In zebrafish, pelvic fin buds appear at 3 weeks post fertilization (wpf) during the larval to juvenile transition (metamorphosis), but their fate is already determined during embryogenesis. Thus, presumptive pelvic fin cells appear to memorize their positional information for three weeks, but no factors expressed in the pelvic fin field from the embryonic to the metamorphic stages have been identified. In mice, Islet1 is proposed to promote nuclear accumulation of β-catenin in the hindlimb field, which leads to the initiation of hindlimb bud outgrowth through activation of the Wnt/βcatenin pathway. Here, we examined the distribution of β-catenin and islet proteins in the pelvic fin field of zebrafish from the embryonic to the metamorphic stages. We found that transcripts of islet2a, but not islet1, are detected in the posterior lateral plate mesoderm, including the presumptive pelvic fin field, at the embryonic stage as well as in the pelvic fin bud at the metamorphic stage. Immunolocalization revealed that β-catenin and islet proteins, which are synthesized during the embryonic stage, remain in the cytoplasm of the presumptive pelvic fin cells during the larval stage, and are then translocated into the nuclei of the pelvic fin bud at the metamorphic stage. We propose that cytoplasmic localization of these proteins in the presumptive pelvic fin cells that remained during the larval stage may underlie the mechanism by which pelvic fin cells memorize their positional information from the embryonic stage to the metamorphic stage.
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Vol. 36 • No. 5