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Two transmembrane signaling mechanisms control expression of the cAMP receptor gene CAR1 during Dictyostelium
J M Louis1, C L Saxe, A R Kimmel
1Laboratory of Cellular and Developmental Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Abstract:
Dictyostelium discoideum is among the best characterized organisms for the study of receptor/guanine nucleotide binding protein-mediated control of differentiation. Dictyostelium grow unicellularly but form fully differentiated multicellular organisms through a developmental program regulated by secreted cAMP activating specific cell-surface receptors. Dictyostelium respond differentially to cAMP at different developmental stages. During early development, expression of certain genes is induced by low-level oscillations of extracellular cAMP. Later, continuous, high cAMP concentrations will promote expression of specific genes in multicellular structures. Here, we show that the cAMP receptor gene CAR1, which is essential for development, utilizes two promoters that are activated at distinct stages of development and respond to different extracellular cAMP conditions. One promoter is active with low-level oscillations of cAMP; exposure to high cAMP concentrations will repress this promoter and induce a second promoter. The CAR1 mRNAs are alternatively spliced but encode identical proteins. Thus, through differential sensitivity to its own ligand, cAMP, two promoters and alternative splicing regulate CAR1 expression during Dictyostelium development.
Insights
Dictyostelium discoideum development relies on the CAR1 gene, which uses two promoters. These promoters respond to different cyclic adenosine monophosphate (cAMP) levels, regulating gene expression during distinct developmental stages.
Area of Science:
- Cellular and Molecular Biology
- Developmental Biology
- Biochemistry
Background:
- Dictyostelium discoideum undergoes a complex developmental program, transitioning from unicellular to multicellular life.
- This development is regulated by secreted cyclic adenosine monophosphate (cAMP), which activates cell-surface receptors.
- Differential gene expression in Dictyostelium is controlled by varying extracellular cAMP concentrations at different developmental stages.
Purpose of the Study:
- To investigate the regulatory mechanisms of the CAR1 gene, essential for Dictyostelium development.
- To determine how CAR1 gene expression is controlled by different extracellular cAMP conditions and developmental stages.
- To elucidate the role of promoters and alternative splicing in CAR1 gene regulation.
Main Methods:
- Analysis of CAR1 gene promoter activity under varying cAMP conditions.
- Examination of CAR1 mRNA expression and alternative splicing patterns during development.
- Utilizing Dictyostelium discoideum as a model organism for developmental studies.
Main Results:
- The essential CAR1 gene in Dictyostelium discoideum is regulated by two distinct promoters.
- One promoter is activated by low-level cAMP oscillations, while high cAMP concentrations repress it and activate a second promoter.
- CAR1 messenger RNAs (mRNAs) are alternatively spliced but result in identical proteins.
Conclusions:
- CAR1 gene expression is precisely regulated during Dictyostelium development through differential promoter activation.
- The two promoters exhibit distinct sensitivities to extracellular cAMP, enabling stage-specific gene expression.
- Alternative splicing of CAR1 mRNA contributes to the regulation of gene expression, ensuring identical protein production.