Abp1 regulates pseudopodium number in chemotaxing Dictyostelium cells

Abstract

When starved, Dictyostelium cells respond to extracellular signals, polarize, and move with strong persistence into aggregation centers. Actin and actin-associated proteins play key roles in regulating both the morphology and directed movements of cells during chemotactic aggregation. Recently, we identified an ortholog of Abp1 in Dictyostelium (Dabp1). The first actin binding protein identified in yeast, Abp1 functions in actin-based endocytosis in yeast and in receptor-mediated endocytosis in mammalian cells. To explore the functions for Abp1 in Dictyostelium, we examined the phenotypes of cells that overexpressed the Dabp1 protein and cells that eliminated Dabp1 expression. In these mutants, most actin-based processes were intact. However, cell motility was altered during early development. During chemotactic streaming, more than 90% of wild-type cells had a single leading pseudopodium and a single uropodium, whereas more than 27% of Dabp1 null cells projected multiple pseuodpodia. Similarly, ∼90% of cells that overexpressed Dabp1 projected multiple pseudopodia during chemotactic streaming, and displayed reduced rates of cell movement. Expression of the SH3 domain of Dabp1 showed this domain to be an important determinant in regulating pseudopodium number. These results suggest that Abp1 controls pseudopodium number and motility in early stages of chemotactic aggregation in Dictyostelium.

PakB binds to the SH3 domain ofDictyosteliumAbp1 and regulates its effects on cell polarity and early development

“…In agreement with previous results, red fluorescent protein (RFP)–dAbp1 was enriched at the leading edge of developed migrating wild-type cells (Figure 4C, top; Supplemental Video S4; Wang and O'Halloran, 2006). In migrating PakBˉ cells, however, RFP-dAbp1 was diffusely distributed in the cytosol (Figure 4C, bottom; see also Figure 6C and Supplemental Video S5).…”

“…The overexpression of dAbp1 in Dictyostelium has been reported to delay early development, including cell elongation, streaming, and aggregate formation, by several hours (Wang and O'Halloran, 2006). We confirmed this phenotype using the wild-type JH10 cell line.…”

“…We demonstrate that this N-terminal segment contains an actin filament–binding module and two closely spaced proline-rich motifs that serve as docking sites for the SH3 domain of Dictyostelium actin-binding protein 1 (dAbp1). dAbp1 binds class I myosins and plays an important role in regulating cell polarity and pseudopod formation during chemotaxis (Wang and O'Halloran, 2006; Dieckmann et al. , 2010).…”

The Mammalian Actin-Binding Protein 1 Is Critical for Spreading and Intraluminal Crawling of Neutrophils under Flow Conditions

“…In this study, the percentage of migrating cells was severely compromised in mAbp1 PMN under static conditions revealed no differences compared with control cells. Similarly, the downregulation of the mAbp1 ortholog Dabp1 in Dictyostelium discoideum by RNAi technique (siDabp1) did not affect cell migration (63). In contrast, the overexpression of Dabp1 led to an impaired migration, suggesting a functional compensation by other signaling molecules in the siDabp1 cells (63).…”

“…Similarly, the downregulation of the mAbp1 ortholog Dabp1 in Dictyostelium discoideum by RNAi technique (siDabp1) did not affect cell migration (63). In contrast, the overexpression of Dabp1 led to an impaired migration, suggesting a functional compensation by other signaling molecules in the siDabp1 cells (63). A compensatory mechanism could also work in mAbp1 2/2 PMN, allowing adhesion, spreading, and migration at least under static conditions.…”