Related items
Showing items related by title, author, creator and subject.
-
Differential regulation of mouse germline Ig gamma 1 and epsilon promoters by IL-4 and CD40Before Ig class switching, RNA transcription through the specific S regions undergoing recombination is induced by cytokines and other activators that induce and direct switching. The resulting germline (GL) transcripts are essential for switch recombination. To understand the differential regulation of mouse IgG1 and IgE, we compared the promoters for GL gamma1 and epsilon transcripts. We addressed the question of why the promoter that regulates GL epsilon transcription is more responsive to IL-4 than the gamma1 promoter and also why GL epsilon transcription is more dependent on IL-4 than is gamma1 transcription. We found that the IL-4-responsive region of the GL epsilon promoter is more inducible than that of the gamma1 promoter, although each promoter contains a binding site for the IL-4-inducible transcription factor Stat6, located immediately adjacent to a binding site for a basic region leucine zipper (bZip) family protein. However, the arrangement and sequences of the sites differ between the epsilon and gamma1 promoters. The GL epsilon promoter binds Stat6 with a 10-fold higher affinity than does the gamma1 promoter. Furthermore, the bZip elements of the two promoters bind different transcription factors, as the GL epsilon promoter binds and is activated by AP-1, whereas the gamma1 promoter binds and is activated by activating transcription factor 2. C/EBPbeta and C/EBPgamma also bind the gamma1 bZip element, although they inhibit rather than activate transcription. However, inhibition of promoter activity by C/EBPbeta does not require the bZip element and may instead occur via inhibiting the activity of NF-kappaB.
-
Constructing a feedback loop with circadian clock molecules from the silkmoth, Antheraea pernyiCircadian clocks are important regulators of behavior and physiology. The circadian clock of Drosophila depends on an autoinhibitory feedback loop involving dCLOCK, CYCLE (also called dBMAL, for Drosophila brain and muscle ARNT-like protein), dPERIOD, and dTIMELESS. Recent studies suggest that the clock mechanism in other insect species may differ strikingly from that of Drosophila. We cloned Clock, Bmal, and Timeless homologs (apClock, apBmal, and apTimeless) from the silkmoth Antheraea pernyi, from which a Period homolog (apPeriod) has already been cloned. In Schneider 2 (S2) cell culture assays, apCLOCK:apBMAL activates transcription through an E-box enhancer element found in the 5' region of the apPeriod gene. Furthermore, apPERIOD can robustly inhibit apCLOCK: apBMAL-mediated transactivation, and apTIMELESS can augment this inhibition. Thus, a complete feedback loop, resembling that found in Drosophila, can be constructed from silkmoth CLOCK, BMAL, PERIOD, and TIMELESS. Our results suggest that the circadian autoinhibitory feedback loop discovered in Drosophila is likely to be widespread among insects. However, whereas the transactivation domain in Drosophila lies in the C terminus of dCLOCK, in A. pernyi, it lies in the C terminus of apBMAL, which is highly conserved with the C termini of BMALs in other insects (except Drosophila) and in vertebrates. Our analysis sheds light on the molecular function and evolution of clock genes in the animal kingdom.
-
The basic helix-loop-helix transcription factor NeuroD1 facilitates interaction of Sp1 with the secretin gene enhancerThe basic helix-loop-helix transcription factor NeuroD1 is required for late events in neuronal differentiation, for maturation of pancreatic beta cells, and for terminal differentiation of enteroendocrine cells expressing the hormone secretin. NeuroD1-null mice demonstrated that this protein is essential for expression of the secretin gene in the murine intestine, and yet it is a relatively weak transcriptional activator by itself. The present study shows that Sp1 and NeuroD1 synergistically activate transcription of the secretin gene. NeuroD1, but not its widely expressed dimerization partner E12, physically interacts with the C-terminal 167 amino acids of Sp1, which include its DNA binding zinc fingers. NeuroD1 stabilizes Sp1 DNA binding to an adjacent Sp1 binding site on the promoter to generate a higher-order DNA-protein complex containing both proteins and facilitates Sp1 occupancy of the secretin promoter in vivo. NeuroD-dependent transcription of the genes encoding the hormones insulin and proopiomelanocortin is potentiated by lineage-specific homeodomain proteins. The stabilization of binding of the widely expressed transcription factor Sp1 to the secretin promoter by NeuroD represents a distinct mechanism from other NeuroD target genes for increasing NeuroD-dependent transcription.
