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Specific nuclear elimination in polyploid plasmodia of the slime mold Physarum polycephalum
A K Werenskiold1, T Schreckenbach, G Valet
1Ludwig Institute for Cancer Research, Bern, Inselspital, Switzerland.
Abstract:
In growing plasmodia of the myxomycete Physarum polycephalum (G2-phase), three distinct classes of nuclei with a relative DNA content of 1x, 2x, and 4x are observed in the presumed haploid strain CL. The 2x and 4x species comprise up to 35% and 5% of the nuclei. Quantitative cytofluorometric studies of nuclei isolated in either G2- or S-phase or after FUDR treatment (G1 arrest) show that the three nuclear populations undergo a synchronous mitotic cycle and that the relative DNA content of the nuclear fractions in G-2 phase reflects the 2c, 4c, and 8c state. The heterogeneity of the nuclear population does, however, seem to be restricted to the growth phase. During a starvation period of 4 days that always preceeds sporulation (and also meiosis), the 4c nuclear population is reduced to 7%, 8c nuclei are no longer detected. These results suggest that a mechanism exists in Physarum for the selective detection and elimination of polyploid nuclei.
Insights
Physarum polycephalum exhibits nuclear DNA content heterogeneity during growth. A selective elimination mechanism for polyploid nuclei is suggested before sporulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Mycology
Background:
- Growing plasmodia of the myxomycete Physarum polycephalum display nuclear DNA content variations.
- A presumed haploid strain (CL) shows three distinct nuclear classes with relative DNA content of 1x, 2x, and 4x.
Purpose of the Study:
- To investigate the nature and dynamics of nuclear DNA content heterogeneity in Physarum polycephalum.
- To determine if this heterogeneity is regulated during the cell cycle and preceding sporulation.
Main Methods:
- Quantitative cytofluorometry was used to analyze isolated nuclei.
- Nuclei were analyzed in different cell cycle phases (G2, S, G1 arrest via FUDR treatment).
- Nuclear populations were examined during growth and starvation periods preceding sporulation.
Main Results:
- Three nuclear populations (1x, 2x, 4x DNA content) were observed in G2-phase, with 2x and 4x comprising up to 35% and 5% of nuclei.
- These populations exhibit synchronous mitotic cycles, with G2 DNA content reflecting 2c, 4c, and 8c states.
- During starvation, the 4x population significantly reduced (to 7%), and 8c nuclei were undetectable, suggesting selective elimination.
Conclusions:
- Nuclear DNA content heterogeneity in Physarum polycephalum is primarily restricted to the growth phase.
- A mechanism for the selective detection and elimination of polyploid nuclei exists in Physarum.
- This regulation is crucial for preparing the organism for sporulation and meiosis.