Isolation and expression of zebrafish zinc-finger transcription factor gene tsh1.

We report the expression patterns of tsh1, a zebrafish homologue of the Drosophila homeotic gene teashirt. Expression of tsh1 is first detected at the 2-somite stage (10h post-fertilization, hpf) at the anterior end of the spinal cord. Expression expands toward the posterior spinal cord, and by the prim-5 stage (24 hpf) tsh1 transcripts are detected throughout spinal cord. Between the 14- and 25-somite stage (16-24 hpf), spinal cord expression shows a clear anterior boundary at the rostral margin of rhombomere 7. Around the prim-25 stage (36 hpf), while the spinal expression of tsh1 decreases, new expression is detected in the pectoral fin buds and dorsal forebrain. By the long-pec stage (48 hpf), spinal cord expression is undetectable, but strong expression is observed in the rhombencephalon, telencephalon, tectum opticum, midbrain-hindbrain boundary, in the first pharyngeal arch and in the eyes. This expression persists at least until the larval stages. Retinoic acid signaling influences tsh1 expression. Zebrafish tsh1 expression was induced in the anterior neural tube in embryos treated briefly with exogenous retinoic acid. Furthermore, tsh1 expression was down-regulated in the spinal cord in the zebrafish neckless mutant in which RA signaling is disrupted due to a missense mutation in the gene encoding retinaldehyde dehydrogenase type 2.