CHARACTERIZATION AND DEVELOPMENTAL EXPRESSION OF TLX-1, THE MURINE HOMOLOG OF HOX11

HOX11, a human homeobox gene with putative oncogenic potential, was or iginally discovered at the chromosome 10 breakpoint in T-cell acute ly mphoblastic leukemias bearing the chromosomal translocation t(10;14)(q 24;q11). To provide insight into the possible roles of this gene in de velopment, we isolated and characterized its murine homolog, Tlx-1, an d examined its profile of expression. Tlx-1 transcripts are first dete cted at E8.5 in the surface ectoderm and central mesenchyme of the fir st branchial arch. This expression subsequently extends to the 2nd, 3r d, and 4th branchial arches, as well as the presumptive pharynx, as th ese structures develop. Between E12.5 and E15.5, the profile of Tlx-1 expression becomes more complex; expression is observed in the develop ing pancreas and salivary glands, as well as in several components of the nervous system, including the trigeminal, glossopharyngeal and ves tibulocochlear ganglia, the spinal cord, and the curvature of the pons -medulla. In addition, expression is seen in the pinna and external au ditory meatus of the outer ear, the tooth primordia, and specific cell populations of the mandible and tongue. These complex patterns of exp ression are consistent with multiple and varied roles for Tlx-1 in dev elopment and suggest that Tlx-l marks, amongst other cell populations, structures derived from cranial neural crest cells and migratory para xial mesoderm that arise at corresponding levels along the rostral-cau dal axis of the developing embryo.