Cytokeratin in early hamster embryogenesis and parthenogenesis: reorganization during mitosis and association with clusters of interchromatinlike granules

Abstract

Abstract In vivo obtained golden hamster embryos were used to study, by immunofluorescence and immunoelec-tron microscopy, the main cytokeratin pattern rearrangements during completion of meiosis and the first cleavage division. Our results point to three major re-organization steps: (1) diffuse immunofluorescent cytokeratin spots characteristic of recently ovulated oocytes rearrange into large cortical patches interconnected by fibrils in one-cell embryos; (2) during mitosis a homogeneous cytokeratin spotty pattern reappears; (3) in two-cell embryos cortical and perinuclear cytokeratin fibrillar networks become prominent. Parthenogenotic oocytes were able to mimic the major cytokeratin patterns observed until the first embryonic mitosis, supporting the concept of a maternally established common response to activation. Despite the lack of fibrillar immunofluorescent reactivity during mitosis, electron microscopy demonstrates persistence of 10 nm filament meshworks. These cytokeratin meshworks often associate with clusters of interchromatinlike granules, which persist in the cytoplasm for a short period after nuclear envelope reassembly.