The C. elegans epidermis is a barrier epithelium that functions as the first line of defense against the environment. The epidermis actively defends worms against pathogen infection and repairs wounds. The death-associated protein kinase
dapk-1 negatively regulates epidermal immunity and wound responses. Loss of function
dapk-1 mutants exhibit hyperactive wound responses and excessive secretion of cuticle.To better understand how DAPK-1 regulates these processes we screened for suppressors of
dapk-1 morphological phenotypes. After EMS mutagenesis we identified two suppressor mutations, both of which affect genes implicated in the microtubule (MT) cytoskeleton. The first suppressor mutation causes complete loss of function in
ptrn-1/pqn-34 which encodes the C. elegans member of the Patronin/Nezha/CAMSAP family of MT minus-end binding proteins. Recent studies have analyzed how Patronin affects MT minus-end dynamics in cultured cells but their in vivo functions are not well understood. Patronin is thought to bind specifically to MT minus ends and protect them against kinesin-13-based depolymerization. We find that loss of
klp-7/kinesin-13 function suppresses the
ptrn-1 suppression phenotype, consistent with the hypothesis that PTRN-1's minus-end protective function is important in the epidermis.
ptrn-1 function is required in the epidermis for
dapk-1's hypersecretion phenotype. GFP::PTRN-1 forms puncta in the cytoplasm and at epidermal attachment structures, possibly the locations of MT minus ends in the worm epidermis. Our second suppressor is a phenotypically silent allele of
dhc-1 (dynein heavy chain). A stronger
dhc-1 allele
or195 fully suppresses
dapk-1 epidermal defects. In simple epithelia MTs are usually oriented with minus ends apically. Thus, we hypothesize that MT-based minus-end directed transport in the epidermis is required for apical secretion, and that DAPK-1 somehow antagonizes this process. These findings reveal the roles of MT cytoskeleton in the function of the differentiated epidermis. We are also investigating roles of PTRN-1 in wound healing and axon regeneration.