The histone H1°/H5 variant and terminal differentiation of cells during development of Xenopus laevis

The maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the H1(0)/H5 subclass. If the H1(0)/H5 variant has an important role in differentiation distinct from that of H1, it should display differential expression in time and position during development. Here we report that this prediction is verified during Xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone H1(0)/H5 expression that is different for the derivatives of each embryonic germ layer. However, the pattern of appearance of this variant during development does not reflect a simple correlation between its presence and the state of differentiation. Therefore, these results are pertinent to current ideas on differentiation and the involvement of lysine-rich histones in the repression of eukaryotic genes.     

Cell membrane-associated mucins and their adhesion-modulating property.

A class of highly sialylated glycoproteins with very large mucin-like domains that protrude high above the plasma membrane have been shown to strongly reduce cellular adhesion. In normal epithelial cells, where the expression is restricted to the luminal side of the cell, these molecules may prevent inadvertent closing of the lumen as a result of weak, non-specific protein-protein interactions between opposite luminal membranes. In malignant tumors cellular polarization is often lost, which can lead to the entire cell surface being covered by these molecules. The resulting strongly reduced adhesion and immune recognition properties may play an important role during invasion and metastasis.     

A single nucleotide polymorphism in an exon dictates allele dependent differential splicing of episialin mRNA

The episialin gene (MUC1) encodes an epithelial mucin containing a variable number of repeats with a length of twenty amino acids, resulting in many different alleles that can be subdivided into two size classes. The episialin pre-mRNA uses either one of two neighbouring splice acceptor sites for exon 2, which mainly encodes the repeats. Using the genetic polymorphism of the episialin gene to identify different alleles, we show here that the splice site recognition is allele dependent and is based on a single A/G nucleotide difference in exon 2 eight nucleotides downstream of the second splice acceptor site. Transfection experiments confirm that this polymorphic nucleotide regulates the splice site selection. The identity of this nucleotide is in most cases correlated with one of the size classes of the alleles, indicating that mutations altering the number of repeats seldom arise by unequal cross-over between the repeat regions.     

Higher ADCC of murine peritoneal cells after immunization with allogenic tumor cells as compared with stimulation by adriamycin, BCG, and thioglycolate

Normal peritoneal cells or spleen cells from C57BL mice could not lyse SRBC in an ADCC assay. After intraperitoneal injection of Adriamycin, BCG or thioglycolate the ADCC of peritoneal cells toward antibody-coated SRBC was elevated to 30% in contrast to the ADCC of spleen cells. However, peritoneal cells but not spleen cells of mice immunized with allogenic tumor cells (DBA SL2) showed ADCC levels at least two times higher than the levels observed after stimulation by other agents. Maximal ADCC levels (55.8%) were observed 10 to 15 days after immunization. Direct cytotoxicity towards SRBC increased to a maximum of 17.7% at 9 days after immunization. The effector cells in this system are thought to be macrophages, for ADCC activity was only present in the plastic-adherent cell fraction. Cell to cell contact was necessary for ADCC to occur; nonsensitized erythrocytes were not lysed when added to a mixture of effector cells and sensitized erythrocytes. Concentrations of antibody of 1 pg/ml were sufficient to induce ADCC, and effector cell to target cell ratios could be as low as 0.05. The finding that macrophages of mice immunized with allogenic tumor cells exhibit higher ADCC levels than macrophages elicited in other ways can contribute to the investigation of combined cancer therapy with antibodies and biological response modifiers.     

Linkage analysis of the Duffy blood group marker with several chromosome 1 genes in an extended pedigree with Charcot-Marie-Tooth disease

Summary We have recently demonstrated tight linkage of the Duffy blood group marker to the -spectrin gene in an extended pedigree with Charcot-Marie-Tooth neuropathy. To determine a more precise location of the Duffy blood group locus on the chromosome 1 map we have tested several more chromosome 1 genes for linkage with this marker. We found suggestive linkage with the antithrombin III and apolipoprotein A2 genes and conclusive linkage with the gene coding for -nerve growth factor.     

Interaction of the salivary low-molecular-weight mucin (MG2) with Actinobacillus actinomycetemcomitans

Periodontitis is associated with the presence of certain Gram-negative bacteria in the oral cavity, among these Actinobacillus actinomycetemcomitans. In order to determine which types of salivary components interact with A. actinomycetemcomitans two strains (HG 1175 and FDC Y4) were incubated with whole saliva and individual glandular secretions, viz. parotid, submandibular, and sublingual saliva. Immunochemical analysis by immunoblotting of bacteria-bound salivary proteins showed that IgA, the low-molecular mucin MG2, parotid agglutinin, and a 300 kDa sublingual and submandibular glycoprotein, were bound to the bacterial strains tested. In addition, adherence of A. actinomycetemcomitans to salivary proteins in a solid-phase was studied. After electrophoresis and transfer of salivary proteins to nitrocellulose membranes A. actinomycetemcomitans adhered only to MG2. In this assay periodate treatment, mild acid hydrolysis or neuraminidase digestion of the saliva glycoproteins abolished binding of two clinical isolates (HG 1175 and NY 664), suggesting that sialic acid residues on MG2 are involved in the binding. In contrast, adherence of the smooth laboratory strain Y4 was not affected by removal of sialic acid residues or even periodate treatment of MG2.Abbreviations S-IgA Secretory IgA - MG1 high-molecular-weight mucin - MG2 low-molecular-weight mucin - EP-GP extra parotid-glycoprotein - PRPs proline-rich proteins - SNA Sambucus nigra agglutinin - MAA Maackia amurensis agglutinin - PNA peanut agglutinin - UEA Ulex europaeus agglutinin     

Reconstitution of a surface transferrin binding complex in insect form Trypanosoma brucei.

In the bloodstream of the mammalian host, Trypanosoma brucei takes up host transferrin by means of a high-affinity uptake system, presumably a transferrin receptor. Transferrin-binding activity is seen in the flagellar pocket and is absent in insect form trypanosomes. By transfection we have reconstituted a transferrin-binding complex in insect form trypanosomes. Formation of this complex requires the products of two genes that are part of a variant surface glycoprotein expression site, expression site-associated gene (ESAG) 6 (encoding a protein with GPI-anchor) and ESAG 7 (encoding a protein without any obvious membrane attachment). This complex can be precipitated by transferrin-Sepharose and by an antibody directed only against the ESAG 6 protein. Transfection of ESAG 6 or 7 alone did not result in transferrin binding. In the transfected trypanosomes, the products of ESAG 6 alone and the combination of ESAG 6 and 7 did not exclusively localize to the flagellar pocket, but were present all over the surface of the trypanosome. The reconstituted transferrin-binding complex also did not result in the uptake of transferrin. Additional proteins present in bloodstream trypanosomes, but not in sufficient amounts in insect form trypanosomes, may therefore be required for the correct routing of the transferrin-binding complex to the flagellar pocket, and for its rapid internalization after ligand binding.