Genetic analysis of Dictyostelium slug phototaxis mutants.

Abstract

Mapping and complementation analysis with 17 phototaxis mutations has established 11 complementation groups phoA-phoK distributed over six linkage groups. Statistical calculations from the complementation data yielded 17 as the maximum likelihood estimate of the number of pho genes assuming all loci are equally mutable. Most of the phototaxis mutants were found to exhibit bimodal phototaxis and all were found to be impaired in positive thermotaxis supporting convergence of the photosensory and thermosensory pathways. The thermotaxis mutant HPF228 was unaltered in phototaxis suggesting that the mutation in this strain affects a gene product whose site of action is before the convergence of the two pathways. Other phenotypes such as multiple tip formation by aggregates, stumpy fruiting bodies with short or absent stalks and short migration were associated with some pho alleles suggesting multiple biological roles for some gene products important in phototransduction.

Photosensory and thermosensory responses in Dictyostelium slugs are specifically impaired by absence of the F-actin cross-linking gelation factor (ABP-120)

“…Qualitative tests revealed that slug phototaxis was normal in each strain lacking one of the actin-binding proteins with the exception of the ABP-120-deficient mutant, which was severely defective (Figure 1). As with other reported phototaxis mutants [13,14], the slugs of this strain were disoriented and their phototaxis was bimodal, with two preferred directions (± α) either side of the direction towards the light source. In qualitative tests of phototaxis [14], the initial inoculum density is not accurately controlled and some growth occurs at the inoculation site as a result of carry over of the bacterial food source.…”

“…As with other reported phototaxis mutants [13,14], the slugs of this strain were disoriented and their phototaxis was bimodal, with two preferred directions (± α) either side of the direction towards the light source. In qualitative tests of phototaxis [14], the initial inoculum density is not accurately controlled and some growth occurs at the inoculation site as a result of carry over of the bacterial food source. It was previously reported that phototaxis is impaired when Dictyostelium slugs are allowed to form and migrate at high cell densities [15].…”

“…Since none of the four Ca 2+regulated actin-binding proteins tested were essential for phototaxis, we conclude that either the Ca 2+ -regulated actin filament cross-linking proteins are functionally redundant or intracellular Ca 2+ signals do not perform their postulated roles in slug orientation behaviour [8] by regulation of these particular proteins. Darcy et al [14] have shown that almost all phototaxis mutations also cause defects in thermotaxis. This is part of the evidence that the photosensory and thermosensory transduction pathways converge early so that most of the proteins involved are required for both phototaxis and thermotaxis.…”

“…Washed amoebae were exposed to a lateral light source for 48 h at 21°C. Trails were digitized and analysed using directional statistics [14,15] (see Supplementary material). In two experiments, pooling results for AX2 at cell densities less than 6 × 10 6 cells cm -2 yielded accuracies of phototaxis (κ) of 109 ± 13 and 119 ± 25.…”

Interactions and Cytotoxicity of Human Neurodegeneration- Associated Proteins Tau and α-Synuclein in the Simple Model Dictyostelium discoideum

“…This is consistent with yeast models of a synergistic relationship between the two proteins, with enhanced defects when both proteins are expressed ( Zabrocki et al, 2005 ; Ciaccioli et al, 2013 ). In D. discoideum , phototaxis and thermotaxis pathways share many downstream genes ( Darcy et al, 1994 ), so that when a phototaxis defect is detected, a thermotaxis defect is usually also present. In support of this, strains expressing α-synuclein displayed no defect in thermotaxis with accuracies similar to AX2 and strains expressing tau displayed reduced accuracies of thermotaxis ( Figure 3D ).…”