Variants in GBP1 and GBP5 associated with PRRS resistance in Uruguayan Creole pigs / Montenegro et al. ________________________
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INTRODUCTION
The porcine reproductive and respiratory syndrome (PRRS) is a
viral disease that causes reproductive and respiratory complications
in pigs (Sus scrofa ferus), signicantly impacting animal welfare and
resulting in considerable economic losses globally within the swine
industry. Reproductive consequences include spontaneous abortions
in females, premature births, and a decline in the quality of semen
from boars. Meanwhile, respiratory issues reduce the growth rate of
pigs throughout the fattening stage [1, 2].
The causative agent of this disease is the PRRS virus (PRRSV),
which is a single–stranded positive–sense RNA virus belonging to
the Betaarterivirus genus and the Arteriviridae family. This virus is
classied into two genotypes: PRRSV–1 (European) and PRRSV–2
(North American) [3, 4].
Transmission of PRRSV can occur through direct or indirect
contact, primarily via respiratory or oral routes, penetrating mucous
membranes or even percutaneously. The virus can be transmitted
airborne, during mating or insemination, through ingestion, contact, or
inoculation [5]. During gestation, the virus has the ability to cross the
placental barrier and infect embryos, potentially leading to the most
severe clinical manifestation of the disease at the end of gestation.
This is characterized by abortions, premature births, mummication,
and the birth of weak and congenitally infected piglets, leading to
high mortality before weaning [6].
PRRSV control involves several key aspects, including early
diagnosis, continuous monitoring, implementation of biosecurity
measures, and proper herd management and vaccination [5].
Currently, there is no fully effective vaccine against PRRSV due to
the virus’s genetic and antigenic variations, as well as its ability to
evade the host immune response. Therefore, it is crucial to explore
alternative control strategies, with genetic improvement of pigs
being one option [7, 8]. In this regard, different pig breeds exhibit
varying levels of resistance to PRRSV, emphasizing the importance
of studying genetic factors to enhance pig resistance to this disease.
Such efforts would contribute to animal welfare and mitigate the
associated economic losses [4, 9].
Through genome–wide association studies, a quantitative trait
locus (QTL) has been identied on chromosome 4 (SSC4), associated
with host resistance to PRRSV, weight gain, and viral load [10]. Within
the single nucleotide polymorphisms (SNPs) identied in this region,
rs80800372 (known as WUR) occurs in the GBP1 gene, and rs340943904
in the GBP5 gene [11, 12]. Since the identication of this QTL, the
effect of the WUR variant has been associated with increased weight
and viral load following PRRS infection [10]. Additionally, it has been
linked to the host response to PRRSV infection, PRRS vaccination, and
coinfection with PRRSV and porcine circovirus type 2b [13]. Subsequent
research by Koltes et al. [12] revealed that the candidate gene is the
one encoding guanylate–binding protein 5 (GBP5), located in the region
surrounding WUR.
The rs80800372 variant in GBP1 corresponds to an A/G mutation in
the 3’ untranslated region (3’UTR), with G being the favorable allele,
while rs340943904 in GBP5 is a G/T variant at a splice site, with the
T allele being favorable [14].
PRRS was rst identied in the late 1980s in North America and
Europe [15]. In South America, PRRSV has been reported in Bolivia,
Chile, Colombia, Peru, Venezuela, Ecuador and Uruguay [16]. In Uruguay,
the rst detection of the virus was carried out by Ramos et al. [17],
identifying the circulation of PRRSV type 2. This study included a
retrospective serological analysis suggesting that the virus may have
been present in the country since 2011.
Pig production in Uruguay, while economically less signicant,
plays a crucial role in supporting low–income producers [18]. In this
context, local zoogenetic resources become more important due
to their better adaptation to local conditions and their production
capacity with lower requirements. These animals are commonly
utilized in small–scale traditional subsistence systems, playing a
fundamental role in ensuring food security [19]. In Uruguay, the Pampa
Rocha breed represents the only creole pig breed [20]. These pigs
stand out for the qualities of their females, including characteristics
such as prolicacy, ability to consume pastures, milk production, and
productive longevity [21]. However, the current number of animals of
this breed is unknown, posing a risk to their conservation.
To date, no studies have been conducted in Uruguay evaluating the
genetic resistance/susceptibility to PRRSV in Pampa Rocha creole
pigs. Based on this gap, the objective is to determine the genotypes
for the variants rs80800372 (in GBP1) and rs340943904 (in GBP5)
in this local pig breed in Uruguay. This preliminary investigation is
relevant for enhancing the understanding of the genetic variability
present in Pampa Rocha pigs and contributing to their conservation.
MATERIALS AND METHODS
Twenty DNA samples from pigs were utilized in this study, including
14 Pampa Rocha, three Pampa Rocha–Duroc hybrids, one Large White,
one Duroc, and one Pietrain. These samples are part of the DNA bank
at the Academic Unit of Animal Genetics and Improvement within
the Faculty of Veterinary Medicine at the University of the Republic
(Udelar) in Montevideo, Uruguay. These animals come from a rescue
center for the conservation of the breed.
Genotypes were determined using the end–point PCR technique,
followed by Sanger sequencing [22]. Specic primers were designed
using the Primer BLAST tool [23].
Amplication was performed using a Multigene II equipment (Labnet
International, Inc. USA). TABLE I provides details of the primers used and
the amplication conditions for the regions containing both variants.
The amplification results were analyzed using agarose gel
electrophoresis (1% agarose gel stained with Goodview Nucleic Acid
Stain) in 1× TBE buffer. Electrophoresis was conducted using an HU13
MIDI Horizontal Gel electrophoresis system (Scie–plas, Great Britain)
and a POWER PAC 3000 power supply (Bio–Rad, USA). The resulting
bands were visualized under UV light using a BIOSENS SC805–BIOTOP
instrument (Shanghai Bio–Tech Co. Ltd. China). Amplicon sequencing
was performed in a sequencer ABI 3500 (Thermosher, USA) by the
company Genexa (Montevideo, Uruguay). Sequence analysis and
determination of genotypes for the studied variants were carried
out through alignment using the BioEdit program [24]. Reference
sequences for porcine GBP1 and GBP5 genes were retrieved from the
Ensembl database (ensembl.org). Allelic and genotypic frequencies, as
well as the calculation of Fis values according to Weir and Cockerham
[25], were determined using the GENETIX V 4.05 program [26]. The
Hardy–Weinberg exact test was performed for each locus using the
Genepop version 4.7.5 web tool [27, 28]. Finally, linkage disequilibrium
between the variants was determined according to Black and Krafsur
[29] in the GENETIX V 4.05 program [26].