Swine MHC, also termed swine leukocyte antigen (SLA), was discovered by Vaiman in 1970 (3). The SLA cluster of genes is divided Wnt activity into three groups of linked genes: SLA class I (SLA-I), SLA class II (SLA-II) and SLA class III (SLA-III). SLA-I has three functional loci: SLA-1, SLA-2 and SLA-3 (4,5). Among these, the SLA-2 locus is easily distinguished
from SLA-1 and SLA-3 by the longer signal peptide than the others. A further dissimilarity to the SLA-1 and SLA-3 loci is in three amino acid residues at the start of the signal peptide (6). The SLA-2 locus might have a more crucial role as an SLA-I molecule (the roles of which include binding and presenting antigen molecules) because it is more polymorphic than the other two SLA-I loci (5,7,8). The Hebao pig is a unique breed reared in China. To study its genetic characteristics, a cloning scheme for Hebao pig SLA-2 was designed and its molecular evolution was analyzed. Hebao pigs were bred on a farm belonging to the Institute of Animal Husbandry of Liaoning Province in China. Fresh spleen tissues were removed from four
pigs for analysis. pMD18-T easy vector, Escherichia coli JM109, avian myeloblastosis virus (AMV) reverse transcriptase, isopropyl β-D-1-thiogalactopyranoside (IPTG), 5-bromo-4-chloro-3-indolyl β-D-galactopyranoside (X-gal), T4 DNA Ligase and EcoR I restriction endonuclease were purchased from Takara Biotechnology
(Dalian, China). The TRIzol Total RNA Extraction Kit was purchased from www.selleckchem.com/products/pci-32765.html Invitrogen (Carlsbad, CA, USA). The GeneClean kit was purchased from BIO 101 (Vista, CA, USA). To amplify the SLA-2 gene from Hebao pig, a pair of primers was used as follows: S1, 5’-AGATGCGGGTCAGGGGCCCTCAAG-3’ (located at sites 24–47 in AF464049); S2, 5’ -CAGTCCCCACAAGGCAGCTGTCTC-3’. (complementary at sites 1119–1142 in AF464049), then, spleens were removed from four slaughtered Hebao pigs. One hundred milligrams of tissue was cut into Dolutegravir pieces and placed in 1.5-mL Eppendorf tubes to which was added 300 μL TRIzol reagent (Invitrogen). Total RNA was extracted from spleen tissues using TRIzol reagent per the manufacturer’s recommendations and the isolated RNA samples were stored at –80° until use for RT-PCR. RT-PCR was carried out according to Gao et al. (9). The PCR products were stored at –20°C for gene cloning. The PCR products were separated on a 1% agarose gel by 1× Tris-acetate-EDTA running buffer electrophoresis. The separated DNA was purified using a DNA recovery kit, and then the purified DNA was ligated to pMD 18-T easy vector according to the manufacturer’s recommendations. The mixture was incubated at 4°C overnight, and then transformed into competent E. coli JM109 coated on LB plates containing ampicillin (100 μg/mL), IPTG (40 μg/mL) and X-gal (200 μg/mL).