Dictyostelium discoideum requires an Alix/AIP1 homolog, DdAlix, for morphogenesis in alkaline environments

Alix and its homologs are involved in various phenomena such as endosomal protein-sorting and adaptation to stress conditions. In this study, we found that development of Dictyostelium discoideum Alix (DdAlix) deletion mutant (alx−) cells was impaired in alkaline pH environments. The fruiting body formation efficiency of alx− cells at pH 9.0 was significantly lower than that of wild-type cells (6.8 ± 4.2% vs 93 ± 6.3%). The alkaline-sensitive phenotype of alx− cells was rescued by addition of salt. The phenotype was rescued by exogenous expression of human Alix as well as DdAlix but not by that of either Saccharomyces cerevisiae Alix homolog Rim20 or Bro1. DdAlix may be, structurally and functionally, more related to human Alix than to yeast Rim20 and Bro1.