Unequal distribution of otx1 mRnas among cleavage stage blastomeres in the teleost, Leucopsarion petersii (shiro-uo).

The otx genes belong to the orthodenticle gene family and play important roles in anterior brain development in vertebrates. We isolated two cDNA sequences, one homologous to human and zebrafish otxl and another homologous to zebrafish otx3, from the teleost Leucopsarion petersii (shiro-uo), which belongs to the family of gobies in the Perciformes. During embryogenesis of shiro-uo, otx1 and otx3 were expressed in the fore- and mid-brain throughout development in a manner similar to that observed in other vertebrates so far studied. However, otx-1 mRNA was also present at earlier stages and we obtained unique results using in situ hybridization and RT-PCR analysis demonstrating that otx-1 signals showed a distinct increase in the upper blastomeres, but not in the lower blastomeres, at the 8-cell stage. These stronger signals were maintained in the animal pole blastomeres during the 16-cell to 64-cell stages, followed by a gradual decrease during blastula stages. Such unexpected unequal distribution of otx1 mRNA revealed that blastomeres at early cleavage stages already showed non-equivalence in the embryogenesis of shiro-uo.