Abstract
Genes encoding casein proteins are important candidates for milk composition traits in mammals. In the case of the domestic horse, our knowledge of casein genes is limited mainly to coding sequence variants. This study involved screening for polymorphism in 5’-flanking regions of four genes encoding equine caseins (CSN1S1, CSN1S2, CSN2, and CSN3) and making a preliminary assessment of their effect on the gene expression (on the mRNA and protein levels) and milk composition traits in selected horse breeds. Altogether, 23 polymorphisms (21 described previously SNPs and two novel InDels) were found in the studied sequences, the majority of which are common in various horse breeds. Statistical analysis revealed that some are putatively associated with gene expression or milk composition — for example, the c.-2047_-2048insAT polymorphism (CSN1S1) turns out to be related to the total milk protein content in Polish Primitive Horse (p < 0.05), whereas c.-2105C>G SNP (CSN2) is related to beta-casein relative mRNA level and milk lactose concentration in the Polish Coldblood Horse breed (p < 0.05). We have also found significant effects of horse breed and lactation time-point on gene expression and mare’s milk composition. Our study indicates that the 5’-regulatory regions of genes encoding casein proteins are interesting targets for functional studies of their expression and the composition traits of mare’s milk.
Highlights
Communicated by: Maciej SzydlowskiElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Investigations into casein genes have been conducted for many years, as they are considered important for milk production traits
Statistical analysis revealed that some are putatively associated with gene expression or milk composition — for example, the c.-2047_-2048insAT polymorphism (CSN1S1) turns out to be related to the total milk protein content in Polish Primitive Horse (p < 0.05), whereas c.-2105C>G SNP (CSN2) is related to beta-casein relative mRNA level and milk lactose concentration in the Polish Coldblood Horse breed (p < 0.05)
Equids are currently considered minor dairy species, research indicates that the consumption of equine milk is one of the oldest forms of horse utility (Outram et al 2009)
Summary
Numerous polymorphic variants of casein genes and proteins have recently been described in the llama (Lama glama), the camel (Camelus dromadarius), and the domestic horse (Equus caballus) (Pauciullo et al 2014; Pauciullo and Erhardt 2015; Cieslak et al 2016; Brinkmann et al 2016). Of these minor dairy species, most attention has been paid to equine milk, because its composition is considered similar to human breast
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