Evolutionary and airway specific analysis of ORMDL in smoke exposed Drosophila melanogaster larvae

<bold>Background:</bold> Gene variants within the ORMDL3/GSDMB locus are strongly associated with childhood onset asthma. The dew fly has just a single ortholog ORMDL gene. Cigarette smoke (CS) exposure is a contributing factor in the development of asthma. To investigate how CS modifies the transcriptional response upon airway specific ORMDL dysregulation, the airway transcriptome of <italic>Drosophila melanogaster</italic> larvae was analysed after CS or air exposure. In a second aspect, we used an evolutionary approach to determine how conserved the ORMDL gene family is across species and how strongly the human and fly ORMDLs have diverged. <bold>Methods:</bold> RNA from the tracheae of 5-day old larvae with airway specific overexpression or knockdown of ORMDL was sequenced with Illumina and analysed with <italic>kallisto</italic> and <italic>edgeR</italic>. The number and divergence of the ORMDL copies in different species was determined with <italic>Orthofinder</italic>. A sitewise <italic>dN/dS</italic> value was estimated using a machine learning tool. <bold>Results:</bold> ORMDL overexpression resulted in 13 differentially expressed genes involved in trachea development as well as 20 in the chitin-based airway cuticle. The gene <italic>speck</italic> was overexpressed (FDR = 0.002) due to CS exposure and is also involved in two biological processes changed by ORMDL overexpression. The ORMDL gene family is highly conserved due to low <italic>dN/dS</italic> values, with vertebrates having mostly three ORMDL copies. <bold>Conclusion:</bold> ORMDL overexpression could have an indirect effect on the response to CS by altering the processes in which <italic>speck</italic> is involved. To investigate functions and interactions of ORMDL, model organisms could provide good insights as it is present in most of them.