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Increased gene dosage for β - and κ -casein in transgenic cattle improves milk composition through complex effects

View Article: PubMed Central - PubMed

ABSTRACT

We have previously generated transgenic cattle with additional copies of bovine β- and κ casein genes. An initial characterisation of milk produced with a hormonally induced lactation from these transgenic cows showed an altered milk composition with elevated β-casein levels and twofold increased κ-casein content. Here we report the first in-depth characterisation of the composition of the enriched casein milk that was produced through a natural lactation. We have analyzed milk from the high expressing transgenic line TG3 for milk composition at early, peak, mid and late lactation. The introduction of additional β- and κ-casein genes resulted in the expected expression of the transgene derived proteins and an associated reduction in the size of the casein micelles. Expression of the transgenes was associated with complex changes in the expression levels of other milk proteins. Two other major milk components were affected, namely fat and micronutrients. In addition, the sialic acid content of the milk was increased. In contrast, the level of lactose remained unchanged. This novel milk with its substantially altered composition will provide insights into the regulatory processes synchronizing the synthesis and assembly of milk components, as well as production of potentially healthier milk with improved dairy processing characteristics.

No MeSH data available.


Sialic acid content in milk from transgenic and control cows.Shown is the level of sialic acids associated with milk proteins from two wild type (WT1, WT2) and three transgenic cows (TG3 1–3). Neu5Gc is represented as solid bars in light red and grey, Neu5Ac as red and black solid bars and total sialic acid as red and black open bars for wild type and transgenic samples, respectively.
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f6: Sialic acid content in milk from transgenic and control cows.Shown is the level of sialic acids associated with milk proteins from two wild type (WT1, WT2) and three transgenic cows (TG3 1–3). Neu5Gc is represented as solid bars in light red and grey, Neu5Ac as red and black solid bars and total sialic acid as red and black open bars for wild type and transgenic samples, respectively.

Mentions: Milk contains high levels of sialic acid, a significant proportion of which is conjugated to the carbohydrate chains of κ-casein22. Moreover, dietary sialic acid has been suggested to be beneficial to brain development23. We therefore determined whether the increased abundance of κ-casein also leads to a higher concentration of this potentially health-promoting substance in the transgenic milk. The abundance of the two most common sialic acid groups, N-Glycolyl-D-neuraminic acid (Neu5Gc) and N-Acetyl-D-neuraminic acid (Neu5Ac) as well as total sialic acid were measured in milk proteins from the TG3 and control cows. The results (Fig. 6) showed a 2.9 fold increase (P = 0.01) of Neu5Ac in the milk from the TG cows (632.1 ± 61.8 μg/ml; n = 3) compared to wild type (220.4 ± 8.7 μg/ml; n = 2). Although all Neu5Gc values for the TG samples where above the measured levels for the wild type samples, the average increase of 1.6 fold did not reach a 95% significance level with the limited numbers of samples. The total sialic acid concentration was also increased by 2.8 fold (P = 0.015; 653.4 ± 64.6 μg/ml versus 233.7 ± 9.2 μg/ml). The most heavily glycosylated protein in milk is κ-casein, for which the protein levels are increased several-fold in milk from the TG cows, as described above. The sialic acid content of the milk per mg of κ-casein (46.9 μg/mg for WT, 41.88 μg/mg for TG3) was not significantly altered between the milk from wild type and TG cows (P = 0.37), suggesting that the increase in sialic acid content is consequent upon the high abundance of κ-casein.


Increased gene dosage for β - and κ -casein in transgenic cattle improves milk composition through complex effects
Sialic acid content in milk from transgenic and control cows.Shown is the level of sialic acids associated with milk proteins from two wild type (WT1, WT2) and three transgenic cows (TG3 1–3). Neu5Gc is represented as solid bars in light red and grey, Neu5Ac as red and black solid bars and total sialic acid as red and black open bars for wild type and transgenic samples, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120311&req=5

f6: Sialic acid content in milk from transgenic and control cows.Shown is the level of sialic acids associated with milk proteins from two wild type (WT1, WT2) and three transgenic cows (TG3 1–3). Neu5Gc is represented as solid bars in light red and grey, Neu5Ac as red and black solid bars and total sialic acid as red and black open bars for wild type and transgenic samples, respectively.
Mentions: Milk contains high levels of sialic acid, a significant proportion of which is conjugated to the carbohydrate chains of κ-casein22. Moreover, dietary sialic acid has been suggested to be beneficial to brain development23. We therefore determined whether the increased abundance of κ-casein also leads to a higher concentration of this potentially health-promoting substance in the transgenic milk. The abundance of the two most common sialic acid groups, N-Glycolyl-D-neuraminic acid (Neu5Gc) and N-Acetyl-D-neuraminic acid (Neu5Ac) as well as total sialic acid were measured in milk proteins from the TG3 and control cows. The results (Fig. 6) showed a 2.9 fold increase (P = 0.01) of Neu5Ac in the milk from the TG cows (632.1 ± 61.8 μg/ml; n = 3) compared to wild type (220.4 ± 8.7 μg/ml; n = 2). Although all Neu5Gc values for the TG samples where above the measured levels for the wild type samples, the average increase of 1.6 fold did not reach a 95% significance level with the limited numbers of samples. The total sialic acid concentration was also increased by 2.8 fold (P = 0.015; 653.4 ± 64.6 μg/ml versus 233.7 ± 9.2 μg/ml). The most heavily glycosylated protein in milk is κ-casein, for which the protein levels are increased several-fold in milk from the TG cows, as described above. The sialic acid content of the milk per mg of κ-casein (46.9 μg/mg for WT, 41.88 μg/mg for TG3) was not significantly altered between the milk from wild type and TG cows (P = 0.37), suggesting that the increase in sialic acid content is consequent upon the high abundance of κ-casein.

View Article: PubMed Central - PubMed

ABSTRACT

We have previously generated transgenic cattle with additional copies of bovine β- and κ casein genes. An initial characterisation of milk produced with a hormonally induced lactation from these transgenic cows showed an altered milk composition with elevated β-casein levels and twofold increased κ-casein content. Here we report the first in-depth characterisation of the composition of the enriched casein milk that was produced through a natural lactation. We have analyzed milk from the high expressing transgenic line TG3 for milk composition at early, peak, mid and late lactation. The introduction of additional β- and κ-casein genes resulted in the expected expression of the transgene derived proteins and an associated reduction in the size of the casein micelles. Expression of the transgenes was associated with complex changes in the expression levels of other milk proteins. Two other major milk components were affected, namely fat and micronutrients. In addition, the sialic acid content of the milk was increased. In contrast, the level of lactose remained unchanged. This novel milk with its substantially altered composition will provide insights into the regulatory processes synchronizing the synthesis and assembly of milk components, as well as production of potentially healthier milk with improved dairy processing characteristics.

No MeSH data available.