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Articles by Jeffrey G. Williams
Total Records ( 2 ) for Jeffrey G. Williams
  Hong-Yu Wang and Jeffrey G. Williams
  The tip of the Dictyostelium slug functions much like an embryonic organiser; when grafted onto the flank of a recipient slug, it recruits a mass of prespore cells and leads them away as part of a secondary slug. CudA is a nuclear protein which is expressed in prespore cells where it acts as a specific transcription factor. CudA is also expressed in an anteriorly located group of cells, the tip-organiser, that is believed to constitute the functional tip. We identify an expansin-like gene, expl7, that is expressed within the tip-organiser region and which is not expressed in a cudA null strain. The expl7 promoter contains a region that binds to CudA in vitro and this region is necessary for expression in the tip-organiser. These results provide an end-point for a previously defined signal transduction pathway in which regionalised expression of the ACA adenylyl cyclase within the tip-organiser leads to localised cAMP-induced activation of STATa and consequent binding of STATa to the cudA promoter. STATa then induces expression of cudA and cudA directs the transcription of target genes such as expl7.
  Hong Yu Wang and Jeffrey G. Williams
  cotC requires the transcription factor CudA for its expression in the posterior, prespore cells of the slug, while the expL7 gene requires CudA for its expression in the anterior, tip-organiser region. In order to identify additional transcription factors that might mediate tip-organiser specific expression, we performed affinity chromatography on slug nuclear extracts. The affinity matrix bore cap-site distal sequences from region A′ of the expL7 promoter; an essential region located upstream of the CudA binding domain. One of the proteins purified was G-box binding factor (GBF), a zinc finger transcription factor which binds to G-rich elements, known as G boxes, that are present in the promoters of many developmental genes, including cotC. Previous work identified an essential sequence motif within region A′ and we show that this element is a G box, that binds recombinant GBF. Moreover, a G box from within the cotC promoter can substitute for region A′ of expL7 in directing tip-organiser specific expression of expL7. Thus the same two transcription factors, CudA and GBF, seem to co-operate to direct both tip-organiser and prespore gene expression. How then is specificity achieved? Replacing a CudA binding region in the cotC promoter with the CudA binding domain from expL7 strongly represses cotC promoter activity. Hence we suggest that differences in the topology of the multiple CudA half- sites contained within the two different CudA binding regions, coupled with differences in the signalling environment between tip-organiser cells and prespore cells, ensure correct expL7 expression.
 
 
 
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