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A developmental mutation (npfL1) resulting in cell death in Physarum polycephalum
J Bailey1, L Solnica-Krezel, R W Anderson
1Department of Genetics, University of Leicester, UK.
Abstract:
In Physarum, microscopic uninucleate amoebae develop into macroscopic multinucleate plasmodia. In the mutant strain, RA614, plasmodium development is blocked. RA614 carries a recessive mutation (npfL1) in a gene that functions in sexual as well as apogamic development. In npfL+ apogamic development, binucleate cells arise from uninucleate cells by mitosis without cytokinesis at the end of an extended cell cycle. In npfL1 cultures, apogamic development became abnormal at the end of the extended cell cycle. The cells developed a characteristic rounded, vacuolated appearance, nuclear fusion and vigorous cytoplasmic motion occurred, and the cells eventually died. Nuclei were not visible by phase-contrast microscopy in most of the abnormally developing cells, but fluorescence microscopy after DAPI staining revealed intensely staining, condensed nuclei without nucleoli. Studies of tubulin organization during npfL1 development indicated a high frequency of abnormal mitotic spindles and, in some interphase cells, abnormally thick microtubules. Some of these features were observed at low frequency in the parental npfL+ strain and may represent a pathway of cell death, resembling apoptosis, that may be triggered in more than one way. Nuclear fusion occurred during interphase and mitosis in npfL1 cells, and multipolar spindles were also observed. None of these features were observed in npfL+ cells, suggesting that a specific effect of the npfL1 mutation may be an incomplete alteration of nuclear structure from the amoebal to the plasmodial state.
Insights
A mutation in Physarum
Area of Science:
- Cell Biology
- Developmental Biology
- Genetics
Background:
- Physarum amoebae transition from microscopic uninucleate to macroscopic multinucleate plasmodia.
- Plasmodium development is crucial for Physarum life cycle and functions.
- Apogamic development involves mitosis without cytokinesis, forming binucleate cells.
Purpose of the Study:
- Investigate the role of the npfL1 mutation in blocking Physarum plasmodium development.
- Characterize the cellular and molecular defects caused by the npfL1 mutation during apogamic development.
- Explore potential links between npfL1 defects and cell death pathways.
Main Methods:
- Comparative analysis of wild-type (npfL+) and mutant (npfL1) Physarum strains.
- Microscopy techniques including phase-contrast and fluorescence microscopy (DAPI staining).
- Tubulin organization studies to assess mitotic spindle and microtubule dynamics.
Main Results:
- npfL1 mutant exhibits abnormal apogamic development, characterized by cell rounding, vacuolation, nuclear fusion, and cell death.
- Abnormal mitotic spindles and thickened microtubules were observed in npfL1 cells.
- Features resembling apoptosis were noted, suggesting a cell death pathway triggered by the mutation.
Conclusions:
- The npfL1 mutation disrupts normal nuclear structure transition from amoebal to plasmodial states.
- npfL1-induced defects may trigger a cell death pathway, potentially similar to apoptosis.
- The npfL1 gene is essential for both sexual and apogamic development in Physarum.