Characterisation of the promoter region of the zebrafish six7 gene

The Drosophila homeobox gene sine oculis and its murine homologue Six3 have both been shown to have regulatory functions in eye and brain development. In zebrafish, three Six3-related genes with conserved expression during ea rly eye and head formation have been identified. One of these, six7, is fir st expressed at the gastrula stage in the involuting axial mesoderm, and la ter in the overlying neuroectoderm from which the forebrain and optic primo rdium develop. To elucidate the mechanisms regulating six7 expression, we i solated a 2.7-kb fragment of the 5'-flanking region. Three sequentially del eted fragments of this upstream region were used to produce GFP reporter co nstructs for analysis of tissue-specific expression in zebrafish embryos. T he results show that a 625-bp upstream fragment is sufficient to direct str ong expression of the reporter during gastrulation and early neurulation. T he proximal part of the promoter contains binding sites for various constit utive transcription factors and an additional upstream element that was sho wn to be critical in directing expression to the anterior region of the zeb rafish brain. (C) 2000 Elsevier Science B.V. All rights reserved.