Biology subjects

Ahi, E. P.

Publications and source records attributed to Ahi, E. P..

7 recordsLinked to original sources

bioRxiv2023

Seasonal and genetic effects on lipid profiles of juvenile Atlantic salmon

Seasonality can influence many physiological traits requiring optimal energetic capacity for life-history stage transitions. In Atlantic salmon, high-energy status is essential for the initiation of maturation. Atlantic salmon lipid reserves are predominantly found in the viscera and myosepta in the muscle while the liver is essential for maintaining lipid metabolism. A genomic study found a region including a transcription co-factor-coding gene, vgll3, linked to Atlantic salmon maturation timing, which acts as an inhibitor of adipogenesis in mice, and mediates maturation via condition factor in Atlantic salmon. Here we investigate the influence of season and vgll3 genotypes associating with early (EE) and late (LL) maturation on lipid profiles in the muscle and liver in juvenile Atlantic salmon. We reared Atlantic salmon for two years until the occurrence of sexually mature males and sampled muscle and liver at two time points: spring and autumn of the second year. We found no seasonal or genotype effect in lipid profiles in muscle of immature males and females. However, in the liver we did detect a triacylglycerol (TG) enrichment and a genotype specific direction of change in membrane lipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), from spring to autumn. Specifically, from spring to autumn membrane lipid concentrations increased in vgll3*EE individuals and decreased in vgll3*LL individuals. This could be explained with two possible scenarios 1) a seasonally more stable capacity of endoplasmic reticulum (ER) functions in vgll3*EE individuals compared to vgll3*LL individuals or 2) vgll3*LL individuals storing larger lipid droplets from spring to autumn in the liver compared to vgll3*EE individuals at the expense of ER capacity. This genotype specific seasonal direction of change in membrane lipid concentrations provides more indirect evidence that a mechanism linking vgll3 with lipid metabolism and storage exists. HighlightsO_LISeasonal lipid species profile separation in muscle and liver in juvenile Atlantic salmon C_LIO_LIGenotype specific direction of change of membrane lipids from spring to autumn C_LIO_LIIndirect evidence that a mechanism linking vgll3 with lipid metabolism and storage exists C_LI

evolutionary biology↗

bioRxiv2022

Expression of m6A RNA methylation markers in the hypothalamus of Atlantic salmon

Methylation at the N6-position of adenosine, m6A, is the most abundant mRNA modification in eukaryotes. It is a highly conserved universal regulatory mechanism controlling gene expression in a myriad of biological processes. The role of m6A methylation in sexual maturation, however, has remained largely unexplored. While the maturation process is known to be affected by many genetic and environmental factors, the molecular mechanisms causing variation in the timing of maturation are still poorly understood. Hence, investigation of whether a widespread mechanism like m6A methylation could be involved in controlling of the maturation timing is warranted. In Atlantic salmon (Salmo salar), two genes associated with the age at maturity in human, vgll3 and six6, have been shown to play an important role in maturation timing. In this study, we investigated the expression of 16 genes involved in the regulation of m6A RNA methylation in the hypothalamus of Atlantic salmon with different homozygous combinations of late (L) and early (E) alleles for vgll3 and six6 genes. We found differential expression of ythdf2.2 which encodes an m6A modification reader and promotes mRNA degradation. Its expression was higher in six6*LL compared to other genotypes as well as immature males compared to matures. In addition, we found that the expression levels of genes coding for an eraser, alkbh5, and for a reader, ythdf1, were higher in the hypothalamus of females than in males across all the different genotypes studied. Our results indicate a potential role of the m6A methylation process in sexual maturation of Atlantic salmon, and therefore, provide the first evidence for such regulatory mechanism in the hypothalamus of any vertebrate. Investigation of additional vertebrate species is warranted in order to determine the generality of these findings.

molecular biology↗

bioRxiv2022

A pituitary gene network linking vgll3 to regulators of sexual maturation in male Atlantic salmon

Age at maturity is a key life history trait and a significant contributor to life history strategy variation. The maturation process is complex and influenced by genetic and environmental factors alike, but specific causes of variation in maturation timing remain elusive. In many species, the increase in the regulatory gonadotropin-releasing hormone 1 (GnRH1) marks the onset of puberty. Atlantic salmon, however, lack the gene encoding GnRH1, suggesting other regulatory factors are involved in the maturation process. Earlier research in Atlantic salmon has found a strong association between alternative alleles of vgll3 and maturation timing, making vgll3 a candidate reproductive axis gene regulator. Recently we reported strong induction of gonadotropin encoding genes (fshb and lhb) in the pituitary of male Atlantic salmon homozygous for the vgll3 allele linked with the early maturation allele (E). The induction of gonadotropins was accompanied by increased expression of their direct upstream regulators, c-jun and sf1 (nr5a1b) in the pituitary. In mammals, the transcriptional activation of c-jun and sf1 is also required for induction of fshb and lhb, however, GnRH1 is responsible for increased transcriptional activity of c-jun and sf1. The absence of gnrh1 in salmon raises the possibility of the involvement of other regulators upstream of these factors. In this study, we investigated such a possibility through a stepwise approach for identifying a gene regulatory network (GRN) containing c-jun and sf1 and using the zebrafish coexpression database and transcription factor motif enrichment analysis. We found a GRN containing c-jun with predicted upstream regulators, e2f1, egr1, foxj1 and klf4, which are also differentially expressed in the pituitary. Finally, we suggest a model for transcriptional regulation of c-jun and sf1in the absence of gnrh1 in the pituitary, which may have broader implications across vertebrates.

molecular biology↗

bioRxiv2022

Gene expression patterns associated with fin shape differ between two lamprologine cichlids

Comparing gene regulatory patterns between seemingly similar phenotypic traits can provide important insights on the molecular mechanisms underlying the evolution of those traits. In this study, we investigate the molecular basis of the formation of a spade-shaped caudal fin, which is a rare phenotype among teleost fish characterized by an elongated medial region of the fin. We examined the expression patterns of candidate fin-shape genes in the spade-shaped caudal fin of the related species Lamprologus tigripictilis, an East African cichlid in the tribe Lamprologini. The candidate gene set consisted of a previously identified gene regulatory network (GRN) associated with the elongation of fin regions in another Lamprologini cichlid species and further genes selected on the basis of co-expression data and transcription factor prediction. Unexpectedly, the anatomical features of elongated fin rays differed and gene expression patterns associated with fin elongation were only weakly conserved between the two related species. We report 20 genes and transcription factors (including angptl5, cd63, csrp1a, cx43, esco2, gbf1 and rbpj), whose expression levels differed between the elongated and the short caudal fin regions of L. tigripictilis, and which are therefore candidates for the regulation of the spade-like fin shape.

evolutionary biology↗

bioRxiv2021

Expression variations in Ectodysplasin-A gene (eda) may contribute to morphological divergence of scales in Haplochromine cichlids

BackgroundElasmoid scales are one of the most common dermal appendages and can be found in almost all species of bony fish differing greatly in their shape. Whilst the genetic underpinnings behind elasmoid scale development have been investigated, not much is known about the mechanisms involved in the shaping of scales. To investigate the links between gene expression differences and morphological divergence, we inferred shape variation of scales from two different areas of the body (anterior and posterior) stemming from ten haplochromine cichlid species from different origins (Lake Tanganyika, Lake Malawi, Lake Victoria and riverine). Additionally, we investigated transcriptional differences of a set of genes known to be involved in scale development and morphogenesis in fish. ResultsWe found that scales from the anterior and posterior part of the body strongly differ in their overall shape, and a separate look on scales from each body part revealed similar trajectories of shape differences considering the lake origin of single investigated species. Above all, nine as well as 11 out of 16 target genes showed expression differences between the lakes for the anterior and posterior dataset, respectively. Whereas in posterior scales four genes (dlx5, eda, rankl and shh) revealed significant correlations between expression and morphological differentiation, in anterior scales only one gene (eda) showed such a correlation. Furthermore, eda displayed the most significant expression difference between species of Lake Tanganyika and species of the other two younger lakes. Finally, we found genetic differences in downstream regions of eda gene (e.g. in the eda-tnfsf13b inter-genic region) that are associated with observed expression differences. This is reminiscent of a genetic difference in the eda-tnfsf13b inter-genic region which leads to gain or loss of armour plates in stickleback. ConclusionThese findings provide evidence for cross-species transcriptional differences of an important morphogenetic factor, eda, which is involved in formation of ectodermal appendages. These expression differences appeared to be associated with morphological differences observed in the scales of haplochromine cichlids indicating potential role of eda mediated signal in divergent scale morphogenesis in fish.

evolutionary biology↗

bioRxiv2021

Strong regulatory effects of vgll3 genotype on reproductive axis gene expression in immature male Atlantic salmon

Age at maturity is a major contributor to the diversity of life history strategies in organisms. The process of maturation is influenced by both genetics and the environment, and includes changes in levels of sex hormones and behavior, but the specific factors leading to variation in maturation timing are not well understood. gnrh1 regulates the transcription of gonadotropin genes at the onset of puberty in many species, but this gene is lacking in certain teleost species including Atlantic salmon (Salmo salar), which raises the possibility of the involvement of other important regulatory factors during this process. Earlier research has reported a strong association of alternative alleles of the vgll3 gene with maturation timing in Atlantic salmon, suggesting it as a potential candidate regulating reproductive axis genes. Here, we investigated the expression of reproductive axis genes in immature Atlantic salmon males with different vgll3 genotypes during the spawning period. We detected strong vgll3 genotype-dependent differential expression of reproductive axis genes (such as fshb, lhb, amh and igf3) tested in the pituitary, and testis of one-year-old immature male Atlantic salmon. In addition, we observed differential expression of jun (ap1) and nr5a1b (sf1), potential upstream regulators of gonadotropins in the pituitary, as well as axin2, id3, insl3, itch, ptgs2a and ptger4b, the downstream targets of amh and igf3 in the testis. Hereby, we provide evidence of strong vgll3 genotype-dependent transcriptional regulation of reproductive axis genes prior to sexual maturation together with models for distinct actions of vgll3 genotypes on the molecular processes controlling spermatogenesis in Atlantic salmon.

physiology↗

bioRxiv2021

Appetite regulating genes in zebrafish gut; a gene expression study

The underlying molecular pathophysiology of feeding disorders, particularly in peripheral organs, is still largely unknown. A range of molecular factors encoded by appetite-regulating genes are already described to control feeding behaviour in the brain. However, the important role of the gastrointestinal tract in the regulation of appetite and feeding in connection to the brain has gained more attention in the recent years. An example of such inter-organ molecular interaction can be the signals mediated by leptin, a key regulator of body weight, food intake and metabolism, with conserved anorexigenic effects in vertebrates. Leptin signal functions through its receptor (lepr) in multiple organs, including the brain and the gastrointestinal tract. So far, the regulatory connections between leptin signal and other appetite-regulating genes remain unclear, particularly in the gastrointestinal system. In this study, we used a zebrafish mutant with impaired function of leptin receptor to explore gut expression patterns of appetite-regulating genes, under different feeding conditions (normal feeding, 7-day fasting, 2 and 6-hours refeeding). We compared these expression patterns to those from wild-type zebrafish, in order to identify leptin-dependent differentially expressed genes located in the zebrafish gut. We provide evidence that most appetite-regulating genes are expressed in the zebrafish gut. On one hand, we did not observed significant differences in the expression of orexigenic genes after changes in the feeding condition, and only one orexigenic gene, hcrt, displayed differential expression under impaired leptin signal. On the other hand, we found 8 anorexigenic genes in wild-types (cart2, cart3, dbi, oxt, nmu, nucb2a, pacap and pomc), as well as 4 genes in lepr mutants (cart3, kiss1, kiss1r and nucb2a), to be differentially expressed in the zebrafish gut after changes in feeding conditions. Most of these genes also showed significant differences in their expression between wild-type and lepr mutant in at least one of the feeding conditions. Finally, we observed that impaired leptin signalling influences potential regulatory connections between anorexigenic genes in zebrafish gut, particularly connections involving cart2, cart3, kiss1, kiss1r, mchr2, nmu, nucb2a and oxt. Altogether, these transcriptional changes propose a potential role of the gastrointestinal tract in the regulation of feeding through changes in expression of certain anorexigenic genes in zebrafish.

physiology↗