Effects of an Anguillicola crassus infection on steady-state mRNA levels in gas gland tissue of the European eel. Anguilla anguilla

We investigated transcriptional changes caused by the nematode Anguillicola crassus within yellow and silver eels by comparing gas gland tissues of uninfected yellow with infected yellow eels, and uninfected silver with infected silver eels, respectively. In yellow eel gas gland, the infection caused a modification of steady state mRNA levels of 1675 genes, most of them being upregulated. Functional annotation analysis based on GO terms was used to categorize identified genes with regard to swimbladder metabolism or response to the infection. In yellow eels, the most prominent category was ‘immune response’, including various inflammatory components, complement proteins, and immunoglobulins. The elevated expression of several glucose and monocarboxylate transporters indicated an attempt to maintain the level of glucose metabolism, even in due to the infection thickened gas gland tissue. In silver eel gas gland tissue, on the contrary, the mRNA levels of only 291 genes were affected. The reaction of the immune system was much less pronounced compared to infected yellow eels, but in the category ‘extracellular matrix’, the mRNA levels of several mucin genes were strongly elevated, suggesting increased mucus production as a defense reaction against the parasite. In summary, we found a strong reaction to an Anguillicola crassus infection on steady state mRNA levels in gas gland tissue of yellow eels, whereas in silver eels the changes ware almost negligible. Overall design: Using Illumina Sequencing to obtain RNA-Seq data and statistical Deseq analysis, the transcriptomes of European eel gas gland tissues of animals with different development stages and different infection states were compared.