay for ABCA1-mediated cholesterol efflux using BODIPY-cholesterol

Studies have shown a negative association between cellular cholesterol efflux and coronary artery disease (CAD). Standard protocol for quantitating cholesterol efflux involves labeling cells with [(3)H]cholesterol and measuring release of the labeled sterol. Using [(3)H]cholesterol is not ideal for the development of a high-throughput assay to screen large numbers of serum as would be required in studying the link between efflux and CAD. We compared efflux using a fluorescent sterol (boron dipyrromethene difluoride linked to sterol carbon-24, BODIPY-cholesterol) with that of [(3)H]cholesterol in J774 macrophages. Fractional efflux of BODIPY-cholesterol was significantly higher than that of [(3)H]cholesterol when apo A-I, HDL(3), or 2% apoB-depleted human serum were used as acceptors. BODIPY-cholesterol efflux correlated significantly with [(3)H]cholesterol efflux (p < 0.0001) when apoB-depleted sera were used. The BODIPY-cholesterol efflux correlated significantly with preβ-1 (r(2) = 0.6) but not with total HDL-cholesterol. Reproducibility of the BODIPY-cholesterol efflux assay was excellent between weeks (r(2) = 0.98, inter-assay CV = 3.31%). These studies demonstrate that BODIPY-cholesterol provides an efficient measurement of efflux compared with [(3)H]cholesterol and is a sensitive probe for ABCA1-mediated efflux. The increased sensitivity of BODIPY-cholesterol assay coupled with the simplicity of measuring fluorescence results in a sensitive, high-throughput assay that can screen large numbers of sera, and thus establish the relationship between cholesterol efflux and atherosclerosis.     

Case Study: Polycystic Livers in a Transgenic Mouse Line

Three mice (2 male, 1 female; age, 5 to 16 mo) from a mouse line transgenic for keratin 14 (K14)-driven LacZ expression and on an outbred Crl:CD1(ICR) background, were identified as having distended abdomens and livers that were diffusely enlarged by numerous cysts (diameter, 0.1 to 2.0 cm). Histopathology revealed hepatic cysts lined by biliary type epithelium and mild chronic inflammation, and confirmed the absence of parasites. Among 21 related mice, 5 additional affected mice were identified via laparotomy. Breeding of these 5 mice (after 5 mo of age) did not result in any offspring; the K14 mice with polycystic livers failed to reproduce. Affected male mice had degenerative testicular lesions, and their sperm was immotile. Nonpolycystic K14 control male mice bred well, had no testicular lesions, and had appropriate sperm motility. Genetic analysis did not identify an association of this phenotype with the transgene or insertion site.Abbreviations: K14, keratin 14 promoter; LacZ, bacterial β-galactosidase LacZ reporter; Lsamp, mouse limbic system-associated membrane proteinPolycystic disease is a multiorgan disorder and is the most common genetic life-threatening disease in people, affecting more than 600,000 Americans.¹⁶ Cystic liver disease in people typically is associated with polycystic kidney disease^22,36 but can exist in its absence. Currently, 2 autosomal dominant genes (PRKCSH and SEC63P) that cause a human polycystic liver disease condition without renal involvement have been identified.^4-6,13Numerous rodent models of polycystic kidneys with concurrent polycystic liver exist.^8,34,39,40 However, effective models of polycystic liver without polycystic kidneys would be useful to address clinical and mechanistic issues of polycystic liver not associated with polycystic kidneys.^6,31Here we report multiple cases of a spontaneous polycystic liver phenotype without a kidney phenotype in a transgenic mouse line. We also describe the effect of the transgene on disease expression and our attempts to develop this stock as an animal model.     

Cellular cholesterol efflux. Role of cell membrane kinetic pools and interaction with apolipoproteins AI, AII, and Cs.

Efflux of [14C]cholesterol from various cells was monitored in the presence of discoidal complexes of egg phosphatidylcholine and purified apolipoproteins, containing either apoAI, AII, or Cs. Particles containing apoAI were more efficient acceptors than those containing apoAII or Cs when the donor cells were J774 macrophages. No differences were observed when the same acceptor preparations were exposed to Fu5AH rat hepatoma or rabbit aortic smooth muscle cells. The differential efficiency of apolipoproteins in stimulating cholesterol removal from J774 cells was maintained in a plasma membrane-enriched fraction isolated from the same cells. Nonlinear regression analysis of kinetic data obtained from J774 cells exposed to apoAI complexes indicated that cholesterol efflux was best fitted to a curve describing the release from two kinetic compartments. Approximately 10% of cholesterol was transferred from a rapidly exchangeable pool with a t1/2 ranging between 1.5 and 3 h, and the remaining fraction was released from a slower pool with a t1/2 of about 20 h. Modulation of cholesterol efflux from J774 cells by either varying the concentration or the apolipoprotein composition of the acceptors influenced the size of the pools and the t1/2 of the slow pool. Kinetics of cholesterol efflux from membranes isolated from J774 cells also best fit a two-compartment model and modification of the apolipoprotein composition of the acceptor induced a pattern of changes in pool size and half-time similar to that described for whole cells. In the three cell lines studied, we consistently resolved a slow pool with a half-time ranging between 15 and 20 h. In smooth muscle cells only the slow pool was evident, whereas in Fu5AH a very large fast pool was also resolved. In contrast to J774 cells, apolipoprotein composition of the acceptor did not influence the pools in these two cell lines. These results led us to propose a new model regarding the influence of multiple kinetic pools of cholesterol on the regulation of cholesterol desorption from the cell membrane.