Differential expression of glycogen synthase kinase 3 genes during zebrafish embryogenesis

Glycogen synthase kinase 3 (GSK-3) belongs to a highly conserved family of protein serine/threonine kinase whose members in high eukaryotes are involved in hormonal regulation, nuclear signaling, and cell fate determination. We have identified two zebrafish homologues related to mammalian GSK-3, ZGSK-3α and ZGSK-3β. ZGSK-3α was expressed uniformly from cleavage onward, and later was found in many but not all tissues, especially in the central nervous system, spinal cord, somites and pronephric ducts. ZGSK-3β was also transcribed maternally but the transcripts were not uniformly distributed during early cleavage stage. Most signals were concentrated in the inner part of the blastomeres. From midblastula stage onward, the ZGSK-3β transcripts remained confined to inner parts of the deep cell layer. During shield stage, both epiblast and hypoblast expressed the transcripts. After late gastrulation, the signals were detected ubiquitously. During segmentation, prominent ZGSK-3β signal was detected in head portion of the neural system. In the trunk, the expression was maintained in the neural tube and paraxial mesoderm and then became prominent in adaxial cells, followed by expression at the posterior region of somites. In pharyngula period ZGSK-3β transcripts were distributed in similar regions as those of ZGSK-3α, namely, neural tissues of the head portion, spinal cord and somites.