Snoods: a periodic network containing cytokeratin in the cortex of starfish oocytes

An extensive fibrous cytoskeletal component in the cortical cytoplasm of oocytes of the starfish Pisaster ochraceus reproducibly stains with anticytokeratin antibody and hence contains cytokeratin. The large-meshed network resembles a snood (hair net). Snood fibers form loops and branches throughout the cortex of a premeiotic oocyte, except at the animal pole where they emanate from a nonstaining zone surrounding the centrosomes. By immunofluorescence microscopy of isolated cortices and electron microscopy of isolated cortices and intact oocytes, snood fibers exhibit complex striations with a periodicity of approximately 0.75 micron. Snoods are not colocalized with the cortical arrays of microtubules and are unaffected by drugs that disrupt microtubules or microfilaments. Stimulation of oocyte maturation by 1-methyladenine causes snoods to disappear, presumably by disassembly, about halfway to the time of germinal vesicle breakdown. They do not reappear during meiosis, fertilization, or development to the two-cell stage, and their functional importance, if any, during oogenesis or development remains to be elucidated.