Constitutively active mutant G(s)α (G225T) and null-mutant Gα(i-2) (G203T) induce primitive endoderm from stem cells

In F9 teratocarcinoma stem cells, retinoic acid induces a primitive endoderm-like phenotype and a sharp decline in Gα(1-2), a response mimicked by expression of RNA antisense to Gα(1-2) in the absence of this morphogen (D.C. Watkins, G. L. Johnson, and C. C. Malbon. Science Wash. DC 258: 1373- 1375, 1992). The role of the G(s)α/Gα(1-2) axis in cellular differentiation was explored. In the absence of retinoic acid, F9 stem cells stably expressing a constitutively active mutant of G(s)α (G225T) progressed to the primitive endoderm phenotype, as judged by morphological and differentiation markers, such as tissue plasminogen activator. Although elevated in cells expressing G225T G(s)α, adenosine 3',5'-cyclic monophosphate does not mimic retinoic acid action and alone fails to induce stem cells to primitive endoderm. In the absence of retinoic acid, expression of a null mutant of Gα(1-2) (G203T) also induced stem cells to primitive endoderm. These observations establish G proteins in the G(s)α/Gα(1-2) axis as a control point for regulating progression to primitive endoderm independent of adenylate cyclase, in the present study's model of early mouse development.