J. Dairy Sci. 2008. 91:4433-4436. doi:10.3168/jds.2008-1228
© 2008 American Dairy Science Association ®
Short Communication: The β-Casein (CSN2) Silent Allele C1 Is Highly Spread in Goat Breeds
S. Chessa*,
D. Rignanese*,
J. Küpper
,
G. Pagnacco*,
G. Erhardt and
A. Caroli
* Dipartimento di Scienze e Tecnologie Veterinarie per la Sicurezza Alimentare, Università degli Studi di Milano, Via Trentacoste 2, Milano, 20134 Italy
Institut für Tierzucht und Haustiergenetik, Justus-Liebig-Universität, Ludwigstr. 21 b, 35390 Gieβen, Germany
Dipartimento di Scienze Biomediche e Biotecnologie, Università degli Studi di Brescia, Viale Europa 11, Brescia, 25123 Italy
1 Corresponding author: stefania.chessa{at}unimi.it
 |
ABSTRACT
|
|---|
Several single nucleotide polymorphisms have been identified in the goat milk casein genes, most of them modifying the amino acid sequence of the coded protein. At least 9 variants have been found in goat β-CN (CSN2); 6 of them were characterized at the DNA level (A, A1, C, E, 0, and 0'), whereas the other 3 variants were described only at the protein level. The recently identified silent A1 allele is characterized by a C
T transition at the 180th nucleotide of the ninth exon. In the present work, typing results from different breeds (3 Italian, 3 German, and a composite of African breeds for a total of 335 samples) demonstrated that the same mutation is carried by the CSN2*C allele. In addition, the T nucleotide at the 180th nucleotide of the ninth exon was always associated with CSN2*C in all the breeds analyzed. Thus, another silent allele occurs at goat CSN2 and can be named CSN2*C1. The much wider distribution of C1 with respect to the A1 allele indicates that the single nucleotide polymorphisms characterizing the silent mutation originated from CSN2*C. A method for the identification of this allele simultaneously with 5 of the 6 DNA-characterized alleles is also proposed. The mutation involved codifies for the same protein of the C allele; nevertheless, its location in the 3' untranslated region of the gene might affect the specific casein expression.
Key Words: β-casein • goat • genetic polymorphism • 3' untranslated region
A large number of single nucleotide polymorphisms (SNP) have been identified in the goat milk casein genes, most of them modifying the amino acid sequence of the coded protein, thus affecting goat casein qualitative and quantitative variability as well as milk protein composition (Martin et al., 2002). At least 9 alleles have been found in goat β-CN (CSN2). Six of these alleles (A, A1, C, E, 0, and 0') were characterized at the DNA level (Rando et al., 1996; Persuy et al., 1999; Chessa et al., 2005; Cosenza et al., 2005), whereas the CSN2*B and the CSN2*D variants were described only at the protein level (Mahé and Grosclaude, 1993; Galliano et al., 2004). A new variant has been recently found by Chianese et al. (2007) at the protein level, but it is not yet characterized. Different techniques were used to type CSN2 at the DNA level, but a complete description of CSN2 variation within the breeds has never been reported. In general, CSN2*A and CSN2*C were found to be the most common alleles in many breeds, with a predominance of the CSN2*A in some African and Indian breeds (Caroli et al., 2007; Chessa et al., 2007), whereas the CSN2*C was the most common variant in some Italian and Turkish breeds (Chessa et al., 2005, 2007; Caroli et al., 2006). The A1 silent allele has been recently identified in an undefined genetic type reared in the province of Naples, with a frequency of 0.23 (Cosenza et al., 2005). It differs from CSN2*A for a CT transition at the 180th nucleotide of the ninth exon, corresponding to the nucleotide position 10562 of the reference CSN2*A GenBank No. AJ011018. The presence of C10562 might represent the ancestral condition of the gene because it has been found also in other ruminant species (Cosenza et al., 2005).
To understand how this mutation is distributed in different breeds and to elucidate if T10562 could be in association with other CSN2 alleles, a total of 335 DNA samples belonging to different breeds (3 Italian breeds, 3 German breeds, and a composite of African breeds) were analyzed at CSN2 level both by the PCR-single strand conformation polymorphism (SSCP) described by Chessa et al. (2005) and by the PCR-RFLP described by Cosenza et al. (2005). The PCR-SSCP discriminates the CSN2*A, CSN2*C, CSN2*E, and CSN2*0' alleles, whereas the PCR-RFLP allows the detection of the transition C10562T10562 identified in CSN2*A1. The African samples were randomly chosen from those previously characterized in the casein genes by Caroli et al. (2007).
The results of the genotyping are listed in Table 1
. No T10562 was found in association with the CSN2*AA genotype in all breeds. On the contrary, T10562 was found in samples homozygous or heterozygous for CSN2*C. Thus, T10562 may be likely associated with CSN2*C in the breeds analyzed. Only the double heterozygous combinations AC x CT might carry the CSN2*A-T10562 haplotype, corresponding to the A1 allele. In particular in the African goats, where CSN2*A is predominant (Caroli et al., 2007), only one sample carrying T10562 at the heterozygous condition associated to the CSN2*CC genotype was observed.
The occurrence of the intragenic haplotype CSN2*C-T10562 was confirmed by sequencing 6 CSN2*C homozygous samples with different RFLP patterns at the nucleotide position 10562 (2 CC, 2 CT, 2 TT). The samples were sequenced by PRIMM Srl (Milano, Italy), using the primers designed for the PCR-RFLP by Cosenza et al. (2005) and confirming the association of T10562 with the T nucleotide at codon 135 of the seventh exon (position 8946 of GenBank accession no. AJ011018), characterizing CSN2*C. Thus, another silent allele occurs at goat CSN2, characterized by T8946 and T10562, that can be named CSN2*C1. Table 2 summarizes the nucleotide and deduced amino acid exchanges between the CSN2 alleles characterized at the DNA level until now. The wide distribution of this silent allele suggests that T10562 originated from CSN2*C, with the following evolutionary pattern, starting from the CSN2*A allele, which is considered the ancestral one (Chessa et al., 2005): CSN2*A-C10562 CSN2*C-C10562 CSN2*C-T10562. This evolutionary hypothesis fits also with the ancestral origin of C10562 (Cosenza et al., 2005). Most probably the A1 silent variant identified by the same authors and characterized by CSN2*A-T10562 haplotype arose from an intragenic recombinant event spread in the population as a consequence of the genetic drift.
To type CSN2*A1 and CSN2*C1 simultaneously with CSN2*A, CSN2*C, CSN2*E, and CSN2*0' without any further analysis, the PCR-SSCP assay described by Chessa et al. (2005) was adapted. Because the mutations distinguishing these variants are located within exons 7 and 9, a multiplex PCR (mPCR) was developed. Primers used for the amplification of the 374-bp fragment of CSN2 containing part of the exon 7 were the ones employed by Chessa et al. (2005), whereas a new pair of primers was designed to amplify a 325-bp fragment within exon 9. The new primers were CSN2–9C1 Fw (5'-CAGAATTGACTGCGACTGGA-3') and CSN2–9C1 Rv (5'-TGCCTAAGGGTTAATTTATTGAAA-3'), designed on the basis of the caprine sequence GenBank accession no. AJ011018, using Primer3 software (Rozen and Skaletsky, 2000).
The PCR was performed in a 25-µL reaction mixture containing 4 µL of DNA solution (200 to 300 ng), 1 x PCR Master Mix (Fermentas, Vilnius, Lithuania) and 10 pmol of each of the 4 primers. The following conditions were used for the mPCR assay: an initial denaturation step of 94°C for 5 min, followed by 35 cycles of 94°C for 60 s, 56°C for 60 s, 72°C for 60 s, and a final extension step of 72°C for 7 min using a PTC-200 DNA Engine Thermal Cycler (MJ Research Inc., Waltham, MA). The mPCR product was subsequently analyzed using the same SSCP technique described by Chessa et al. (2005). The only modification to this protocol was the duration of the run, which was reduced from 14 to 13 h to not have the fast migrating bands at the far end of the gel (Figure 1). Two series of bands were obtained by the PCR-SSCP analysis, slow (Figure 1, part A) and fast migrating (Figure 1, part B), corresponding to the exon 7 and 9 PCR product, respectively. As for the exon 7 PCR product, the patterns obtained were the same described by Chessa et al. (2005) and Caroli et al. (2007). As for the exon 9 PCR product, 3 different patterns were found. Each pattern was composed of 2 bands, corresponding to the 2 DNA strands. The fastest set of strands corresponded to the T10562 polymorphism, the slowest one to C10562. The genotype is given by the combination of the 2 series of bands. The method was validated on all the Italian samples already analyzed by using both the PCR-SSCP and the PCR-RFLP assays. Full agreement was found between the PCR-SSCP assay here developed and the 2 separated analyses. As expected, no CSN2*A1 was identified in the analyzed samples; nevertheless, the new method could easily detect this allele, which is not included in Figure 1 due to the nonavailability of a reference sample. To understand the association between nucleotide position 10562 and the CSN2*0' allele, not found in the breeds analyzed, different reference samples available from previous studies (Sacchi et al., 2005) were also analyzed by the new assay (Figure 1). Only the intragenic haplotype CSN2*0'-C10562 was found in the samples analyzed (data not shown).
View larger version (168K):
[in this window]
[in a new window]
|
Figure 1. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis of different β-casein (CSN2) genotypes. A) The 374-bp fragment containing exon 7 is fixed in the higher part of the gel at the end of the electrophoretic run. Two bands are visible for each allele. White star = CSN2*C, white circle = CSN2*A, black triangle = CSN2*0', and black rhombus = CSN2*E. B) The 325-bp fragment containing exon 9 is fixed in the lower part of the gel. Two bands are visible for each variant. White square = C10562, black square = T10562. The genotype is given by the combination of the results obtained for the 2 fragments. In the gel a reference sample homozygous for CSN2*0' was also used.
|
|
The possibility of typing the CSN2*C1 allele here described simultaneously with 5 of the 6 DNA characterized alleles may provide an opportunity to have a more refined picture of goat CSN2 variability, which is important given the wide distribution of the new allele. Even if the nucleotide exchange does not result in a different protein variant, particular attention should be given to this SNP because it is located in the 3' untranslated of the gene, possibly affecting the mRNA stability and, consequently, the expression of the specific protein (Xu et al., 1997; Cosenza et al., 2005).
|
ACKNOWLEDGEMENTS
|
|---|
The research was supported by PRIN2005-2005075887_001 contract and by the Vigoni project.
Received for publication April 3, 2008.
Accepted for publication July 1, 2008.
|
REFERENCES
|
|---|
Caroli, A., F. Chiatti, S. Chessa, D. Rignanese, P. Bolla, and G. Pagnacco. 2006. Focusing on the goat casein gene complex. J. Dairy Sci. 89:3178–3187.[Abstract/Free Full Text]
Caroli, A., F. Chiatti, S. Chessa, D. Rignanese, E. Ibeagha-Awemu, and G. Erhardt. 2007. Characterization of the casein gene complex in West Africa goats and description of a new aS1-casein polymorphism. J. Dairy Sci. 90:2989–2996.[Abstract/Free Full Text]
Chessa, S., E. Budelli, F. Chiatti, A. M. Cito, P. Bolla, and A. Caroli. 2005. Predominance of β-casein (CSN2) C allele in goat breeds reared in Italy. J. Dairy Sci. 88:1878–1881.[Abstract/Free Full Text]
Chessa, S., F. Chiatti, D. Rignanese, E. M. Ibeagha-Awemu, C. Özbeyaz, Y. A. Hassan, M. M. Baig, G. Erhardt, and A. Caroli. 2007. The casein genes in goat breeds from different continents: Analysis by polymerase chain reaction – single strand conformation polymorphism (PCR-SSCP). Ital. J. Anim. Sci. 6:73–75.
Chianese, L., S. Caira, G. Garro, M. Quarto, R. Mauriello, and F. Addeo. 2007. Occurrence of genetic polymorphism at goat β-CN locus. Page 69 in 5th Int. Symp. Challenge to Sheep and Goats Milk Sectors. Alghero 2007, Sardinia, Italy.
Cosenza, G., A. Pauciullo, D. Gallo, D. Di Berardino, and L. Ramunno. 2005. A SspI PCR-RFLP detecting a silent allele at the goat CSN2 locus. J. Dairy Res. 72:456–459.[CrossRef][Medline]
Galliano, F., R. Saletti, V. Cunsolo, S. Foti, D. Marletta, S. Bordonaro, and G. D’Urso. 2004. Identification and characterization of a new β-casein variant in goat milk by high-performance liquid chromatography with electrospray ionization mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry. Rapid Commun. Mass Spectrom. 18:1972–1982.[CrossRef][Medline]
Mahé, M. F., and F. Grosclaude. 1993. Polymorphism of β-casein in the Creole goat of Guadeloupe, evidence for a null allele. Genet. Sel. Evol. 25:403–408.[CrossRef]
Martin, P., M. Szymanowska, L. Zwierzchowski, and C. Leroux. 2002. The impact of genetic polymorphisms on the protein composition of ruminants milks. Reprod. Nutr. Dev. 42:433–459.[CrossRef][Medline]
Persuy, M. A., C. Printz, J. F. Medrano, and J. C. Mercier. 1999. A single nucleotide deletion resulting in a premature stop codon is associated with marked reduction of transcript from a goat β-casein null allele. Anim. Genet. 30:444–451.[CrossRef][Medline]
Rando, A. 1998. GenBank Accession no. AJ011018 [Capra hircus csn2 gene, exons 1 to 9, allele A]. http://www.ncbi.nlm.nih.gov/ Accessed Feb. 21, 2005.
Rando, A., M. Pappalardo, M. Capuano, P. Di Gregorio, and L. Ramunno. 1996. Two mutations might be responsible for the absence of β-casein in goat milk. Anim. Genet. 27:31.
Rozen, S., and H. J. Skaletsky. 2000. Primer3 on the WWW for general users and for biologist programmers. Pages 365–386 in Bioinformatics Methods and Protocols: Methods in Molecular Biology. S. Krawetz and S. Misener, ed. Humana Press, Totowa, NJ. Whitehead Institute for Biomedical Research. http://frodo.wi.mit.edu/cgi-bin/primer3/primer3.cgi Accessed Oct. 20, 2006.
Sacchi, P., S. Chessa, E. Budelli, P. Bolla, G. Ceriotti, D. Soglia, R. Rasero, E. Cauvin, and A. Caroli. 2005. Casein haplotype structure in five Italian goat breeds. J. Dairy Sci. 88:1561–1568.[Abstract/Free Full Text]
Xu, N., C.-Y. A. Chen, and A. B. Shyu. 1997. Modulation of the fate of cytoplasmic mRNA by AU-rich elements: Key sequence features controlling mRNA deadenylation and decay. Mol. Cell. Biol. 17:4611–4621.[Abstract]
This article has been cited by other articles:
|
|
|
|
 
A. M. Caroli, S. Chessa, and G. J. Erhardt
Invited review: Milk protein polymorphisms in cattle: Effect on animal breeding and human nutrition
J Dairy Sci,
November 1, 2009;
92(11):
5335 - 5352.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
ACKNOWLEDGEMENTS
