Studies on milk proteins revealed that a qualitative and quantitative polymorphism may be often found regarding alpha-lactalbumin (a-LA). In mammals, a similar phenomenon was widely documented in the alpha globin system as the result of a gene duplication and recently, also in the case of the alpha-lactalbumin locus (LALBA) in buffalo. Generally, the presence of several, differently expressed alpha-lactalbumin gene (LALBA) products suggests that the mechanism underlying this phenomenon may involve non allelic genes. Particularly, in Podolic cattle a different expression was observed in a cow that was supposedly AB heterozygous at the alpha-lactalbumin locus (LALBA), with the A and B variants accounting for 40% and 60% of total protein, respectively. Based on the relative amount of protein inferred from the different band intensity, the genotype of the sampled animal was assumed to be composed by two non allelic genes directing the synthesis of the same a-LA B and two encoding for a-LA A. This finding was consistent with a gene duplication and then an experiment was set up to investigate the LALBA gene arrangement of the above subject. Thus, leukocyte DNA was extracted from a blood sample of the cow and amplified with four primers (IIRV- IVFW for PCR and IVFW- IRV for nested PCR). The intergenic segments of the assumed duplicated gene were then amplified with two different PCR protocols. First, the segment limited by the 3rd exon in the upstream gene and the 2nd exon in the downstream gene was amplified by simple-PCR which gave aspecific results. Second, this PCR product was subjected to nested PCR, amplifying the segment limited by the 4th exon in the upstream gene and the 1st exon in the downstream gene, yielding an amplified nucleotide fragment of about 6200 bp. Blood samples from an additional 10 calves at the slaughter house were then analyzed in the same manner. The results obtained from the new samples confirmed the presence of an amplified nucleotide fragment of about 6200 bp in all of them. These results confirm the hypothesis that, similarly to what found in buffalo, a tandemly repeated copy of the LALBA gene is present in cattle. Our results lend further support to the hypothesis that milk and mammary genes are more likely to be duplicated in therians than in other genes of the bovine genome and that variation in copy number of the milk protein genes may contribute to the taxonomic diversity of milk composition.
Evidence of gene duplication at the alpha-lactalbumin locus in cattle (Bos bovis).
Rosario Rullo;
2010
Abstract
Studies on milk proteins revealed that a qualitative and quantitative polymorphism may be often found regarding alpha-lactalbumin (a-LA). In mammals, a similar phenomenon was widely documented in the alpha globin system as the result of a gene duplication and recently, also in the case of the alpha-lactalbumin locus (LALBA) in buffalo. Generally, the presence of several, differently expressed alpha-lactalbumin gene (LALBA) products suggests that the mechanism underlying this phenomenon may involve non allelic genes. Particularly, in Podolic cattle a different expression was observed in a cow that was supposedly AB heterozygous at the alpha-lactalbumin locus (LALBA), with the A and B variants accounting for 40% and 60% of total protein, respectively. Based on the relative amount of protein inferred from the different band intensity, the genotype of the sampled animal was assumed to be composed by two non allelic genes directing the synthesis of the same a-LA B and two encoding for a-LA A. This finding was consistent with a gene duplication and then an experiment was set up to investigate the LALBA gene arrangement of the above subject. Thus, leukocyte DNA was extracted from a blood sample of the cow and amplified with four primers (IIRV- IVFW for PCR and IVFW- IRV for nested PCR). The intergenic segments of the assumed duplicated gene were then amplified with two different PCR protocols. First, the segment limited by the 3rd exon in the upstream gene and the 2nd exon in the downstream gene was amplified by simple-PCR which gave aspecific results. Second, this PCR product was subjected to nested PCR, amplifying the segment limited by the 4th exon in the upstream gene and the 1st exon in the downstream gene, yielding an amplified nucleotide fragment of about 6200 bp. Blood samples from an additional 10 calves at the slaughter house were then analyzed in the same manner. The results obtained from the new samples confirmed the presence of an amplified nucleotide fragment of about 6200 bp in all of them. These results confirm the hypothesis that, similarly to what found in buffalo, a tandemly repeated copy of the LALBA gene is present in cattle. Our results lend further support to the hypothesis that milk and mammary genes are more likely to be duplicated in therians than in other genes of the bovine genome and that variation in copy number of the milk protein genes may contribute to the taxonomic diversity of milk composition.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
