Zebrafish twist1 is expressed in craniofacial, vertebral, and renal precursors

TWIST1 encodes a transcription factor that contains a highly conserved basic helix-loop-helix DNA-binding domain and a WR motif. We have isolated a full-length complementary DNA of the zebrafish ortholog of TWIST1 and determined its genomic organization. Inter-species comparisons reveal a remarkable degree of conservation at the gene structure, nucleotide, and predicted peptide levels across large evolutionary distances. Using reverse-transcription polymerase chain reaction analysis and in situ hybridization analyses of whole mount and cryosectioned zebrafish embryos, we detected maternal twist1 transcript in the zygote. During somitogenesis, twist1 transcripts were detected in the intermediate mesoderm from the 2-somite to 18-somite stages, followed by expression in the somites from the 5-somite stage to the 24-somite stage. Also, beginning at the two-somite stage, twist1 expression was observed in head mesenchyme and, subsequently, in neural crest-derived pharyngeal arches as the embryo developed. At the 24-hpf stage, twist1 transcripts were also observed in the ventral tail-bud region. These observations are consistent with a role for twist1 in craniofacial, vertebral, and early renal development.