IDENTIFICATION AND CHARACTERIZATION OF LMO4, AN LMO GENE WITH A NOVELPATTERN OF EXPRESSION DURING EMBRYOGENESIS

LMO4 is a novel member of the LIM-only (LMO) subfamily of LIM domain-c ontaining transcription factors. LMO1, LMO2, and LMO4 have distinct ex pression patterns in adult tissue, and we demonstrate that nuclear ret ention of LMO proteins is enhanced by the nuclear LIM interactor (NLI) . In Situ hybridization to early mouse embryos of 8-14.5 days revealed a complex pattern of LMO4 expression spatially overlapping with NLI a nd LHX genes, LMO4 expression in somite is repressed in mice mutant fo r the segment polarity gene Mesp2 and expanded in Splotch mutants. Dur ing jaw and limb outgrowth, LMO4 and LMO2 expression define mesenchyme that is uncommitted to regional fates, Although both LMO2 and LMO4 ar e activated in thymic blast cells, only LMO4 is expressed in mature T cells. Mesenchymal and thymic blast cell expression patterns of LMO4 a nd LMO2 are consistent with the suggestion that LMO genes inhibit diff erentiation.