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Biomedical subjects

G J Veenstra

Publications and source records attributed to G J Veenstra.

6 recordsLinked to original sources
PubMed1996

Ultrastructural organization and regulation of a biomaterial adhesin of Staphylococcus epidermidis.

Coagulase-negative staphylococci have emerged as important pathogens in infections associated with intravascular devices. Microbial adherence to biomaterial surfaces is a crucial step in the pathogenesis of these infections. Staphylococcal surface proteins (herein referred to as SSP-1 and SSP-2) are involved in the attachment of Staphylococcus epidermidis 354 to polystyrene. In the present study we show that the adhesin protrudes from the cell surface as a fimbria-like polymer. Furthermore, in vitro proteolytic cleavage of SSP-1 produces an SSP-2-like protein which coincides with a loss of adhesive function. SSP-1 expression is down-regulated in a phenotypical variant of S. epidermidis 354 whereas SSP-2 expression is not. These results could suggest that proteolytic cleavage is a key to the regulation of the adhesive state of S. epidermidis in vivo.

Adhesins, Bacterial↗
PubMed1995

Dynamic and differential Oct-1 expression during early Xenopus embryogenesis: persistence of Oct-1 protein following down-regulation of the RNA.

As a first step towards the elucidation of the role of the transcription factor Oct-1 in development, we prepared a monoclonal antibody to study the spatio-temporal distribution of Oct-1 protein in vivo. Here we report differential expression of the Oct-1 gene in the Xenopus embryo both at the RNA and the protein level. Transcripts and protein are detected in ectodermal and mesodermal cell lineages, in which the expression exhibits a pattern of progressive spatial restriction in the course of development. The Oct-1 expression as reported here is not correlated with cell density or cell proliferation in the embryo. Our results suggest a role of Oct-1 in the specification and differentiation of neuronal and neural crest cells. In many other cells, the developmental decision to down regulate Oct-1 is delayed, probably due to a high stability of the protein.

Animals↗
PubMed1994

The promoter of the Xwnt-5C gene contains octamer and AP-2 motifs functional in Xenopus embryos.

The Xwnt-5C gene is expressed in Xenopus embryos from the early gastrula stage onwards. The transcription of Xwnt-5C is regulated differentially with respect to transcript size, timing and localization. To gain insight into the generation of the Xwnt-5C expression pattern, we started to analyze the transcriptional regulation of this gene. We isolated Xwnt-5C genomic DNA sequences. By microinjection of chimaeric reporter constructs into Xenopus embryos we demonstrate that the upstream region contains a promoter functional in vivo. Of the several putative binding sites for trans-acting factors, present in a minimal promoter fragment, some have been studied in more detail. Mutations in an octamer motif and in an AP-2 consensus sequence interfere with the activity of the Xwnt-5C minimal promoter. In vitro binding assays with extracts from gastrula stage Xenopus embryos show that the octamer motif of the Xwnt-5C promoter can bind several Octamer binding factors, one of which is Oct1.

Animals↗
PubMed1993

Differential expression of the human, mouse and rat IGF-II genes.

The IGF-II gene is a complex transcription unit. Multiple transcripts are synthesized as a result of alternate promoter usage and the splicing of unique 5' untranslated regions to common coding exons. In order to characterize the mechanisms of IGF-II gene regulation we performed comparative studies to define essential features of IGF-II expression in human, rat and mouse. Homologous promoter regions of the human, mouse and rat IGF-II genes were fused to the luciferase reporter gene and expression was measured in various cell lines that have an endogenously active or inactive IGF-II gene expression pattern, respectively. The transient promoter activity of the human, mouse and rat IGF-II constructs was further compared with the endogenous activity of the IGF-II gene in various tissues and cell lines of human, mouse and rat origin. The results indicate that in transient expression assays employing heterologous systems (e.g., mouse promoter in human cells), most IGF-II promoter constructs are active, albeit at low levels. Maximal promoter activity is only observed, however, in homologous systems (e.g., human promoter constructs tested in human cells). This suggests that each promoter, despite the strong sequence conservation of the homologous human, rat and mouse promoters, is adapted to the levels of the transcription factors present in its natural environment. Finally, IGF-II gene expression is not only regulated at the level of transcription but also depends on mRNA stability. We show that human, rat and also mouse IGF-II mRNAs are subjected to specific endonucleolytic cleavage, suggesting that specific cleavage of IGF-II mRNAs must be of general physiological importance.

Aging↗