Regional distribution of maternal mRNA sox‐19 in the zebrafish early embryo

Summary— Asymmetric distribution of mRNA has been associated with polarisation and cell fate determination during early development of animal embryos. In this report we determine the distribution pattern of Zf‐Sox 19 mRNA during early embryogenesis of zebrafish. Zf‐Sox 19 mRNA is found in one pole of the embryo at the 8‐cell stage and in the deep cell layer close to the yolk, perhaps under the influence of yolk determinants. Zf‐Sox 19 is the earliest gene in zebrafish development whose RNA shows a restricted localisation. This result indicates that the first eight blastomeres are not equivalent in their molecular components.