p38 Mitogen-Activated Protein Kinase Can Be Involved in Transforming Growth Factor β Superfamily Signal Transduction in Drosophila Wing Morphogenesis

p38 mitogen-activated protein kinase (p38) has been extensively studied as a stress-responsive kinase, but its role in development remains unknown. The fruit fly,Drosophila melanogaster , has two p38 genes,D-p38a andD-p38b . To elucidate the developmental function of theDrosophila p38’s, we used various genetic and pharmacological manipulations to interfere with their functions: expression of a dominant-negative form of D-p38b, expression of antisense D-p38b RNA, reduction of theD-p38 gene dosage, and treatment with the p38 inhibitor SB203580. Expression of a dominant-negative D-p38b in the wing imaginal disc caused adecapentaplegic (dpp )-like phenotype and enhanced the phenotype of adpp mutant. Dpp is a secretory ligand belonging to the transforming growth factor β superfamily which triggers various morphogenetic processes through interaction with the receptor Thick veins (Tkv). Inhibition of D-p38b function also caused the suppression of the wing phenotype induced by constitutively active Tkv (TkvCA ). Mosaic analysis revealed that D-p38b regulates the Tkv-dependent transcription of theoptomotor-blind (omb ) gene in non-Dpp-producing cells, indicating that the site of D-p38b action is downstream of Tkv. Furthermore, forced expression of TkvCA induced an increase in the phosphorylated active form(s) of D-p38(s). These results demonstrate that p38, in addition to its role as a transducer of emergency stress signaling, may function to modulate Dpp signaling.