. "A series of molecular signals initiated by the binding of an extracellular ligand to an activin receptor on the surface of a target cell, and ending with regulation of a downstream cellular process, e.g. transcription." . . "activin receptor signaling pathway" . "activin receptor signalling pathway" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .