[Messenger proteins].

Many proteins are internalized by live cells following a pathway that differs from classical endocytosis. Thus, they gain direct access to the cell cytoplasm and nucleus. The same proteins, very often, are secreted even though they lack a signal peptide. This very original mechanism of signal transduction opens the way to the reinterpretations of several developmental phenomenons and physiological observations. In addition, the discovery of this type of intercellular signalling has opened the way to the development of widely used peptidic vectors.