DIFFERENTIAL EXPRESSION OF THE HMG BOX FACTORS TCF-1 AND LEF-1 DURINGMURINE EMBRYOGENESIS

The recent identification of a number of T lymphocyte-specific enhance rs has allowed the cloning of several novel transcription factors. Two of these, TCF-1 and LEF-1, contain a virtually identical DNA-binding domain of the High Mobility Group (HMG-1) box type. TCF-1 and LEF-1 or iginate from a recent gene duplication event as evidenced by compariso n with the chicken homologue, chTCF. We have now analyzed the differen tial expression of these two transcription factors. In a panel of lymp hoid cell lines, TCF-1 was exclusively expressed in the T cell lineage . In contrast, LEF-1 mRNA was detected at equivalent levels in pro- an d pre-B cells and in all T lineage cells. In situ hybridization on mur ine embryos revealed that TCF-1 and LEF-1 were widely expressed at day 7.5 of gestation. At later stages, the expression patterns were compl ex and only partially overlapping. The expression of TCF-1 and LEF-1 c oincided until day 10.5, when mRNAs were detected in limb buds, neural crest, pharyngeal arches and nasal process. At later time points (day 13.5 to 14.5), sites of overlapping expression included lung, the uro genital system, tooth buds, thymus and choroid plexus. Unique expressi on sites for TCF-1 included Reichert's membrane and trophectoderm-deri ved cells, the ribs and thoracic prevertebrae, craniofacial structures , the adrenal gland and meninges. Unique LEF-1 expression was observed in the tail prevertebrae, brain and inner ear. Postnatally, expressio n of both genes could only be detected in lymphoid tissues. These obse rvations suggest that TCF-1 and LEF-1 exert differential functions dur ing murine embryogenesis.