Cloning of zebrafish T-box genes tbx15 and tbx18 and their expression during embryonic development.

Members of the T-box (tbx) gene family encode developmentally regulated transcription factors, several of which are implicated in human hereditary diseases. We have cloned the paralogous genes tbx15 and tbx18 in zebrafish and have characterised their expression in detail. tbx15 is expressed in paraxial head mesenchyme and its derivatives, the extraocular and jaw musculature and the posterior neurocranium. Further areas of tbx15 expression are in the anterior somitic mesoderm, in periocular mesenchyme and in the pectoral fin mesenchyme throughout larval development. Areas of strong tbx18 expression are found in the developing somitic and presomitic mesoderm, in the heart and in pectoral fin mesenchyme, as well as the ventral neuroectoderm and the developing palate. Both genes exhibit particular differences in expression compared to their murine orthologs.