Hex expression suggests a role in the development and function of organs derived from foregut endoderm

Hex is a divergent homeobox gene expressed as early as E4.5 in the mouse an d in a pattern that suggests a role in anterior-posterior patterning. Later in embryogenesis, Hex is expressed in the developing thyroid, lung, and li ver. We now show Hex expression during thymus, gallbladder, and pancreas de velopment and in the adult thyroid, lung, and liver. At E10.0, Hex is expre ssed in the 3rd pharyngeal pouch, from which the thymus originates, the end odermal cells of Liver that are invading the septum transversum, the thyroi d, the dorsal pancreatic bud, and gall-bladder primoridum. At E13.5, expres sion is maintained at high levels in the thyroid, liver, epithelial cells l ining the pancreatic and extrahepatic biliary ducts and is present in both the epithelial and mesenchymal cells of the lung. Expression in the thymus at this age is less than in the other organs. In the E16.5 embryo, expressi on persists in the thyroid, pancreatic, and bile duct epithelium, lung, and liver, with thymic expression dropping to barely detectable levels. By E18 .5, expression in the thyroid and bile ducts remains high, whereas lung exp ression is markedly decreased. At this age, expression in the pancreas and thymus is no longer present. Finally, we show the cell types in the adult t hyroid, lung, and liver that express Hex in the mature animal. Our results provide more detail on the potential role of Hex in the development of seve ral organs derived from foregut endoderm and in the maintenance of function of several of these organs in the mature animal. (C) 2000 Wiley-Liss, Inc.