Molecular characterization and activity of the hypothalamus-pituitary-gonads axis in Astyanax altiparanae (Teleostei, Characiformes) during the reproductive cycle in captivity

Abstract

Teleost fish reproduction is internally regulated by a hierarchical and orchestrated system, the hypothalamus-pituitary-gonad (HPG) axis. At the hypothalamic level, the regulation occurs by the gonadotropin releasing hormone (Gnrh), which stimulates the secretion of follicle-stimulation hormone (Fsh) and luteinizing hormone (Lh) from the pituitary. They reach the bloodstream and activate their receptors (Fshr and Lhr) present in target cells in the gonads, triggering the synthesis of different sexual steroids; which in turn regulates the gonadal development phases, gamete release and the reproductive behavior of each species. The knowledge about the endocrine control of reproduction in South American species is scarce, even in species widely used in aquaculture. Over recent years, our laboratory has focused its studies to understand the organization and physiology of the HPG axis in Astyanax altiparanae, an endemic Characiform of the Paraná River Basin. This species has economic and ecological importance, and has increasingly been used as a biological model. Recently we characterized the distribution of Gnrh neurons (Gomes et al. 2013) and the semi cystic spermatogenesis in this species (Costa et al. 2014), as well as we cloned the cDNAs for fshb, lhb, gpha, gnrh2 and gnrh3. Now, in this project, we propose to perform the molecular characterization of fshr and lhr of A. altiparanae, analyse their specificity and cellular distribution. Also, we aim to analyze the activity of the HPG axis during the annual reproductive cycle of females and males in captivity. The data about the changes in the gene expression and plasma levels of their components (neuropeptides, gonadotropins and their receptors, sex steroids and steroidogenic enzymes) will be correlated with each other, as well as the histology, cell proliferation and death analyses in the gonads. Using a Characiform species as a model and different methodological approaches, we intend to expand and obtain consistent data about the endocrine control of reproduction in South American teleosts and also indirectly contribute to improve techniques of induced breeding in A. altiparanae and other Characiformes. (AU)