The developmental transcriptome of the synanthropic fly Chrysomya megacephala and insights into olfactory proteins

Background: Chrysomya megacephala (Fabricius) is a prevalent and synanthropic blowfly which has two sides, for being a pathogenic vector, an efficient pollinator, a promising resource of proteins, lipids, chitosan, biofuel et al., and an important forensic indicator. Moreover olfactory proteins are crucial component to function in related processes. However, the genomic platform of C. megacephala remains relatively unavailable. Developmental transcriptomes of eggs, larvae from 1st instar to before pupa stage and adults from emergence to egg laying period were built by RNA-sequencing to establish sequence background of C. megacephala with special lights on olfactory proteins. Results: Clean reads in eggs, larvae and adults were annotated into 59486 transcripts. Transcripts were assembled into 22286, 17180, 18934 and 35900 unigenes in eggs, larvae, adults and the combined datasets, respectively. Unigenes were annotated using Nr (NCBI non-redundant protein sequences), Nt (NCBI non-redundant nucleotide sequences), GO (Gene Ontology), PFAM (Protein family), KOG/COG (Clusters of Orthologous Groups of proteins), Swiss-Prot (A manually annotated and reviewed protein sequence database), and KO (KEGG Orthology). Totally 12196 unigenes were annotated into 51 sub-categories belonging to three main GO categories; 8462 unigenes were classified functionally into 26 categories to KOG classifications; 5160 unigenes were functionally classified into 5 KEGG categories. Moreover, according to RSEM, the number of differentially expressed genes between larvae and eggs, adults and eggs, adults and larvae, and the common differentially expressed genes were 2637, 1804, 2628 and 258, respectively. Among them, 17 odorant-binding proteins (OBPs), 7 chemosensory proteins (CSPs) and 8 ionotropic receptors (IRs) were differently expressed in adults and larvae. Ten were confirmed as significant differentially expressed genes. Furthermore, OBP Cmeg32081-c4 was highly expressed in the female head and Cmeg33593_c0 were up-regulated with the increase of larval age. Conclusions: A comprehensive sequence resource with desirable quality was built by comparative transcriptome of eggs, larvae and adults, enriching the genomic platform of C. megacephala. The identified differentially expressed genes would facilitate the understanding of metamorphosis, development and the fitness to environmental change of C. megacephala. OBP Cmeg32081- c4 and Cmeg33593_ c0 might play a crucial role in the interactions between olfactory system and biological processes.