Expression of three zebrafish Six4 genes in the cranial sensory placodes and the developing somites

The homeobox gene Six4/AREC3 is a member of the vertebrate Six family of transcription factor genes. In this study we describe the cloning and expression of three zebrafish homologues of Six4/AREC3, six4.1, six4.2 and six4.3. These zebrafish Six4 proteins show high homology to the mammalian Six4/AREC3 proteins in the most C-terminal region in addition to the Six domain and homeodomain. Whole-mount in situ hybridization showed that six4.1 is expressed in the presumptive cranial placodal precursor cells, and later in the olfactory, otic and lateral line placodes. six4.2 is expressed in the presomitic mesoderm, somites and pectoral fin bud. six4.3 appears to be a unique member of the Six4 proteins and is expressed ubiquitously at gastrulation and later in the tectum.