THE MUP-4 LOCUS IN CAENORHABDITIS-ELEGANS IS ESSENTIAL FOR HYPODERMALINTEGRITY, ORGANISMAL MORPHOGENESIS AND EMBRYONIC BODY-WALL MUSCLE POSITION

mup-4 is a member of a set of genes essential for correct embryonic bo dy wall muscle cell positions in Caenorhabditis elegans. The mup-4 phe notype is variably expressed and three discrete arrest phenotypes aris e during the phase of embryonic development when the worm elongates fr om a ball of cells to its worm shape (organismal morphogenesis). Mutan ts representing two of the phenotypic classes arrest without successfu l completion of elongation. Mutants of the third phenotypic class arre st after completion of elongation. Mutants that arrest after elongatio n display profound dorsal and ventral body wall muscle cell position a bnormalities and a characteristic kinked body shape (the Mup phenotype ) due to the muscle cell position abnormalities. Significantly, geneti c mosaic analysis of mup-4 mutants demonstrates that mup-4 gene functi on is essential in the AB lineage, which generates most of the hypoder mis (epidermis), a tissue with which muscle interacts. Consistent with the genetic mosaic data, phenotypic characterizations reveal that mut ants have defects in hypodermal integrity and morphology. Our analyses support the conclusion that mup-4 is essential for hypodermal functio n and that this function is necessary for organismal morphogenesis and for the maintenance of body wall muscle position.