Transcriptional regionalization of the fruit fly's airway epithelium

Although airway epithelia are primarily devoted to gas exchange, they have to fulfil a number of different tasks including organ maintenance and the epithelial immune response to fight airborne pathogens. These different tasks are at least partially accomplished by specialized cell types in the epithelium. In addition, a proximal to distal gradient mirroring the transition from airflow conduction to real gas exchange, is also operative. We analysed the airway system of larval Drosophila melanogaster with respect to region-specific expression in the proximal to distal axis. The larval airway system is made of epithelial cells only. Previously, it had been anticipated that these cells are very similar in their functional and transcript properties. We found differential expression between primary trunks of the airways and more distal ones comprising secondary and tertiary ones. Among these genes are especially those involved in signal transduction. A more detailed analysis was performed using DNA-microarray analyses to identify cohorts of genes that are either predominantly expressed in the primary or in the secondary/tertiary parts of the airways. Genes, including a putative mucin and the neuropeptide FMRFamide are predominantly found in primary branches, whereas the wnt- and the TGF-beta signalling pathways appear to be overrepresented in the secondary/tertiary ones. This differential expression is indicative for a proximal to distal transcriptional regionalization presumably reflecting functional differences in these parts of the fly’s airway system. Trachea of wildtype L3 larvae were dissected and primary branches were processed seperately from secondary and tertiary branches. 3 biological replicates were included per group.

尽管气道上皮（airway epithelia）主要负责气体交换，但仍需承担多项不同功能，包括气道组织维持以及对抗空气传播病原体的上皮免疫应答。这些不同功能至少部分由上皮内的特化细胞类型完成。此外，存在一条沿近端至远端的梯度轴，其对应气流传导向真正气体交换的转变，该梯度轴同样发挥功能。我们针对黑腹果蝇（Drosophila melanogaster）幼虫的气道系统，分析其沿近端-远端轴的区域特异性基因表达。该幼虫气道系统仅由上皮细胞构成。此前学界曾认为这些细胞在功能与转录特征上高度相似。我们发现气道主干与包含次级、三级分支的远端分支之间存在基因差异表达，其中尤以参与信号转导的基因为代表。我们进一步采用DNA微阵列（DNA microarray）分析，筛选出在气道主干或次级/三级分支中优势表达的基因簇。包括推定黏蛋白（putative mucin）以及神经肽FMRFamide在内的基因，均在气道主分支中优势表达；而Wnt信号通路（Wnt signalling pathway）与转化生长因子β（TGF-beta）信号通路则在次级/三级分支中富集。这种差异表达提示存在沿近端至远端的转录区域化模式，推测该模式对应果蝇气道系统不同区段的功能差异。我们解剖了野生型L3幼虫的气管，将主分支与次级、三级分支分别进行处理，每组设置3次生物学重复。