Search PubMed⌕ Search

Biomedical subjects

M Brand

Publications and source records attributed to M Brand.

At least 37 records · Page 2Linked to original sources
PubMed2000

Zebrafish no isthmus reveals a role for pax2.1 in tubule differentiation and patterning events in the pronephric primordia.

Pax genes are important developmental regulators and function at multiple stages of vertebrate kidney organogenesis. In this report, we have used the zebrafish pax2.1 mutant no isthmus to investigate the role for pax2.1 in development of the pronephros. We demonstrate a requirement for pax2.1 in multiple aspects of pronephric development including tubule and duct epithelial differentiation and cloaca morphogenesis. Morphological analysis demonstrates that noi(- )larvae specifically lack pronephric tubules while glomerular cell differentiation is unaffected. In addition, pax2.1 expression in the lateral cells of the pronephric primordium is required to restrict the domains of Wilms' tumor suppressor (wt1) and vascular endothelial growth factor (VEGF) gene expression to medial podocyte progenitors. Ectopic podocyte-specific marker expression in pronephric duct cells correlates with loss of expression of the pronephric tubule and duct-specific markers mAb 3G8 and a Na(+)/K(+) ATPase (&agr;)1 subunit. The results suggest that the failure in pronephric tubule differentiation in noi arises from a patterning defect during differentiation of the pronephric primordium and that mutually inhibitory regulatory interactions play an important role in defining the boundary between glomerular and tubule progenitors in the forming nephron.

Animals↗
PubMed2000

Ace/Fgf8 is required for forebrain commissure formation and patterning of the telencephalon.

Fibroblast growth factors (Fgfs) form a large family of secreted signalling proteins that have a wide variety of roles during embryonic development. Within the central nervous system (CNS) Fgf8 is implicated in patterning neural tissue adjacent to the midbrain-hindbrain boundary. However, the roles of Fgfs in CNS tissue rostral to the midbrain are less clear. Here we examine the patterning of the forebrain in zebrafish embryos that lack functional Fgf8/Ace. We find that Ace is required for the development of midline structures in the forebrain. In the absence of Ace activity, midline cells fail to adopt their normal morphology and exhibit altered patterns of gene expression. This disruption to midline tissue leads to severe commissural axon pathway defects, including misprojections from the eye to ectopic ipsilateral and contralateral targets. Ace is also required for the differentiation of the basal telencephalon and several populations of putative telencephalic neurons but not for overall regional patterning of forebrain derivatives. Finally, we show that ace expression co-localises with anterior neural plate cells that have previously been shown to have forebrain patterning activity. Removal of these cells leads to a failure in induction of ace expression indicating that loss of Ace activity may contribute to the phenotypes observed when anterior neural plate cells are ablated. However, as ace mutant neural plate cells still retain at least some inductive activity, then other signals must also be produced by the anterior margin of the neural plate.

Animals↗
PubMed2000

Induction and differentiation of the zebrafish heart requires fibroblast growth factor 8 (fgf8/acerebellar).

Vertebrate heart development is initiated from bilateral lateral plate mesoderm that expresses the Nkx2.5 and GATA4 transcription factors, but the extracellular signals specifying heart precursor gene expression are not known. We describe here that the secreted signaling factor Fgf8 is expressed in and required for development of the zebrafish heart precursors, particularly during initiation of cardiac gene expression. fgf8 is mutated in acerebellar (ace) mutants, and homozygous mutant embryos do not establish normal circulation, although vessel formation is only mildly affected. In contrast, heart development, in particular of the ventricle, is severely abnormal in acerebellar mutants. Several findings argue that Fgf8 has a direct function in development of cardiac precursor cells: fgf8 is expressed in cardiac precursors and later in the heart ventricle. Fgf8 is required for the earliest stages of nkx2.5 and gata4, but not gata6, expression in cardiac precursors. Cardiac gene expression is restored in acerebellar mutant embryos by injecting fgf8 RNA, or by implanting a Fgf8-coated bead into the heart primordium. Pharmacological inhibition of Fgf signalling during formation of the heart primordium phenocopies the acerebellar heart phenotype, confirming that Fgf signaling is required independently of earlier functions during gastrulation. These findings show that fgf8/acerebellar is required for induction and patterning of myocardial precursors.

Animals↗
PubMed1999

Three-dimensional structures of the TAFII-containing complexes TFIID and TFTC.

TBP (TATA-binding protein)-associated factors (TAF(II)s) are components of large multiprotein complexes such as TFIID, TFTC, STAGA, PCAF/GCN5, and SAGA, which play a key role in the regulation of gene expression by RNA polymerase II. The structures of TFIID and TFTC have been determined at 3.5-nanometer resolution by electron microscopy and digital image analysis of single particles. Human TFIID resembles a macromolecular clamp that contains four globular domains organized around a solvent-accessible groove of a size suitable to bind DNA. TFTC is larger and contains five domains, four of which are similar to TFIID.

DNA-Binding Proteins↗
PubMed1999

Zebrafish (Danio rerio) presenilin promotes aberrant amyloid beta-peptide production and requires a critical aspartate residue for its function in amyloidogenesis.

Alzheimer's disease (AD) is characterized by the invariable accumulation of senile plaques composed of amyloid beta-peptide (Abeta). Mutations in three genes are known to cause familial Alzheimer's disease (FAD). The mutations occur in the genes encoding the beta-amyloid precursor protein (betaAPP) and presenilin (PS1) and PS2 and cause the increased secretion of the pathologically relevant 42 amino acid Abeta42. We have now cloned the zebrafish (Danio rerio) PS1 homologue (zf-PS1) to study its function in amyloidogenesis and to prove the critical requirement of an unusual aspartate residue within the seventh putative transmembrane domain. In situ hybridization and reverse PCR reveal that zf-PS1 is maternally inherited and ubiquitously expressed during embryogenesis, suggesting an essential housekeeping function. zf-PS1 is proteolytically processed to produce a C-terminal fragment (CTF) of approximately 24 kDa similar to human PS proteins. Surprisingly, wt zf-PS1 promotes aberrant Abeta42 secretion like FAD associated human PS1 mutations. The unexpected pathologic activity of wt zf-PS1 may be due to several amino acid exchanges at positions where FAD-associated mutations have been observed. The amyloidogenic function of zf-PS1 depends on the conserved aspartate residue 374 within the seventh putative transmembrane domain. Mutagenizing this critical aspartate residue abolishes endoproteolysis of zf-PS1 and inhibits Abeta secretion in human cells. Inhibition of Abeta secretion is accompanied by the accumulation of C-terminal fragments of betaAPP, suggesting a defect in gamma-secretase activity. These data provide further evidence that PS proteins are directly involved in the proteolytic cleavage of betaAPP and demonstrate that this function is evolutionarily conserved.

Alzheimer Disease↗
PubMed1999

Identification of TATA-binding protein-free TAFII-containing complex subunits suggests a role in nucleosome acetylation and signal transduction.

Recently we identified a novel human (h) multiprotein complex, called TATA-binding protein (TBP)-free TAFII-containing complex (TFTC), which is able to nucleate RNA polymerase II transcription and can mediate transcriptional activation. Here we demonstrate that TFTC, similar to other TBP-free TAFII complexes (yeast SAGA, hSTAGA, and hPCAF) contains the acetyltransferase hGCN5 and is able to acetylate histones in both a free and a nucleosomal context. The recently described TRRAP cofactor for oncogenic transcription factor pathways was also characterized as a TFTC subunit. Furthermore, we identified four other previously uncharacterized subunits of TFTC: hADA3, hTAFII150, hSPT3, and hPAF65beta. Thus, the polypeptide composition of TFTC suggests that TFTC is recruited to chromatin templates by activators to acetylate histones and thus may potentiate initiation and activation of transcription.

Acetylation↗
PubMed1999

Requirement for the zebrafish mid-hindbrain boundary in midbrain polarisation, mapping and confinement of the retinotectal projection.

The organizer at the midbrain-hindbrain boundary (MHB organizer) has been proposed to induce and polarize the midbrain during development. We investigate the requirement for the MHB organizer in acerebellar mutants, which lack a MHB and cerebellum, but retain a tectum, and are mutant for fgf8, a candidate inducer and polarizer. We examine the retinotectal projection in the mutants to assay polarity in the tectum. In mutant tecta, retinal ganglion cell (RGC) axons form overlapping termination fields, especially in the ventral tectum, and along both the anterior-posterior and dorsal-ventral axis of the tectum, consistent with a MHB requirement in generating midbrain polarity. However, polarity is not completely lost in the mutant tecta, in spite of the absence of the MHB. Moreover, graded expression of the ephrin family ligand Ephrin-A5b is eliminated, whereas Ephrin-A2 and Ephrin-A5a expression is leveled in acerebellar mutant tecta, showing that ephrins are differentially affected by the absence of the MHB. Some RGC axons overshoot beyond the mutant tectum, suggesting that the MHB also serves a barrier function for axonal growth. By transplanting whole eye primordia, we show that mapping defects and overshooting largely, but not exclusively, depend on tectal, but not retinal genotype, and thus demonstrate an independent function for Fgf8 in retinal development. The MHB organizer, possibly via Fgf8 itself, is thus required for midbrain polarisation and for restricting axonal growth, but other cell populations may also influence midbrain polarity.

Animals↗
PubMed1999

What's the 'best buy' for treatment of constipation? Results of a systematic review of the efficacy and comparative efficacy of laxatives in the elderly.

Constipation is a common cause of general practice consultations in elderly people, and laxative use is common among this group of patients. However, there appears to be little evidence to guide laxative treatment in this population. This paper reports the results of a systematic review of randomized controlled trials of the efficacy of laxatives in the treatment of constipation in the elderly. While the results of the review suggest that laxatives can improve bowel movement frequency, stool consistency, and symptoms of constipation, with a few exceptions, the relevant trials have serious methodological shortcomings. However, the review finds little evidence of marked differences in effectiveness between laxatives and, in particular, there appears to be no evidence to support the current National Health Service (NHS) trend towards prescribing the more expensive stimulant laxatives. This is an area where good quality trial evidence is now needed.

Aged↗
PubMed1998

Function of TAF(II)-containing complex without TBP in transcription by RNA polymerase II.

Initiation of transcription of a gene from a core promoter region by RNA polymerase II requires the assembly of several initiation factors to form a preinitiation complex. Assembly of this complex is thought to be nucleated exclusively by the sequence-specific binding of the TFIID transcription factor complex, which is composed of the TATA-binding protein (TBP) and TBP-associated factors (TAF(II)s), to the different promoters. Here we isolate and characterize a new multiprotein complex that does not contain either TBP or a TBP-like factor but is composed of several TAF(II)s and other proteins. This complex can replace TFIID on both TATA-containing and TATA-lacking promoters in in vitro transcription assays. Moreover, an anti-TBP antibody that inhibits TBP- and TFIID-dependent transcription does not inhibit activity of this new complex. These results indicate that TBP-free RNA polymerase II mediated transcription may be able to occur in mammalian cells and that multiple preinitiation complexes may play an important role in regulating gene expression.

DNA Footprinting↗
PubMed1998

Ontogeny of endothelins-1 and -3, their receptors, and endothelin converting enzyme-1 in the early human embryo.

The targeted gene inactivation of endothelins-1 and -3 (ET-1 and ET-3) and of one of their receptors, ETB, in the mouse causes severe defects in the embryonic development. These defects, cardiovascular and craniofacial malformations for ET-1, and colonic agangliogenesis associated with skin pigmentation anomalies for ET-3 and the ETB receptor, reproduce pathological phenotypes due to natural mutations of the same genes in the mouse and the human. The mutant phenotypes have been causatively linked to deficient migration/proliferation/differentiation of neural crest cells, i.e., neurocristopathies. To bring new insight about the exact roles of ETs in development and the involvement of neural crest cells in these processes, we have explored, by in situ hybridization, the ontogeny in the early human embryo of the ET system (ET-1 and ET-3, ETA and ETB receptors, ET converting enzyme-1). ET receptor mRNA expression in neural crest cells starts at 3 wk of gestation and continues during the entire period studied (up to 6 wk of gestation). During this period, ETA expression progressively spreads to undifferentiated mesodermal components of various structures and organs (head and axial skeleton, lateral and ventral subdermal mesoderm), whereas ETB expression remains more restricted to fewer differentiated cells (neural tube, sensory and sympathetic ganglia, endothelium). Some of these tissues and structures that express either one of the receptors do not appear to be of neural crest origin. In the digestive tract and the cardiovascular area, the present observations on the sources of ETs and their target cells in the young embryo provide the basis for a dynamic interpretation of the results of gene targeting of the mouse and the human phenotypes, and point to other possible roles of ETs in other ontogenetic processes. The results support the concept of local, rather than hormonal, interactions between the sources and targets of ETs during development.

Aspartic Acid Endopeptidases↗
PubMed1998

Zebrafish vimentin: molecular characterization, assembly properties and developmental expression.

To provide a basis for the investigation of the intermediate filament (IF) protein vimentin in one of the most promising experimental vertebrate systems, the zebrafish (Danio rerio), we have isolated a cDNA clone of high sequence identity to and with the characteristic features of human vimentin. Using this clone we produced recombinant zebrafish vimentin and studied its assembly behaviour. Unlike other vimentins, zebrafish vimentin formed unusually thick filaments when assembled at temperatures below 21 degrees C. At 37 degrees C few filaments were observed, which often also terminated in aggregated masses, indicating that its assembly was severely disturbed at this temperature. Between 21 and 34 degrees C apparently normal IFs were generated. By viscometry, the temperature optimum of assembly was determined to be around 28 degrees C. At this temperature, zebrafish vimentin partially rescued, in mixing experiments, the temperature-dependent assembly defect of trout vimentin. Therefore it is apparently able to "instruct" the misorganized trout vimentin such that it can enter normal IFs. This feature, that assembly is best at the normal body temperature of various species, puts more weight on the assumption that vimentin is vital for some aspects of generating functional adult tissues. Remarkably, like in most other vertebrates, zebrafish vimentin appears to be an abundant factor in the lens and the retina as well as transiently, during development, in various parts of the central and peripheral nervous system. Therefore, promising cell biological investigations may now be performed with cells involved in the generation of the vertebrate eye and brain, and, in particular, the retina. Moreover, the power of genetics of the zebrafish system may be employed to investigate functional properties of vimentin in vivo.

Amino Acid Sequence↗
PubMed1998

Efficacy of the subcutaneous reformulated triptorelin depot in children with central precocious puberty.

The efficacy, safety and acceptance of newly formulated triptorelin s.c. (Decapeptyl Depot, DDsc) was compared to triptorelin i.m. (DDim) in seven children with central precocious puberty (CPP) in a prospective study. Both formulations were given for 6 months consecutively. During both treatment periods suppression of basal and gonadotropin-releasing hormone (GnRH)-stimulated levels of luteinizing hormone and follicle-stimulating hormone, suppression of sex steroids, arrest of the maturation of gonads and uterus, and slowing of bone maturation were achieved. The height standard deviation score for bone age increased significantly during DDsc treatment (-1.33+/-0.90 to 1.07+/-0.92, p < 0.05). The ratio bone age/chronological age decreased significantly during both treatment periods (1.25+/-0.24 to 1.20+/-0.23,p < 0.05, and 1.20+/-0.23 to 1.16+/-0.22, p < 0.05). With the injection of DDsc in the abdominal wall, a palpable, non-irritating resistance which gradually decreased in size occurred in one patient. With injection into the thigh no indurations were seen. No allergic reactions were encountered. Five of the patients considered DDsc therapy as more pleasant and described a definite decrease in fear of injections. All parents considered DDsc treatment as equal or better than DDim in respect to the suppression of their child' s puberty. It was concluded that DDsc is equipotent to DDim in the treatment of CPP. For the majority of patients DDsc was more acceptable than DDim. The thigh is recommended for the subcutaneous application of DD.

Child↗
PubMed1998

Fgf8 is mutated in zebrafish acerebellar (ace) mutants and is required for maintenance of midbrain-hindbrain boundary development and somitogenesis.

We describe the isolation of zebrafish Fgf8 and its expression during gastrulation, somitogenesis, fin bud and early brain development. By demonstrating genetic linkage and by analysing the structure of the Fgf8 gene, we show that acerebellar is a zebrafish Fgf8 mutation that may inactivate Fgf8 function. Homozygous acerebellar embryos lack a cerebellum and the midbrain-hindbrain boundary organizer. Fgf8 function is required to maintain, but not initiate, expression of Pax2.1 and other marker genes in this area. We show that Fgf8 and Pax2.1 are activated in adjacent domains that only later become overlapping, and activation of Fgf8 occurs normally in no isthmus embryos that are mutant for Pax2.1. These findings suggest that multiple signaling pathways are independently activated in the midbrain-hindbrain boundary primordium during gastrulation, and that Fgf8 functions later during somitogenesis to polarize the midbrain. Fgf8 is also expressed in a dorsoventral gradient during gastrulation and ectopically expressed Fgf8 can dorsalize embryos. Nevertheless, acerebellar mutants show only mild dorsoventral patterning defects. Also, in spite of the prominent role suggested for Fgf8 in limb development, the pectoral fins are largely unaffected in the mutants. Fgf8 is therefore required in development of several important signaling centers in the zebrafish embryo, but may be redundant or dispensable for others.

Amino Acid Sequence↗
PubMed1998

A series of no isthmus (noi) alleles of the zebrafish pax2.1 gene reveals multiple signaling events in development of the midbrain-hindbrain boundary.

Generation of cell diversity in the vertebrate central nervous system starts during gastrulation stages in the ectodermal germ layer and involves specialized cell groups, such as the organizer located at the midbrain-hindbrain boundary (MHB). Mutations in the zebrafish no isthmus (noi) gene alter development of the MHB, and affect the pax2.1 gene (formerly pax(zf-b)). Analysis of the structure of pax2.1 reveals at least 12 normal splice variants. The noi alleles can be arranged, by molecular and phenotypic criteria, into a series of five alleles of differing strength, ranging from a null allele to weak alleles. In keeping with a role in development of the MHB organizer, gene expression is already affected in the MHB primordium of the gastrula neural ectoderm in noi mutants. eng3 activation is completely and eng2 activation is strongly dependent on noi function. In contrast, onset of wnt1, fgf8 and her5 expression occurs normally in the null mutants, but is eliminated later on. Our observations suggest that three signaling pathways, involving pax2.1, wnt1 and fgf8, are activated independently in early anterior-posterior patterning of this area. In addition, analysis of the allelic series unexpectedly suggests that noi activity is also required during dorsal-ventral patterning of the MHB in somitogenesis stages, and possibly in a later eng expression phase. We propose that noi/pax2.1 participates in sequential signaling processes as a key integrator of midbrain-hindbrain boundary development.

Alleles↗
PubMed1998

Characterization of three novel members of the zebrafish Pax2/5/8 family: dependency of Pax5 and Pax8 expression on the Pax2.1 (noi) function.

The mammalian Pax2, Pax5 and Pax8 genes code for highly related transcription factors, which play important roles in embryonic development and organogenesis. Here we report the characterization of all members of the zebrafish Pax2/5/8 family. These genes have arisen by duplications before or at the onset of vertebrate evolution. Due to an additional genome amplification in the fish lineage, the zebrafish contains two Pax2 genes, the previously known Pax[b] gene (here renamed as Pax2.1) and a novel Pax2.2 gene. The zebrafish Pax2.1 gene most closely resembles the mammalian Pax2 gene in its expression pattern, as it is transcribed first in the midbrain-hindbrain boundary region, then in the optic stalk, otic system, pronephros and nephric ducts, and lastly in specific interneurons of the hindbrain and spinal cord. Pax2.2 differs from Pax2.1 by the absence of expression in the nephric system and by a delayed onset of transcription in other Pax2.1 expession domains. Pax8 is also expressed in the same domains as Pax2.1, but its transcription is already initiated during gastrulation in the primordia of the otic placode and pronephric anlage, thus identifying Pax8 as the earliest developmental marker of these structures. The zebrafish Pax5 gene, in contrast to its mouse orthologue, is transcribed in the otic system in addition to its prominent expression at the midbrain-hindbrain boundary. The no isthmus (noi) mutation is known to inactivate the Pax2.1 gene, thereby affecting the development of the midbrain-hindbrain boundary region, pronephric system, optic stalk and otic region. Although the different members of the Pax2/5/8 family may potentially compensate for the loss of Pax2.1 function, we demonstrate here that only the expression of the Pax2.2 gene remains unaffected in noi mutant embryos. The expression of Pax5 and Pax8 is either not initiated at the midbrain-hindbrain boundary or is later not maintained in other expression domains. Consequently, the noi mutation of zebrafish is equivalent to combined inactivation of the mouse Pax2 and Pax5 genes with regard to the loss of midbrain-hindbrain boundary development.

Amino Acid Sequence↗