Transcriptional regionalization of the fruit fly's airway epithelium. Drosophila melanogaster

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. Overall design: 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.