A developmental mutation (npfL1) resulting in cell death in Physarum polycephalum

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 (npfzl) in a gene that functions in sexual as well as apogamic development. In npfz+ apogamic development, binucleate cells arise from uninucleate cells by mitosis without cytokinesis at the end of an extended cell cycle. In npfzl 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 npfzl 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 npfz+ 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 npfzl cells, and multipolar spindles were also observed. None of these features were observed in npfz+ cells, suggesting that a specific effect of the npfzl mutation may be an incomplete alteration of nuclear structure from the amoebal to the plasmodia1 state.

Characterization of npf mutants identifying developmental genes in Physarum

“…The mutant strain C L 6 l l l carries the recessive npfA1 mutation; this strain was isolated from thegadAh strain CL following mutagenesis of amoebae and enrichment for cells that failed to form plasmodia (Anderson & Dee, 1977 strains carrying different m a t A alleles, indicating that the npfA+ allele was not essential for sexual development. The npfA locus is unlinked to the developmental loci n p p , npfz and matA (Anderson & Dee, 1977;Bailey et al, 1992a). Our analyses showed that npfA was also unlinked to npfG, npfx and npfM (data not shown; P > 0.05, x2 tests).…”

Physarum polycephalum mutants in the photocontrol of sporulation display altered patterns in the correlated expression of developmentally regulated genes

“…The plates were incubated at 24°C for 48 h to facilitate hatching of amoebae from cysts and subsequently at 30°C to allow amoebal growth while suppressing the unwanted formation of haploid plasmodia by apogamic development (Bailey et al . , ; Bailey ). After several days at 30°C, amoebal colonies became visible.…”

“…100 lL of the diluted amoebal cyst suspension were mixed on a plate with 100 lL of a standardized formalin-killed E. coli suspension that served as a food source for the amoebae (FKB; [Dee 1986]) and the droplet was spread evenly over a DSPB agar plate (diluted semidefined phosphate buffered medium; [Anderson et al 1997]) by streaking with the conical tip of a 10-mL glass pipette. The plates were incubated at 24°C for 48 h to facilitate hatching of amoebae from cysts and subsequently at 30°C to allow amoebal growth while suppressing the unwanted formation of haploid plasmodia by apogamic development (Bailey et al 1987(Bailey et al , 1992Bailey 1995). After several days at 30°C, amoebal colonies became visible.…”

Plasmodium development in the myxomycete Physarum polycephalum: genetic control and cellular events

“…l a ; Bailey et al, 1992;Solnica-Krezel e t al., 1995). This is consistent with previous studies implicating the second half of this cell cycle as a crucial one for development, when many alterations in gene expression and cellular organization begin (e.g.…”