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Differential Gene Expression Turning Genes on or keeping them off? Differential Gene Regulation • Transcriptional regulation • Post-transcriptional regulation • Translational regulation • Post-translational regulation Differential Gene Expression • Transcriptional • Transcription factor binding • Translational • Transcription factor interactions • Post-translational • Methylation • Post-transcriptional • Nucleosome/chromatin structure Differential Gene Expression • Transcriptional • Splicing • Post-transcriptional • Polyadenylation • Translational • Post-translational • Stability Differential Gene Expression • Transcriptional • Masking • Post-transcriptional • Antisense RNA • Translational • Post-translational Differential Gene Expression • Transcriptional • Glycosylation • Post-transcriptional • Acylation • Translational • Proteolytic processing • Post-translational Differential Gene Regulation • Hierarchies of transcriptional regulatory proteins – Transcription Factors • Regulators of regulators Transcription Initiation Transcriptional Activation Transcription Control Elements • Promoter – Basal elements (sites) • TATAA box • CCAAT box • GC boxes – Orientation and position dependent • Enhancer – Any combination of transcription factor binding sites – Orientation and position independent • Silencer – Binding site for proteins which make DNA inaccessible to txn factors Transcription Factors • Basal/General Txn Factors – TFIID • TBP - TATA binding protein • TAFs – TBP associated factors – CBP – CCAAT binding protein – SP1 – GGCGGG binding protein • Give a low level of txn • Often found as the only txn control elements of housekeeping genes Transcription Factors • Gene Specific Txn Factors – Classified by DNA binding domains & mechanism of transcriptional activation Transcription Factor Flavors Family Homeodomain Representative Hox POU LIM Paired Box Hoxa-1, Antp, eve, en Pit-1,Unc-86, Oct-2, Brn-5 Lim-1, Isl-1 Pax-1,2,6, Prd Forkhead/Winged Helix Fkh, HNF-3 Basic-helix-loop-helix MyoD, Ac, da, emc Basic leucine-zipper Zinc-finger AP1, Myc, C/EBP standard steroid receptors WT-1, Krox-20, Kr, hb GR, ER, RAR, kni Sox Sry, SoxD, Sox2 MADS box MEF-1, MCM-1 Take A Look www.devbio.com Website 5.4 Physical Arrangement of Regulatory Elements Cell-Type Specific Transcription • Tissue specificity • Promoter • Enhancer • Tissue specific txn factor and cognizant DNA element (site) Epigenetic Gene Regulation Differential Gene Expression Via Posttranscriptional Regulation Alternative or Differential Splicing Differential Splicing • Differential splicing requires cell-type specific splicing factors • Often one spliced mRNA does not encode a functional protein • When both alternative mRNAs encode functional proteins, one protein typically lacks an entire functional domain Differential Splicing Sex Determination in Drosophila Regulated by Differential Splicing Differential Splicing & Sex Girls Boys 3’ UTR Mediates Stability or Instability U-Rich 3’UTR mediates degradation of Regulation of mRNA Stability RNA masking and Polyadenylation • Factors bind to stored mRNA and prevent translation – smaug protein binds nanos mRNA • mRNAs not polyadenylated – deadenylated transcripts stable in oocyte • Adenylation of transcript allows translation Antisense RNA Regulates Translation Lin-4 RNA is complementary to several regions of lin-14 3’ UTR Formation of dsRNA prevents translation of lin-14
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