Mutual activation of Ets-1 and AML1 DNA binding by direct interaction of their autoinhibitory domains.
(41/18504)
The transcription factors Ets-1 and AML1 (the alphaBl subunit of PEBP2/CBF) play critical roles in hematopoiesis and leukemogenesis, and cooperate in the transactivation of the T cell receptor (TCR) beta chain enhancer. The DNA binding capacity of both factors is blocked intramolecularly but can be activated by the removal of negative regulatory domains. These include the exon VII domain for Ets-1 and the negative regulatory domain for DNA binding (NRDB) for alphaB1. Here we report that the direct interaction between the two factors leads to a reciprocal stimulation of their DNA binding activity and activation of their transactivation function. Detailed mapping revealed two independent contact points involving the exon VII and NRDB regions as well as the two DNA binding domains. Using deletion variants and dominant interfering mutants, we demonstrate that the interaction between exon VII and NRDB is necessary and sufficient for cooperative DNA binding. The exon VII and NRDB motifs are highly conserved in evolution yet deleted in natural variants, suggesting that the mechanism described is of biological relevance. The mutual activation of DNA binding of Ets and AML1 through the intermolecular interaction of autoinhibitory domains may represent a novel principle for the regulation of transcription factor function. (+info)
Tissue-specific distribution of breast-muscle-type and leg-muscle-type troponin T isoforms in birds.
(42/18504)
In order to show the tissue-specific distribution of troponin T (TnT) isoforms in avian skeletal muscles, their expression was examined by electrophoresis of the breast and leg muscles of seven avian species and immunoblotting with the antiserum against fast skeletal muscle TnT. It has been reported in the chicken that breast-muscle-type (B-type) and leg-muscle-type (L-type) TnT isoforms are expressed specifically in the adult breast and leg muscles, respectively. Their differential expression patterns were confirmed in all birds examined in this study. The expression of a segment encoded by the exon x series of TnT was also examined by immunoblotting with the antiserum against a synthetic peptide derived from the exon x3 sequence, because the segment has been shown to be included exclusively in the B-type, but not in the L-type TnT. The expression of the segment was found only in the breast muscle, but not in the leg muscle of all birds examined. TnT cDNA sequences from the duck breast and leg muscles were determined and showed that only B-type TnT had an exon x-related sequence, suggesting that the expression of B-type TnT containing the exon x-derived segment is conserved consistently in the birds. (+info)
Cloning and expression of a novel chicken sulfotransferase cDNA regulated by GH.
(43/18504)
We have used mRNA differential display to compare gene expression in normal and GH receptor-deficient dwarf chickens, and report here the characterization of one differentially expressed gene, which shows significant sequence identity to the sulfotransferase gene family. Partial cDNA clones were isolated from a chicken liver cDNA library and an additional sequence was obtained using 5' rapid amplification of cDNA ends. A complete cDNA probe hybridizes to three transcripts (2.4, 2.0 and 1.45 kb) on Northern blots of chicken liver RNA, which differ in the length of the 3' untranslated region. All three transcripts are expressed at higher levels in normal vs dwarf chickens, as expected for a GH-regulated gene. The expression of this sulfotransferase mRNA was also detected in skeletal muscle, but not other tissues. The administration of GH to chickens increased the hepatic expression within 1 h, suggesting this sulfotransferase could be directly regulated by GH. Sulfotransferase activity, using estradiol or corticosterone as substrate, is detected in cells transfected with an expression vector containing the full-length cDNA. The sequence of this sulfotransferase does not show significant similarity with any subfamily of the sulfotransferases and its endogenous substrate is presently unknown. However, we speculate that GH activation of sulfotransferase activity could play a role in reducing concentrations of growth-antagonistic steroid hormones in GH target tissues. These results demonstrate the usefulness of differential display in this model system to identify genes that play a role in mediating GH action. (+info)
Comparative genomic analysis of the interferon/interleukin-10 receptor gene cluster.
(44/18504)
Interferons and interleukin-10 are involved in key aspects of the host defence mechanisms. Human chromosome 21 harbors the interferon/interleukin-10 receptor gene cluster linked to the GART gene. This cluster includes both components of the interferon alpha/beta-receptor (IFNAR1 and IFNAR2) and the second components of the interferon gamma-receptor (IFNGR2) and of the IL-10 receptor (IL10R2). We report here the complete gene content of this GART-cytokine receptor gene cluster and the use of comparative genomic analysis to identify chicken IFNAR1, IFNAR2, and IL10R2. We show that the large-scale structure of this locus is conserved in human and chicken but not in the pufferfish Fugu rubripes. This establishes that the receptor components of these host defense mechanisms were fixed in an ancestor of the amniotes. The extraordinary diversification of the interferon ligand family during the evolution of birds and mammals has therefore occurred in the context of a fixed receptor structure. (+info)
A model for studying megakaryocyte development and biology.
(45/18504)
The limited current understanding of megakaryocyte-lineage development and megakaryocyte biology is in large part because of a paucity of useful systems in which to conduct experiments. To overcome this problem, we have developed a transgenic mouse that uses the GP-Ibalpha regulatory sequences to achieve megakaryocyte-lineage restricted expression of an avian retroviral receptor. Through the transgenic avian receptor, avian retroviruses can efficiently and selectively infect megakaryocyte-lineage cells in vitro and in vivo. Serial infections can be performed to introduce and express multiple genes in the same cell. We have used this system to generate and characterize a pure population of primary CD41-positive megakaryocyte progenitors. (+info)
Apoptosis of villous epithelial cells and follicle-associated epithelial cells in chicken cecum.
(46/18504)
The process of the disappearance of epithelial cells was examined in chicken cecal villi and follicle-associated epithelium (FAE). The apoptotic epithelial cells with intense DNA-fragmentation and their exfoliation were found in the villous tips. The epithelial cells with weak DNA-fragmentation were seen in the upper portion of the villi and their sparse exfoliations were also found there. Numerous epithelial cells in the intestinal lumen expressed the apoptotic features. A row of apoptotic epithelial cells with DNA-fragmentation was also found in the apical FAE, whereas no M cells exhibited any apoptotic signs. In all cecal regions, CD3+, CD8+, and TCR2+ lymphocytes were predominant in the epithelium at the upper portion of the villi and the FAE. CD4+ lymphocytes were mainly seen in the lamina propria. TCR1+ lymphocytes were not abundant in comparison with TCR2+ lymphocytes in the epithelium. TCR3+ T lymphocytes were rarely detected. These results suggest that the chicken cecal epithelial cells exfoliated into the lumen after the induction of the apoptosis, and that the induction may be involved with CD3+, CD8+, and TCR2+ lymphocytes. No death in M cells suggests that M cells may transform into microvillous epithelial cells. (+info)
Differential usage of two 5' splice sites in a complex exon generates additional protein sequence complexity in chicken CLIP-170 isoforms.
(47/18504)
Reverse transcription-polymerase chain reaction amplification and cloning of cDNA encoding the chicken CLIP-170(11) isoform of the Cytoplasmic Linker Protein 170 gene revealed an unusual source of protein sequence variation. In addition to differential combinatorial splicing of two cassette exons to yield four CLIP-170 protein isoforms, we found differential usage of alternative 5'-splice junctions in a single exon. Splicing at the downstream site yields message containing 18 bp of nucleotide sequence that is missing from message spliced at the more 5' site. This 18 bp sequence encodes a segment of 6 amino acids that fills a gap in the alignment of chicken and human CLIP-170 homologue sequences. Differential usage of the 5'-splice junctions in this complex exon appears to be tissue- rather than isoform-specific. (+info)
Clonal expansion of antigen-specific CD4 T cells following infection with Salmonella typhimurium is similar in susceptible (Itys) and resistant (Ityr) BALB/c mice.
(48/18504)
The results show that CD4 T cells specific for a recombinant antigen expressed in Salmonella typhimurium proliferate normally in mice that express the susceptible form of the Ity gene at early times after infection but do not retain the capacity to produce gamma interferon later in the infection. (+info)