Pomc Plays an Important Role in Sexual Size Dimorphism in Tilapia

Pro-Opiomelanocortin and Melanocortin Receptor 3 and 4 Mutations in Genetic Obesity

Genetic obesity results from loss-of-function mutations, including those affecting the leptin-melanocortin system, which regulates body weight. Pro-opiomelanocortin (POMC)-derived neurohormones act as ligands for melanocortin receptors (MCRs), regulating the leptin-melanocortin pathway through protein-protein interactions. Loss-of-function mutations in the genes encoding POMC, MC3R, and MC4R can lead to the dysregulation of energy expenditure and feeding balance, early-onset obesity, and developmental dysregulation. Recent studies have identified new genetic regulatory mechanisms and potential biomarker regions for the POMC gene and MC4R secondary messenger pathway associated with obesity. Recent advances in crystal structure studies have enhanced our understanding of the protein interactions in this pathway. This narrative review focuses on recent developments in two key areas related to POMC regulation and the leptin-melanocortin pathway: (1) genetic variations in and functions of POMC, and (2) MC3R and MC4R variants that lead to genetic obesity in humans. Understanding these novel mutations in POMC and MC4R/MC3R, as well as their structural and intracellular mechanisms, may help identify strategies for the treatment and diagnosis of obesity, particularly childhood obesity.

Characteristic Muscle Quality Parameters of Male Largemouth Bass (Micropterus salmoides) Distinguished from Female and Physiological Variations Revealed by Transcriptome Profiling

Male largemouth bass (Micropterus salmoides) are often overlooked because females grow faster. We explored the value of male largemouth bass by comparing muscle nutrition, texture, and transcriptomes between males and females. Females grew faster than males (p < 0.05) because of lipid accumulation. Male fish muscles had higher contents of serine, valine, methionine, arginine, nervonic acid, and α-linolenic acid (p < 0.05), and female fish muscles had higher contents of aspartic acid, glycine, cysteine, leucine, palmitic acid, docosahexaenoic acid, and 11,14,17-eicosatrienoic acid (p < 0.05). Male muscles had a higher concentration of collagen fibers and greater shear force, indicative of a chewier texture. Male muscles had a lighter color, suggesting that they were less susceptible to oxidation and deterioration. Transcriptomic analyses revealed upregulation of lpl, sadb, dgat2, bhmt, tecrb, and hsd3b7, encoding components of amino acid and fatty acid metabolism; and upregulation of akt2, src, and kras, encoding crucial regulators of cellular immunity and homeostasis, in male muscles. Immunity-related pathways, including apoptosis, ErbB signaling, and cellular senescence, were enriched in male fish muscles, indicating heightened immune function. The muscles of male fish have a unique profile and distinctive advantages in terms of nutrition, flavor, texture, and transcriptional regulation.

Thermal modulation of energy allocation during sex determination in the European sea bass (Dicentrarchus labrax)

Water temperature governs physiological functions such as growth, energy allocation, and sex determination in ectothermic species. The European sea bass (Dicentrarchus labrax) is a major species in European aquaculture, exhibiting early dimorphic growth favoring females. The species has a polygenic sex determination system that interacts with water temperature to determine an individual's sex, with two periods during development that are sensitive to temperature. The current study investigated the influence of water temperature on energy allocation and sex-biased genes during sex determination and differentiation periods. RNA-Sequencing and qPCR analyses were conducted in two separate experiments, of either constant water temperatures typical of aquaculture conditions or natural seasonal thermal regimes, respectively. We focused on eight key genes associated with energy allocation, growth regulation, and sex determination and differentiation. In Experiment 1, cold and warm temperature treatments favored female and male proportions, respectively. The RNA-seq analysis highlighted sex-dependent energy allocation transcripts, with higher levels of nucb1 and pomc1 in future females, and increased levels of egfra and spry1 in future males. In Experiment 2, a warm thermal regime favored females, while a cold regime favored males. qPCR analysis in Experiment 2 revealed that ghrelin and nucb1 were down-regulated by warm temperatures. A significant sex-temperature interaction was observed for pank1a with higher and lower expression for males in the cold and warm regimes respectively, compared to females. Notably, spry1 displayed increased expression in future males at the all-fins stage and in males undergoing molecular sex differentiation in both experimental conditions, indicating that it provides a novel, robust, and consistent marker for masculinization. Overall, our findings emphasize the complex interplay of genes involved in feeding, energy allocation, growth, and sex determination in response to temperature variations in the European sea bass.

Sexual size dimorphism in mammals is associated with changes in the size of gene families related to brain development

In mammals, sexual size dimorphism often reflects the intensity of sexual selection, yet its connection to genomic evolution remains unexplored. Gene family size evolution can reflect shifts in the relative importance of different molecular functions. Here, we investigate the associate between brain development gene repertoire to sexual size dimorphism using 124 mammalian species. We reveal significant changes in gene family size associations with sexual size dimorphism. High levels of dimorphism correlate with an expansion of gene families enriched in olfactory sensory perception and a contraction of gene families associated with brain development functions, many of which exhibited particularly high expression in the human adult brain. These findings suggest a relationship between intense sexual selection and alterations in gene family size. These insights illustrate the complex interplay between sexual dimorphism, gene family size evolution, and their roles in mammalian brain development and function, offering a valuable understanding of mammalian genome evolution.

Effects of exogenous steroid hormones on growth, body color, and gonadal development in the Opsariichthys bidens

To investigate the effects of exogenous steroid hormones on growth, body color, and gonadal development in the Opsariichthys bidens (O. bidens), synthetic methyltestosterone (MT) and 17β-estradiol (E2) were used for 28 days' treatment of 4-month-old O. bidens before the breeding season. Our results suggested that MT had a significant growth-promoting effect (P < 0.05), whereas E2 played an inhibitory role. On the body surface, the females in the MT group showed gray stripes, and the fish in other groups showed no obvious stripes. The males with MT treatment displayed brighter blue-green stripes compared to the CK and E2 groups. The histological analysis showed that the MT significantly promoted testes development in males, blocked oocyte development, and caused massive apoptosis in females, whereas the E2 group promoted ovarian development and inhibited testes development. Based on qRT-PCR analysis, in females, the expression of igf-1, dmrt1, and cyp19a1a genes revealed that E2 treatment resulted in down-regulation of igf-1 expression and up-regulation of cyp19a1a expression. In males, igf-1 and dmrt1 were significantly up-regulated after MT treatment, and E2 treatment led to down-regulation of igf-1. Therefore, this study demonstrates that MT and E2 play an important role in reversing the morphological sex characteristics of females and males.

Tilapia, a good model for studying reproductive endocrinology

The Nile tilapia (Oreochromis niloticus), with a system of XX/XY sex determination, is a worldwide farmed fish with a shorter sexual maturation time than that of most cultured fish. Tilapia show a spawning cycle of approximately 14 days and can be artificially propagated in the laboratory all year round to obtain genetically all female (XX) and all male (XY) fry. Its genome sequence has been opened, and a perfect gene editing platform has been established. With a moderate body size, it is convenient for taking enough blood to measure hormone level. In recent years, using tilapia as animal model, we have confirmed that estrogen is crucial for female development because 1) mutation of star2, cyp17a1 or cyp19a1a (encoding aromatase, the key enzyme for estrogen synthesis) results in sex reversal (SR) due to estrogen deficiency in XX tilapia, while mutation of star1, cyp11a1, cyp17a2, cyp19a1b or cyp11c1 affects fertility due to abnormal androgen, cortisol and DHP levels in XY tilapia; 2) when the estrogen receptors (esr2a/esr2b) are mutated, the sex is reversed from female to male, while when the androgen receptors are mutated, the sex cannot be reversed; 3) the differentiated ovary can be transdifferentiated into functional testis by inhibition of estrogen synthesis, and the differentiated testis can be transdifferentiated into ovary by simultaneous addition of exogenous estrogen and androgen synthase inhibitor; 4) loss of male pathway genes amhy, dmrt1, gsdf causes SR with upregulation of cyp19a1a in XY tilapia. Disruption of estrogen synthesis rescues the male to female SR of amhy and gsdf but not dmrt1 mutants; 5) mutation of female pathway genes foxl2 and sf-1 causes SR with downregulation of cyp19a1a in XX tilapia; 6) the germ cell SR of foxl3 mutants fails to be rescued by estrogen treatment, indicating that estrogen determines female germ cell fate through foxl3. This review also summarized the effects of deficiency of other steroid hormones, such as androgen, DHP and cortisol, on fish reproduction. Overall, these studies demonstrate that tilapia is an excellent animal model for studying reproductive endocrinology of fish.

Molecular Analysis and Sex-specific Response of the Hepcidin Gene in Yellow Perch (Perca Flavescens) Following Lipopolysaccharide Challenge

Hepcidin antimicrobial peptide (hamp) is active in teleosts against invading pathogens and plays important roles in the stress and immune responses of finfish. The response of hamp gene was studied in yellow perch (yp) (Perca flavescens) challenged with lipopolysaccharides to understand if this immunity response is sex-specifically different. The cloned hamp gene consists of an open-reading frame of 273 bp and encodes a deduced protein of 90 amino acids (a.a.), which includes a signal peptide of 24 a.a., a pro-domain of 40 a.a. and a mature peptide of 26 a.a. Yp hamp involves 8 cysteine residues with 4 disulfide bonds, and a protein with an internal alpha helix flanked with C- and N-terminal random coils was modeling predicted. RT-qPCR was used to analyze the relative abundances (RAs) of hamp mRNA in the livers of juvenile female and male yellow perch challenged with lipopolysaccharide. The expression levels of hamp were significantly elevated by 3 h (RA = 7.3) and then peaked by 6 h (RA = 29.4) post-treatment in females but the peak was delayed to 12 h (RA = 65.4) post-treatment in males. The peak mRNA level of challenged males was shown 7.6-fold higher than females. The post-treatment responses in both genders decreased to their lowest levels by 24 h and 48 h. Overall, female perch had an earlier but less-sensitive response to the lipopolysaccharide challenge than male.

Chromosome-level genome sequence of the Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus) highlights regions of introgression with O. mossambicus

BACKGROUND

The Nile tilapia (Oreochromis niloticus) is the third most important freshwater fish for aquaculture. Its success is directly linked to continuous breeding efforts focusing on production traits such as growth rate and weight. Among those elite strains, the Genetically Improved Farmed Tilapia (GIFT) programme initiated by WorldFish is now distributed worldwide. To accelerate the development of the GIFT strain through genomic selection, a high-quality reference genome is necessary.

RESULTS

Using a combination of short (10X Genomics) and long read (PacBio HiFi, PacBio CLR) sequencing and a genetic map for the GIFT strain, we generated a chromosome level genome assembly for the GIFT. Using genomes of two closely related species (O. mossambicus, O. aureus), we characterised the extent of introgression between these species and O. niloticus that has occurred during the breeding process. Over 11 Mb of O. mossambicus genomic material could be identified within the GIFT genome, including genes associated with immunity but also with traits of interest such as growth rate.

CONCLUSION

Because of the breeding history of elite strains, current reference genomes might not be the most suitable to support further studies into the GIFT strain. We generated a chromosome level assembly of the GIFT strain, characterising its mixed origins, and the potential contributions of introgressed regions to selected traits.

Neurosecretory protein GL in GIFT tilapia (Oreochromis niloticus): cDNA cloning, tissue distribution and effects of feeding on its expression

Neurosecretory protein GL (NPGL), a novel neuropeptide, has been identified in the hypothalamus of chicks and rodents. NPGL plays a crucial role in monitoring energetic status via the regulation of feeding and metabolism. However, no study on NPGL has been reported in fish thus far. In the present study, the full-length cDNA of NPGL was identified from the hypothalamus of GIFT tilapia (Oreochromis niloticus). The ORF of tilapia NPGL is 471 bp and encodes a precursor peptide with a size of 156 a.a, consisting of a 26 a.a signal peptide and an 82 a.a mature peptide. Tissue distribution profiles of npgl in tilapia were acquired using semiquantitative PCR and in situ hybridization (ISH). The results showed that the highest npgl mRNA is expressed in the telencephalic-preoptic complex, which comprises both the telencephalon and the anterior preoptic area (POA) of male tilapia, and in the ovary of female tilapia. In addition, in male tilapia, the ISH results showed that the cells containing npgl mRNA were distributed exclusively in the anterior periventricular pretectal nucleus (Ppa) of the POA. FISH results demonstrated that npgl mRNA is also expressed in the lateral tuberal nucleus of the hypothalamus (NLT). Real-time PCR showed that npgl mRNA significantly increased in the telencephalic-preoptic complex of male tilapia that were fasted for 24 h and then fed a full diet for 20 min compared with the unfed group. Results of the FISH study showed that parvocellular cells containing npgl mRNA in the Ppa of fed fish were apparently more abundant than those of the unfed group. Few npgl positive signals also appeared in the NLT after full feeding, where pomc mRNA is highly expressed. These results indicate that NPGL may be a short-term satiety factor in fish and that the coexpression of NPGL and POMC may be present in the hypothalamus of male tilapia.

The Insertion in the 3' UTR of Pmel17 Is the Causal Variant for Golden Skin Color in Tilapia

Understanding of the relationships between genotypes and phenotypes is a central problem in biology. Although teleosts have colorful phenotypes, not much is known about their underlying mechanisms. Our previous study showed that golden skin color in Mozambique tilapia was mapped in the major locus containing the Pmel gene, and an insertion in 3' UTR of Pmel17 was fully correlated with the golden color. However, the molecular mechanism of how Pmel17 determines the golden skin color is unknown. In this study, knockout of Pmel17 with CRISPR/Cas9 in blackish tilapias resulted in golden coloration, and rescue of Pmel17 in golden tilapias recovered the wild-type blackish color, indicating that Pmel17 is the gene determining the golden and blackish color. Functional analysis in vitro showed that the insertion in the 3' UTR of Pmel17 reduced the transcripts of Pmel17. Our data supplies more evidence to support that Pmel17 is the gene for blackish and golden colors, and highlights that the insertion in the 3' UTR of Pmel17 is the causative mutation for the golden coloration.

Sex determination mechanisms and sex control approaches in aquaculture animals

Aquaculture is one of the most efficient modes of animal protein production and plays an important role in global food security. Aquaculture animals exhibit extraordinarily diverse sexual phenotypes and underlying mechanisms, providing an ideal system to perform sex determination research, one of the important areas in life science. Moreover, sex is also one of the most valuable traits because sexual dimorphism in growth, size, and other economic characteristics commonly exist in aquaculture animals. Here, we synthesize current knowledge of sex determination mechanisms, sex chromosome evolution, reproduction strategies, and sexual dimorphism, and also review several approaches for sex control in aquaculture animals, including artificial gynogenesis, application of sex-specific or sex chromosome-linked markers, artificial sex reversal, as well as gene editing. We anticipate that better understanding of sex determination mechanisms and innovation of sex control approaches will facilitate sustainable development of aquaculture.

Domestication of farmed fish via the attenuation of stress responses mediated by the hypothalamus-pituitary-inter-renal endocrine axis

Human-directed domestication of terrestrial animals traditionally requires thousands of years for breeding. The most prominent behavioral features of domesticated animals include reduced aggression and enhanced tameness relative to their wild forebears, and such behaviors improve the social tolerance of domestic animals toward both humans and crowds of their own species. These behavioral responses are primarily mediated by the hypothalamic-pituitary-adrenal (inter-renal in fish) (HPA/I) endocrine axis, which is involved in the rapid conversion of neuronal-derived perceptual information into hormonal signals. Over recent decades, growing evidence implicating the attenuation of the HPA/I axis during the domestication of animals have been identified through comprehensive genomic analyses of the paleogenomic datasets of wild progenitors and their domestic congeners. Compared with that of terrestrial animals, domestication of most farmed fish species remains at early stages. The present review focuses on the application of HPI signaling attenuation to accelerate the domestication and genetic breeding of farmed fish. We anticipate that deeper understanding of HPI signaling and its implementation in the domestication of farmed fish will benefit genetic breeding to meet the global demands of the aquaculture industry.

Tissue-Specific Expression Pattern in Ancherythroculter nigrocauda, a Sexually Size Dimorphic Fish

Certain members of the Actinopterygii class are known to exhibit sexual dimorphism (SD) that results in major phenotypic differences between male and female fishes of a species. One of the most common differences between the two sexes is in body weight, a factor with a high economic value in aquaculture. In this study, we used RNA sequencing (RNA-seq) to study the liver and brain transcriptomes of Ancherythroculter nigrocauda, a fish exhibiting SD. Females attain about fourfold body weight of males at sexual maturity. Sample clustering showed that both sexes were grouped well with their sex phenotypes. In addition, 2,395 and 457 differentially expressed genes (DEGs) were identified in the liver and brain tissues, respectively. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses predicted the association of PPAR signaling, cytochrome P450, and steroid hormone biosynthesis to the differences in sexual size. In addition, weighted gene co-expression network analyses (WGCNA) were conducted, and the green module was identified to be significantly correlated with sexual size dimorphism (SSD). Altogether, these results improve our understanding of the molecular mechanism underlying SSD in A. nigrocauda.