Common Carp mef2 Genes: Evolution and Expression

Identification of two MEF2s and their role in inhibiting the transcription of the mstn2a gene in the yellowfin seabream, Acanthopagrus latus (Hottuyn, 1782)

Myocyte-specific enhancer binding factor 2 (MEF2), which belongs to the MADS superfamily, is a pivotal and conserved transcription factor that combines with the E-box motif to control the expression of muscle genes. Myostatin (mstn), a muscle growth inhibitor, is a vital member of the TGF-β superfamily. Currently, an understanding of the mechanisms of A. latus mstn (Almstn) transcriptional regulation mediated by MEF2 in fish muscle development is lacking. In the present study, two AlMEF2s (AlMEF2A and AlMEF2B) and Almstn2a were characterized from Acanthopagrus latus. AlMEF2A and AlMEF2B had 456 and 315 amino acid (aa) residues, respectively. Two typical regions, a MADS-box, MEF2, and transcriptionally activated (TAD) domains, are present in both AlMEF2s. The expression profiles of the two AlMEF2 genes were similar. The AlMEF2 genes were mainly expressed in the brain, white muscle, and liver, while Almstn2a expression was higher in the brain than in other tissues. Moreover, the expression trends of AlMEF2s and Almstn2a were significantly changed after starvation and refeeding in the five groups. Additionally, truncation experiments showed that -987 to +168 and -105 to +168 were core promoters of Almstn2a that responded to AlMEF2A and AlMEF2B, respectively. The point mutation experiment confirmed that Almstn2a transcription relies on the mutation binding sites 1 or 5 (M1/5) and mutation binding sites 4 or 5 (M4/5) for AlMEF2A and AlMEF2B regulation, respectively. The electrophoretic mobile shift assay (EMSA) further verified that M1 (-527 to -512) was a pivotal site where AlMEF2A acted on the Almstn2a gene. Furthermore, a siRNA interference gene expression experiment showed that reduced levels of AlMEF2A or AlMEF2B could prominently increase Almstn2a transcription. These results provide new information about the regulation of Almstn2a transcriptional activity by AlMEF2s and a theoretical basis for the regulatory mechanisms involved in muscle development in fish.

The MEF2 homolog of Penaeus vannamei is essential for maintaining the WSSV latent infection

White spot syndrome virus (WSSV) is a lethal shrimp pathogen that has a latent infection cycle. The latent virus can easily turn into an acute infection when the culture environment changes, leading to widespread shrimp mortality. However, the mechanism of WSSV latent infection is poorly understood. Bioinformatic analysis revealed that the promoters of WSSV latency-related genes (i.e., wsv151, wsv366, wsv403, and wsv427) contained putative myocyte enhancer factor 2 (MEF2) binding sites. This suggested that the transcription factor MEF2 may be involved in WSSV latent infection. To further investigate this, a MEF2 homolog (PvMEF2) was cloned from Penaeus vannamei and its role in WSSV latent infection was explored. The results showed that knockdown of PvMEF2 led to an increase in the copy number of WSSV, indicating reactivation of WSSV from a latent infection. It was further demonstrated that suppression of PvMEF2 significantly decreased expression of the viral latency-related genes in WSSV-latent shrimp, while overexpression of PvMEF2 in Drosophila S2 cells activated the promoter activity of the viral latency-related gene. Additionally, we demonstrated that silencing of PvMEF2 was able to upregulate the expression of pro-apoptosis genes, thereby promoting cell apoptosis during latent infection. Collectively, the present data suggest that PvMEF2 could promote the expression of virus latency-related genes and enhance cell survival to maintain WSSV latent infection. This finding would contribute to a better understanding of the maintenance mechanism of WSSV latent infection.

Gene Structure, Expression and Function Analysis of MEF2 in the Pacific White Shrimp Litopenaeus vannamei

The Pacific white shrimp Litopenaeus vannamei is the most economically important crustacean in the world. The growth and development of shrimp muscle has always been the focus of attention. Myocyte Enhancer Factor 2 (MEF2), a member of MADS transcription factor, has an essential influence on various growth and development programs, including myogenesis. In this study, based on the genome and transcriptome data of L. vannamei, the gene structure and expression profiles of MEF2 were characterized. We found that the LvMEF2 was widely expressed in various tissues, mainly in the Oka organ, brain, intestine, heart, and muscle. Moreover, LvMEF2 has a large number of splice variants, and the main forms are the mutually exclusive exon and alternative 5′ splice site. The expression profiles of the LvMEF2 splice variants varied under different conditions. Interestingly, some splice variants have tissue or developmental expression specificity. After RNA interference into LvMEF2, the increment in the body length and weight decreased significantly and even caused death, suggesting that LvMEF2 can affect the growth and survival of L. vannamei. Transcriptome analysis showed that after LvMEF2 was knocked down, the protein synthesis and immune-related pathways were affected, and the associated muscle protein synthesis decreased, indicating that LvMEF2 affected muscle formation and the immune system. The results provide an important basis for future studies of the MEF2 gene and the mechanism of muscle growth and development in shrimp.

Influence of Varying Dietary ω6 to ω3 Fatty Acid Ratios on the Hepatic Transcriptome, and Association with Phenotypic Traits (Growth, Somatic Indices, and Tissue Lipid Composition), in Atlantic Salmon (Salmo salar)

Simple Summary

Plant oils are routinely used in fish feeds as a fish oil replacement. However, these terrestrial alternatives typically contain high levels of ω6 fatty acids (FA) and, thus, high ω6 to ω3 (ω6:ω3) FA ratios, which influence farmed fish and their consumers. The ω6:ω3 ratio is known to affect many biological processes (e.g., inflammation, FA metabolism) and human diseases; however, its impacts on fish physiology and the underlying molecular mechanisms are less well understood. In this study, we used 44 K microarrays to examine which genes and molecular pathways are altered by variation in dietary ω6:ω3 in Atlantic salmon. Our microarray study showed that several genes related to immune response, lipid metabolism, cell proliferation, and translation were differentially expressed between the two extreme ω6:ω3 dietary treatments. We also revealed that the PPARα activation-related transcript helz2 is a potential novel molecular biomarker of tissue variation in ω6:ω3. Further, correlation analyses illustrated the relationships between liver transcript expression and tissue (liver, muscle) lipid composition, and other phenotypic traits in salmon fed low levels of fish oil. This nutrigenomic study enhanced the current understanding of Atlantic salmon gene expression response to varying dietary ω6:ω3.

Abstract

The importance of dietary omega-6 to omega-3 (ω6:ω3) fatty acid (FA) ratios for human health has been extensively examined. However, its impact on fish physiology, and the underlying molecular mechanisms, are less well understood. This study investigated the influence of plant-based diets (12-week exposure) with varying ω6:ω3 (0.4–2.7) on the hepatic transcriptome of Atlantic salmon. Using 44 K microarray analysis, genes involved in immune and inflammatory response (lect2a, itgb5, helz2a, p43), lipid metabolism (helz2a), cell proliferation (htra1b), control of muscle and neuronal development (mef2d) and translation (eif2a, eif4b1, p43) were identified; these were differentially expressed between the two extreme ω6:ω3 dietary treatments (high ω6 vs. high ω3) at week 12. Eight out of 10 microarray-identified transcripts showed an agreement in the direction of expression fold-change between the microarray and qPCR studies. The PPARα activation-related transcript helz2a was confirmed by qPCR to be down-regulated by high ω6 diet compared with high ω3 diet. The transcript expression of two helz2 paralogues was positively correlated with ω3, and negatively with ω6 FA in both liver and muscle, thus indicating their potential as biomarkers of tissue ω6:ω3 variation. Mef2d expression in liver was suppressed in the high ω6 compared to the balanced diet (ω6:ω3 of 2.7 and 0.9, respectively) fed fish, and showed negative correlations with ω6:ω3 in both tissues. The hepatic expression of two lect2 paralogues was negatively correlated with viscerosomatic index, while htra1b correlated negatively with salmon weight gain and condition factor. Finally, p43 and eif2a were positively correlated with liver Σω3, while these transcripts and eif4b2 showed negative correlations with 18:2ω6 in the liver. This suggested that some aspects of protein synthesis were influenced by dietary ω6:ω3. In summary, this nutrigenomic study identified hepatic transcripts responsive to dietary variation in ω6:ω3, and relationships of transcript expression with tissue (liver, muscle) lipid composition and other phenotypic traits.