Analysis of the Central Nervous System Transcriptome of the Eastern Rock Lobster Sagmariasus verreauxi Reveals Its Putative Neuropeptidome

Neuropeptides have been discovered in many arthropod species including crustaceans. The nature of their biological function is well studied and varies from behavior modulation to physiological regulation of complex biochemical processes such as metabolism, molt and reproduction. Due to their key role in these fundamental processes, neuropeptides are often targeted for modulating these processes to align with market demands in commercially important species. We generated a comprehensive transcriptome of the eyestalk and brain of one of the few commercially important spiny lobster species in the southern Hemisphere, the Eastern rock lobster Sagmariasus verreauxi and mined it for novel neuropeptide and protein hormone-encoding transcripts. We then characterized the predicted mature hormones to verify their validity based on conserved motifs and features known from previously reported hormones. Overall, 37 transcripts which are predicted to encode mature full-length/partial peptides/proteins were identified, representing 21 peptide/protein families/subfamilies. All transcripts had high similarity to hormones that were previously characterized in other decapod crustacean species or, where absent in crustaceans, in other arthropod species. These included, in addition to other proteins previously described in crustaceans, prohormone-3 and prohormone-4 which were previously identified only in insects. A homolog of the crustacean female sex hormone (CFSH), recently found to be female-specific in brachyuran crabs was found to have the same levels of expression in both male and female eyestalks, suggesting that the CFSH female specificity is not conserved throughout decapod crustaceans. Digital gene expression showed that 24 out of the 37 transcripts presented in this study have significant changes in expression between eyestalk and brain. In some cases a trend of difference between males and females could be seen. Taken together, this study provides a comprehensive neuropeptidome of a commercially important crustacean species with novel peptides and protein hormones identified for the first time in decapods

Y-linked iDmrt1 paralogue (iDMY) in the Eastern spiny lobster, Sagmariasus verreauxi: The first invertebrate sex-linked Dmrt

Sex determination pathways are extensively diverse across species, with the master sex-determinants being the most variable element. Despite this, there is a family of DM-domain transcription factors (Dmrts), which hold a highly conserved function in sexual development. This work is the first to describe a heterogametic sex-linked Dmrt in an invertebrate species, the Eastern spiny lobster, Sagmariasus verreauxi. We have termed the Y-linked, truncated paralogue of the autosomal iDmrt1, Sv-iDMY. Considering the master sex-determining function of both DMY in medaka and DM-W in frog, we hypothesised a similar function of Sv-iDMY. By conducting temporal expression analyses during embryogenesis we have identified a putative male sex-determining period during which iDMY>iDmrt1. Employing a GAL4-transactivation assay we then demonstrate the dominant negative suppression of iDMY over its autosomal iDmrt1 paralogue, suggesting the mechanism with which iDMY determines sex. Comparative analyses of Sv-iDMY, DM-W and medaka DMY, highlight the C′-mediated features of oligomerisation and transactivation as central to the mechanism that each exerts. Indeed, these features may underpin the plasticity facilitating the convergent emergence of these three sporadic sex-linked master-Dmrts

Applying the Power of Transcriptomics: Understanding Male Sexual Development in Decapod Crustacea

The decapod Crustacea are the most species-rich order of the Crustacea and include some of the most charismatic and highly valued commercial species. Thus the decapods draw a significant research interest in relation to aquaculture, as well as gaining a broader understanding of these species’ biology. However, the diverse physiology of the group considered with the lack of a model species have presented an obstacle for comparative analyses. In reflection of this, the recent integration of comparative transcriptomics has rapidly advanced our understanding of key regulatory pathways and developmental phenomena, an example being our understanding of sexual development. We discuss our work in the Eastern spiny lobster, Sagmariasus verreauxi, in the context of what is currently known about male sexual development in the decapods, highlighting the importance of transcriptomic techniques in achieving our recent advancements. We describe the progression made in our understanding of male sexual differentiation and maturation, as mediated by the insulin-like androgenic gland hormone (IAG), integrating the role of regulatory binding proteins (IGFBPs), a tyrosine kinase insulin receptor (TKIR), as well as the upstream effect of neuroendocrine hormones (GIH and MIH). We then consider the less well understood mechanism of male sex determination, with an emphasis on what we believe to be the key regulatory factors, the Dsx- and mab-3-related transcription factors (Dmrts). Finally, we discuss the function of the antennal gland (AnG) in sexual development, relating to the emergence of male-biased upregulation in the AnG in later sexual maturation and the sexually dimorphic expression of two key genes Sv-TKIR and Sv-Dmrt1. We then present the AnG as a case study to illustrate how comparative transcriptomic techniques can be applied to guide preliminary analyses, like the hypothesis that the AnG may function in pheromone biosynthesis. In summary, we describe the power of transcriptomics in facilitating the progress made in our understanding of male sexual development, as illustrated by the commercial decapod species, S. verreauxi. Considering future directions, we suggest that the integration of multiple omics-based techniques offers the most powerful tool to ensure we continue to piece together the biology of the important group of decapod Crustacea