A novel mammalian T-box-containing gene, Tbr2, expressed in mouse developing brain

We have identified and characterized a new member of the mammalian brain-sp ecific T-box gene family, Tbr2, which is closely related to mouse Tbr1, and to the Xenopus earliest mesodermal gene, Eomesodermin. As Tbr1, Tbr2 is pr edominantly expressed in some regions of the developing brain, but in a str ikingly complementary manner. On embryonic day 14.5 (E14.5), Tbr2 mRNA expr ession was observed in the mesencephalon and rhombencephalon in contrast to Tbr1 which was expressed mostly in the telencephalon. At this stage, Tbr2 mRNA was readily detectable in the postmitotic and differentiating neurons located in various brain regions, i.e., oculomotor, red, trigeminal, vestib ular, facial, and hypoglossal nuclei. However, expression of Tbr2 in these nuclei became undetectable on E18.5. In contrast, Tbr2 mRNA expression was detected in the hippocampus only from E18.5 onwards. Whereas Tbr2 expressio n disappeared in most parts of the mature adult brain, it remained detectab le in the hippocampus and olfactory bulb, regions where some neuronal precu rsors retain their differentiation potential. These results suggest that Tb r2 may play a crucial role in differentiating neurons rather than in prolif erating or already differentiated neurons. In addition, similarly to Xenopu s Eomesodermin, mouse Tbr2 showed biphasic expression; a first peak around E6.5 and a second peak around E14.5, suggesting that Tbr2 may also be impor tant at early stages of gastrulation. (C) 1999 Elsevier Science B.V. All ri ghts reserved.