Differentially expressed genes in the pituitary of the Amazonian fish Arapaima gigas

Vitellogenin Ab structure of the amazonian Arapaima gigas

The vitellogenin is composed by polypeptides that are precursors of egg yolk proteins that provides embryo and larvae nutrition. The mRNA encoding for vitellogenin Ab (Vtg-Ab; 4,536 bp long and 1,512 amino acids) were obtained by RNA-Seq library sequencing of pirarucu gonads. The Vtg-Ab sequences had high homology with Vtgs of other three teleosts species of the order Osteoglossiformes. The transcript of ovarian Vtg was identified based on structural criteria, and so we classify the Vtg of pirarucu as Vtg-Ab due to the truncated or shortened phosvitin (N-terminal end) and phosvitinless domain (C-terminal end). The Vtg-Ab of pirarucu present two major deletions with 133 amino acids in the Lipovitellin I domain and 89 amino acids in the truncated or shortened Phosvitin domain, both located in the N-terminal end region. The three-dimensional (3-D) structure Vtg-Ab protein shows the presence of a typical 4α-helices bundle protein that runs in anti-parallel. In general, the characterization of Vtg-Ab may be the useful elucidation of the hormonal regulation of vitellogenesis and improve the production of pirarucu for broodstock management in aquaculture and preparation of Vtg antibody production (species-specific) for sex identification.

Environmental RNA: A Revolution in Ecological Resolution?

Current advancements in environmental RNA (eRNA) exploit its relatively fast turnover rate relative to environmental DNA (eDNA) to assess 'metabolically active' or temporally/spatially recent community diversity. However, this focus significantly underutilizes the trove of potential ecological information encrypted in eRNA. Here, we argue for pushing beyond current species-level eDNA detection capabilities by using eRNA to detect any organisms with unique eRNA profiles, potentially including different life-history stages, sexes, or even specific phenotypes within a species. We also discuss the future of eRNA as a means of assessing the physiological status of organisms and the ecological health of populations and communities, reflecting ecosystem-level conditions. We posit that eRNA has the potential to significantly improve the resolution of organism detection, biological monitoring, and biomonitoring applications in ecology.

Identification and structural characterization of the factors involved in vitellogenesis and its regulation in the African Osteoglossiforme of aquacultural interest Heterotis niloticus (Cuvier, 1829)

The African bonytongue (Heterotis niloticus) is an excellent candidate for fish farming because it has outstanding biological characteristics and zootechnical performances. However, the absence of sexual dimorphism does not favor its reproduction in captivity or the understanding of its reproductive behavior. Moreover, no molecular data related to its reproduction is yet available. This study therefore focuses on the structural identification of the different molecular actors of vitellogenesis expressed in the pituitary gland, the liver and the ovary of H. niloticus. A transcriptomic approach based on de novo RNA sequencing of the pituitary gland, ovary and liver of females in vitellogenesis led to the creation of three transcriptomes. In silico analysis of these transcriptomes identified the sequences of pituitary hormones such as prolactin (PRL), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and their ovarian receptors (PRLR, FSHR, LHR). In the liver and ovary, estrogen receptors (ER) beta and gamma, liver vitellogenins (VtgB and VtgC) and their ovarian receptors (VLDLR) were identified. Finally, the partial transcript of an ovarian Vtg weakly expressed compared to hepatic Vtg was identified based on structural criteria. Moreover, a proteomic approach carried out from mucus revealed the presence of one Vtg exclusively in females in vitellogenesis. In this teleost fish that does not exhibit sexual dimorphism, mucus Vtg could be used as a sexing biomarker based on a non-invasive technique compatible with the implementation of experimental protocols in vivo.

Morphological characterization of pirarucu Arapaima gigas (Schinz, 1822) gonadal differentiation

Arapaima gigas is a giant air-breathing and bony tongue fish from the Amazon basin and a promising species for aquaculture. A. gigas farming industry is still not established because of the lack of information on its reproductive physiology. Reproduction in captivity cannot be manipulated or stimulated, and the identification of males and females in a broodstock is not easy. We aimed to reveal the morphological sex differentiation of pirarucu as studies involving gonad development are essential to understanding the reproductive physiology of any species. We performed histological analysis on the whole body and extracted the gonads of 150 juveniles. The first sign of ovary differentiation is the sex-specific rearrangement of the germ cells. In 9 cm total length females, the germ cells group into nests and are restricted to the lateral face of the gonad, in close contact with the abdomen wall. With further development, this region invaginates and that later develops into ovigerous lamellae. Meiosis starts soon after ovary differentiation. In males, the germ cells are scattered along the elongated differentiating testis at first, and later become more restricted to the central region where the spermatogonial cysts start to develop. Somatic and germ cells are jointly involved in the cellular reorganization during gonadal differentiation, specifically when the germ cells begin to establish new associations during the development of both the germinal epithelium and stroma. RESEARCH HIGHLIGHTS: In Arapaima gigas, the ovary differentiation occurs in 9 cm TL females and it is marked by the rearrangement of germ and somatic cells; and the germ cells entering meiosis with no formation of ovarian cavity; testis differentiation occurs later and meiosis does not start in males smaller than 80 cm TL.