Insights into Reproduction Through Gonadal Tissue Methylation Analysis and Transcriptomic Integration.

Fish exhibit diverse mechanisms of sex differentiation and determination, shaped by both external and internal influences, often regulated by distinct DNA methylation patterns responding to environmental changes. In aquaculture, reproductive issues in captivity pose significant challenges, particularly the lack of fertilization capabilities in captive-bred males, hindering genetic improvement measures. This study analyzed the methylation patterns and transcriptomic profiles in gonadal tissue DNA from groups differing in rearing conditions and sexual maturity stages.

Effects of seawater and freshwater challenges on the Gh/Igf system in the saline-tolerant blackchin tilapia .

Prolactin (Prl) and growth hormone (Gh) as well as insulin-like growth factor 1 (Igf1) are involved in the physiological adaptation of fish to varying salinities. The Igfs have been also ascribed other physiological roles during development, growth, reproduction and immune regulation. However, the main emphasis in the investigation of osmoregulatory responses has been the endocrine, liver-derived Igf1 route and local regulation within the liver and osmoregulatory organs.

Polymorphism of Sex Determination Amongst Wild Populations Suggests its Rapid Turnover Within the Nile Tilapia Species.

Sex-determining regions have been identified in the Nile tilapia on linkage groups (LG) 1, 20 and 23, depending on the domesticated strains used. Sex determining studies on wild populations of this species are scarce. Previous work on two wild populations, from Lake Volta (Ghana) and from Lake Koka (Ethiopia), found the sex-determining region on LG23.

Different transcriptomic architecture of the gill epithelia in Nile and Mozambique tilapia after salinity challenge.

Tilapiine fishes of the genus Oreochromis vary in their euryhaline capabilities, therefore inhabiting aquatic environments of different salinities across the African continent. We analyzed the differential gene expression in the gills before and after 6 weeks salinity challenge between the highly tolerant Mozambique tilapia (Oreochromis mossambicus) and the less tolerant Nile tilapia (O. niloticus).

Structure and Sequence of the Sex Determining Locus in Two Wild Populations of Nile Tilapia.

In domesticated strains of the Nile tilapia, phenotypic sex has been linked to genetic variants on linkage groups 1, 20 and 23. This diversity of sex-loci might reflect a naturally polymorphic sex determination system in Nile tilapia, or it might be an artefact arising from the process of domestication. Here, we searched for sex-determiners in wild populations from Kpandu, Lake Volta (Ghana-West Africa), and from Lake Koka (Ethiopia-East Africa) that have not been subjected to any genetic manipulation.

Mismatches between the genetic and phenotypic sex in the wild Kou population of Nile tilapia .

Sex determination and sex chromosomes can be very diverse between teleost species. The group of tilapias shows a polymorphism in sex determination not only between closely related species but also between domestic strains within a species. In the Nile tilapia, the major effect genes and therefore the Y chromosome have been located on either linkage group 1 (LG1) or LG23 depending on the strains.

Species-Specific Marker Discovery in Tilapia.

Tilapias (family Cichlidae) are of importance in aquaculture and fisheries. Hybridisation and introgression are common within tilapia genera but are difficult to analyse due to limited numbers of species-specific genetic markers. We tested the potential of double digested restriction-site associated DNA (ddRAD) sequencing for discovering single nucleotide polymorphism (SNP) markers to distinguish between 10 tilapia species.

The Reversible Sex of Gonochoristic Fish: Insights and Consequences.

Fish sex reversal is a means to understand sex determination and differentiation, but it is also used to control sex in aquaculture. This review discusses sex reversal in gonochoristic fish, with the coexistence of genetic and environmental influences. The different periods of fish sensitivity to sex reversal treatments are presented with the mechanisms implicated.

Comparative analysis of a sex chromosome from the blackchin tilapia, Sarotherodon melanotheron.

Background: Inversions and other structural polymorphisms often reduce the rate of recombination between sex chromosomes, making it impossible to fine map sex-determination loci using traditional genetic mapping techniques. Here we compare distantly related species of tilapia that each segregate an XY system of sex-determination on linkage group 1. We use whole genome sequencing to identify shared sex-patterned polymorphisms, which are candidates for the ancestral sex-determination mutation.

Endocrine and Local IGF-I in the Bony Fish Immune System.

A role for GH and IGF-I in the modulation of the immune system has been under discussion for decades. Generally, GH is considered a stimulator of innate immune parameters in mammals and teleost fish. The stimulatory effects in humans as well as in bony fish often appear to be correlated with elevated endocrine IGF-I (liver-derived), which has also been shown to be suppressed during infection in some studies.

The sensitive period for male-to-female sex reversal begins at the embryonic stage in the Nile tilapia and is associated with the sexual genotype.

In this study, we sought to determine the mechanism of early sex reversal in a teleost by applying 4 hr feminization treatments to XY (17α-ethynylestradiol 2000 μg L(-1) ) and YY (6500 μg L(-1) ) Nile tilapia embryos on the first day post-fertilization (dpf). We then searched for changes in the expression profiles of some sex-differentiating genes in the brain (cyp19a1b, foxl2, and amh) and in sex steroids (testosterone, 17β-estradiol, and 11-ketotestosterone) concentrations during embryogenesis and gonad differentiation. No sex reversal was observed in YY individuals, whereas sex-reversal rates in XY progeny ranged from 0-60%.

Genetic inactivation of European sea bass (Dicentrarchus labrax L.) eggs using UV-irradiation: observations and perspectives.

Androgenesis is a form of uniparental reproduction leading to progenies inheriting only the paternal set of chromosomes. It has been achieved with variable success in a number of freshwater species and can be attained by artificial fertilization of genetically inactivated eggs following exposure to gamma (γ), X-ray or UV irradiation (haploid androgenesis) and by restoration of diploidy by suppression of mitosis using a pressure or thermal shock. The conditions for the genetic inactivation of the maternal genome in the European sea bass (Dicentrarchus labrax L.

The genomic substrate for adaptive radiation in African cichlid fish.

Cichlid fishes are famous for large, diverse and replicated adaptive radiations in the Great Lakes of East Africa. To understand the molecular mechanisms underlying cichlid phenotypic diversity, we sequenced the genomes and transcriptomes of five lineages of African cichlids: the Nile tilapia (Oreochromis niloticus), an ancestral lineage with low diversity; and four members of the East African lineage: Neolamprologus brichardi/pulcher (older radiation, Lake Tanganyika), Metriaclima zebra (recent radiation, Lake Malawi), Pundamilia nyererei (very recent radiation, Lake Victoria), and Astatotilapia burtoni (riverine species around Lake Tanganyika). We found an excess of gene duplications in the East African lineage compared to tilapia and other teleosts, an abundance of non-coding element divergence, accelerated coding sequence evolution, expression divergence associated with transposable element insertions, and regulation by novel microRNAs.

Oestrogen and insulin-like growth factors during the reproduction and growth of the tilapia Oreochromis niloticus and their interactions.

Oestrogens and insulin-like growth factors (Igfs) play both a central role in the regulation of reproduction and growth and can interact especially in species showing a clear-cut sex-linked growth dimorphism (SGD) like in tilapia. Aromatase is essential in ovarian differentiation and oogenesis since it controls oestrogen synthesis. During tilapia sex differentiation, aromatase cyp19a1a expression increases from 9 days post-fertilization (dpf), resulting in high oestradiol level.

Temperature induced-masculinisation in the Nile tilapia causes rapid up-regulation of both dmrt1 and amh expressions.

Nile tilapia has primarily a XX/XY sex determining system but minor genetic factors as well as temperature can override the major factors. Female XX progenies can be sex-reversed into functional males by rearing at high temperatures (>34°C) from 10dpf onwards. Temperature effects on the molecular pathways during sex differentiation in teleosts need to be deciphered.

The vertebrate makorin ubiquitin ligase gene family has been shaped by large-scale duplication and retroposition from an ancestral gonad-specific, maternal-effect gene.

Background: Members of the makorin (mkrn) gene family encode RING/C3H zinc finger proteins with U3 ubiquitin ligase activity. Although these proteins have been described in a variety of eukaryotes such as plants, fungi, invertebrates and vertebrates including human, almost nothing is known about their structural and functional evolution.

Results: Via partial sequencing of a testis cDNA library from the poeciliid fish Xiphophorus maculatus, we have identified a new member of the makorin gene family, that we called mkrn4.

Comparative physical maps derived from BAC end sequences of tilapia (Oreochromis niloticus).

Background: The Nile tilapia is the second most important fish in aquaculture. It is an excellent laboratory model, and is closely related to the African lake cichlids famous for their rapid rates of speciation. A suite of genomic resources has been developed for this species, including genetic maps and ESTs.

Genetic and physical mapping of sex-linked AFLP markers in Nile tilapia (Oreochromis niloticus).

Identification of the sex-determining genes of the Nile tilapia (Oreochromis niloticus) has important implications for commercial aquaculture. We previously identified an XX/XY sex-determining locus in this species within a 10-cM interval between markers GM201 and UNH995 on linkage group one (LG1). In order to refine this region, we developed new AFLP markers using bulked segregant analysis of the mapping families.

Seawater and freshwater challenges affect the insulin-like growth factors IGF-I and IGF-II in liver and osmoregulatory organs of the tilapia.

Contradictory studies suggest IGF-I in fish liver and gills is involved in osmoregulation, but nothing is known about the kidney and intestine's role nor about IGF-II's role in any organ. Tilapia were transferred from freshwater (FW) to seawater (SW) for 1week (wk) and retransferred to FW for another week. At 4h, 1d, 2d, 3d and 1wk after SW-transfer and FW-retransfer IGF-I, IGF-II and growth hormone receptor (GHR1) mRNA were measured by real-time PCR.

An EST resource for tilapia based on 17 normalized libraries and assembly of 116,899 sequence tags.

Background: Large collections of expressed sequence tags (ESTs) are a fundamental resource for analysis of gene expression and annotation of genome sequences. We generated 116,899 ESTs from 17 normalized and two non-normalized cDNA libraries representing 16 tissues from tilapia, a cichlid fish widely used in aquaculture and biological research.

Results: The ESTs were assembled into 20,190 contigs and 36,028 singletons for a total of 56,218 unique sequences and a total assembled length of 35,168,415 bp.

Challenge with 17alpha-ethinylestradiol (EE2) during early development persistently impairs growth, differentiation, and local expression of IGF-I and IGF-II in immune organs of tilapia.

The enormous expansion of world-wide aquaculture has led to increasing interest in the regulation of fish immune system. Estrogen has recently been shown to inhibit the endocrine (liver-derived) and autocrine/paracrine local insulin-like growth factor-I system in fish. In order to address the potential actions of estrogen on the IGF system in immune organs, tilapia were fed with 17alpha-ethinylestradiol (EE2)-enriched food from 10 to 40 days post fertilization (DPF) to induce functional feminization, an approach commonly used in aquaculture.

Transcriptional responses of the black-chinned tilapia Sarotherodon melanotheron to salinity extremes.

Sarotherodon melanotheron is one of the most euryhaline teleosts able to withstand variations in environmental salinity ranging from freshwater (FW) to 130‰ hyper-saline waters (HSW). Although significant progress has been made in exploring the cellular and molecular changes that accompany salinity adaptation in teleosts, little is known about the effects of long-term acclimation to HSW. We sought to identify in this tilapia species the genes whose transcription is induced by long-term acclimation either to HSW or FW.

Ethinylestradiol differentially interferes with IGF-I in liver and extrahepatic sites during development of male and female bony fish.

Growth and sexual development are closely interlinked in fish; however, no reports exist on potential effects of estrogen on the GH/IGF-I-axis in developing fish. We investigate whether estrogen exposure during early development affects growth and the IGF-I system, both at the systemic and tissue level. Tilapia were fed from 10 to 40 days post fertilization (DPF) with 17alpha-ethinylestradiol (EE(2)).