The effect of gene SKI polymorphism on carcass traits in pigs

Animal Science Papers and Reports vol. 24 (2006) no. 2, 163-168
Institute <strong>of</strong> Genetics and Animal Breeding, Jastrzębiec, Poland
SHORT REPORT
<strong>The</strong> <strong>effect</strong> <strong>of</strong> <strong>gene</strong> <strong>SKI</strong> <strong>polymorphism</strong>
on carcass traits in pigs
Paweł Urbański 1 , Mariusz Pierzchała 1 , Agnieszka Korwin-Kossakowska 1 ,
Jolanta Kurył 1 , Marian Kamyczek 2 , Marian Różycki 3
1
Polish Academy <strong>of</strong> Sciences Institute <strong>of</strong> Genetics and Animal Breeding,
Jastrzębiec, 05-552 Wólka Kosowska, Poland
2
Pig Hybridization Centre, National Research Institute <strong>of</strong> Animal Production,
Pawłowice, 64-122 Pawłowice, Poland
3
National Research Institute <strong>of</strong> Animal Production, 32-083 Balice/Cracow, Poland
(Received April 24, 2006, accepted June 06, 2006)
Phosprotein, the product <strong>of</strong> proto-onco<strong>gene</strong> <strong>SKI</strong>, plays a role in the control <strong>of</strong> cell growth and in
skeletal muscle differentiation. <strong>The</strong> aim <strong>of</strong> this study was to characterize the <strong>polymorphism</strong> <strong>of</strong> <strong>gene</strong>
<strong>SKI</strong> identified with restriction endonuclease BsmAI in gilts <strong>of</strong> Polish Large White (PLW, n=117)
and Polish Landrace (PL, n=51), and to analyse the relation between the <strong>SKI</strong> genotypes and carcass
traits. <strong>The</strong> animals were free <strong>of</strong> RYR1 T allele. In both breeds, the frequency <strong>of</strong> homozygote CC at
the <strong>SKI</strong> locus occurred very low. <strong>The</strong> only significant relations between genotype and carcass traits
were observed in PLW gilts for weight <strong>of</strong> loin and weight <strong>of</strong> sirloin.
KEY WORDS: carcass quality / <strong>gene</strong> <strong>polymorphism</strong> /pig / <strong>SKI</strong>
Selection for increased growth rate or decreased backfat thickness was important
in pig breeding during last two decades, based, among others, on OTL identification.
Within this area, one <strong>of</strong> the methods used is evaluation <strong>of</strong> candidate <strong>gene</strong>s <strong>polymorphism</strong>
<strong>effect</strong> on phenotypic variation [Kurył 2000 – a review].
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Recently, the <strong>SKI</strong> proto-onco<strong>gene</strong> was suggested as potentially influencing
carcass traits in pigs [Stratil et al. 2002]. <strong>SKI</strong> encodes a nuclear protein, binds to
DNA in association with other cellular factors, and modulates transcription [Berk
et al. 1997]. <strong>The</strong>se proteins are involved in cell proliferation, differentiation and
apoptosis. <strong>The</strong> <strong>gene</strong> <strong>SKI</strong> has also been found implicated in the control <strong>of</strong> myo<strong>gene</strong>sis
processes [Berk et al. 1997]. Earlier Colmenares and Stavnezer [1989] reported that
the proto-onco<strong>gene</strong> <strong>SKI</strong> induces muscle cell differentiation. Transgenic pigs and mice
carrying <strong>SKI</strong> sequences show marked muscle hypertrophy characterized by my<strong>of</strong>ibretype
specificity [Sutrave et al. 1990, Pursel et al. 1992]. <strong>The</strong> induction <strong>of</strong> MYOD1
and MYF4 expression by the <strong>SKI</strong> suggests, that this proto-onco<strong>gene</strong> acts early in the
pathway, perhaps in the determination step next to MYOD1 and(or) MYF5. Thus,
induction <strong>of</strong> my<strong>of</strong>ibre hypertrophy suggests the <strong>SKI</strong> activity during postnatal muscle
growth, perhaps in cooperation with other <strong>gene</strong>s [Colmenares et al. 1991]. In order to
determine a normal function <strong>of</strong> this <strong>gene</strong> in vivo, Berk et al. [1997] have disrupted the
mouse <strong>SKI</strong> <strong>gene</strong>. <strong>The</strong> results confirmed its function in skeletal muscle development
and showed a novel role <strong>of</strong> the factor in the morpho<strong>gene</strong>sis <strong>of</strong> crani<strong>of</strong>acial structures
and the central nervous system. But the exact role <strong>of</strong> the <strong>gene</strong> in development <strong>of</strong>
skeletal muscle still remains unclear.
In the porcine <strong>SKI</strong> mapped to pig chromosome 6, double nucleotide substitution
CG→TC at positions 304-305 resulting in an amino acid substitution in the protein
(Arg→Ser), was described by Stratil et al. [2002]. This <strong>polymorphism</strong> is located
in exon 1, encoding functional domain responsible for transformation and muscle
differentiation.
<strong>The</strong> aim <strong>of</strong> this study was to evaluate the <strong>effect</strong> <strong>of</strong> the mutation described on
porcine growth rate and carcass traits. A similar analysis has not been reported in
literature to date.
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Material and methods
Included were Polish Large White (PLW, n=117) and Polish Landrace (PL, n=51)
gilts free <strong>of</strong> RYR1 T allele. <strong>The</strong> pigs were fattened and slaughtered at the Pig Testing
Station <strong>of</strong> the National Research Institute <strong>of</strong> Animal Production, Pawłowice near
Leszno Wlkp, Poland. From 25 to 100 kg live body weight the commercial mixed
feed was applied ad libitum. Right carcass side was dissected into lean, fat and bone
according to the procedure described by Różycki [1996]. In the present study the
following traits were considered: weight <strong>of</strong> right carcass side, weight <strong>of</strong> ham with
shank, height <strong>of</strong> loin eye, loin eye area, loin weight, sirloin weight, meat content
<strong>of</strong> valuable carcass cuts and meat content <strong>of</strong> carcass. Genomic DNA was isolated
from leukocytes according to Kawasaki [1990]. <strong>The</strong> <strong>SKI</strong> genotyping was performed
using PCR/RFLP technique with BsmAI (Alw26I) endonuclease, recognizing G→
C substitution, according to Stratil et al. [2002]. An amplified 350 bp fragment
encompassed part <strong>of</strong> <strong>SKI</strong> exon 1. Association analyses were carried out for each <strong>of</strong> two

<strong>SKI</strong> <strong>gene</strong> <strong>polymorphism</strong> and carcass traits in pigs
breeds separately using the least squares method <strong>of</strong> the GLM procedure [Statistical
Analysis Systems Institute Inc. 2001, according to the following model:
where:
Y ijkl
= µ + G i
+ O j
+ β(x ij
- x) + e ij
y ij
– trait measured on ij-th animal;
µ – overall mean;
G i
– <strong>effect</strong> <strong>of</strong> <strong>SKI</strong> genotype;
O j
– sire <strong>effect</strong>;
β(x ij
- x) – linear regression for weight <strong>of</strong> right carcass side (for carcass traits)
and age at slaughter (for growth rate traits);
e ij
– random error.
Results and discussion
<strong>The</strong> frequency <strong>of</strong> genotypes and alleles at the <strong>SKI</strong> locus is shown in Table 1. <strong>The</strong>
G305C <strong>polymorphism</strong> present in exon 1 was identified with enzyme BsmAI. Three
<strong>SKI</strong> /G305C genotypes were observed in breeds tested, but the frequency <strong>of</strong> genotype
CC was low in both (11.1% in PLW and 1.96% in PL). In PLW the frequency <strong>of</strong>
homozygotes GG was similar to that <strong>of</strong> heterozygotes whereas in PL the most frequent
was GG genotype. Stratil et al. [2002] reported the highest frequency <strong>of</strong> <strong>SKI</strong> C allele
in Pietrain pigs, whereas Meishan pigs appeared to be monomorphic for the allele G.
However, one should mention that in a cited study by Stratil et al. [2002] number <strong>of</strong>
animals <strong>of</strong> individual breeds was very low (6 and 12, respectively).
Table 1. Frequency <strong>of</strong> genotypes and alleles at locus <strong>SKI</strong> in Polish Large White (PLW) and Polish
Landrace (PL) gilts
Breed
Number
<strong>of</strong> animals
Number and frequency
genotypes
alleles
GG GC CC G C
PLW 117 50
(42.7%)
PL 51 37
(72.5%)
54
(46.1%)
13
(25.4%)
13
(11.11%)
1
(1.96%)
0.66 0.34
0.85 0.15
A significant relationship between production traits and the genotype at the
<strong>SKI</strong> locus was observed for two traits and in PLW gilts only (Tab. 2). <strong>The</strong> tested
transversion – G305C – was found significant for weight <strong>of</strong> loin and weight <strong>of</strong> sirloin.
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P. Urbański et al.
Table 2. Least squares means (LSM) and their standard errors (SE) for two carcass traits as
affected significantly by genotype at the <strong>SKI</strong> locus in Polish Large White pigs
Carcass trait
<strong>SKI</strong> genotype at nucleotide G305C
GG GC CC
LSM SE LSM SE LSM SE
Weight <strong>of</strong> sirloin (kg) 0.359 Aa 0.006 0.340 B 0.005 0.339 b 0.009
Weight <strong>of</strong> loin (kg) 6.769 a 0.089 6.556 b 0.084 6.749 0.138
aA... Within rows means bearing different superscripts differ significantly at: small letters −
P≤0.05; capital − P≤0.01.
<strong>The</strong> homozygotes <strong>of</strong> the G allele showed the highest value <strong>of</strong> these traits, compared to
heterozygotes and homozygotes <strong>of</strong> allele C. Heterozygotes showed the lowest weight
<strong>of</strong> loin compared to both homozygotes. Such phenomenon observed earlier for certain
human <strong>gene</strong>s was named a negative (or positive) heterosis – Comings and MacMurray
[2000] – who suggested that if the regulation <strong>of</strong> the <strong>gene</strong> is dose-dependent, the
presence <strong>of</strong> a regulatory sequence in a heterozygous state could modify the <strong>gene</strong>
function. Similar associations were also observed in our earlier studies regarding
MyoD <strong>gene</strong>s family [Cieślak et al. 2002, Urbański et al. 2005, 2006, Wyszyńska-
Koko et al. 2006].
We did not observe any significant relation between <strong>SKI</strong> genotypes and carcass
traits in PL pigs tested in this study. A low number <strong>of</strong> animals (51 only) may be the
reason for insignificance <strong>of</strong> associations studied (Tab. 1).
<strong>The</strong> <strong>SKI</strong> proto-onco<strong>gene</strong> has been mapped to chromosome 6 by Stratil et al.
[2002], where two other <strong>gene</strong>s – RYR1 [Fujii et al. 1991] and H-FABP [Gerbens et
al. 1997] – as well as QTLs important for growth rate and carcass traits [Paszek et al.
1999 and Geldermann et al. 2003] have been localized. <strong>The</strong> RYR1 genotype is known
to affect carcass quality. In the present study, however, this was excluded as the gilts
analysed were free <strong>of</strong> RYR1 T allele. Thus, the observed <strong>effect</strong> <strong>of</strong> <strong>SKI</strong> genotype on
carcass traits has not been modified by RYR1 <strong>gene</strong> linked to <strong>SKI</strong> locus.
1.
2.
3.
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Paweł Urbański, Mariusz Pierzchała, Agnieszka Korwin-Kossakowska,
Jolanta Kurył, Marian Kamyczek, Marian Różycki
Analiza wpływu polimorfizmu genu <strong>SKI</strong> na cechy tuszy świń
S t r e s z c z e n i e
Protoonkogen <strong>SKI</strong> pełni ważną rolę w procesie wzrostu i rozwoju organizmu oraz jest zaangażowany
w proces rozwoju mięśni szkieletowych. Produktami tego genu są białka jądrowe, uczestniczące, między
innymi, w indukcji procesów mio<strong>gene</strong>zy. Celem badań była charakterystyka polimorfizmu genu <strong>SKI</strong> świń
dwóch ras hodowanych w Polsce – wielkiej białej polskiej (PLW) i polskiej białej zwisłouchej (PL) – i
ocena wpływu tego polimorfizmu na cechy tuszy. Badaniami objęto zwierzęta wolne od genu RYR1 T , aby
wykluczyć wpływ genotypu RYR1 na cechy tuszy. W obu rasach zaobserwowano bardzo niską frekwencję
osobników homozygotycznych CC. Istotne zależności między genotypem a badanymi cechami stwierdzono
tylko w rasie wbp (PLW) i to wyłącznie w odniesieniu do masy polędwicy i masy polędwiczki. Autorzy
wnioskują, że znajomość genotypu <strong>SKI</strong> może być przydatna w selekcji ukierunkowanej na poprawę
wymienionych cech tuszy, jednak badania te powinny być kontynuowane na materiale obejmującym inne
rasy i linie, aby stwierdzić, czy zaobserwowane zależności mają charakter uniwersalny.
168