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Advances in Environmental Biology, 8(4) March 2014, Pages: 862-867
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Advances in Environmental Biology
ISSN-1995-0756
EISSN-1998-1066
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The Effect of Igf-1 and Pit-1 Genes Polymorphisms on Fat-Tail Measurements
(Fat-Tail Dimensions( In Makooei Sheep
1
Reyhaneh Chelongar, 2Abbas.Hajihosseinlo, 3Marziyeh Ajdary
1
Department of Biology, Payame Noor University, I.R. of IRAN.
Department of Animal Science, Faculty of Agriculture, Urmia University, Urmia, Iran.
3
Young Researchers & Elits Club, Khorasgan Branch, Islamic Azad University, Isfahan, Iran.
2
ARTICLE INFO
Article history:
Received 11 Feb 2014
Received in revised form 24
February 2014
Accepted 29 March 2014
Available online 5 May 2014
Key words:
Association analysis; Makooei sheep;
fat-tail Measurements; IGF-1 gene;
PIT-1gene
ABSTRACT
The study of candidate genes, based on physiological effects, is an important tool to
identify genes to be used in marker-assisted selection programs. Use of genetic markers
can aid in the identification of animals with highest breeding values in sheep. On the
basis of sheep genome mapping information the ovine IGF1, PIT1 genes were
examined as a possible genetic marker for growth traits in sheep. The current study was
designed to investigate the association of IGF-1 and PIT-1 genes Single Nucleotide
Polymorphisms (SNPs) with fat-tail Measurements of growth traits in Makooei sheep.
In the tested Makooei sheep population, significant statistical results were found in all
traits as to fat-tail Measurements for IGF-1 and PIT-1 Genes. Individuals with the P3
genotype of PIT-1 gene had superiority of tail length (Rump length) (P <0.001), tail
width (Rump width) when compared to those of individuals with other genotypes
(P <0.01). also Individuals with the P4 genotype of PIT-1 gene had superiority of fat
thickness (the thick rump) when compared to those of individuals with other
genotypes (P <0.01). Also the AA, AG conformational patterns of IGF1 gene in
individuals have a significant effect on fat thickness (the thick rump). And this patterns
of IGF1 gene (AA, AG) had the highest fat thickness (the thick rump) (P<0.05).
© 2014 AENSI Publisher All rights reserved.
To Cite This Article: Reyhaneh Chelongar, Abbas.Hajihosseinlo, Marziyeh Ajdary., The Effect of Igf-1 and Pit-1 Genes Polymorphisms on
Fat-Tail Measurements (Fat-Tail Dimensions (In Makooei Sheep. Adv. Environ. Biol., 8(4), 862-867, 2014
INTRODUCTION
Makooei sheep is a medium-frame (mid-size) fat-tailed breed and a multi-purpose breed for milk, carpet
wool, and meat production. It originated and is dominant in western Iran. All Iranian native sheep breeds, except
the Zel breed, are fat-tailed. The fat-tail that is regarded as an adaptive response of animals to harsh
environmental conditions, serves as an energy source during migration and winter when grazing is limited due
to low pasture quality and quantity[1]. Almost all Iranian sheep breeds have large fat tails Fat tail and other
adipose depots; negatively affect the sale of sheep by sheep industries in some country like Iran. Fat tail is not
desirable to costumers even though it appears to be affordable (the price of 1 kg of fat-tail is less than one sixth
price of 1kg red meat). Fat-tail plays an important role as a source of energy for adult ewe during periods of
food shortage (autumn and especially winter). In young lambs, carcass adiposity, particularly the fat tail, reduces
meat value. Lean lamb can be produced from manipulation of nutritional regimen, slaughter in early age,
docking the fat-tail in early days after birth or by a genetic selection program. Fat tail breeds are an important
class of sheep breeds that are first documented as being present 5000 years ago. The earliest depiction of a fat
tail sheep is on an Uruk III stone vessel of 3000 BC and fat and thin tail sheep appear together on a mosaic
standard from Uruk dated around 2400 BC [2,3]. The fact that the fat tail breeds are now prevalent in the Fertile
Crescent, where sheep were originally domesticated, while thin tail sheep breeds are predominant in peripheral
areas [3]. and that the wild ancestor of sheep is thin tail, suggest that the first domesticated sheep were thin tail
and fat tail was developed later. The evidence shows that sheep were being farmed throughout Europe 5000
years ago [4]. The fat tail is considered as an adaptive response of animals to a hazardous environment and is a
valuable energy reserve for the animal during migration and winter. Until recently it had additional value to the
herder because it was used to preserve cooked meat for longer periods of time and also as an energy reserve
during times of drought and famine. Therefore the climatic variation as well as the associated requirements of
humans led to artificial selection for higher fat tail weight across generations [5,6,7]. Nowadays in intensive and
semi intensive systems most of the advantages of a large fat tail have reduced their importance and therefore, a
decrease in fat tail size is often desirable for producers and consumers. Fat deposition requires more energy than
Corresponding Author: Abbas.Hajihosseinlo, Department of Animal Science, Faculty of Agriculture, Urmia University,
Urmia, Iran.
E-mail: [email protected]
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Advances in Environmental Biology, 8(4) March 2014, Pages: 862-867
the deposition of lean tissue and animal fat has lost much of its market demand and monetary value and sheep
producers have easy access to other forms of auxiliary feeding [25]. These breeds are commonly found in a wide
range of countries in Asia especially the Middle East and North Africa [3] .The study of genes underlying
phenotypic variation can be performed in two different ways, first, from phenotype to genome, which is
performed by LD based association mapping or by targeting particular candidate genes identified based on
homology to known genes, and second, from genome to phenotype, which involves the statistical evaluation of
genomic data to identify likely targets of past selection using selective sweep analysis [9,10]. In contrast to
natural populations, domesticated species provide an exciting opportunity to understand how artificial selection
promotes rapid phenotypic evolution [11]. With an hypothesis that different selection pressures operated in thin
and fat tail breeds over the history of time and somehow the selection acts on a variant that is advantageous only
in one breed, it is expected that the frequency of that variant may differ across populations to a greater extent
than predicted for variants evolving neutrally in all populations [10]. Identifying these genome regions, which
have been subject to such selective sweeps, could reveal the mutations which are responsible for the fat
deposition in these breeds. The examination of variation in SNP allele frequencies between populations, which
can be quantified by the statistic FST, is a promising strategy for detecting signatures of selection [10,12]. The
Makooei sheep is one of the Iranian fat-tailed, medium-size breeds. They are distributed in the mountainous
areas of the country, especially in West-Azerbaijan province. Also, they are found in Turkey and called White
Karaman. They are valuable primarily for meat and also for their wool and milk. The wool produced is coarse
and usually used for carpet weaving [13]. Today, there are about 2,700,000 heads of Makooei sheep in WestAzerbaijan and due to the large population of this breed, there is an increasing interest in the genetic
improvement of this breed. Data were collected from 1995 to 2005 at the Makooei Sheep Breeding Station in
Makoo (36°, 35′S and 48°, 22′E) in West-Azerbaijan province. In general, the flock is managed under a semimigratory system. Ewes are raised in an annual breeding cycle starting in August. There is one breeding season
in August-October. Ewes in heat are exposed to pre-defined rams at morning. Lambing begins in mid-January
and continues until April. Ewes are supplemented, depending upon the ewes’ requirements, for a few days after
lambing. All lambs are identified at birth and birth weights, as well as sex, birth type and pedigree information
are recorded. During the suckling period, lambs are fed with their mothers’ milk and also allowed dry alfalfa
after 3 weeks of age. Lambs are weaned at approximately 100 days of age. Animals are kept on natural pasture
during spring, summer and autumn. Range conditions are poor during the winter months and, therefore, animals
are kept indoors during the winter. Appropriate breeding strategies are necessary to improve the productivity of
the local breeds in the region. Sheep is one of the species that has relatively high biodiversity in the Middle East.
For example, sheep population in Iran comprises 26 breed populations [14] . The main application and potential
for use of markers to enhance genetic improvement in livestock is through within-breed selection [15]. IGF1 is a
mediator of many biological effects; for example, it increases the absorption of glucose, stimulates myogenesis,
inhibits apoptosis, participates in the activation of cell cycle genes, increases the synthesis of lipids, stimulates
the production of progesterone in granular cells, and intervenes in the synthesis of DNA, protein, RNA, and in
cell proliferation [17].The transcription factor pituitary-1 (Pit-1, official nomenclature now POU1F1) plays a
major role in pituitary development and hormone expression. The objective of this study was to establish an
association of genotypes with fat-tail measurements of growth traits in Makooei sheep. Finally, the aim of this
study was to investigate the relationship between IGF-1 and PIT-1 conformational patterns with fat-tail
measurements (fat-tail dimensions) traits using SSCP method in Makooei sheep.
MATERIALS AND METHODS
Sheep, blood sample collection and genomic DNA extraction 'Makooei' sheep breeds examined in this
study were fat-tailed sheep with medium body size, white colour with black spots on face and feet. They are
kept in East and West Azerbaijan provinces of Iran and their main products are meat and wool [16]. Blood
samples were collected into a 5 ml EDTA contained vacutainer tube and transferred to the laboratory for DNA
extraction within 2 hours. Total DNA extractions were made with a modified salting out method [18].from
whole fresh blood. Quality and quantity of extracted DNA were measured on 0.8% agaroze gel prepared in 0.5×
TBE buffer (45 Mm Tris base, 45 Mm boric acid, 1mM EDTA pH 8.0) and visualized with ethidium bromide
(1.0 μgml-1) and photographed under UV light.
PIT1 genotyping:
The PIT1 gene was genotyped by PCR-SSCP (Polymerase chain reaction-single strand conformation
polymorphism). A 295bp fragment was amplified from (a part of intron2, exon3 and a part of intron3). Primers
used were those designed by (E. Bastos, I. Santos, et al. 2006). PIT-1-UP: 5'GAGGGATAATTACAAATGGTCC-3 and PIT-1-down: 5’-TGTTAACAGCTGTGGGACACAC-3'.PCR
contained 25-50ng genomic DNA, 10pmoL of each primer, 2 μL 10X PCR buffer, 1.5mM MgCl2, 200Μm
dNTP and 1 unit Taq-polymerase, in a total volume of 20 μL. DNA amplifications were performed using Master
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Advances in Environmental Biology, 8(4) March 2014, Pages: 862-867
cycler (Eppendorf, Germany) programmed for a preliminary step of 15 min at 95°C, followed by 34cycles of 45
s at 94°C, 1 min at 58°C and 45 s at 72°C, with a final extension of 5min at 72°C.
IGF-1 genotyping:
Two polymerase chain reaction (PCR) primers, IGF-1-up (5′-ATTACAG CTGCCTGCCCCTT-3′ ) and
IGF-1-down( 5'-CACATCTGCTAATACACCTTACCCG-3') targeting a fragment of 265bp were employed in
DNA amplifications as described by (A.Yilmaz, 2000). PCR contained 25-50ng genomic DNA, 10pmoL of
each primer, 2μL 10X PCR buffer, 1.5mM MgCl2, 200Μm dNTP and 1 unit Taq-polymerase, in a total volume
of 20μL. DNA amplifications were performed using Master cycler (Eppendorf, Germany) programmed for a
preliminary step of 2 min at 95°C, followed by 31cycles of 45 s at 94°C, 30 s at 58°C and 30 s at 72°C, with a
final extension of 3min at 72°C.
Single strand confirmation polymorphism (SSCP):
Two pairs of oligonucleotide primers were designed and a standard PCR protocol was used to amplify Two
fragments .A total number of 100 lambs of known pedigree were randomly selected from a breeding station of
Makooei sheep (in Makoo, West-Azerbaijan provinces of Iran). For single-strand conformation polymorphism
(SSCP) analysis, several factors were tested to optimize the methodology: the amount of PCR product (4 – 15
μL), dilution in denaturing solution (20 - 85%), denaturing solution (A: 95% of formamide, 10mM NaOH,
0.05% xylene-cyanol and 0.05% bromophenol blue; B: same as A, plus 20mM of EDTA), acrylamide
concentration (6 - 14%), 6 percentage for PIT1, 7 percentage for IGF-1,percentage of cross linking (1.5 to 5%),
presence (10%) or absence of glycerol, voltage (100 - 350 V), running time (2-12 h) and running temperature (4,
6, 10 and 15 °C). Each PCR reaction was diluted in denaturing solution, denatured at 95 °C for 5 min, chilled on
ice and resolved on non-denaturing polyacrylamide gel. The electrophoresis was carried in a vertical unit
(Payapajoohesh VEU-7350, 160×140×0.75 mm), in 1× TBE buffer. The gels were stained with silver.
Statistical analysis
Studied traits:
The traits measured were tail length (Rump length), fat thickness (the thick rump), tail width (Rump width).
SAS [19]. software was used to calculate least squares means, and for multiple comparisons among the different
genotypes in Makooei sheep. Least square analysis using the General Linear Model (GLM) procedure was done
to identify the fixed effects on a model that were to be included in the model and then the model was made
using the fixed effects (sex: 2 classes; type of birth:2 classes; IGF-1: 3 classes; PIT-1: 4 classes, according to the
following statistical model:
Yijklm= μ + Gi+Pd +eijklm
Where:
Yijklm= growth traits, μ = the overall mean, Gi= the fixed effect of the ith genotype for IGF-1, Pd= the fixed
effect of the dth genotype for PIT-1, Sj= = the fixed effect of sex (j = 1, 2), eijklm=the random residual error.
Result:
The relationship between body measurements and polymorphism of IGF-1:
According to statistical analysis no significant effect (P>0.05) was found between IGF1 genotypes with tail
length (Rump length) and tail width (Rump width) in present population (Table 1) although, fat thickness (The
thick rump) was influenced significantly by igf1 genotypes. Also, the analysis of fat-tail Measurements traits
showed that AA, AG conformational patterns of IGF1 gene have a significant effect on fat thickness (the thick
rump). And this patterns of IGF1 gene (AA, AG) had the highest fat thickness (the thick rump) (P<0.05).
Levels of significance, least squares means, and standard errors are reported in (Table 1).
Table 1: Least square means and standard errors for fat-tail dimensions of Makooei sheep according to the different IGF-1 patterns.
fat-tail dimensions
IGF-1
Tail length
Tail width
Fat thickness
AA
29.72±0.509
37.87±0.63
0.494± 0.019
AG
30.58±0.595
38.60±0.74
0.479±0.022
GG
29.36±1.51
39.14±1.89
0.377±0.055
P value
0.71ns
1.97ns
2.90*
Same letters in column show no significant difference (P> 0.05)
Dissimilar letters in column show significant difference (P< 0.05)
The relationship between body measurements and polymorphism of PIT-1:
Effect of PIT-1 SSCP Variants on the fat-tail measurements traits in Makooei sheep are presented in Table
1. The table demonstrates that we observed a significant effect of this polymorphism on tail length (Rump
length), fat thickness (the thick rump), tail width (Rump width) (all trait) in PIT-1 conformational patterns. In
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addition the results demonstrated that individuals with the P3 genotype of PIT-1 gene had superiority of tail
length (Rump length) (P <0.001) and tail width (Rump width) when compared to those of individuals with
other genotypes (P <0.01). also individuals with the P4 genotype of PIT-1 gene had superiority of fat
thickness (the thick rump) when compared to those of individuals with other genotypes (P <0.01). Levels
of significance, least squares means, and standard errors are reported in (Table 2).
Table 2:Least square means and standard errors for fat-tail dimensions of Makooei sheep according to the different PIT-1 patterns.
fat-tail dimensions
PIT-1
Tail length
Tail width
Fat thickness
P1
27.54±0.65
36.36±0.83
0.425±0.026
P2
28.23±1.33
34.44±1.68
0.378±0.065
P3
30.82±0.77
37.93±0.98
0.475±0.036
P4
28.22±2.01
30.92±2.54
0.623±0.097
P value
5.95 ***
3.79**
3.40**
Discussion:
The successful application of marker-assisted selection in commercial animal populations will depend on a
number of factors. Among these is the ability to identify the genes or closely linked markers to the genes
underlying the QTL, the ability to test whether allelic variations at these loci are segregating in the population,
and under-standing how these genes interact with the environment or with other genes affecting economic traits.
All this must be done in an efficient and cost effective manner in order for the technology to be adopted by the
livestock industries [20]. These genes can be closely bound to genetic markers, being able to be segregated
jointly. An ideal genetic marker should be polymorphic, must have a simple inherence mode, and should be
easily detectable [21]. The study of genes underlying phenotypic variation can be performed in two different
ways, first, from phenotype to genome, which is performed by LD based association mapping or by targeting
particular candidate genes identified based on homology to known genes; and second, from genome to
phenotype, which involves the statistical evaluation of genomic data to identify likely targets of past selection
using selective sweep analysis [22,23].Approximately 25% of the world sheep population comprises fat tail
breeds that are grazed in a wide range of countries especially in Asia and northern parts of Africa. In these
typically arid countries sheep breeding has an important place in the local economy and as a source of protein.
Due to the overt and easily defined nature of a fat tail, the gene variants affecting the phenotypic expression of
this trait are a topic of both theoretical and economic curiosity. The fat-tail is considered as an adaptive response
of animals to a hazardous environment and is a valuable energy reserve for the animal during migration and
winter. Nowadays in intensive and semi -intensive systems most of the advantages of a large fat-tail have
reduced their importance and, therefore, a decrease in fat-tai l size is often desirable for producers and
consumers [8].Therefore, reducing the size of the fat-tail of native sheep can be an objective for the sheep
industry of the country. In sheep breeding, it is well known that type traits have an important influence on sheep
performance. Measures of size and body form are desired in many experiments with sheep, including studies of
growth, inheritance and nutrition [25].In meat-producing species, body conformation and growth rate of animals
are important selection criteria [26]. Fat tail average was shown to be 1.03 kg. Furthermore, tail fat as a
proportion of carcass also varied widely. This could be a biological diversity criterion in this breed, and
could be used for selecting lambs with smaller fat-tail. The fat-tail of Makoei breed was relatively light
compared to Turkish Awassi sheep where mean tail fat weight averaged 3 kg and represented %15of
the carcass weight [27]. compared to Lori breed (Farahani et al., 2002, unpublished) or Mehraban and
Ghezel breeds of Iran [1]. There is limited information about the relationship between gene polymorphisms
with fat-tail Measurements in sheep. More studies were conducted on the association polymorphism of the
genes on Carcass Traits. Up to now, there were very few reports about IGF-1, PIT-1 genes SNPs and their
relationship with fat-tail dimensions, especially for sheep. Until now, a few polymorphisms of IGF-1 and PIT-1
genes have been detected in small ruminants and sheep have been studied much less. Very little information is
currently available to compare different Iranian sheep breeds. To date, this was the (first) study that attempted to
detect association between allele variation in the ovine IGF-1, PIT-1 genes and fat-tail dimensions traits in
Iranian sheep breeds. The previous breeding programs in most research centers of Iran were based on only
phenotypic characters. Thus, adding sheep varieties, expanding samples, and doing further correlation studies
are still needed to accumulate quantitative molecular genetics data in studying the relationship between the IGF1, PIT-1 genes and fat-tail dimensions traits in sheep. Evaluation of relationships between genotypes and fat-tail
Measurements were done with 100 samples. Levels of significance, least squares means, and standard errors are
reported in Table 1 for the effects of IGF-1 and PIT-1 genes on fat-tail Measurements in Makooei Sheep. In the
tested Makooei sheep population, significant statistical results were found in all traits as to fat-tail
Measurements for IGF-1 and PIT-1 Genes. Individuals with the P3 genotype of PIT-1 gene had superiority of
tail length(Rump length) (P <0.001), tail width(Rump width) when compared to those of individuals with
other genotypes (P <0.01). Also Individuals with the P4 genotype of PIT-1 gene had superiority of fat
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Advances in Environmental Biology, 8(4) March 2014, Pages: 862-867
thickness(the thick rump)when compared to those of individuals with other genotypes (P <0.01). Also the
AA, AG conformational patterns of IGF1 gene individuals have a significant effect on fat thickness (the thick
rump). And this patterns of IGF1 gene (AA, AG) had the highest Fat thickness (the thick rump) (P<0.05). The
statistical analysis showed no significant associations of the SNPs in the 5’ flanking region of the ovine IGF-I
Gene (P >0.05) with carcass traits in Zel (tailed) and Lori-Bakhtiari (fat-tailed) breed sheep [6].There was
significant association between genotypes of exon 17 region of the DGAT1 gene with carcass weight and
dressing percentage in two Lori-Bakhtiari and Zel breed (P < 0.05) [16].Also there was significant association
between genotypes of various transferrin proteins with Fat-tail weight, Hot carcass weight, Hot carcass weight
free fat-tail in the Makooei sheep breed [28].It has been reported that the relationship seen between band
patterns with tail length and tail down circumference was close to the significant level in fourth exon of growth
hormone gene in Kermanian sheep [9]. Also the statistical analysis were showed significant relationship
between the band patterns (exon 3 Ovine Leptin gene) with the tail, chest, abdomen and neck circumference
(p<0.05) and body length (p <0.01), in the Zel breed. Also in the Bakhtiari breed the patterns were associated
with Stature, gap tail length and middle and down tail width (p <0.05)
[10]. Also Statistical analysis showed significant association between band patterns (part of exon and intron 2
Leptin gene in fat-tailed Lori-Bakhtiari and tailed Zel breed) and hip circumference, tail length and blood
triglyceride in the Zel breed (P<0.05). But there were no significant association between observed bands and
measured traits in the Bakhtiari breed [10].Also Statistical analysis showed significant association between band
patterns 16–17 exon of DGAT1 gene in Lori-Bakhtiari sheep (LB) and Zel sheep (Z) breeds. At the DGAT1
locus, CC sheep showed the significantly greater fat-tail weight (P < 0.05) and backfat thickness (P < 0.01). The
results of this study demonstrate novel associations in which the C allele had a positive effect on fat-tail weight
and backfat thickness in fat-tailed sheep [17].
ACKNOWLEDGMENTS
We thank the Makooei Sheep Breeding Station (MSBS) staff for providing us the data used in this study.
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