Characterization and embryonic expression of four amphioxus Frizzled genes with important functions during early embryogenesis

The Wnt signaling pathway plays crucial roles in the embryonic patterning of all metazoans. Recent studies on Wnt genes in amphioxus have shed important insights into the evolution of the vertebrate Wnt gene family and their functions. Nevertheless, the potential roles of Wnt family receptors encoded by Frizzled (Fz) genes in amphioxus embryonic development remain to be investigated. In the present study, we identified four amphioxus Fz genes-AmphiFz1/2/7, AmphiFz4, AmphiFz5/8, and AmphiFz9/10-and analyzed their expression patterns during amphioxus embryogenesis. We found that these four Fz genes were maternally expressed and might be involved in early animal-vegetal axis establishment. The AmphiFz1/2/7 transcripts were detected in the central dorsal neural plate, mesoderm, the Hatschek's pit, and rim of the mouth, whereas those of AmphiFz4 were detected in the mesoderm, pharyngeal endoderm, and entire gut region. AmphiFz5/8 was exclusively expressed in the anterior-most region, whereas AmphiFz9/10 was expressed in the neural plate, somites, and tail bud. The dynamic and diverse expression patterns of amphioxus Fz genes suggest that these genes are not only associated with early embryonic axis establishment but also are involved in the development of several organs in amphioxus.