Anti-FUS-1 antibody first detects FUS-1 in a punctate pattern within the gut cells of embryos at approximately the comma stage (~6 hr pf); it is undetectable in epidermal cells at this early stage. FUS-1 is also detected in the excretory cell and the apical membrane of gut cells starting later in embryogenesis. In the epidermis, the protein is first conspicuously detected in 2-fold stage embryos shortly after most epidermal cell fusions occur. Initially, FUS-1 expression is seen at approximately equal levels throughout the dorsal, ventral, and anterior epidermal cells; it is specifically excluded from the lateral seam cells. FUS-1 remains virtually undetectable in seam cells, which neither fuse in wild-type embryos and
fus-1 mutants nor express EFF-1.