Identification and characterization of Lbh, a novel conserved nuclear protein expressed during early limb and heart development

We report the cloning, protein characterization, and expression of a novel vertebrate gene, termed Lbh (Limb-bud-and-heart), with a spatiotemporal exp ression pattern that marks embryologically significant domains in the devel oping limbs and heart. Lbh encodes a highly conserved nuclear protein, whic h in tissue culture cells possesses a transcriptional activator function. D uring limb development, expression of Lbh initiates in the ectoderm of the presumptive limb territory in the lateral body wall. As the limb buds appea r, Lbh expression is restricted primarily to the distal ventral limb ectode rm and the apical ectodermal ridge, and overlaps in these ectodermal compar tments with En1 and Fgf8 expression. During heart formation, Lbh is express ed as early as Nkx2.5 and dHand in the bilateral heart primordia, with the highest levels in the anterior promyocardium. After heart tube fusion and l ooping, Lbh expression is confined to the ventricular myocardium, with the highest intensity in the right ventricle and atrioventricular canal, as wel l as in the sinus venosus. Based on the molecular characteristics and the d omain-specific expression pattern, it is possible that Lbh functions in syn ergy with other genes known to be required for heart and limb development. (C) 2001 Academic Press.