The basic helix-loop-helix transcription factor, Tal2, marks the lateral floor plate of the spinal cord in zebrafish

Basic helix-loop-helix (bHLH) transcription factors play key roles in the development of the central nervous system. Here we report the isolation of a zebrafish gene that encodes a homologue of the mammalian bHLH transcription factor, Tal2. In zebrafish embryos, tal2, like its mammalian homologue, is strongly expressed in the diencephalon and the mesencephalon, with the latter expression located in post-mitotic cells of the tectum. However, in addition to this conserved brain expression, we also detect expression in the floor plate of the spinal cord. By the location of this expression relative to other genes expressed in the floor plate and by analysing expression in a selection of midline mutants, we reveal that tal2 is expressed within the lateral floor plate as opposed to the medial floor plate, and also in more dorsal cells which are distinct from motorneurons and depend on either sonic hedgehog signalling or a signal coming from the lateral floor plate. This is to our knowledge the first report of a gene expressed specifically in lateral cells of the floor plate in the spinal cord.