Biomedical subjects

S Stachel

Publications and source records attributed to S Stachel.

8 recordsLinked to original sources

PubMed2000

Xotx5b, a new member of the Otx gene family, may be involved in anterior and eye development in Xenopus laevis.

We describe the cloning, expression pattern and functional overexpression analysis of Xotx5b, a new member of the Otx gene family in Xenopus laevis. Early expression of Xotx5b resembles that of Xotx2, being detected in the organizer region at early gastrula stage, and, shortly after, also in anterior neuroectoderm. During neurula stages Xotx5b exhibits a changing and dynamic pattern of expression. After neural tube closure, Xotx5b is expressed in the eye and pineal gland, both involved in photoreception. Overexpression of Xotx5b has a similar effect to that of Xotx2, producing posterior truncations and inducing ectopic cement gland and neural tissue in whole embryos. In animal cap assays, Xotx5b and Xotx2 are both able to activate XAG, to strongly suppress the expression of the epidermal marker XK81, and to reciprocally activate each other. Finally, in einsteck transplantation assays, Xotx5b is able to respecify a tail/trunk organizer to a head organizer.

Amino Acid Sequence↗

PubMed1998

Follistatin and noggin are excluded from the zebrafish organizer.

The patterning activity of the Spemann organizer in early amphibian embryos has been characterized by a number of organizer-specific secreted proteins including Chordin, Noggin, and Follistatin, which all share the same inductive properties. They can neuralize ectoderm and dorsalize ventral mesoderm by blocking the ventralizing signals Bmp2 and Bmp4. In the zebrafish, null mutations in the chordin gene, named chordino, lead to a severe reduction of organizer activity, indicating that Chordino is an essential, but not the only, inductive signal generated by the zebrafish organizer. A second gene required for zebrafish organizer function is mercedes, but the molecular nature of its product is not known as yet. To investigate whether and how Follistatin and Noggin are involved in dorsoventral (D-V) patterning of the zebrafish embryo, we have now isolated and characterized their zebrafish homologues. Overexpression studies demonstrate that both proteins have the same dorsalizing properties as their Xenopus homologues. However, unlike the Xenopus genes, zebrafish follistatin and noggin are not expressed in the organizer region, nor are they linked to the mercedes mutation. Expression of both genes starts at midgastrula stages. While no patterned noggin expression was detectable by in situ hybridization during gastrulation stages, later expression is confined to presumptive cartilage cells in the branchial arches and the neurocranium and to proximal regions of the pectoral fin buds. follistatin transcripts in gastrulating embryos are confined to anterior paraxial regions, which give rise to head mesoderm and the first five somites. The dorsolateral extent of this expression domain is regulated by Bmp2b, Chordino, and Follistatin itself. In addition, transient expression was observed in a subset of cells in the posterior notochord anlage. Later, follistatin is expressed in brain, eyes, and somites. Comparison of the spatiotemporal expression pattern of follistatin and noggin with those of bmp2b and bmp4 and overexpression studies suggest that Noggin and Follistatin may function as Bmp antagonists in later processes of zebrafish development, including late phases of D-V patterning, to refine the early pattern set up by the interaction of Chordino and Bmp2/4. It thus appears that many, but not all, aspects of early dorsoventral patterning are shared among different vertebrate species.

Amino Acid Sequence↗

PubMed1989

Cloning of a lymphocyte homing receptor reveals a lectin domain.

Lymphocytes express cell surface molecules, termed homing receptors, that mediate their selective attachment to specialized high endothelial venules found within secondary lymphoid organs. Previous work has demonstrated that the adhesive interaction between lymphocytes and the endothelium of peripheral lymph nodes appears to involve a lectin-like activity. Moreover, MEL-14, a monoclonal antibody that blocks lymphocyte-peripheral lymph node binding and presumably recognizes the homing receptor mediating this adhesive interaction, appeared to detect the lectin-like receptor. In this paper we describe the cloning of a murine cDNA that encodes the antigen recognized by the MEL-14 antibody. Characterization of the cDNA encoding the putative mouse peripheral lymph node-specific homing receptor shows that it contains a lectin domain that appears to be involved in the binding of lymphocytes to peripheral lymph node endothelium, thus defining a new type of cellular adhesion molecule. This result supports a novel mechanism for the distribution of lymphocyte populations to various lymphoid organs.

Amino Acid Sequence↗

PubMed1987

Characterization of Agrobacterium tumefaciens virulence proteins induced by the plant factor acetosyringone.

The Ti plasmid virulence (vir) loci encode functions essential for the transfer of the T-DNA element from Agrobacterium tumefaciens to plant cells. The expression of these loci is specifically signaled by plant phenolics such as acetosyringone. Here, we characterize the protein products that are induced in Agrobacterium grown in the presence of acetosyringone. More than 10 to 15 proteins are induced in strains harboring different Ti plasmids. Two general classes of acetosyringone-induced proteins are observed, encoded either within or outside the vir region. Synthesis of both classes of proteins requires acetosyringone and the products of the vir regulatory genes A and G. Those proteins encoded outside the vir region define a novel category of proteins, the virulence-related proteins, which are both chromosomally and Ti plasmid-encoded. The molecular weight and subcellular localization of several pTiA6 vir-induced proteins are identified. The most abundant induced protein has a molecular weight of 65,000, and is the single product of the virE locus; this protein distributes into both cell envelope and soluble fractions. Three proteins with molecular weights of approximately 33,000, 80,000 and 25,000 fractionate with the cell envelope and are encoded by genes within the 5' half of the virB locus. The envelope localization of the virB proteins suggests that they play a role in directing T-DNA transfer events that occur at the bacterial surface.

Acetophenones↗

PubMed1986

Promoters of Agrobacterium tumefaciens Ti-plasmid virulence genes.

The DNA sequences of the promoter and 5' upstream regions of six Agrobacterium tumefaciens Ti-plasmid encoded virulence (vir) genes were determined. The transcription initiation sites were mapped by the S1 nuclease protection assay. In the -10 region, the vir promoters share a consensus sequence that is homologous to a DNA sequence found in the same region of E. coli promoters. In contrast, the -35 region sequences are variable. Several vir genes contain two common hexanucleotide sequences, 5'CGAGTA3' and 5'GCAATT3'. Translation initiation codons for all vir genes, except virG, are preceded by sequences homologous to the ribosome binding site sequences found in E. coli.

Base Sequence↗

PubMed1986

Analysis of Agrobacterium tumefaciens virulence mutants in leaf discs.

The leaf disc transformation system provides a simple means to score expression of various T-DNA markers within days of infection by Agrobacterium tumefaciens as well as long-term selection for growth of transformed callus and shoots. In this report, we describe the application of this system to evaluation of marker transfer and integration in a comprehensive set of defined avirulent mutants of A. tumefaciens. We conclude that virC is not essential when the T-DNA is present on a binary vector. The most likely explanation for this is that the virC gene product is involved in generation of a T-DNA intermediate.

Arginine↗

PubMed1985

New cloning vehicles for transformation of higher plants.

We have constructed a set of small vectors based on the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens which allow the transfer of exogenous DNA into plant chromosomes. These vectors contain: (i) a chimeric gene containing the transcriptional control signals from the nopaline synthase gene and the coding sequence for neomycin phosphotransferase; (ii) the ColE1 replicon; (iii) the cos site of bacteriophage lambda; (iv) the border sequences from the ends of the T-DNA region of the Ti plasmid; and (v) a wide host range replicon. Due to the small size of these cosmid vectors, DNA fragments up to 35 kbp can be inserted by an in vitro packaging method in Escherichia coli. The ability of these vectors to be stably replicated in both E. coli and A. tumefaciens allows their subsequent transfer to and maintenance in Agrobacterium without intermediate genetic manipulations. We demonstrate that DNA cloned into these vectors in A. tumefaciens can efficiently transform plants when in trans with a wild-type Ti plasmid which donates the functions necessary for DNA transfer and integration. We also show that only the right border of the T-DNA is necessary for DNA transformation.

Journal Article↗

PubMed1982

Nopaline synthase: transcript mapping and DNA sequence.

The DNA sequence of the nopaline synthase gene (nos) from Agrobacterium tumefaciens Ti plasmid pTiT37 and adjacent regions up to the right border of the T-DNA was determined. The 5' and 3' termini of the polyadenylated nos mRNA, isolated from a T37 tobacco teratoma tumor line, were localized by S1 mapping. The final mRNA is unspliced, encoded by a region of about 1450 bp, and specifies an open reading frame of 413 amino acids. Potential transcriptional signals in the 5' flanking DNA, such as CATAAA ("TATA box") and GGTCACTAT ("CAT box"), bear close resemblance to other eukaryotic promoters. Two putative polyadenylation signals, AATAAA and AATAAT, are found about 135 and 50 bp from the 3' end, respectively. This study may provide information for the development of expression vectors for genes in plant cells; moreover, the structural gene can be used as an easy screenable marker.

Amino Acid Oxidoreductases↗