INDUCTION OF SOMATOSTATIN IMMUNOREACTIVITY IN CULTURED CILIARY GANGLION NEURONS BY ACTIVIN IN CHOROID CELL-CONDITIONED MEDIUM

We have previously shown that the expression of somatostatin-like immu noreactivity in cultured ciliary ganglion neurons is stimulated by a m acromolecule found in choroid cell-conditioned medium (ChCM). Here, we present the following evidence that this somatostatin-stimulating act ivity (SSA) is activin: human recombinant activin induces somatostatin -like immunoreactivity in CG neurons; ChCM induces hemoglobin synthesi s in K562 cells, a biological activity characteristic of activin; acti vin A-specific antibodies recognize a protein in ChCM; cultured choroi d cells contain activin RNA; and SSA is inhibited by follistatin, a sp ecific activin-binding protein. Thus, activin is likely to be a neurod ifferentiation factor for CG neurons in vivo.