Changes in the gene expression profiles of the brains of male European eels (Anguilla anguilla) during sexual maturation

Abstract

BackgroundThe vertebrate brain plays a critical role in the regulation of sexual maturation and reproduction by integrating environmental information with developmental and endocrine status. The European eel Anguilla anguilla is an important species in which to better understand the neuroendocrine factors that control reproduction because it is an endangered species, has a complex life cycle that includes two extreme long distance migrations with both freshwater and seawater stages and because it occupies a key position within the teleost phylogeny. At present, mature eels have never been caught in the wild and little is known about most aspects of reproduction in A. anguilla. The goal of this study was to identify genes that may be involved in sexual maturation in experimentally matured eels. For this, we used microarrays to compare the gene expression profiles of sexually mature to immature males.ResultsUsing a false discovery rate of 0.05, a total of 1,497 differentially expressed genes were identified. Of this set, 991 were expressed at higher levels in brains (forebrain and midbrain) of mature males while 506 were expressed at lower levels relative to brains of immature males. The set of up-regulated genes includes genes involved in neuroendocrine processes, cell-cell signaling, neurogenesis and development. Interestingly, while genes involved in immune system function were down-regulated in the brains of mature males, changes in the expression levels of several receptors and channels were observed suggesting that some rewiring is occurring in the brain at sexual maturity.ConclusionsThis study shows that the brains of eels undergo major changes at the molecular level at sexual maturity that may include re-organization at the cellular level. Here, we have defined a set of genes that help to understand the molecular mechanisms controlling reproduction in eels. Some of these genes have previously described functions while many others have roles that have yet to be characterized in a reproductive context. Since most of the genes examined here have orthologs in other vertebrates, the results of this study will contribute to the body of knowledge concerning reproduction in vertebrates as well as to an improved understanding of eel biology.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-799) contains supplementary material, which is available to authorized users.

Brain Transcriptional Profiles of Male Alternative Reproductive Tactics and Females in Bluegill Sunfish

“…The role of tac in influencing sexual behaviors in teleosts has not been addressed, but tac expression significantly increases in the brain of male eels ( Anguilla anguilla ) during sexual maturation [95] and leads to increased male aggression in Drosophila [90]. In bluegill, the primary role of tac expression may not be male-male aggression, considering higher expression levels of this gene are also observed in the non-aggressive satellite and sneaker males when compared to females.…”

Transcriptomic profiling of male European eel ( Anguilla anguilla ) livers at sexual maturity

“…In general, immune competency is depressed by activation of HPA (reviewed in Norris and Hobbs, 2006) and the down-regulation of immune system genes is associated with increased stress at reproduction. In our previous study, we found that genes involved in immune system function were down-regulated in the brains of eels at sexual maturity (Churcher et al, 2014). Furthermore, previous work in other fish has shown that treatment with 17-β estradiol resulted in a decrease in the expression of immune related transcripts (Tilton et al, 2006;Williams et al, 2007).…”

“…A false discovery rate of 5% was used and only genes with a minimum fold change of 1.5 were considered. The array and methods used in this study have previously been verified using qPCR and a subset of eight genes in Churcher et al (2014).…”

“…The livers were dissected from 12 sexually mature and 12 immature fish and frozen immediately in liquid nitrogen. The tissue samples used in this study are from the fish used in our previous survey (Churcher et al, 2014) where the characterization of maturational state is described. Before shipping on dry ice, tissues were then placed in RNAlater® (Sigma R0901) and kept overnight at 4°C then stored temporarily at −20°C.…”

Development of innovative methods for induction of European eel (Anguilla anguilla) spermatogenesis

“…The most notable results from the transcriptomic data from all the tissues were the enrichment of GO terms related to the immune response in the brain and have been hypothesized to be part of the adaptation of eels in preparation for migration (Pankhurst and Lythgoe 1983). Furthermore, the upregulation of genes involved in photo signal transduction and visual system development (Churcher et al 2014), and alterations to the retina, have previously been observed in developing European eels (Pankhurst and Lythgoe 1983).…”