Ovine milk proteins : DNA, mRNA, and protein analyses and their associations to milk performance traits
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Isoelectric focusing was applied for screening milk protein variants in milk samples from 1,078 animals of six different sheep breeds (Black Faced Mutton sheep, East Friesian Dairy sheep, Gray Horned Heath, Merinoland sheep, Merino Mutton sheep, and Rhön sheep). The known genetic variants of αs1-casein (CN; CSN1S1*A, C, D), αs2-CN (CSN1S2*A, B), and β lactoglobulin (LG; LGB*A, B, C) were confirmed. CSN1S1*C was predominant in all breeds with frequencies of 0.90 to 1.00. CSN1S2*A accumulated in Gray Horned Heath, Merinoland, Merino Mutton, and Rhön sheep (0.73 to 0.93), whereas CSN1S2*B was most frequent in Black Faced Mutton and East Friesian Dairy sheep. Within β-LG LGB*A was predominant in all breeds with frequencies of 0.54 to 0.80, whereas LGB*C showed breed specific distribution within the Merino breeds. Furthermore, the patterns of αs1-CN X were also detected in East Friesian Dairy sheep and named αs1 CN H. One and two additional patterns were identified within αs1-CN (I) and αs2 CN (C and D), respectively. All animals analysed were monomorph for κ-casein and α lactalbumin.In addition, isoelectric focusing identified seven αs1-/αs2-CN-haplotypes within the breeds analysed, while haplotypes CA and CB were most frequent. Continuative biochemical and molecular genetic analyses of CSN1S1 confirmed the occurrence of variants H and I, both caused by alternative splicing events. Within CSN1S1*H skipping of exon 8 is caused by a deletion and an insertion within DNA sequence of exon 8 (g.739_742delAAGGinsTTATTTTAATAAA). Additionally, three SNPs both in intron 6 and in intron 7 were identified by DNA sequence analyses, whereas one of the latter ones (g.656T>A) caused an alternative splicing event in CSN1S1*I by disrupting the donor splice site of intron 7.CSN1S2*C and D are both due to different single nucleotide polymorphisms within exon 7, leading to amino acid exchanges p.Val45Ile and p.Ala48Ser in αs2-CN C and p.Arg46Ser in αs2-CN D, associated with a SNP in exon 2 in both variants. Molecular genetic analyses of CSN1S2 revealed a further variant G, caused by a non-synonymous SNP in exon 15 (p.Arg161His), and a sub form of CSN1S2*A, namely A , due to a synonymous A>C mutation in exon 10. Additionally, one SNP both in exon 17 and exon 18, ten SNPs in total in introns 1, 2, 6, and 7, as well as three intron insertions were identified. The biochemical and molecular genetic results were used to postulate nomenclature for ovine CSN1S1 and CSN1S2 variation. Denomination of the new variants was carried out considering known polymorphisms and their names. In CSN1S2 we defined also already described but not named variants with CSN1S2*E and F. DNA tests were established for CSN1S1 variants H and I, as well as for CSN1S2*B, C, D, and G, allowing to type sheep independent of age, lactation, and sex. Additionally, association studies were established between milk protein variants and milk production traits in East Friesian Dairy sheep concerning milk protein genotypes and casein haplotypes. Significant positive associations between αs1-CN CH and fat percentage and yield, between αs2-CN AB and protein yield, and between β-LG AA and fat and protein percentage of sheep milk were identified. Furthermore, αs1-/αs2-CN-haplotype HB was associated with the highest fat and protein percentage and yield, respectively.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Giessen : VVB Laufersweiler