The Pituitary Gland of the European Eel Reveals Massive Expression of Genes Involved in the Melanocortin System

Abstract

Hormones secreted from the pituitary gland regulate important processes such as development, growth and metabolism, reproduction, water balance, and body pigmentation. Synthesis and secretion of pituitary hormones are regulated by different factors from the hypothalamus, but also through feedback mechanisms from peripheral organs, and from the pituitary itself. In the European eel extensive attention has been directed towards understanding the different components of the brain-pituitary-gonad axis, but little is known about the regulation of upstream processes in the pituitary gland. In order to gain a broader mechanistic understanding of the eel pituitary gland, we have performed RNA-seq transcriptome profiling of the pituitary of prepubertal female silver eels. RNA-seq reads generated on the Illumina platform were mapped to the recently assembled European eel genome. The most abundant transcript in the eel pituitary codes for pro-opiomelanocortin, the precursor for hormones of the melanocortin system. Several genes putatively involved in downstream processing of pro-opiomelanocortin were manually annotated, and were found to be highly expressed, both by RNA-seq and by qPCR. The melanocortin system, which affects skin color, energy homeostasis and in other teleosts interacts with the reproductive system, has so far received limited attention in eels. However, since up to one third of the silver eel pituitary’s mRNA pool encodes pro-opiomelanocortin, our results indicate that control of the melanocortin system is a major function of the eel pituitary.

Large scale gene duplication affected the European eel (Anguilla anguilla) after the 3R teleost duplication

“…Likewise, previous published eel RNA-sequencing experiments were also mapped to the eel genome and transcriptome. In this case, 52.2% (Coppe et al 2010), 57.9% (Burgerhout et al 2016), and 66.18% (Ager-Wick et al 2013) reads mapped concordantly against the eel genome whereas 84.3% (Coppe et al 2010), 69.5% (Burgerhout et al 2016), and 87.32 % (Ager-Wick et al 2013) mapped against the transcriptome.…”

A new model army: Emerging fish models to study the genomics of vertebrate Evo‐Devo

“…For elopomorphs, draft genome assemblies for two species of eel, European eel ( Anguilla anguilla ) and Japanese eel ( A. japonica ), are available (Henkel et al, 2012a,b). Transcriptome data from the European eel (Coppe et al, ; Ager‐Wick et al, ) and a genetic map for the Japanese eel based on microsatellites and AFLP data (Nomura et al, ) are available as well. Developmental studies of eels are hindered by their enigmatic, catadromous life styles that start with spawning in the open ocean, impeding artificial breeding efforts—a major drawback considering the economic importance of eels (Henkel et al, 2012a,b).…”

“…Clupeocephalans have two pomc TGD paralogs, called pomca and pomcb (de Souza et al, ). In contrast, eels have a single pomc gene (Ager‐Wick et al, ). From pilot genome sequencing, we identified only one pomc gene for goldeye (I. Braasch, P. Batzel, A. Amores, J. H. Postlethwait, unpublished data).…”

Unravelling the changes during induced vitellogenesis in female European eel through RNA-Seq: What happens to the liver?

“…The technological advancements and the availability of the first genome assembly and annotation [27] provide the opportunity to increase the number of such types of high-throughput analysis, such as RNA-Seq, in this species. This has allowed to conduce broader gene expression investigations that has lead, for example, to the first characterizations and differentiations of the pituitary and ovary gland among yellow and silver eels [28,29].…”