UDP-glucose dehydrogenase required for cardiac valve formation in zebrafish.

Cardiac valve formation is a complex process that involves cell signaling events between the myocardial and endocardial layers of the heart across an elaborate extracellular matrix. These signals lead to marked morphogenetic movements and transdifferentiation of the endocardial cells at chamber boundaries. Here we identify the genetic defect in zebrafish jekyll mutants, which are deficient in the initiation of heart valve formation. The jekyll mutation disrupts a homolog of Drosophila Sugarless, a uridine 5'-diphosphate (UDP)-glucose dehydrogenase required for heparan sulfate, chondroitin sulfate, and hyaluronic acid production. The atrioventricular border cells do not differentiate from their neighbors in jekyll mutants, suggesting that Jekyll is required in a cell signaling event that establishes a boundary between the atrium and ventricle.

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.

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.

A general affinity chromatographic method for preparing monospecific antibody to mammalian serum haptoglobin.

A general affinity chromatographic method for preparation of monospecific antibody to serum haptoglobin of any species is described. Hemoglobin prepared from the species to be immunized is coupled to an organomercurical substituted agarose gel support (Affi-Gel 501). The immobilized hemoglobin binds haptoglobin with great affinity and allows removal of other serum proteins by extensive washing. The haptoglobin-hemoglobin complexes are then specifically eluted by buffers containing dithiothreitol or other thiols and are further purified by chromatography on concanavalin A-agarose and Sephacryl S-200 columns. The pure complexes are very effective immunogens. Potent monospecific antisera to rabbit and to human haptoglobin have been prepared. The potential usefulness of affinity chromatography support media with specifically cleavable ligand sites in studies of haptoglobin and in other biological studies is discussed.

Endogenous mediators of the acute-phase reaction. I. Rabbit granulocytic pyrogen and its chromatographic subfractions.

LP, a saline extract of exudate-derived rabbit granulocytes, shown to be free of endotoxin contamination by sensitive LAL assay, can elicit brisk acute-phase responses in the rabbit. Following a single large intravenous dose of LP (875 mce) there is a brisk fall in serum iron at 8 hr and marked elevations in concentrations of CxRP, haptoglobin, fibrinogen, and ceruloplasmin and a lesser rise in sialic acid in the blood at 24 hr, which return toward baseline to varying degrees by 48 hr. When the crude LP solution is fractionated by column chromatography on Sephadex G75, all detectable acute-phase mediating activity elutes in a fraction (pool C) which contains all the pyrogenic activity and about 15% of the total eluted protein. Within the limitations of the methods employed, the acute phase stimulating activity and the pyrogenic activity of LP preparations appear to be closely linked.

Translation of Pseudomonas aeruginosa bacteriophage PP7 RNA by a cell-free amino acid incorporating system from Escherichia coli.

We have compared the activities of the RNA genomes of Pseudomonas aeruginosa phage PP7 and coliphages Qbeta and f2 in a cell-free amino acid incorporating system derived from Escherichia coli. The rate of incorporation of [(14)C]leucine in the PP7 RNA-directed system is greater than in the systems directed by either Qbeta or f2 RNA. The response to changes in phage RNA concentrations is similar in all the systems, reaching a saturation level at 0.75 to 1.0 mg of RNA per ml of reaction mixture. Analysis of complete reaction mixtures of the PP7 RNA and of the Qbeta RNA systems by sucrose gradient centrifugation shows generally similar patterns for both RNAs. The principal differences are that in the PP7 system a slightly higher percentage of RNA forms ribosome complexes and that the polysomes are somewhat smaller. PP7 RNA is also degraded more extensively during the reaction than is Qbeta RNA. Analysis of the products of the reactions by acrylamide gel electrophoresis shows that PP7 coat protein is the only identifiable product of the PP7 RNA-directed system, suggesting that only the coat protein cistron is translated by E. coli ribosomes.