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Spore coat protein synthesis during development of Dictyostelium discoideum requires a low-molecular-weight inducer
Abstract:
The major spore coat proteins of Dictyostelium discoideum are synthesized during the culmination stage of development. In an attempt to examine the regulatory mechanisms involved, spore coat protein synthesis by pseudoplasmodia harvested prior to culmination and incubated in submerged culture under various environmental conditions has been monitored. It is reported that the synthesis of spore coat proteins SP170, SP103, SP94, SP82, SP76, and SP55 is dependent upon the presence of a low-molecular-weight (Mr approx 100), heat-stable factor secreted by cells incubated at high density in buffer. Previous studies have implicated cyclic AMP, ammonia, and amino acids in spore cell differentiation. Partial purification of the spore coat protein inducing factor (SPIF), together with attempts to mimic its activity, indicate that SPIF is not identical with any of these molecules and it is probably also distinct from DIF and "fruit juice," two other factors which regulate the spore-stalk decision and the initiation of culmination, respectively, in D. discoideum. In addition to SPIF, the continued expression of the spore coat protein genes also requires that the integrity of the pseudoplasmodium be maintained. Unlike the expression of many other genes after aggregation, this latter requirement cannot be replaced by exogenous cyclic AMP. Termination of spore coat protein gene expression occurs despite the presence of excess exogenous SPIF and hence involves mechanisms other than the destruction or depletion of SPIF.
Insights
A novel heat-stable factor, spore coat protein inducing factor (SPIF), regulates Dictyostelium discoideum spore coat protein synthesis. Pseudoplasmodium integrity is also essential for continued gene expression, independent of cyclic AMP.
Area of Science:
- Cellular and Molecular Biology
- Developmental Biology
- Biochemistry
Background:
- Spore coat proteins in Dictyostelium discoideum are crucial for development and synthesized during culmination.
- Previous research suggested roles for cyclic AMP, ammonia, and amino acids in spore cell differentiation.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling the synthesis of major spore coat proteins in Dictyostelium discoideum.
- To identify and characterize the factors involved in inducing spore coat protein synthesis.
Main Methods:
- Monitoring spore coat protein synthesis in pseudoplasmodia under various environmental conditions.
- Partial purification of the spore coat protein inducing factor (SPIF).
- Assessing the impact of pseudoplasmodium integrity and exogenous factors on gene expression.
Main Results:
- Spore coat protein synthesis (SP170, SP103, SP94, SP82, SP76, SP55) depends on a low-molecular-weight, heat-stable factor (SPIF) secreted by high-density cells.
- SPIF is distinct from cyclic AMP, ammonia, amino acids, DIF, and "fruit juice."
- Maintaining pseudoplasmodium integrity is required for continued spore coat protein gene expression, a process not replaceable by exogenous cyclic AMP.
Conclusions:
- A novel factor, SPIF, is identified as a key regulator of Dictyostelium discoideum spore coat protein synthesis.
- Pseudoplasmodium integrity is a critical, non-cyclic AMP-dependent requirement for sustained spore coat protein gene expression.
- The termination of spore coat protein gene expression involves mechanisms beyond SPIF depletion.