The non-muscle myosin phosphatase PP1beta (flapwing) negatively regulates JNK in wing imaginal discs of Drosophila

Drosophila flapwing (flw) codes for serine/threonine protein phosphatase type 1beta (PP1beta). Regulation of non-muscle myosin activity is the single essential flw function that is non-redundant with the three closely related PP1alpha genes. Flw is thought to dephosphorylate the non-muscle myosin regulatory light chain, Spaghetti Squash (Sqh); this inactivates the non-muscle myosin heavy chain, Zipper (Zip). Thus, strong flw mutants lead to hyperphosphorylation of Sqh and hyperactivation of non-muscle myosin activity. Here, we show genetically that a Jun N-terminal kinase (JNK) mutant suppresses the semi-lethality of a strong flw allele. Alleles of the JNK phosphatase puckered (puc) genetically enhance the weak allele flw1, leading to severe wing defects. Introducing a mutant of the non-muscle myosin binding subunit (Mbs) further enhances this genetic interaction to lethality. We show that puc expression is upregulated in wing imaginal discs mutant for flw1 and pucA251, and that this upregulation is modified by JNK and Zip. The level of phosphorylated (active) JNK is elevated in flw1 enhanced by puc. Together, we show that disruption of non-muscle myosin activates JNK and puc expression in wing imaginal discs.

Key Words: Drosophila, JNK, non-muscle myosin phosphatase, serine/threonine protein phosphatase type 1

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