Cytoplasmic intermediate filaments provide mechanical strength to cells. Essential protein, involved in attachment structures in epidermal cells that connect muscles to the external cuticle. Required for epidermal morphogenesis in embryos. Probable component of embryonic epidermal attachment structures. Forms some heteromeric filaments with ifb-1. Expressed in the embryonic and larval hypodermis. Also expressed in the ventral nerve cord of larvae. Expressed in embryos and larvae. Not expressed in adults. Belongs to the intermediate filament family.