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Gonadal transcriptome analysis of wild contaminated female European eels during artificial gonad maturation

ABSTRACT: Since the early 1980s, the population of European eels (Anguilla anguilla) has dramatically declined. Nowadays, the European eel is listed on the red list of threatened species (IUCN Red List) and is considered as critically endangered of extinction. Pollution is one of the explanations of the collapse of this species. Among their possible effects, pollutants gradually accumulated in eels during their somatic growth phase (yellow eel stage) would be remobilized during their reproductive migration leading to potential toxic events in gonads. The aim of this study was to investigate the potential effect of pollution on the gonad development of wild female silver eels. Female silver eels from two sites with differing contamination levels were artificially matured. Transcriptomic analyses by means of a 1000 candidate gene cDNA microarray were performed on gonads after 11 weeks of maturation. The results showed that the transcription levels of several genes that were associated to the gonadosomatic index (GSI) were involved in mitotic cell division but also in spermatogenesis. Genes associated to pollution were mainly involved in the mechanisms of protection against oxidative stress, in DNA repair, in the purinergic signaling pathway and in steroidogenesis, suggesting an impairment of gonad development in eels from the polluted site. This was in agreement with the fact that eels from the reference site showed a higher gonad growth in comparison to contaminated fish.

ORGANISM(S): Anguilla anguilla Anguilla rostrata

PROVIDER: GSE64278 | GEO | 2015/01/01

SECONDARY ACCESSION(S): PRJNA270623

REPOSITORIES: GEO

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Project description:In spite of many decades of research, the spawning migration of the European eel Anguilla anguilla from the European coast to the Sargasso Sea remains a mystery. In particular, the role of the swimbladder as a buoyancy regulating structure is not yet understood. In this study, we exercised silver eels in a swim tunnel under elevated hydrostatic pressure. The transcriptome of gas gland tissue of these exercised eels was then compared to the known transcriptome of not exercised (control) silver eel gas gland cells. Due to the high infection rate of the eel population with the swimbladder parasite Anguillicola crassus, the comparison also included an exercised group of silver eels with a heavily damaged swimbladder, and we compared the previously published transcriptome of not exercised silver eels with a highly damaged swimbladder with the exercised group of silver eels with a heavily damaged swimbladder. The comparisons of unexercised (control) silver eels with exercised silver eels with functional swimbladder (EF), as well as with exercised silver eels with damaged swimbladder(ED), both showed a significant elevation in transcripts related to glycolytic enzymes. This could also be observed within the comparison of unexercised silver eels with a highly infected swimbladder with exercised eels with a damaged swimbladder (DED). In contrast to EF, in ED a significant elevation in transcript numbers of mitochondrial NADH dehydrogenase was observed. While in EF the transcriptional changes suggested that acid production and secretion was enhanced, in ED these changes appeared to be related to thickened tissue and thus elevated diffusion distances. The remarkable number of differentially expressed transcripts coding for proteins connected to cAMP-dependent signaling pathways indicated that metabolic control in gas gland cells includes cAMP-dependent pathways. In contrast to ED, in EF significant transcriptional changes could be related to the reconstruction of the extracellular matrix, while in ED tissue repair and inflammation was more pronounced. Surprisingly, in exercised eels hypoxia inducible transcription factor expression was elevated. In EF, a large number of genes related to the circadian clock were transcriptionally modified, which may be connected to the circadian vertical migrations observed during the spawning migration.

Project description:Ecotoxicogenomic studies face the problem of the lack of gene sequence information available for toxicologically relevant non-model pollution sentinel species. In this sense, next generation sequencing technologies allow obtaining deep de novo sequence information cost-effectively. We have thus employed the platform GS-FLX of Roche technologies, in order to sequence the multitissue transcriptome of a fish species under severe population decline, the European eel (Anguilla anguilla), using normalized cDNA (Evrogen). The European eel could be successfully employed in pollution biomonitoring studies as it is a euryhaline teleost that is quite resistant to chemical exposure. We have completed a one whole plate sequencing-run using the Titanium kit of Roche from which a total of 7.8x105 reads were obtained with a length average of 303.53 bp. Annotated genes, for instance, could be further assessed as biomarkers of exposure to specific chemical compounds in marine, estuarine and river waters. Designed tool will be thus useful, in the study of: a.- the mode of action of chemical compounds in active monitoring studies using caged eels, b.- the physiological processes that are specific to freshwater eels such as the one of sexual development and reproduction, c.- reasons that could explain the disappearance of the species from European waters. In the first context, a caging experiment was performed to measure the putative effects of a paper industry effluent on eel hepatic transcription levels. For this purpose, eels were caged upstream and downstream to the SMURFFIT-KAPPA paper industry in Iurreta (Biscay, Basque Country). Thus, hepatic transcription profiles reflect the stress levels suffered by eels. The experiment contains a time serial sampling: T0 = before sampling; T1 = after 3 days of exposure; T2=after 15 days of exposure. In addition, caged eels were placed in 2 sites, Upstream (Up) and Downstream (Do) of the hotspot. 6 samples were dissected per sampling group (5 groups= ToUP; T1UP; T1Do; T2Up; T2Do), 30 samples in total

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Gonadal transcriptome analysis of wild contaminated female European eels during artificial gonad maturation

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