Expression of the beta3 tubulin gene (beta Tub60D) in the visceral mesoderm of Drosophila is dependent on a complex enhancer that binds Tinman and UBX.
The beta3 tubulin gene of Drosophila is expressed in the major mesodermal derivatives during their differentiation. The gene is subject to complex stage- and tissue-specific transcriptional control by upstream as well as downstream regions. Analysis of the vm1 enhancer, which is responsible for tissue-specific expression in the visceral mesoderm and is localized in the intron, revealed a complex modular arrangement of regulatory elements. In vitro and in vivo experiments uncovered two binding sites, termed UBX1 and UBX2, for the product of the homeotic gene Ultrabithorax (Ubx), which are required for high-level expression in pPS6 and PS7. Further analysis of the vm1 enhancer revealed that deletion of a specific element, termed element 7 (e7), abolishes transcription of the lacZ reporter gene in all parasegments except pPS6/PS7. Gel-retardation and footprint analysis identified a binding site for the homeodomain protein Tinman, which is essential for the specification of the dorsal mesoderm, within e7. Simultaneous deletion of two further sequence blocks in the vml enhancer, named elements 3 (e3), and 6 (e6), results in a reduction analogous to that caused by removal of e7. The e6 sequence contains conserved motifs also found in the visceral enhancer of the Ubx gene. Therefore we conclude that these elements act in concert with the Tinman binding site to achieve high expression levels. Thus the vm1 enhancer of the beta3 tubulin gene contains a complex array of elements that are involved in transactivation by a combination of tissue- and position-specific factors including Tinman and UBX.
Kremser
T
T
Fachbereich Biologie, Entwicklungsbiologie, Philipps-Universität Marburg, Germany.
Hasenpusch-Theil
K
K
Wagner
E
E
Buttgereit
D
D
Renkawitz-Pohl
R
R
D000818:Animals; D051943:Antennapedia Homeodomain Protein; D001483:Base Sequence; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D014404:Tubulin / Q000235:genetics*
D051943:Antennapedia Homeodomain Protein; C497974:Antp protein, Drosophila; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D014404:Tubulin; C066177:Ubx protein, Drosophila; C403179:betaTub60D protein, Drosophila; C102933:tin protein, Drosophila