Characterization of equine cDNA sequences for α_S1-, β- and κ-casein

Abstract

Here we report the entire cDNA sequences for equine αS1-, β- and κ-casein. Based on interspecies comparison, nine exons were found in equine β-casein and five in κ-casein. In equine αS1-casein cDNA the exon 5 was missing, which resulted in the total of 18 exons instead of 19 theoretically possible exons in αS1-casein cDNA. Comparison of DNA sequences representing exon 5 in other species with corresponding equine genomic region confirmed the presence of cryptic exon in horse genomic DNA. Equine αS1-casein mRNA was present in three forms in the lactating mammary gland and we showed that the two shorter forms were produced by skipping either the exon 8 or exon 15. In horse, as in some other mammals, β- and κ-casein are considerably more conserved (sequence identity 53% to 59% and 57% to 67%, respectively) than αS1-casein which appears as the most variable casein among species (sequence identity 40% to 54%). Interestingly, horse caseins resemble human much more than bovine caseins which may also explain the high dietetic value of mares' milk.

Distal regulation of alternative splicing by splicing enhancer in equine β-casein intron 1

“…Amplified fragments were analyzed by gel electrophoresis and sequencing and were quantified by capillary electrophoresis. In the a S1 -casein mRNA, we confirmed the presence of two previously described alternatively included exons (Milenkovic et al 2002;Lenasi et al 2003), exon 8 (GenBank AY579422) and exon 15 (GenBank AY579423) (Fig. 1, AEX8, AEX15; Fig.…”

“…Therefore, casein genes are good candidates for studying the cotranscriptional splicing process. There have been two reports on alternative splicing of a S1 -casein mRNA in horses (Milenkovic et al 2002;Lenasi et al 2003). In this study, we discovered a splicing enhancer in b-casein intron 1 (ISE1) that increases the inclusion of several weak exons.…”

Sequence determination of αs1‐casein isoforms from donkey by mass spectrometric methods

“…[14] On the other hand, the existence of the two isoforms lacking a glutamine residue is probably related to a cryptic splice site occurring at the first codon (CAG) of exon 11 (encoding this glutamine residue) as already reported for ewe, [25] goat, [26] cow and water buffalo [27] α s1 -CNs.…”

Comparative characteristics of DNA polymorphisms of κ-casein gene (CSN3) in the horse and donkey

“…Due to their economical importance, κ-caseins and their genetic polymorphisms have been widely investigated in many ruminant species (Pinders et al, 1991;Prinzenberg et al, 2005;Moioli et al, 2007;Caroli et al, 2009;Selvaggi and Tufarelli, 2012;Selvaggi et al, 2014a,b). The comparison of amino acids sequences of the equine caseins with corresponding camel, pig, human, bovine, ovine and goat counterparts revealed sequences identity between 40 and 67% (Lenasi et al, 2003). Equine κ-casein proves to be the most conserved casein, closely followed by β-casein in agreement with the physiological function of these two proteins in micelles formation and with the role of κ-casein in milk coagulation (Holt, 1992).…”

“…Conversely, other researchers showed its presence, albeit at a low concentration (Kotts and Jenness, 1976;Malacarne et al, 2000;Iametti et al, 2001Iametti et al, , 2002Egito et al, 2002). The primary structure of equine κ-casein has been derived (Iametti et al, 2001;Lenasi et al, 2003;Miranda et al, 2004); it contains 165 amino acids residues (four less than bovine κ-casein but three more than human κ-casein). Equine κ-casein shows several biochemical properties similar to those of bovine and human κ-casein, such as the presence of carbohydrate moieties and the susceptibility to hydrolysis by chymosin-group II (Egito et al, 2001).…”