Spatial expression of the genome: the signal hypothesis at forty.

The signal hypothesis, formulated by Günter Blobel and David Sabatini in 1971, and elaborated by Blobel and his colleagues between 1975 and 1980, fundamentally expanded our view of cells by introducing the concept of topogenic signals. Cells were no longer just morphological entities with compartmentalized biochemical functions; they were now active participants in the creation and perpetuation of their own form and identity, the decoders of linear genetic information into three dimensions.