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Updated: Jul 27, 2025
A Rapid In Vivo Bioassay for Developmentally Active Enhancers
Characterization of Developmentally Regulated cAMP/Ca
Steven Pelech1, Harry Paddon1, Linda Kwong2
1The Biomedical Research Centre, The University of British Columbia, Vancouver, B.C., Canada V6T 1W5.
Abstract:
Cell-free extracts of the slime mold Dictyostelium discoideum were assayed for phosphorylating activity towards endogenous proteins and towards histone H1, casein and myelin basic protein (MBP). During development, protein kinase activity towards all of these substrates steadily increased and peaked between the aggregation and the pseudoplasmodial stages. Particulate-associated kinase activity was solubilized with 1% CHAPS, and separated into 300-400 kDa and ∼ 100 kDa components on Sephacryl S-300. The 300-400 kDa peak exhibited the most pronounced developmental increase in MBP phosphorylating activity. It was further fractionated on DEAE-Sephacel and heparin-Sepharose, and in each case, it coeluted with the histone H1 phosphorylating activity. The activity of this kinase was unaffected by cAMP and calmodulin, but it was reduced to 50% by ∼ 350 mM NaCl, 5 mM NaF and 40 μg polylysine/ml. The ∼ 100 kDa peak exhibited the most pronounced increase in casein kinase activity during development. Most of the casein phosphorylating activity did not bind to DEAE-Sephacel; it was distinct from casein kinase 2, which was not developmentally regulated. In parallel with these elevated kinase activities during development, there was increased in vitro phosphorylation of a number of Dictyostelium proteins, including two major phosphoproteins of 140 and 94 kDa.
Insights
Protein kinase activity in Dictyostelium discoideum increases during development, peaking at specific stages. This study identifies distinct kinase fractions with varying substrate specificities and developmental regulation.
Area of Science:
- Cellular and Molecular Biology
- Developmental Biology
- Biochemistry
Background:
- Slime mold Dictyostelium discoideum undergoes complex developmental processes.
- Protein phosphorylation plays a crucial role in regulating cellular functions and developmental transitions.
- Understanding the regulation of protein kinases is key to deciphering developmental pathways.
Purpose of the Study:
- To investigate the developmental regulation of protein phosphorylating activities in Dictyostelium discoideum.
- To characterize the properties and substrate specificities of key protein kinases involved in development.
- To identify specific protein kinase fractions that exhibit significant changes in activity during development.
Main Methods:
- Assay of cell-free extracts for phosphorylating activity against endogenous proteins, histone H1, casein, and myelin basic protein (MBP).
- Solubilization of particulate-associated kinase activity using CHAPS and separation via Sephacryl S-300 chromatography.
- Further fractionation using DEAE-Sephacel and heparin-Sepharose chromatography to characterize kinase properties.
Main Results:
- Protein kinase activity towards all tested substrates increased during development, peaking between aggregation and pseudoplasmodial stages.
- Two major kinase fractions (300-400 kDa and ~100 kDa) were identified, with the larger fraction showing pronounced developmental increase in MBP and histone H1 activity.
- The ~100 kDa fraction showed the most significant increase in casein kinase activity, distinct from non-developmentally regulated casein kinase 2.
- Increased in vitro phosphorylation of endogenous Dictyostelium proteins (140 and 94 kDa) was observed in parallel with elevated kinase activities.
Conclusions:
- Protein kinase activity is developmentally regulated in Dictyostelium discoideum, with distinct fractions exhibiting specific substrate preferences and developmental profiles.
- The identified kinase fractions are likely involved in mediating key developmental transitions.
- Further characterization of these kinases will provide insights into the molecular mechanisms governing Dictyostelium development.
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