7 Genomic Approaches in Aquaculture and Fisheries
229
such as insulin and glucagon. The liver also plays an important role during growth
due to its ability to respond to GH by synthesizing and secreting insulin-like growth
factor I (IGF-I), an important mediator of GH growth-promoting effects. Due to
the central physiological role of the liver and to the complexity of its function and
regulation, genomic approaches are very well suited to assist us in understanding its
function and its response to physiological or environmental alterations. To date, several studies have described the response of the hepatic transcriptome and proteome
in relation to growth and nutrition in teleost fish.
7.4.4.1 Transcriptional Changes in the Liver in Relation to Growth
and Nutrition
Recent studies have addressed the response of the hepatic transcriptome to the
growth-promoting actions of GH in salmonid fish using the GRASP 16 K microarray platform. In GH transgenic coho salmon, one of the major transcriptional
changes observed was an increase in the expression of genes involved in mitochondrial activity (Rise et al. 2006). It was postulated that this could be due to
the higher energy demand of GH transgenic fish with a higher metabolic rate
related to their higher growth rate. In addition, hemoglobin genes were also induced
in the liver of GH transgenic fish, which was attributed to the possible need to
synthesize hemoglobin in relation to the higher metabolic rate of these animals.
Surprisingly, this microarray analysis detected only a small set of genes coding for
hepatic enzymes, most notably fatty acid desaturase and prostaglandin D synthase.
Similarly, a more recent study evaluating the transcriptional response of the rainbow trout liver to a short-term (3 days) treatment with GH and using the same
GRASP microarray also reported changes in a small set of genes, very few of those
corresponding to hepatic enzymes (Gahr et al. 2008). In this study, the two major
functional categories that responded to administration of GH were genes involved
in metabolism and immune response. In view of the scarce information on the liver
transcriptome in response to GH, it is possible that an important part of the regulation is at the level of translation or post-translation modifications. Therefore, it will
be necessary to study the physiological response of the liver also by a proteomic
approximation.
From a nutritional point of view, changes in the hepatic transcriptome in response
to the adaptation to diets with vegetable oil have been examined. In particular, the
hepatic response of Atlantic salmon to diets containing 75% vegetable oil has been
studied using a microarray platform constructed with Atlantic salmon ESTs (Jordal
et al. 2005). The results showed clear evidence of changes in the expression of genes
involved in hepatic liver metabolism. On one hand, an increase in the expression of
fatty acid desaturases 5 and 9 was observed. On the other hand, the expression
of long-chain acetyl CoA synthase decreased in the liver of fish adapted to the vegetable oil rich diet. Furthermore, several mitochondrial genes and proteins from the
external mitochondrial membrane were down-regulated in response to the vegetable
oil rich diet. These observations suggested that these fish, as a result of their nutritional challenge, decreased their capacity for β-oxidation in the liver. More recently,
229
such as insulin and glucagon. The liver also plays an important role during growth
due to its ability to respond to GH by synthesizing and secreting insulin-like growth
factor I (IGF-I), an important mediator of GH growth-promoting effects. Due to
the central physiological role of the liver and to the complexity of its function and
regulation, genomic approaches are very well suited to assist us in understanding its
function and its response to physiological or environmental alterations. To date, several studies have described the response of the hepatic transcriptome and proteome
in relation to growth and nutrition in teleost fish.
7.4.4.1 Transcriptional Changes in the Liver in Relation to Growth
and Nutrition
Recent studies have addressed the response of the hepatic transcriptome to the
growth-promoting actions of GH in salmonid fish using the GRASP 16 K microarray platform. In GH transgenic coho salmon, one of the major transcriptional
changes observed was an increase in the expression of genes involved in mitochondrial activity (Rise et al. 2006). It was postulated that this could be due to
the higher energy demand of GH transgenic fish with a higher metabolic rate
related to their higher growth rate. In addition, hemoglobin genes were also induced
in the liver of GH transgenic fish, which was attributed to the possible need to
synthesize hemoglobin in relation to the higher metabolic rate of these animals.
Surprisingly, this microarray analysis detected only a small set of genes coding for
hepatic enzymes, most notably fatty acid desaturase and prostaglandin D synthase.
Similarly, a more recent study evaluating the transcriptional response of the rainbow trout liver to a short-term (3 days) treatment with GH and using the same
GRASP microarray also reported changes in a small set of genes, very few of those
corresponding to hepatic enzymes (Gahr et al. 2008). In this study, the two major
functional categories that responded to administration of GH were genes involved
in metabolism and immune response. In view of the scarce information on the liver
transcriptome in response to GH, it is possible that an important part of the regulation is at the level of translation or post-translation modifications. Therefore, it will
be necessary to study the physiological response of the liver also by a proteomic
approximation.
From a nutritional point of view, changes in the hepatic transcriptome in response
to the adaptation to diets with vegetable oil have been examined. In particular, the
hepatic response of Atlantic salmon to diets containing 75% vegetable oil has been
studied using a microarray platform constructed with Atlantic salmon ESTs (Jordal
et al. 2005). The results showed clear evidence of changes in the expression of genes
involved in hepatic liver metabolism. On one hand, an increase in the expression of
fatty acid desaturases 5 and 9 was observed. On the other hand, the expression
of long-chain acetyl CoA synthase decreased in the liver of fish adapted to the vegetable oil rich diet. Furthermore, several mitochondrial genes and proteins from the
external mitochondrial membrane were down-regulated in response to the vegetable
oil rich diet. These observations suggested that these fish, as a result of their nutritional challenge, decreased their capacity for β-oxidation in the liver. More recently,