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Developmental mechanisms regulating the rapid decrease in a cohesion glycoprotein mRNA in Dictyostelium function
A Chandrasekhar1, M Rotman, B Kraft
1Department of Biology, University of Iowa, Iowa City 52242.
Abstract:
During the morphogenetic program in Dictyostelium discoideum, the transcript of the gene encoding the cohesion glycoprotein gp80 accumulates to a maximum level between 4 and 6 hr, (just prior to the onset of aggregation), remains high between 6 and 10 hr (the ripple to loose aggregate stages), and then decreases to less than 10% of the maximum level between 10 and 12 hr (the tight aggregate stage). The level of gp80 transcript also decreases precipitously at the time of the erasure event in the program of dedifferentiation, or when cAMP is added to a dedifferentiating cell population prior to the erasure event. In the dedifferentiation-defective mutant HI4, the cAMP-stimulated system for rapidly reducing the level of gp80 transcript is intact, but the mechanism functioning at the time of the erasure event is defective, demonstrating that the two reduction mechanisms are dissociable. By comparing the levels of gp80 transcript with the levels of in vitro transcription of the gene in isolated nuclei, it is demonstrated that the rapid reduction of gp80 transcript immediately after aggregation and immediately after addition of 10(-4) M cAMP are the result of increased transcript degradation. The rapid reduction of gp80 transcript at the erasure event may also be due to increased transcript degradation, but transcriptional regulation cannot be completely ruled out in this case.
Insights
The gp80 glycoprotein transcript in Dictyostelium discoideum is regulated during development. Its rapid reduction is primarily due to increased transcript degradation, with distinct mechanisms for aggregation and dedifferentiation.
Area of Science:
- Cellular and Molecular Biology
- Developmental Biology
- Gene Regulation
Background:
- The morphogenetic program in Dictyostelium discoideum involves precise gene expression changes.
- The glycoprotein gp80 is crucial for cell adhesion and its transcript levels fluctuate during development.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling gp80 transcript levels during Dictyostelium discoideum development.
- To differentiate between transcriptional control and post-transcriptional regulation (degradation) of the gp80 gene.
Main Methods:
- Quantification of gp80 transcript levels during different developmental stages.
- Analysis of in vitro transcription rates using isolated nuclei.
- Comparison of transcript levels in wild-type and dedifferentiation-defective mutants (HI4).
Main Results:
- gp80 transcript levels peak before aggregation and decrease significantly during later stages.
- Rapid reduction of gp80 transcript occurs upon aggregation and cAMP addition, primarily via increased degradation.
- The cAMP-stimulated reduction mechanism is distinct from the one involved in the dedifferentiation erasure event, as shown in mutant HI4.
Conclusions:
- Two dissociable mechanisms regulate gp80 transcript reduction: one triggered by aggregation/cAMP and another at the dedifferentiation erasure event.
- Increased transcript degradation is the primary mechanism for rapid gp80 transcript reduction post-aggregation and upon cAMP stimulation.
- While degradation is likely involved, transcriptional regulation cannot be entirely excluded for the gp80 transcript reduction during the erasure event.