Yang X. Development of cellular polarity of hamster embryos during compaction. Biol Reprod

Development of cellular polarity is an important event during early mammalian embryo development and differentiation. Blas-tomeres of hamster embryos at various stages were examined by scanning electron microscopy (SEM) and immunocytochem-ical staining. SEM observations revealed that 1- to 7-cell-stage embryos showed a uniform distribution of microvilli throughout the cell surface. Microvillous polarization was initially noted in the blastomeres (10–35%) of 8-cell-stage embryos. The polar-ized microvilli were observed mostly in the basal region of cell-cell contact and occasionally at the apical, outward-facing sur-face of the blastomere. Fluorescein-isothiocyanate-conjugated concanavalin A failed to reveal any polarity in the blastomeres regardless of the stages of the embryos. Actin staining showed that microfilaments were present beneath the cell surface, and in addition, areas of cell contact were more heavily stained, indicating a thick microfilament domain. Microtubules were lo-cated throughout the cytoplasm and were heavily concentrated near the nucleus during interphase, although they became re-distributed in the region of the mitotic spindle during karyoki-nesis. The position of nucleus changed from the cell center to the apical, outward-facing surface of the cell, and it distanced itself from the basal microvillous pole. It is suggested that the changes in the cell surface and nuclear position are the first manifestations of cell polarity in peri-compacted hamster em-bryos, which appear as early as the 8-cell stage; furthermore, the outward migration of the nuclei may parallel the redistri-bution of microtubules in the cytoplasm