Direct is correct

A challenge to conventional thinking has been met and answered by two new articles in this issue. Hua et al. (page 1035) and Paladino et al. (page 1023) have imaged live three-dimensional cells to reaffirm that a class of proteins takes a direct route to the apical membrane.

The suggestion that GPI-linked apical proteins traffic directly from the Golgi to the apical plasma membrane was made—and widely accepted—years ago based on classical biochemical experiments. But a recent article proposed instead that, in MDCK cells, this class of proteins were delivered first to the basolateral membrane, and then endocytosed and sent across the cell to the apical membrane. Striking images were presented to support this view, but the work also involved a somewhat controversial new assay.

The new papers...