158 research outputs found
De verwondering begrijpen
Rede In verkorte vorm uitgesproken ter gelegenheid van het aanvaarden van het ambt van bijzonder hoogleraar met als leeropdracht Functionele neurogenetica aan het Erasmus MC, faculteit van de Erasmus Universiteit Rotterdam op 23 mei 201
Hepatic lipase is localized at the parenchymal cell microvilli in rat liver
Hepatic lipase (HL) is thought to be located at the vascular endothelium
in the liver. However, it has also been implicated in the binding and
internalization of chylomicron remnants in the parenchymal cells. In view
of this apparent discrepancy between localization and function, we
re-investigated the localization of HL in rat liver using biochemical and
immunohistochemical techniques. The binding of HL to endothelial cells was
studied in primary cultures of rat liver endothelial cells. Endothelial
cells bound HL in a saturable manner with high affinity. However, the
binding capacity accounted for at most 1% of the total HL activity present
in the whole liver. These results contrasted with earlier studies, in
which non-parenchymal cell (NPC) preparations had been found to bind HL
with a high capacity. To study HL binding to the different components of
the NPC preparations, we separated endothelial cells, Kupffer cells and
blebs by counterflow elutriation. Kupffer cells and endothelial cells
showed a relatively low HL-binding capacity. In contrast, the blebs,
representing parenchymal-cell-derived material, had a high HL-binding
capacity (33 m-units/mg of protein) and accounted for more than 80% of the
total HL binding in the NPC preparation. In contrast with endothelial and
Kupffer cells, the HL-binding capacity of parenchymal cells could account
for almost all the HL activity found in the whole liver. These data
strongly suggest that HL binding occurs at parenchymal liver cells. To
confirm this conclusion in situ, we studied HL localization by
immunocytochemical techniques. Using immunofluorescence, we confirmed the
sinusoidal localization of HL. Immunoelectron microscopy demonstrated that
virtually all HL was located at the microvilli of parenchymal liver cells,
with a minor amount at the endothelium. We conclude that, in rat liver, HL
is localized at the microvilli of parenchymal cells
Generation and Characterization of Fmr1 Knockout Zebrafish
Fragile X syndrome (FXS) is one of the most common known causes of inherited mental retardation. The gene mutated in FXS is named FMR1, and is well conserved from human to Drosophila. In order to generate a genetic tool to study FMR1 function during vertebrate development, we generated two mutant alleles of the fmr1 gene in zebrafish. Both alleles produce no detectable Fmr protein, and produce viable and fertile progeny with lack of obvious phenotypic features. This is in sharp contrast to published results based on morpholino mediated knock-down of fmr1, reporting defects in craniofacial development and neuronal branching in embryos. These phenotypes we specifically addressed in our knock-out animals, revealing no significant deviations from wild-type animals, suggesting that the published morpholino based fmr1 phenotypes are potential experimental artifacts. Therefore, their relation to fmr1 biology is questionable and morpholino induced fmr1 phenotypes should be avoided in screens for potential drugs suitable for the treatment of FXS. Importantly, a true genetic zebrafish model is now available which can be used to study FXS and to derive potential drugs for FXS treatment
Dopaminergic Neuronal Loss and Dopamine-Dependent Locomotor Defects in Fbxo7-Deficient Zebrafish
Recessive mutations in the F-box only protein 7 gene (FBXO7) cause PARK15, a Mendelian form of early-onset, levodopa-responsive parkinsonism with severe loss of nigrostriatal dopaminergic neurons. However, the function of the protein encoded by FBXO7, and the pathogenesis of PARK15 remain unknown. No animal models of this disease exist. Here, we report the generation of a vertebrate model of PARK15 in zebrafish. We first show that the zebrafish Fbxo7 homolog protein (zFbxo7) is expressed abundantly in the normal zebrafish brain. Next, we used two zFbxo7-specific morpholinos (targeting protein translation and mRNA splicing, respectively), to knock down the zFbxo7 expression. The injection of either of these zFbxo7-specific morpholinos in the fish embryos induced a marked decrease in the zFbxo7 protein expression, and a range of developmental defects. Furthermore, whole-mount in situ mRNA hybridization showed abnormal patterning and significant decrease in the number of diencephalic tyrosine hydroxylase-expressing neurons, corresponding to the human nigrostriatal or ventral tegmental dopaminergic neurons. Of note, the number of the dopamine transporter-expressing neurons was much more severely depleted, suggesting dopaminergic dysfunctions earlier and larger than those due to neuronal loss. Last, the zFbxo7 morphants displayed severe locomotor disturbances (bradykinesia), which were dramatically improved by the dopaminergic agonist apomorphine. The severity of these morphological and behavioral abnormalities correlated with the severity of zFbxo7 protein deficiency. Moreover, the effects of the co-injection of zFbxo7- and p53-specific morpholinos were similar to those obtained with zFbxo7-specific morpholinos alone, supporting further the contention that the observed phenotypes were specifically due to the knock down of zFbxo7. In conclusion, this novel vertebrate model reproduces pathologic and behavioral hallmarks of human parkinsonism (dopaminergic neuronal loss and dopamine-dependent bradykinesia), representing therefore a valid tool for investigating the mechanisms of selective dopaminergic neuronal death, and screening for modifier genes and therapeutic compounds
New rat model that phenotypically resembles autosomal recessive polycystic kidney disease
Numerous murine models of polycystic kidney disease (PKD) have been
described. While mouse models are particularly well suited for
investigating the molecular pathogenesis of PKD, rats are well established
as an experimental model of renal physiologic processes. Han:SPRD-CY: rats
have been proposed as a model for human autosomal dominant PKD. A new
spontaneous rat mutation, designated wpk, has now been identified. In the
mutants, the renal cystic phenotype resembles human autosomal recessive
PKD (ARPKD). This study was designed to characterize the clinical and
histopathologic features of wpk/wpk mutants and to map the wpk locus.
Homozygous mutants developed nephromegaly, hypertension, proteinuria,
impaired urine-concentrating capacity, and uremia, resulting in death at 4
wk of age. Early cysts were present in the nephrogenic zone at embryonic
day 19. These were localized, by specific staining and electron
microscopy, to differentiated proximal tubules, thick limbs, distal
tubules, and collecting ducts. In later stages, the cysts were largely
confined to collecting ducts. Although the renal histopathologic features
are strikingly similar to those of human ARPKD, wpk/wpk mutants exhibited
no evidence of biliary tract abnormalities. The wpk locus maps just
proximal to the CY: locus on rat chromosome 5, and complementation studies
demonstrated that these loci are not allelic. It is concluded that the
clinical and renal histopathologic features of this new rat model strongly
resemble those of human ARPKD. Although homology mapping indicates that
rat wpk and human ARPKD involve distinct genes, this new rat mutation
provides an excellent experimental model to study the molecular
pathogenesis and renal pathophysiologic features of recessive PKD
Heritabilities, proportions of heritabilities explained by GWAS findings, and implications of cross-phenotype effects on PR interval
Electrocardiogram (ECG) measurements are a powerful tool for evaluating cardiac function and are widely used for the diagnosis and prediction of a variety of conditions, including myocardial infarction, cardiac arrhythmias, and sudden cardiac death. Recently, genome-wide association studies (GWASs) identified a large number of genes related to ECG parameter variability, specifically for the QT, QRS, and PR intervals. The aims of this study were to establish the heritability of ECG traits, including indices of left ventricular hypertrophy, and to directly assess the proportion of those heritabilities explained by GWAS variants. These analyses were conducted in a large, Dutch family-based cohort study, the Erasmus Rucphen Family study using variance component methods implemented in the SOLAR (Sequential Oligogenic Linkage Analysis Routines) software package. Heritability estimates ranged from 34 % for QRS and Cornell voltage product to 49 % for 12-lead sum. Trait-specific GWAS findings for each trait explained a fraction of their heritability (17 % for QRS, 4 % for QT, 2 % for PR, 3 % for Sokolow–Lyon index, and 4 % for 12-lead sum). The inclusion of all ECG-associated single nucleotide polymorphisms explained an additional 6 % of the heritability of PR. In conclusion, this study shows that, although GWAS explain a portion of ECG trait variability, a large amount of heritability remains to be explained. In addition, larger GWAS for PR are likely to detect loci already identified, particularly those observed for QRS and 12-lead sum
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