De novo genome sequencing and comparative stage-specific transcriptomic analysis of Dirofilaria repens

The zoonotic mosquito-borne filarial nematode Dirofilaria repens causes subcutaneous and ocular infections in dogs, cats and humans. Microfilariae (mf) are taken up by mosquitoes from infected vertebrate hosts which develop in the mosquito to the infective L3. These are transmitted to new vertebrate hosts and develop over two further moults to adult worms. The aims of the project were i) the de novo sequencing and annotation of the D. repens genome and ii) comparative transcriptomic analyses of the two developmental stages, mf and L3. Genomic DNA was obtained from adult male D. repens. RNA was extracted from mf from naturally infected dogs and from L3 produced in Aedes aegypti mosquitoes fed on blood spiked with mf. The 99.59 MB genome was approximately 17% larger than that of the related species Dirofilaria immitis (dog heartworm) and contained 8.9% fewer predicted genes (10,357). Approximately 1.8% of identified proteins (206/11,262) could not be mapped to D. immitis. Out of these, six (2.9%) presented an ortholog in all other considered filarial nematodes (e.g. Loa loa) and Caenorhabditis elegans. A significantly higher number of D. repens proteins, compared with D. immitis, mapped to the filarial nematode L. loa, reflecting the similarity in biology of D. repens and L. loa. A total of 876 genes were differentially expressed, of which 591 could be annotated in UniProtKB/Swiss-Prot. In particular, 155 genes with a UniProtKB/Swiss-Prot annotation to C. elegans and filarial nematodes were upregulated in the L3 and 57 in the mf stage, respectively. Fifteen Gene Ontology Biological Processes were significantly enriched for the L3 group and 12 for the mf. To our knowledge these data provide the first insight into the differential gene expression profiles of this filarial nematode and can serve future investigations of metabolic processes and stage-specific diagnostics.