Immunocytochemical characterization of murine Hex, a homeobox-containing protein

A polyclonal antibody against a glutathione: S-transferase fusion protein c ontaining the 76 COOH-terminal amino acids of Hex, a divergent homeobox gen e, was raised in rabbits. Western blot and immunofluorescence reveal that H ex is a 35-37-kD soluble protein present both in the nucleus and cytoplasm of transfected and nontransfected cultured cells as well as in whole mouse embryo. Confocal microscopy of whole mount immunostained mouse embryos at E 7.5 and E8.5 demonstrates that Hex is differentially localized in the cytop lasm and nucleus of definitive endoderm, developing blood islands, and hepa tic diverticulum, In particular, in the region of the foregut that gives ri se to the liver, Hex expression is nuclear in the endodermal cells of the h epatic diverticulum, whereas expression is primarily cytoplasmic in cells l ateral to the liver-forming region. This suggests that nuclear localization of Hex is involved in early hepatic specification and that compartmentaliz ation of Hex protein plays an important role in its function during mouse d evelopment.