pag gene-like protein (ABP-25) of the Cynops embryo: regional distribution and gene expression during early embryogenesis.

A maternal protein showing a unique distribution during early Cynops embryogenesis was screened by monoclonal antibody. The antigen protein, designated as ABP-25 (animal blastomere protein, molecular weight 25,000), was distributed uniformly in the uncleaved egg and concentrated into blastomeres of the animal half during cleavage. At the blastula stage, ABP-25 was definitely localized in cells of the animal half and a polarized distribution was observed within the cytoplasm. During gastrulation, immunohistochemical analysis indicated that the reactivity of the marginal zone (presumptive mesoderm) to the monoclonal antibody ABP-25 decreased after involution. At the end of gastrulation, a polarized distribution was still clearly observed in the ventral epidermis, but not in the neuroectoderm. Both Western and Northern blots indicated that the amount of antigen protein and the intensity of gene expresion were almost constant until the neurula stage. The deduced amino acid sequence of the ABP-25 cDNA showed a strong homology (84%) with that of the pag gene associated with cell proliferation.