PHOTOSENSORY AND THERMOSENSORY RESPONSES IN DICTYOSTELIUM SLUGS ARE SPECIFICALLY IMPAIRED BY ABSENCE OF THE F-ACTIN CROSS-LINKING GELATION FACTOR (ABP-120)

Chemotactic aggregation of starving amoebae of Dictyostelium discoideu m leads to formation of a motile, multicellular organism - the slug - whose anterior tip controls its phototactic and thermotactic behaviour , To determine whether proteins that regulate the in vitro assembly of actin are involved in these responses, we tested phototaxis and therm otaxis in mutant slugs in which the gene encoding one of five actin-bi nding proteins had been disrupted. Of the proteins tested - severin, a lpha-actinin, fimbrin, the 34 kD actin-bundling protein and the F-acti n cross-linking gelation factor (ABP-120) - only ABP-120 proved essent ial for normal phototaxis and thermotaxis in the multicellular slugs. The related human protein ABP-280 is required for protein phosphorylat ion cascades initiated by lysophosphatidic acid and tumor necrosis fac tor alpha. The repeating segments constituting the rod domains of ABP- 120 and ABP-280 may be crucial for the function of both proteins in sp ecific signal transduction pathways by mediating interactions with reg ulatory proteins.