Together with KRT19, helps to link the contractile apparatus to dystrophin at the costameres of striated muscle. Heterotetramer of two type I and two type II keratins. Keratin-8 associates with keratin-18 (By similarity). Expressed in oocytes, eggs, embryos, liver and intestinal mucosa. Synthesized in the oocyte in early and late embryonic stages. There are two types of cytoskeletal and microfibrillar keratin: I (acidic; 40-55 kDa) and II (neutral to basic; 56-70 kDa). Belongs to the intermediate filament family.