Nutrient-Gene Interactions in fishes

INTRODUCTION:-

A nutrient can be considered as chemical element or compound that an animal can utilize in metabolism or growth. An essential nutrient is one that animal can synthesise. Thus ,an animal’s requirement for essential nutrients must be met through its diet. While the determination of individual nutrient requirements or the growing no of cultivatble species would continued to be important, there is an increasing need to find way to meet these requirements using greater diversity of feedstuffs and gene.

Nutrient ha marked influences on gene interaction and an understanding of interaction between nutrient & gene expression is important in order to provide a basis for determining the nutritional requirements on an individual basis. The effect of nutrition can be there at many stages between transcription of genetic sequence and production of a functional protein. The dietary long chain n-3 PUFA in fish oil stimulates the gene expression of lipoprotein lipase in human adipose tissue. The complexity of nutrient–gene interactions has led to the development of a new branch in the nutrition sciences, the nutrigenomics. The individual susceptibility to nutrient on environment → genotype → phenotype interplay makes this new research field extremely promising although complex.

Development of new tools enabling exploration of the cause-effect phenomena at the molecular level stimulated scientists to develop hypotheses and conduct experiments to lay the foundation for a deeper level of understanding of gene-diet interactions. Today, an emerging field of nutritional research focuses on identifying the molecular interactions between nutritional bioactive components and processes through which genome-encoded proteins are expressed.

The analysis of gene–nutrient interactions rapidly became a focal point of applicative research, since several types of environmental stimuli are able to modify genomes and diet is by far the most important of them. Furthermore, the gastrointestinal system is an interface between the external environment and the

body and functions to extract nutrients from food as well as handle the non-nutrient components in foods. Investigation of how genes and gene products metabolize nutritional factors and, conversely, how dietary compounds regulate gene expression by determining phenotype modification has been defined as “nutrigenomics”.

The tenets of nutrigenomics are essentially based on the concepts that:

(1) Diet can be an important risk factor for a wide number of diseases.

(2) Dietary compounds can directly or indirectly interact with the genome by altering gene expression.

(3) The individual genetic pattern can influence the balance between physiological and pathological condition determined by diet.

(4) Several diet-regulated genes can play a fundamental role in the incidence and progression of many chronic diseases.

(5) A personalized diet on the basis of nutritional status and genotype can be very helpful in preventing and curing chronic diseases.

Nutrient-Gene Interactions

With the ongoing expansion of molecular biology and genetics at rapid pace, scientists are now beginning to address this link between nutrition and genetics. An ability to define interaction between nutrition and gene expression will enable nutritionists to identify individuals with particular dietary needs. In abroad sense this enable understanding of how the role of nutrients in metabolism is linked to biochemical events which lead to gene expression .

Fig shows the influence of nutrient intake to gene expression and protein synthesis. It also reflects the influence of nutrient intake and nutrient requirements. In short, it involves in addressing of important fundamental questions: which gene, particularly those involved in the control of metabolism, growth and differentiation, are regulated by nutrition, how do nutrients and diet

regulate the expression of genes, and how the expression of specific gene products is involved in metabolism and channelling of nutrients.

Fig: scheme of two interlinked processes.

The effect of feeding frequency, feeding level and temperature on energy metabolism Sparus aurata (medeterranean carnivorous fishes) has been trace down to molecular levels. It has been shown that 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase gene expression is regulated by diet composition and ration size in liver of gilthead seabream, Sparus aurata . however liver insulin-like growth factor-I mRNA is not effected by diet composition or ration size but shows diurnal variation is regularly fed gilthead seabream (Sparus aurata). Unlike mammals, high CHO & low protein diet have been shown to have increased expression of glucokinase with no effect on hepatic G6Pase indicating favour of glycolytic process over gluconeogenesis in carnivorous fish. It is studied that very limited ability of marine fishes to convert dietary C18 precursor fatty acid to highly unsaturated fatty acids may be due to high content of HUfA in diet commonly used to feed marine fish. Study with trout have also indicated that

Nutrient intake

Nutrient requiremen

Gene expression DNA→RNA→Protein

Nutrient uptake, channelling & metabolism

dietary protein can modify white skeletal muscle characteristics both at cellular (fibre size) and molecular (myosin heavy chain) expression levels. Rainbow trout (Oncorhynchus mykiss) are recognized for their inefficiency in utilizing high levels of dietary carbohydrates, leading to prolonged postprandial hyperglycemia after oral administration of glucose or a carbohydrate-rich meal. In contrast to non-diabetic mammals, rainbow trout exhibit a persistent high level of mRNAs of hepatic gluconeogenic enzymes ( fructose-1,6-bisphosphatase and glucose-6-phosphatase) . Dietary lipids or proteins affect the activities of enzymes involved in hepatic carbohydrate metabolism in fish. Diets of rainbow trout generally contain 40% protein, amino acids are utilized as an energy source but also constitute substrates for endogenous glucose synthesis. Interaction of Fish Oil and Conjugated Linoleic Acid in Affecting Hepatic Activity of Lipogenic Enzymes and Gene Expression in Liver and Adipose Tissue:-The interaction of dietary fish oil and conjugated linoleic acid (CLA) in affecting the activity of hepatic lipogenic enzymes and gene expression in liver and adipose tissue was examined in mice. Different amounts (1.5, 3, and 6%) of fish oil added to CLA-containing diets dose-dependently downregulated parameters of lipogenesis and were accompanied by a parallel decrease in the triacylglycerol level in the liver. The supplementation of CLA-containing diets with fish oil was also associated with an increase in fat pad mass and mRNA levels of many adipocyte-abundant genes in epididymal adipose tissue along with a normalization of serum concentrations of leptin and adiponectin in a dose-dependent manner. Dietary Rapeseed Oil Affects the Expression of Genes Involved in Hepatic Lipid Metabolism in Atlantic Salmon (Salmo salar L.) Low Protein Intake Is Associated with Reduced Hepatic Gluconeogenic Enzyme Expression in Rainbow Trout (Oncorhynchus mykiss)

CONCLUSION: Now it has been accepted that the core of nutrition is integrative biology. Nutrient and gene regulation is an important adaptation allowing survival or energy conservation depending on qualitative and quantitative food supplies. This adoptive process exist in all species from yeast to mammal including aquatic

species. This response to particular nutrient in term of gene transcription and formation of functional protein varies accourding to species. Nutritionist need to understand these responses to gain better insight of system physiology and integrate this knowledge to formulate practically sustainable and economic diet across species.

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Academic press. 368po JADHAO S., (2002). Nutrient gene interactions and metabolic research in

aquaculture. C.I.F.E. 85-88po TOM LOVELL, (2009). Nutrition and feeding of fish, second edition. Kluwer

Academic Publishers. Springer. 267po Fishing chimes ,july2007