Lhx9: A novel LIM-homeodomain gene expressed in the developing forebrain

A novel LIM-homeodomain gene, Lhx9, was isolated by degenerate RT-PGR follo wed by mouse embryonic library screening. Lhx9 cDNA encodes a protein that is most closely related to Drosophila apterous and rodent Lhx2 proteins. Th e Lhx9 spatiotemporal pattern of expression during embryogenesis was simila r but distinct from Lhx2. Highest expression levers were found in the dienc ephalon, telencephalic vesicles, and dorsal mesencephalon. Domains of expre ssion respected the proposed neuromeric boundaries (Puelles and Rubenstein, 1993). Lhx9 was also expressed in the spinal cord, forelimb and hindlimb m esenchyme, and urogenital system. Although Lhx9 expression was sustained in diencephalon and mesencephalon from embryonic day 10.5 (E10.5) to postnata l stages, it was transient in the future cerebral cortex, where it was turn ed off between E14.5 and E16.5. Lhx9 expression was highest if not exclusiv ely located (depending on the region of interest) in the intermediate and m antle zones, as opposed to the mitotic ventricular zone. Lhx9 protein was t ested for interaction with the recently discovered cofactors of LIM-homeodo main proteins and was found to interact strongly both with CLIM1 and CLIM2. The expression pattern and structural characteristics of Lhx9 suggest that it encodes a transcription factor that might be involved in the control of cell differentiation of several neural cell types. Furthermore, Lhx9 prote in could act in a combinatorial manner with other LIM-homeodomain factors e xpressed in overlapping pattern.