A Rab-based view of membrane traffic in the ciliate Tetrahymena thermophila.

Biologists have long recognized that some single-celled organisms show striking morphological and behavioral complexity, and details of the genetic underpinnings can be mined from the trove of newly-sequenced genomes. Ciliates, among which Tetrahymena thermophila and Paramecium tetraurelia have received most attention, provide clear examples of a lineage in which, as in animal cells, the core pathways of membrane traffic have undergone dramatic expansion and elaboration to facilitate multiple modes of exocytosis and endocytosis. Recent surveys of the Rab GTPases in T. thermophila, including analysis of a large set of GFP-tagged copies, provide a new set of compartmental markers for this lineage, as well as striking views of membrane dynamics in these cells. In addition, phylogenetic analysis of the Tetrahymena Rabs suggests that different eukaryotic lineages may have independently evolved some functionally similar pathways.