. "Any process that modulates the frequency, rate or extent of the activity of any activin receptor signaling pathway." . . "regulation of activin receptor signaling pathway" . "regulation of activin receptor signalling pathway" . "regulation of activin signaling pathway" . "regulation of activin signalling pathway" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .