Required for apical extracellular matrix organization and epithelial junction maintenance. In L1 larvae, expressed in a subset of epithelial cells including epidermal, vulval and rectal cells and the excretory duct and pore. Also detected in some neurons. Absent from internal epithelia such as the gut and pharyngeal tubes. Expression begins around the ventral closure stage of embryogenesis, continues throughout larval development and decreases in adulthood. Lethal at early L1 larval stage due to excretory defects. Maternal copy required for survival.