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.
Highlights
The vertebrate brain plays a critical role in the regulation of sexual maturation and reproduction by integrating environmental information with developmental and endocrine status
Functional annotation using DAVID To obtain a list of gene identifiers that could be used for the functional analysis of differentially expressed genes, the A. anguilla transcriptome assembly contigs that were used to design the microarray were used in a BLASTX search of SwissProt proteins
Of the set of differentially expressed genes, 991 were expressed at higher levels in sexually mature males while 506 were expressed at lower levels than in immature males. This finding shows that the brains of eels undergo major changes at the molecular level during reproduction
Summary
The vertebrate brain plays a critical role in the regulation of sexual maturation and reproduction by integrating environmental information with developmental and endocrine status. A major function of the brain is to establish the appropriate developmental and endocrine status for reproduction, and to co-ordinate this with aspects of behavior and sexual maturation. In vertebrates, this coordination is established through the hypothalamus and pituitary gland [1]. Sex steroids produced by gonad feedback to the brain and pituitary provide information about reproductive status [2,3]
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