Overlapping expression of zebrafish T-brain-1 and eomesodermin during forebrain development

T-box transcription factors are important determinants of embryonic cell fa te and behaviour. Two T-box genes are expressed in the developing telenceph alon of several vertebrate species, including amphibia, birds and mammals. Here we report the cloning of zebrafish T-brain-1 (tbr1) and eomesodermin ( eom). As a prelude to genetic studies of neuro-ectodermal fate determinatio n we studied their expression pattern during embryogenesis and early larval development. Eom is expressed in the presumptive telencephalon from around the 4-5 somite stage in bilaterally symmetric groups of cells; the number of positive cells increases dramatically with time and encompasses the enti re dorsal telencephalon by the 22 somite stage. Tbr1 is expressed from the 18 somite stage in a subset of eom-expressing cells. By 24 hpf eom and tbr1 are expressed in largely overlapping domains in the dorsal telencephalon, tbr1 is expressed in postmitotic cells whereas eomes is also expressed in p roliferative ventricular zone cells. Both genes are also found in a small d omain of the diencephalon bordering the telencephalon. A detailed analysis of the expression of tbr1 and eom in the brain of 4 day old larvae shows th at the two T-box genes are differentially expressed in various cell populat ions of the developing brain. (C) 2001 Elsevier Science Ireland Ltd. All ri ghts reserved.