Expression of murine early embryonic antigens, SSEA-1 and antigenic determinant of EMA-1, in embryos and ovarian follicles of a teleost medaka (Oryzias latipes)

Stage-specific embryonic antigen-1 (SSEA-1) and the antigenic determinant o f monoclonal antibody EMA-I are expressed in a stage-specific manner in mou se early embryos. To study whether these antigens generally exist in fish, expression of the antigens was examined in embryos, ovarian follicles, and adult tissues of a teleost medaka (Oryzias latipes), using immunohistochemi cal techniques. In 1-cell-stage embryos, these carbohydrate antigens were f ound in numerous cytoplasmic granules in the blastodisc and the cortical cy toplasm. These granules gradually decreased in number as the embryos develo ped. In 4-cell-stage embryos, the antigens appeared on the cleavage planes and were located on the cleavage planes within the blastoderm in the follow ing cleavage stages. In blastula-stage embryos, the expression was ubiquito usly found on the cell surface of blastomeres. At the mid-gastrula stage, t he antigens were restricted to the enveloping layer, yolk syncytial layer, and cortical cytoplasm, but were rarely found in deep cells that contribute to formation of the embryonic body. In later-stage embryos and adult fish, the antigens were located in various tissues. In ovarian follicles, the an tigens were found in granules of oocytes and granulosa cells. These observa tions were basically consistent with those in mice; however, expression in I-cell-stage embryos and ovarian follicles has not been observed in mice. T his unexpected finding suggests that the antigens are produced in gyanulosa cells and transferred to I-cell-stage embryos via oocytes, and that the an tigens involved in the early developmental process are maternally prepared in teleosts.