Bradyzoite-specific gene expression in Toxoplasma gondii requires minimal genomic elements.
BAG1 is a small heat-shock protein of Toxoplasma gondii that is specifically expressed in the cyst-forming bradyzoite stage of the parasite. Upregulation of BAG1 mRNA occurs early during the differentiation pathway from tachyzoites to bradyzoites. In order define genomic elements involved in bradyzoite-specific gene regulation, chloramphenicol acetyltransferase (CAT)-reporter gene studies were performed with 5' flanking sequences of the BAG1 gene. Tachyzoites, transiently transfected with the BAG1/cat construct, exhibited very low CAT activity (200 fold less than in parasites transfected with a tubulin promoter/cat construct). After induction of bradyzoite differentiation by alkaline pH shift, however, CAT activity increased 50 fold, demonstrating bradyzoite-specific expression of the CAT reporter gene under control of 5' flanking sequences of BAG1. Stage-specific regulation of BAG1/CAT was independent of the 3'-flanking region, since constructs containing 3'-flanking sequences of the tachyzoite-specific SAG1 gene showed identical regulation to those containing the BAG1 3'-flanking region. The kinetics of BAG1/CAT induction in stably transfected parasites is similar to the kinetics of endogenous BAG1 expression: increased CAT activity was first detected on day 3 after alkaline pH shift (20 fold) and was dramatically upregulated 250 fold on day 4. A series of deletions in the BAG1 5'-flanking sequences demonstrated that a 324 nucleotide (nt) fragment, starting 60 nt upstream of the BAG1 transcription start, is sufficient to confer stage-specific regulation on the CAT reporter. These deletion analyses demonstrate that bradyzoite-specific expression of a heterologeous reporter gene requires only minimal genomic sequences.
Bohne
W
W
Institute of Hygiene and Microbiology, University of Wuerzburg, Germany.
Wirsing
A
A
Gross
U
U
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000235:genetics; D004252:DNA Mutational Analysis; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000096:biosynthesis / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid; D017384:Sequence Deletion; D014122:Toxoplasma / Q000235:genetics* / Q000254:growth & development; D014162:Transfection / Q000379:methods; D015854:Up-Regulation; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
C106179:BAG1 protein, Toxoplasma; D006360:Heat-Shock Proteins; D015800:Protozoan Proteins; D015500:Chloramphenicol O-Acetyltransferase; D001616:beta-Galactosidase