Introduction
Selenium (Se) is a vital trace element crucial for the well-being of humans and animals, participating in the structure of diverse selenoproteins with functions in antioxidant defense, immunity, and thyroid hormone metabolism. The effectiveness of Se varies based on its chemical form, and recent advancements have introduced Se nanoparticles (nano-Se) in aquafeeds to enhance fish performance due to their low toxicity and heightened efficacy. qRT-PCR and modern omics approaches like transcriptomics, proteomics, and metabolomics have provided insights into the molecular mechanisms behind the biological effects of Se.
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Application of Nano-Se in Aquafeeds
The inclusion of nano-Se in aquafeeds is crucial for fish growth, with organic and nano-Se sources showing higher bioavailability than inorganic sources. Studies reveal that nano-Se, such as selenomethionine (SeMet), has a superior impact on growth compared to other forms (sodium selenite, SeMet) in various fish species. The growth-promoting effects may be linked to selenoprotein functions, such as deiodinases regulating thyroid hormones and influencing growth hormone gene transcription. Nano-Se enhances endogenous digestive enzyme production, improving digestion, absorption, and metabolism of micronutrients. Additionally, nano-Se positively affects antioxidant status by increasing glutathione peroxidase (GPx) activity, reducing oxidative damage, and enhancing other antioxidant enzymes. In the realm of immunomodulation, nano-Se triggers selenoprotein synthesis, benefiting immune cells and improving humoral immune parameters. Nano-Se also boosts survivability in fish challenged with pathogens. Regarding reproductive performance, nano-Se supplementation improves fertilization, hatching rates, and larval survival, with positive effects on both male and female broodfish. Overall, nano-Se emerges as a promising dietary supplement in aquaculture, offering multifaceted benefits for fish growth, immune function, and reproductive success.
qRT-PCR in Nano-Se Research
qRT-PCR serves as a pivotal tool in Nano-Se research, particularly in elucidating its effects on gene expression in various organisms. Nano-Se, known for its diverse applications in areas such as aquaculture and stress mitigation, demonstrates its impacts at the molecular level through the modulation of gene expression.
In studies involving fish, qRT-PCR has been extensively employed to analyze the expression of key genes related to immunity, antioxidant mechanisms, growth, and other physiological processes. For instance, in Nile tilapia trials comparing different forms of selenium (sodium selenite and nano-Se), qRT-PCR analysis revealed significantly higher expression rates of immune-related (e.g., lysozyme and immunoglobulin M) and antioxidant-related genes (e.g., superoxide dismutase and glutathione peroxidase) in the nano-Se supplemented group compared to control or sodium selenite groups after a bacterial challenge.
Moreover, qRT-PCR has been instrumental in understanding the synergistic effects of nano-Se with other nutritional factors. Studies investigating combined supplementation of nano-Se with vitamins (E and C), Spirulina platensis, and chitosan nanoparticles showcase the up-regulation or down-regulation of specific genes, revealing the intricate interactions influencing fish performance, immunity, and stress response.
Additionally, qRT-PCR has been employed in exploring the impact of nano-Se under various conditions such as exposure to heavy metals (e.g., cadmium), endocrine-disrupting substances (e.g., 4-tert-butylphenol), and heat stress. The gene expression patterns elucidated through qRT-PCR shed light on the protective effects of nano-Se against oxidative stress, immune response modulation, and alleviation of heat stress-induced damages.
Transcriptomics in Nano-Se Research
Transcriptomics is a technique for studying gene expression within an organism by analyzing RNA transcripts, revealing the activity of genes under specific conditions. In the application of nanoscale selenium (Se) in fish feed research, transcriptomics can be employed to gain a deep understanding of the gene responses of fish to nanoscale Se. By examining the gene expression profiles in fish tissues, the impact of nanoscale Se on fish growth, immune system, redox reactions, and more can be elucidated. This aids in optimizing feed formulations to enhance fish growth performance and immunity. Furthermore, transcriptomics provides gene-level information for assessing the safety of nanoscale Se, serving as a scientific basis for establishing feed standards.
Proteomics in Nano-Se Research
While transcriptomics provides insights into gene expression, proteomics offers a closer look at the actual proteins involved in cellular processes. Limited studies have investigated the impact of nano-Se on fish liver proteome. Rainbow trout fed with nano-Se showed increased expression of metabolic enzymes responsible for glycolytic pathways, amino acid metabolism, and energy production. Notably, enzymes with anti-tumor activity were up-regulated, suggesting potential health benefits.
In another study, nano-Se was explored as an anti-heat stress micronutrient in rainbow trout. Proteomic analysis revealed that nano-Se supplementation mitigated the apoptotic effects of heat stress by up-regulating heat shock proteins and selenoproteins, while simultaneously suppressing proteins associated with lipid metabolism. The correlation between proteomic changes and physiological parameters further emphasized the protective role of nano-Se under heat stress conditions.
Metabolomics in Nano-Se Research
Metabolomics focuses on the global profiling of small molecules, providing insights into metabolic changes in response to various stimuli. A singular study on rainbow trout investigated the metabolic modifications induced by nano-Se under heat stress conditions. Metabolomic analysis revealed that nano-Se supplementation countered the adverse effects of heat stress by down-regulating galactose metabolism and activating pathways related to glutamate and glutamine metabolism.
Multi-Omics Approach in Nano-Se Research
Systems biology, integrating transcriptomics, proteomics, and metabolomics, offers a comprehensive understanding of complex biological systems. A recent study on zebrafish applied a multi-omics approach to elucidate the molecular mechanisms of nano-Se in both healthy and disease conditions. The results highlighted the immunomodulatory effects of nano-Se, regulating genes involved in antioxidant defense, lipid metabolism, and innate immunity. Interestingly, nano-Se exhibited differential regulation of reactive oxygen species (ROS) formation, suppressing ROS in healthy fish and stimulating its formation in infected individuals, potentially as a defense mechanism against pathogens.
Conclusion
The application of molecular techniques, including qRT-PCR, transcriptomics, proteomics, metabolomics, and multi-omics approaches, has significantly advanced our understanding of the molecular mechanisms underlying the effects of nano-Se in aquaculture. These studies collectively highlight the immunomodulatory, antioxidant, and growth-promoting properties of nano-Se in various fish species. The comprehensive insights provided by multi-omics approaches pave the way for further exploration of nano-Se's potential applications in improving fish health, resilience to stressors, and overall aquaculture sustainability.
References
- Khaled A.A., et al. Exploring the impact of nano-Se and nano-clay feed supplements on interleukin genes, immunity and growth rate in European Sea Bass (Dicentrarchus labrax). Scientific Reports. 2024, 14(1): 2631.
- Keyvanshokooh S. A review of the quantitative real-time PCR and Omics approaches applied to study the effects of dietary selenium nanoparticles (nano-Se) on fish. Comparative Immunology Reports. 2023, 200127.
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