Hoxb-5 control of early airway formation during branching morphogenesis inthe developing mouse lung

Hox proteins control structural morphogenesis, pattern formation and cell f ate in the developing embryo. To determine if Hoxb-5 participates in patter ning of early airway branching during lung morphogenesis, gestational day 1 1.5 embryonic lung cultures were treated with retinoic acid (RA) to up-regu late and antisense oligonucleotides to down-regulate Hoxb-5 protein express ion. RA (10(-6) M) and Hoxb-5 antisense oligonucleotide (20 mu M) treatment each significantly decreased branching morphogenesis (P < 0.001), but the morphology of branching under these conditions was very different. RA-treat ed lungs had elongated primary branches but decreased further branching wit h increased Hoxb-5 immunostaining in subepithelial regions underlying these elongated airways. Western blots confirmed that Hoxb-5 protein was increas ed by 189 +/- 20% (mean +/- S.E.M., P < 0.05) in RA-treated lungs compared to controls. In contrast, lungs treated with Hoxb-5 antisense oligos plus R A had foreshortened primary branches with rudimentary distal clefts resulti ng in decreased numbers of primary and subsequent branches. Immunohistochem istry confirmed that Hoxb-5 antisense oligos inhibited Hoxb-5 protein expre ssion even in the presence of RA. We conclude that regional and quantitativ e changes in Hoxb-5 protein expression influence morphogenesis of the first airway divisions from the mainstem bronchi. RA-induced alterations in bran ching are mediated in part through regulated Hoxb-5 expression. (C) 2000 El sevier Science B.V. All rights reserved.