Protein kinase A is involved in the induction of early mesodermal marker genes by activin

In this study we have investigated the role of cAMP-dependent protein kinas e A (PKA) in the induction of the early mesodermal marker genes goosecoid a nd no tail by activin in zebrafish embryos. We show that upon treatment wit h activin, zebrafish blastula cells exhibit a rapid and transient increase in PKA activity. In these cells, activin rapidly induces the expression of the immediate early response genes goosecoid and no rail. Stimulation and i nhibition of PKA by activin, respectively: enhances and reduces the inducti on of goosecoid and no tail mRNA expression. Similar effects of PKA stimula tion and inhibition on the induction by activin of a 1.8 kb zebrafish goose coid promoter construct were observed. The induction by activin of a fragme nt of the zebrafish goosecoid promoter that mediates an immediate early res ponse to activin is blocked by inhibition of PKA. Activation of PKA alone h as no effect in these experiments. Finally, inhibition of PKA in whole embr yos by overexpression of a dominant negative regulatory subunit of PKA redu ces the expression of no tail and goosecoid, whereas the expression of even -skipped1 remains unaltered. Overexpression of the catalytic subunit of PKA in embryos does not affect expression of goosecoid, no tail or even-skippe d1. These data show that in dissociated blastulae, PKA is required, but not sufficient for activin signalling towards induction of goosecoid and no mi l. In intact zebrafish embryos, PKA contributes to induction of goosecoid a nd no tail, although it is not required or sufficient. (C) 1998 Elsevier Sc ience Ireland Ltd. All rights reserved.