MLT-11 is a transient apical extracellular matrix component required for cuticle patterning and function

Abstract

ABSTRACTApical extracellular matrices (aECMs) are associated with all epithelia and form a protective layer against biotic and abiotic threats in the environment. Despite their importance, we lack a deep understanding of their structure and dynamics in development and disease.C. elegansmolting offers a powerful entry point to understanding developmentally programmed aECM remodeling. A transient matrix is formed in embryos and at the end of each larval stage, presumably to pattern the new cuticle. Focusing on targets of NHR-23, a key transcription factor which drives molting, we identified the Kunitz family protease inhibitor genemlt-11as an NHR-23 target. We identified NHR-23-binding sites that are necessary and sufficient for epithelial expression.mlt-11is necessary to pattern every layer of the adult cuticle, suggesting a broad patterning role prior to the formation of the mature cuticle. MLT-11::mNeonGreen::3xFLAG transiently localized to the aECM in the cuticle and embryo. It was also detected in lining openings to the exterior (vulva, rectum, mouth). Reduction ofmlt-11function disrupted the barrier function of the cuticle. Tissue-specific RNAi suggestedmlt-11activity is primarily necessary in seam cells and we observed alae and seam cell fusion defects uponmlt-11inactivation. Predictedmlt-11null mutations caused fully penetrant embryonic lethality and elongation defects suggestingmlt-11also plays an important role in patterning the embryonic sheath. Finally, we found thatmlt-11inactivation suppressed the blistered cuticle phenotype of mutants ofbli-4mutants, a subtilisin protease gene but did not affect BLI-4::sfGFP expression. These data could suggest that MLT-11 may be necessary to assure proper levels of BLI-4 activity.