NO TAIL (NTL) IS THE ZEBRAFISH HOMOLOG OF THE MOUSE-T (BRACHYURY) GENE

The mouse T (Brachyury) gene is required for normal mesoderm developme nt and the extension of the body axis. Recently, two mutant alleles of a zebrafish gene, no fail (ntl), have been isolated (Halpern, M.E., H o., R.K., Walker, C. and Kimmel, C.B. (1993) Cell 75, 99-111). ntl mut ant embryos resemble mouse TIT mutant embryos in that they lack a diff erentiated notochord and the caudal region of their bodies. We report here that this phenotype is caused by mutation of the zebrafish homolo gue of the T gene. While nfl embryos express mutant mRNA, they show no nuclear protein product. Later, expression of mRNA in mutants,but not in wild types, is greatly reduced along the dorsal midline where the notochord normally forms. This suggests that the protein is required f or maintaining transcription of its own gene.