Refining a steroidogenic model: an analysis of RNA-seq datasets from insect prothoracic glands

Panagiotis Moulos,Alexandros Alexandratos,Ioannis Nellas,Skarlatos G Dedos

doi:10.1186/s12864-018-4896-2

Abstract

BackgroundThe prothoracic gland (PG), the principal steroidogenic organ of insects, has been proposed as a model for steroid hormone biosynthesis and regulation.ResultsTo validate the robustness of the model, we present an analysis of accumulated transcriptomic data from PGs of two model species, Drosophila melanogaster and Bombyx mori. We identify that the common core components of the model in both species are encoded by nine genes. Five of these are Halloween genes whose expression differs substantially between the PGs of these species.ConclusionsWe conclude that the PGs can be a model for steroid hormone synthesis and regulation within the context of mitochondrial cholesterol transport and steroid biosynthesis but beyond these core mechanisms, gene expression in insect PGs is too diverse to fit in a context-specific model and should be analysed within a species-specific framework.

Highlights

The prothoracic gland (PG), the principal steroidogenic organ of insects, has been proposed as a model for steroid hormone biosynthesis and regulation
On V-0, the high juvenile hormone titre as well as the neurally-derived Bommo-FMRFamide (BRFa) suppress the ecdysteroidogenic activity of the PGs [35, 36], whereas on V-6, which is the day of the onset of wandering behaviour in Bombyx mori (Bm), the juvenile hormone titre is low, PG cells secrete high amounts of ecdysteroids [35, 36] and the PG cells are not fully stimulated by prothoracicotropic hormone [36]
Expression profiles of cytochrome P450 and ecdysteroidogenesis-regulating genes in the prothoracic glands of Bombyx mori we focused on the CYP family of proteins to benchmark under a single method of absolute quantification the large number of CYP genes identified in publications from different research groups, reviewed in [2, 26], as playing a role in ecdysteroid synthesis and secretion in Drosophila melanogaster (Dm) and Bm

Summary

Introduction

The prothoracic gland (PG), the principal steroidogenic organ of insects, has been proposed as a model for steroid hormone biosynthesis and regulation. The Drosophila melanogaster ring glands (Dm RGs), a composite organ that comprises three glands, the Beyond the well-established role of vertebrate steroidogenic enzymes described extensively in authoritative reviews [1, 8,9,10], research on mammalian cells has identified a large complex of proteins, termed the transduceosome [10,11,12], which mediates the transport of cholesterol across the outer mitochondrial membrane (OMM) to the inner mitochondrial membrane (IMM) This enables the conversion of cholesterol to pregnenolone, the precursor of all mammalian steroids, by the mitochondrial CYP11A1 [13], which is the rate-limiting step in steroidogenesis. The activity of this large multi-protein complex is regulated by signalling

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