The RN locus for meat quality maps to pig chromosome 15

Could the pale, soft, and exudative condition be explained by distinctive histological characteristics?1

Pork quality depends on various genetic and environmental factors. Despite the improvement of slaughter conditions, the PSE type is still one of the main concerns in this field. This study was conducted on nonstressed animals to evaluate the tissue characteristics of some muscles usually involved during stress compared with a reference muscle, the M. triceps brachii, which is actually not subject to stress-caused damages. Samples of M. triceps brachii, M. longissimus dorsi, M. biceps femoris, and M. semimembranosus were taken from pigs exhibiting 1 of the 3 HAL genotypes (NN, Nn, or nn) and 2 of the 3 RN genotypes (rn+rn+ or rn+RN-). Histoenzymology and immunohistochemistry were used to compare the fiber typing and capillary network in these muscles within these different stress susceptibility genotypes. In comparison with the reference muscle, M. triceps brachii, the combination of a high value of the number of type IIb fibers and a low vascular network showed a primary effect on muscles usually involved during stress. This led to the definition of a PSE index. A dramatic increase (P < 0.001) in this PSE index was systematically found in muscles usually involved in the PSE-type condition. These results show that distinctive histological characteristics were associated with the vulnerability of some muscles independently of the genotypes. Moreover, this study highlights the distinctive histological features of each genotype and is likely to suggest some interactions between them.

Cloning and analysis of differentially expressed ESTs in swine muscle tissue

The obvious difference in muscle growth and meat quality traits exists between Chinese indigenous pig and exotic pigs. In order to study the reason of these phenotypic differences and search the potential gene related to growth and meat quality traits, silver-stained mRNA differential display technique was used to detect the difference with mRNA of loin-eye muscle tissue from maturity pigs of Lantang in Guangdong Province and Large Yorkshire. One of the newly discovered expressed sequence tag (ESTsp3) was analyzed by using bioinformatic technique. The results showed: (1) nearly 2000 cDNA fragments were detected with 30 primer pairs, and 6 differentially expressed ESTs in the loin-eye muscle tissues from the two breeds were isolated and obtained. The differential fragments were cloned and sequenced. The all sequences were recorded in the GenBank. (2) The 786 bp fragment of ESTsp3 was obtained with in silico elongation system, the ORF analysis revealed that it existed as an 83 aa complete open reading frame, and the elongation sequences were verified by RT-PCR. The analysis of in silico expression profile showed that ESTsp3 is expressed in various growth stages and in most tissues and organs, such as soft tissue, skin, skeletal muscle and kidney, but with variant expression quantity.

Mapping of 22 expressed sequence tags isolated from a porcine small intestine cDNA library

Complementary DNA sequences were selected from a resource of tentatively identified clones from a porcine small intestine cDNA library. Forty PCR primer pairs were designed to amplify 101-309 base pairs of the 3' untranslated region of the genes. The PCR conditions were optimized by altering both formamide and magnesium concentrations on samples of pig, mouse, and hamster DNA. Twenty primer pairs that, under stringent conditions, were pig-specific and amplified the expected fragments were chosen for regional assignment in a pig/rodent hybrid cell panel. Furthermore, 22 primer pairs were chosen to amplify DNA from the parental animals of the PiGMaP shared reference families in order to detect possible polymorphisms. Primer pairs that generated polymorphisms were used for genetic mapping. A total of 22 porcine expressed sequence tags (ESTs) were cytogenetically or genetically mapped by this approach. Twelve of the mapped ESTs could be added to the human-porcine comparative map.

The Kiel RN experiment: final porcine chromosome 15 mapping results

SUMMARY

A marker experiment with pigs from commercially selected lines is described. One important goal of the experiment was to map the porcine RN locus, a major gene responsible for lowered terminal pH and increased glycogen level in muscle tissue. Experimental families comprised 15 Piétrain × Hampshire boars, of which 14 were heterozygous at the RN locus, 61 homozygous rn(+) /rn(+) sows (five Landrace, 12 Large White, and 44 Landrace × Large White crossbreds), and 509 progenies, 496 of them from heterozygous boars, in total 585 animals. Genotyping was done for seven chromosome 15 microsatellite loci: Sw919, Sw964, S0088, Sw120, Sw906, Sw936, and Sw312. Genotype assignment for the RN locus was based on musculus longissimus dorsi glycogen content. The heterozygosity of markers ranged from 0.47 to 1 in boars and from 0.71 to 0.88 in sows. RN was mapped to the centre of an interval, flanked by Sw120 and the marker pair Sw906/Sw936. Male multipoint distances between RN and Sw120, Sw906, and Sw936 were estimated as 5 cM, 5 cM, and 6.9 cM, respectively. Two-point recombination rates between these markers and RN were 0.05 in all cases, with corresponding lod scores of 52.09, 29.30, and 42.53. Concordances and disconcordances of mapping results in the RN region from different studies are discussed. The male map length of the chromosome region covered was 68.8 cM, in contrast to the female map length of 124.7 cM. Significant differences in recombination rates between sexes were found in intervals Sw919-Sw964, Sw964-S0088, and Sw936-Sw312, but not in the neighbourhood of the RN gene. ZUSAMMENFASSUNG: Es wird ein Kartierungsexperiment mit Schweinen aus kommerziell genutzten Linien beschrieben. Vordringliches Ziel dieses Experimentes war es, das RN-Gen zu kartieren, das für einen erniedrigten End-pH-Wert und einen erhöhten Glykogengehalt im Musklegewebe verantwortlich ist. Die Daten stammen von 15 Hampshire × Piétrain Ebern, von denen 14 am RN Locus heterozygot waren, 61 homozygoten rn(+) /rn(+) Sauen (5 Landrasse-, 12 Large White und 44 Landrasse × Large White Kreuzungssauen) sowie 509 Nachkommen, 496 davon von heterozygoten Ebern, insgesamt also 585 Tiere. Für sieben Mikrosatellitenmarker auf Chromosom 15 wurden die Tiere typisiert: Sw919, Sw964, S0088, Sw120, Sw906 und Sw312. Die Bestimmung der Genotypen am RN-locus erfolgte anhand des Glykogenghalts im Musculus longissimus dorsi. Der Heterozygotiegrad der Marker lag zwischen 0, 47 und 1 bei Ebern und zwischen 0, 71 und 0, 88 bei den Sauen. Als Position des RN-Gens wurde die Mitte eines Intervalles bestimmt, der von dem Marker Sw120 sowie dem Markerpaar Sw906/Sw936 begrenzt wird. Für das männliche Geschlect wurden die Kartenabstände zwischen RN und Sw120, Sw906 und Sw936 in einer Mehrpunktanalyse auf 5 cM, 5 cM und 6, 9 cM geschätzt. Paarweise Schätzungen der Rekombinationsraten zwischen diesen Markern und RN betrugen in allen Fällen 0, 5, mit zugehörigen lod scores vol 52, 09, 29, 30 und 42, 53. übereinstimmungen und Diskrepanzen zwischen Kartierungsergebnissen verschiedener Arbeitsgruppen werden diskutiert. Die Kartenlänge des mit Markern abgedeckten Teils von Chromsom 15 betrug beim männlichen Geschlecht 68, 8 cM, im Gegensatz zu einer Länge von 124, 7 cM beim weiblichen Geschlecht. Signifikante Unterschiede in den Rekombinationsraten beider Geschlechter wurden in den Intervallen Sw919-Sw964, Sw964-S0088 und Sw936-Sw312 gefunden, nicht jedoch in der Umgebung des RN-Genes.

Livestock genomics comes of age

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Accurate mapping of the "acid meat" RN gene on genetic and physical maps of pig chromosome 15

It has been shown that a major gene, called RN, is responsible for the RTN technological yield, a meat quality porcine trait. Experimental families informative for the segregation of RN gene were constituted from animals belonging to the Laconie composite line. We have previously mapped the RN gene to Chromosome (Chr) 15 (Milan et al. Genet. Sel. Evol. 27, 195-199, 1995). A Chr 15 map was established with 16 markers. The RN gene was found to be located between markers Sw120 and Sw936, at 2 cM from Sw936 (LOD = 38.1). In addition, by localizing Sw936 at 15q21-22 using DISC-PCR, we also located RN on the physical map.

A major locus (RN) affecting muscle glycogen content is located on pig chromosome 15

The RN locus in pigs has a major effect on the amount of stored glycogen in white muscle and affects meat quality. The fully dominant RN- allele, associated with high glycogen content, occurs in the Hampshire breed. We have mapped the RN locus using a large half-sib family comprising one heterozygous RN-/rn+ Hampshire boar mated to homozygous rn+/rn+ Swedish Landrace x Swedish Yorkshire sows. The segregation at the RN locus was inferred from data on glycolytic potential and residual glycogen in white muscle which both showed clear bimodal distributions. Highly significant evidence for genetic linkage was obtained against microsatellite markers on Chromosome (Chr) 15. Multipoint analysis revealed the order Sw1111-8.0-S0088-10.6-RN-4.8-Sw936,Sw906 (recombination estimates are given as Kosambi cM). Comparative mapping data imply that the human homolog of RN is located on Chr 2q.