Molecular characterization of different preproGnRHs in Astyanax altiparanae (Characiformes): Effects of GnRH on female reproduction

Fishing for the gonadotropin releasing hormone from the genome of Salminus brasiliensis (Characiformes: Bryconidae)

The technological development of tools that enable the spawning of different native species is paramount to enable ex situ conservation initiatives, as well as providing means for commercial hatchery of threatened fish which, in turn, relieve fisheries pressure over wild stocks. Neotropical migratory freshwater fish depend on hormonal induction for spawning in hatcheries, through expensive methods of limited efficiency. Salminus brasiliensis is one of the largest Neotropical freshwater fish, a piscivorous top-predator, prized in angling, highly valued in the market, and appreciated in gastronomy. Teleost fish have either, two or three GnRH paralogous genes: GnRH1, GnRH2 and the GnRH3. The expression products of these paralogous isoforms consist of a larger prepro-GnRH polypeptide, which undergoes post-translational proteolytic processing to yield the active decapeptide hormone. There is increasing interest in characterizing and understanding these neuropeptides, because of its practical application in hatchery spawning. We present the characterization of GnRH1's coding sequence for the prepro-GnRH1 polypeptide of S. brasiliensis. An annotation from a genomic assembly was used for searching for GnRH paralogues, based on data from anonymous predicted transcripts. The sequence retrieved for GnRH1 was then used as a query for searching the uncharacterized GnRH paralogues from full genomes of Characiformes deposited at NCBI. The S. brasiliensis GnRH1 gene sequence retrieved was targeted for PCR and submitted to Sanger sequencing, allowing for its confirmation. It spans 423 bp (exon 1: 128 bp; intron: 161 bp; and exon 2: 1134 bp), with open reading frames coding for 264 and 88 amino acids, respectively. The different variants retrieved for the prepro-GnRH (1, 2 and 3) from Characiformes genomes and deposited sequences from NCBI grouped in three distinct clades in a neighbor joining tree, each forming a monophyletic branch and with the S. brasiliensis sequences nested within the expected groups. Here we observed a variation at a proteolytic site (GKR→GRR), reported as highly conserved in vertebrates up to now, that can potentially alter the cleavage site and modify the peptide topology. This work has characterized, for the first time, the sequence of the GnRH1 coding for its prepro-GnRH peptide, for a member of the Charaficormes order. This will help to promote research and development of tools for broodstock spawning and environmental management of S. brasiliensis and related migratory fish.

Long-lasting redundant gnrh1/3 expression in GnRH neurons enabled apparent switching of paralog usage during evolution

Expressed subtype of paralogous genes in functionally homologous cells sometimes show differences across species, the reasons for which have not been explained. The present study examined hypophysiotropic gonadotropin-releasing hormone (GnRH) neurons in vertebrates to investigate this mechanism. These neurons express either gnrh1 or gnrh3 paralogs, depending on the species, and apparent switching of the expressed paralogs in them occurred at least four times in vertebrate evolution. First, we found redundant expression of gnrh1 and gnrh3 in a single neuron in piranha and hypothesized that it may represent an ancestral GnRH system. Moreover, the gnrh1/gnrh3 enhancer of piranha induced reporter RFP/GFP co-expression in a single hypophysiotropic GnRH neuron in both zebrafish and medaka, whose GnRH neurons only express either gnrh3 or gnrh1. Thus, we propose that redundant expression of gnrh1/3 of relatively recent common ancestors may be the key to apparent switching of the paralog usage among present-day species.

Effects of vitamin A supplementation on ovarian development of Astyanax lacustris (Teleostei: Characidae) during the non-breeding season

Vitamin A (VA) is essential for fish reproduction, however, knowledge of VA requirement of broodstock fish is scarce. We investigated the physiological role of VA supplementation in the ovarian maturation of Astyanax lacustris throughout the non-breeding season. Adult females were distributed in five nutritional treatments, which differed by the amount of VA supplemented in a plant-based diet: T1 = 0, T2 = 1800, T3 = 3600, T4 = 7200, and T5 = 14,400 IU kg^-1 of VA for 60 days after a period of 16 days feeding on a diet poor in VA to reduce body VA content. Plasma total lipids (TL), lipoproteins, and 17β-estradiol (E₂) levels were measured after 30 and 60 days. Somatic indexes and morphophysiological ovarian parameters were calculated and VA concentration was analyzed in the ovaries and liver after 60 days. VA supplementation did not increase the concentration of this nutrient in the liver and ovaries. E₂ plasma level increased in animals fed on 3600 IU kg^-1 of VA (T3) after 60 days and females from T5 group presented a higher RF after 60 days. Ovarian development increased after 60 days compared to that after 30 days, confirmed by the higher gonadosomatic index (all groups). The supplementation with the highest VA level increased RF and decreased plasma TL (after 30 days) and low-density lipoprotein (LDL) (after 60 days) concentrations, showing a potential to improve reproduction even during the non-breeding season; however, its nutritional requirements of VA could be higher.

Paternal exposure to aluminum, acidity, and temperature affect fatty acid seminal profile, embryonic and larval development of Astyanax altiparanae

We investigated the effects of water acidity, temperature, and aluminum (Al) on the fatty acid (FA) seminal profile, reproductive parameters (fertilization and hatching) and embryonic development of Astyanax altiparanae. We treated males with different experimental treatments, corresponding to the combination of water temperature (20 °C; 25 °C), pH (neutral - 7.0; acidic - 5.5), and the absence or presence of Al (0.5 mg L^-1). After 96 h, we analyzed the FA profile of semen and performed artificial fertilization in activating medium with neutral pH or activating medium in the same experimental conditions of the males (neutral pH, acidic pH, and Al) to evaluate fertilization and hatching rates and to monitor embryonic development. Polyunsaturated FA percentage decreased in semen of fish from the neutral group, while monounsaturated FA increased in all groups maintained at 20 °C compared to 25 °C. Aluminum exposure decreased the percentage of C20:4n6 and increased the percentage of C22:5n3 at 20 °C. Males exposed to acidic pH and Al showed lower fertilization and hatching rates, as well as increased mortality of embryos and larvae. Moreover, Al favoured a higher percentage of abnormal larvae. Fertilization in Al activating medium harmed the embryos and larvae since fertilization and hatching rates decreased. Finally, temperature influenced fertilization time, hatching rate, and the morphology of embryos and larvae. Males exposed to Al had lower fertilizing capacity, which negatively affected the embryonic development of the species. Furthermore, Al activating medium reduced the number of fertilized oocytes, hatched embryos, and normal larvae. All events were temperature dependent.