Bellusci S, Henderson R, Winnier G, Oikawa T, Hogan B L
Howard Hughes Medical Institute, Department of Cell Biology, Vanderbilt University Medical Center, Nashville, TN 37232-2175, USA.
Development. 1996 Jun;122(6):1693-702. doi: 10.1242/dev.122.6.1693.
Epithelial-mesenchymal interactions are critical for the branching and differentiation of the lung, but the mechanisms involved are still unclear. To investigate this problem in mouse embryonic lung, we have studied the temporal and spatial expression of genes implicated in the morphogenesis of other organs. At 11.5 days p.c., hepatocyte nuclear factor-3beta (Hnf-3beta) is expressed uniformly throughout the epithelium, while Wnt-2 expression is confined to the distal mesenchyme. Sonic hedgehog (Shh) transcripts are found throughout the epithelium, with high levels in the distal tips of the terminal buds, while bone morphogenetic protein-4 (Bmp-4) transcripts are localized at high levels in the distal tips of the epithelium, with lower levels in the adjacent mesenchyme. Epithelial expression is also seen for Bmp-7, but transcripts are less dramatically upregulated at the distal tips. The Type I Bone morphogenetic protein receptor gene (Bmpr/Tfr-11/Brk-1) is expressed at low levels in the epithelium and in the distal mesenchyme. To investigate the role of Bmp-4 in lung development, we have misexpressed the gene throughout the distal epithelium of transgenic lungs using a surfactant protein C enhancer/promoter. From 15.5 days p.c., transgenic lungs are smaller than normal, with grossly distended terminal buds and, at birth, contain large air-filled sacs which do not support normal lung function. Labeling with BrdU reveals an inhibition of epithelia] proliferation in 15.5 days p.c. transgenic lungs. A small but significant stimulation of proliferation of mesenchymal cells is also observed, but this is accompanied by an increase in cell death. In situ hybridization with riboprobes for the proximal airway marker, CC10, and the distal airway marker, SP-C, shows normal differentiation of bronchiolar Clara cells but a reduction in the number of differentiated Type II cells in transgenic lungs. A model is proposed for the role of BMP4 and other signalling molecules in embryonic lung morphogenesis.
上皮-间充质相互作用对肺的分支和分化至关重要，但其中涉及的机制仍不清楚。为了在小鼠胚胎肺中研究这个问题，我们研究了与其他器官形态发生相关基因的时空表达。在胚胎第11.5天，肝细胞核因子-3β（Hnf-3β）在上皮中均匀表达，而Wnt-2表达局限于远端间充质。音猬因子（Shh）转录本在上皮中均有发现，在终末芽的远端顶端水平较高，而骨形态发生蛋白-4（Bmp-4）转录本在上皮的远端顶端高水平定位，在相邻间充质中水平较低。Bmp-7也有上皮表达，但转录本在远端顶端上调程度较小。I型骨形态发生蛋白受体基因（Bmpr/Tfr-11/Brk-1）在上皮和远端间充质中低水平表达。为了研究Bmp-4在肺发育中的作用，我们使用表面活性蛋白C增强子/启动子在转基因肺的整个远端上皮中错误表达该基因。从胚胎第15.5天开始，转基因肺比正常肺小，终末芽严重扩张，出生时含有大的充气囊，不支持正常肺功能。用BrdU标记显示在胚胎第15.5天的转基因肺中上皮增殖受到抑制。还观察到间充质细胞增殖有轻微但显著的刺激，但这伴随着细胞死亡增加。用近端气道标志物CC10和远端气道标志物SP-C的核糖探针进行原位杂交显示，转基因肺中小支气管克拉拉细胞分化正常，但II型分化细胞数量减少。提出了一个关于BMP4和其他信号分子在胚胎肺形态发生中作用的模型。
