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Abstract The objective of this study was to search for polymorphisms in the coding region of the estrogen receptors 1 and 2 (ESR1 and ESR2 )and to analyze the effects of these variants and the well known intronic ESR1 Pvu II polymorphism on litter size in a Chinese-European pig line. We identified five silent single nucleotide polymorphisms (SNP) in the ESR1 cDNA: c.669T > C (exon 3), c.1227C > T (exon 5), c.1452C > T (exon 7), c.1665T > C and c.1755A > G (exon 8). One pair of these SNP (c.1665T > C and c.1755A > G) co-segregated in the analyzed line, and the SNP c.669T > C showed the same segregation pattern as the Pvu II polymorphism. These polymorphisms were tested in this study, although the c.1452C > T SNP within exon 7 was not analyzed due to its low informativeness. In the ESR2 cDNA, one missense SNP was found within exon 5, which caused an amino acid substitution in the coded protein: "c.949G > A (p.Val317Met)" and was tested on sow litter size. Information on 1622 litter records from 408 genotyped sows was analyzed to determine whether these SNP influenced the total number of piglets born (TNB) or the number of born alive (NBA). The polymorphisms ESR1: [Pvu II; c.669T > C], ESR1: [c.1665T > C; c.1755A > G] and ESR2: c.949G > A showed no statistically significant association with litter size. However, the ESR1: c.1227T allele was significantly associated with TNB. The additive substitution effect was estimated to be 0.40 piglets born per litter (P < 0.03), and no dominance effects were observed. This SNP could be useful in assisted selection for litter size in some pig lines, as a new genetic marker in linkage disequilibrium with the causative mutation.

Abstract One QTL affecting backfat thickness (BF), intramuscular fat content (IMF) and eye muscle area (MA) was previously localized on porcine chromosome 6 in an F2 cross between Iberian and Landrace pigs. This work was done to study the effect of two positional candidate genes on these traits: H-FABP and LEPR genes. The QTL mapping analysis was repeated with a regression method using genotypes for seven microsatellites and two PCR-RFLPs in the H-FABP and LEPR genes. H-FABP and LEPR genes were located at 85.4 and 107 cM respectively, by linkage analysis. The effects of the candidate gene polymorphisms were analyzed in two ways. When an animal model was fitted, both genes showed significant effects on fatness traits, the H-FABP polymorphism showed significant effects on IMF and MA, and the LEPR polymorphism on BF and IMF. But when the candidate gene effect was included in a QTL regression analysis these associations were not observed, suggesting that they must not be the causal mutations responsible for the effects found. Differences in the results of both analyses showed the inadequacy of the animal model approach for the evaluation of positional candidate genes in populations with linkage disequilibrium, when the probabilities of the parental origin of the QTL alleles are not included in the model.

Abstract Background Unique structural characteristics of centromere chromatin enable it to support assembly of the kinetochore and its associated tensions. The histone H3 variant CENH3 (centromeric histone H3) is viewed as the key element of centromere chromatin and its interaction with centromere DNA is epigenetic in that its localization to centromeres is not sequence-dependent. Results In order to investigate what influence the DNA sequence exerts on CENH3 chromatin structure, we examined CENH3 nucleosome footprints on maize centromere DNA. We found a predominant average nucleosome spacing pattern of roughly 190-bp intervals, which was also the dominant arrangement for nucleosomes genome-wide. For CENH3-containing nucleosomes, distinct modes of nucleosome positioning were evident within that general spacing constraint. Over arrays of the major ~156-bp centromeric satellite sequence (tandem repeat) CentC, nucleosomes were not positioned in register with CentC monomers but in conformity with a striking ~10-bp periodicity of AA/TT dimers within the sequence. In contrast, nucleosomes on a class of centromeric retrotransposon (CRM2) lacked a detectable AA/TT periodicity but exhibited tightly phased positioning. Conclusions These data support a model in which general chromatin factors independent of both DNA sequence and CENH3 enforce roughly uniform centromeric nucleosome spacing while allowing flexibility in the mode in which nucleosomes are positioned. In the case of tandem repeat DNA, the natural bending effects related to AA/TT periodicity produce an energetically-favourable arrangement consistent with conformationally rigid nucleosomes and stable chromatin at centromeres.

Abstract Background The aim of this work was to study the effects on litter size of variants of the porcine genes RBP4, ESR1 and IGF2, currently used in genetic tests for different purposes. Moreover, we investigated a possible effect of the interaction between RBP4-MspI and ESR1-PvuII polymorphisms. The IGF2-intron3-G3072A polymorphism is actually used to select lean growth, but other possible effects of this polymorphism on reproductive traits need to be evaluated. Methods Detection of polymorphisms in the genomic and cDNA sequences of RBP4 gene was carried out. RBP4-MspI and IGF2-intron3-G3072A were genotyped in a hyperprolific Chinese-European line (Tai-Zumu) and three new RBP4 polymorphisms were genotyped in different pig breeds. A bivariate animal model was implemented in association analyses considering the number of piglets born alive at early (NBA12) and later parities (NBA3+ ) as different traits. A joint analysis of RBP4-MspI and ESR1-PvuII was performed to test their possible interaction. In the IGF2 analysis, paternal or maternal imprinting effects were also considered. Results Four different RBP4 haplotypes were detected (TGAC, GGAG, GAAG and GATG) in different pig breeds and wild boars. A significant interaction effect between RBP4-MspI and ESR1-PvuII polymorphisms of 0.61 ± 0.29 piglets was detected on NBA3+. The IGF2 analysis revealed a significant increase on NBA3+ of 0.74 ± 0.37 piglets for the paternally inherited allele A. Conclusions All the analyzed pig and wild boar populations shared one of the four detected RBP4 haplotypes. This suggests an ancestral origin of the quoted haplotype. The joint use of RBP4-MspI and ESR1-PvuII polymorphisms could be implemented to select for higher prolificacy in the Tai-Zumu line. In this population, the paternal allele IGF2-intron3-3072A increased litter size from the third parity. The non-additive effects on litter size reported here should be tested before implementation in other pig breeding schemes.

Abstract Background Prolificacy is the most important trait influencing the reproductive efficiency of pig production systems. The low heritability and sex-limited expression of prolificacy have hindered to some extent the improvement of this trait through artificial selection. Moreover, the relative contributions of additive, dominant and epistatic QTL to the genetic variance of pig prolificacy remain to be defined. In this work, we have undertaken this issue by performing one-dimensional and bi-dimensional genome scans for number of piglets born alive (NBA) and total number of piglets born (TNB) in a three generation Iberian by Meishan F2 intercross. Results The one-dimensional genome scan for NBA and TNB revealed the existence of two genome-wide highly significant QTL located on SSC13 (P < 0.001) and SSC17 (P < 0.01) with effects on both traits. This relative paucity of significant results contrasted very strongly with the wide array of highly significant epistatic QTL that emerged in the bi-dimensional genome-wide scan analysis. As much as 18 epistatic QTL were found for NBA (four at P < 0.01 and five at P < 0.05) and TNB (three at P < 0.01 and six at P < 0.05), respectively. These epistatic QTL were distributed in multiple genomic regions, which covered 13 of the 18 pig autosomes, and they had small individual effects that ranged between 3 to 4% of the phenotypic variance. Different patterns of interactions (a × a, a × d, d × a and d × d) were found amongst the epistatic QTL pairs identified in the current work. Conclusions The complex inheritance of prolificacy traits in pigs has been evidenced by identifying multiple additive (SSC13 and SSC17), dominant and epistatic QTL in an Iberian × Meishan F2 intercross. Our results demonstrate that a significant fraction of the phenotypic variance of swine prolificacy traits can be attributed to first-order gene-by-gene interactions emphasizing that the phenotypic effects of alleles might be strongly modulated by the genetic background where they segregate.