PvuII polymorphisms at the porcine oestrogen receptor locus (ESR)

Diversity across major and candidate genes in European local pig breeds

The aim of this work was to analyse the distribution of causal and candidate mutations associated to relevant productive traits in twenty local European pig breeds. Also, the potential of the SNP panel employed for elucidating the genetic structure and relationships among breeds was evaluated. Most relevant genes and mutations associated with pig morphological, productive, meat quality, reproductive and disease resistance traits were prioritized and analyzed in a maximum of 47 blood samples from each of the breeds (Alentejana, Apulo-Calabrese, Basque, Bísara, Majorcan Black, Black Slavonian (Crna slavonska), Casertana, Cinta Senese, Gascon, Iberian, Krškopolje (Krškopoljski), Lithuanian indigenous wattle, Lithuanian White Old Type, Mora Romagnola, Moravka, Nero Siciliano, Sarda, Schwäbisch-Hällisches Schwein (Swabian Hall pig), Swallow-Bellied Mangalitsa and Turopolje). We successfully analyzed allelic variation in 39 polymorphisms, located in 33 candidate genes. Results provide relevant information regarding genetic diversity and segregation of SNPs associated to production and quality traits. Coat color and morphological trait-genes that show low level of segregation, and fixed SNPs may be useful for traceability. On the other hand, we detected SNPs which may be useful for association studies as well as breeding programs. For instance, we observed predominance of alleles that might be unfavorable for disease resistance and boar taint in most breeds and segregation of many alleles involved in meat quality, fatness and growth traits. Overall, these findings provide a detailed catalogue of segregating candidate SNPs in 20 European local pig breeds that may be useful for traceability purposes, for association studies and for breeding schemes. Population genetic analyses based on these candidate genes are able to uncover some clues regarding the hidden genetic substructure of these populations, as the extreme genetic closeness between Iberian and Alentejana breeds and an uneven admixture of the breeds studied. The results are in agreement with available knowledge regarding breed history and management, although largest panels of neutral markers should be employed to get a deeper understanding of the population's structure and relationships.

yellow0, a marker for low body weight in Drosophila melanogaster

Marker-assisted selection (MAS) is an important modern breeding technique, but it has been found that the effect of the markers for quantitative trait loci (QTL) is inconsistent, leading in some cases to MAS failure and raising doubts about its effectiveness. Here the model organism Drosophila melanogaster was employed to study whether an effective marker could be found and applied to MAS. We crossed the stock carrying the y (0) marker (a recessive mutation allele of the yellow gene on the X chromosome) with three other stocks carrying corresponding wild-type markers in an F2 design, and found that the y (0) marker was in significant association with low body weight (P<0.001). This association was consistent across different backgrounds and the marker effects in female and male were approximately 0.95 sigma (P) (phenotypic standard deviation) and 0.68 sigma (P), respectively. We next introgressed a fragment via the y (0) marker into a wild stock background over 20 generations of marker-assisted introgression (MAI), and constructed the introgression stock y (0)(OR)20 in which body weight decreased by 13% and 7%, in female and male, respectively, compared to the wild stock (P<0.0001). This indicated that there must be a single QTL for low body weight that is tightly linked to the y (0) marker. We then shortened the introgressed fragment to less than 1.5 cM by a deeper MAI using the y (0) marker and the white marker. This narrower fragment also resulted in a similar decrease in body weight to that induced by y (0)(OR)20, indicating that the QTL for low body weight is located within this less-than-1.5 cM interval. Molecular characteristics of the y (0) marker by PCR amplification and Southern blotting revealed that yellow gene was deficient in the y (0) stock, leading to disappearance of melanin from the cuticle and probably influencing the developmental process. The above results confirmed the existence of effective QTL markers applicable to MAS breeding schemes, and their potential application in breeding new stocks.

Genetic selection of boars

Selection of boars by visual appraisal is the simplest and oldest method used by the swine industry. However, individual performance testing, and later use of computers to incorporate relatives' data and account for environmental variation, resulted in greater rate of improvement for economically important traits. Examples of molecular genetic tools that have increased improvement for some traits are also discussed. Accurate identification of genetic merit is increasingly important with widespread use of AI and resultant greater progeny number per sire. Historically, selection was to produce desirable progeny; however, with the majority of boars now housed in dedicated boar facilities, and the efficiency of sperm production being recorded, boar stud personnel are increasingly interested in selection of boars for fertility traits. Selecting boars that are lean and heavily muscled and have good semen parameters may be problematic, given the genetic relationships among the traits. Whereas conventional animal breeding methods will remain important, use of molecular tools will increase, and identification of a boar's fertility potential at birth will allow earlier and more efficient selection of high-fertility boars. Ability to achieve acceptable female reproduction with frozen semen would facilitate selection for longevity. However, this would lengthen the generation interval and could dilute selection intensity for other traits, as it requires indirect selection for semen freezability.

The FUT1 and ESR genes--their variability and associations with reproduction in Prestice Black-Pied sows

The determination of genetic variability by means of molecular genetic markers FUT1 and ESR2, and the evaluation of their associations with reproduction traits in population of Prestice Black-Pied sows have been implemented. A lower frequency of the allele FUT1A than the frequency of the allele FUT1G in the FUT1 gene was ascertained. In the ESR2 polymorphism, a higher frequency of the allele ESR2A compared with the allele ESR2B was determined. In the second to sixth litters as well as in the first to sixth litters, a significantly lower number of piglets born alive and number of weaned piglets from sows of the FUT1/IFUT1A genotype was found. Moreover, the homozygotes FUT1G /FUT1G significantly exceeded sows of the FUT1A/FUT1A genotype in the total number of born piglets in the first to sixth litters. No significant effect of the ESR2 polymorphism on reproduction was observed.

A dynamic model for ovulation rate reveals an effect of the estrogen receptor genotype on ovarian follicular development in the pig

A mathematical model that describes the recruitment and growth of ovarian follicles was fitted to data on ovulation rate and the measurements of plasma estradiol collected at times during the estrous cycle for individual gilts. The method of least squares was used to obtain estimates of the parameters of the mathematical model. The estimated model parameters were the maximum estradiol production for a follicle, development of each follicle after commitment, and a function describing the initial estradiol production of committed follicles. The estimated parameters for each pig were classified by estrogen receptor (ER) genotype (AA or BB) and analyzed using a multivariate analysis of variance. There were differences between genotypes (P < 0.05) for the parameter that described the initial distribution of individual follicles at recruitment. Gilts with ER genotype BB recruited follicles that varied more in size but had fewer very small follicles, indicating that the ER gene affects the relative estradiol secretion of the follicles at commitment. This analysis is an example of a general approach to genetic studies that uses a mathematical model of the physiology as a statistical basis for estimating gene action.

Impact of theESRgene on litter size and production traits in Czech Large White pigs

To evaluate the effect of the PvuII polymorphism of the oestrogen receptor gene on litter size and production traits in Czech Large White swine, data from 1250 sows and 3600 litters were analysed with two four-trait animal models. The traits in the first model were number of piglets born alive in a sow's first litter, number of piglets born alive in second and subsequent litters, lifetime daily gain and lean meat percentage. The second model included number of piglets born, number of piglets born alive, number of piglets weaned and litter weight at weaning from first and subsequent litters. The oestrogen receptor (ESR) locus significantly affected prolicacy in the first parity and averaged over all parities (P < 0.05), with allele A superior to allele B. In the first parity, AA sows produced approximately 0.5 more live piglets per litter than BB sows. Averaged over all parities, this difference was c. 0.25 piglets. Results for total number of piglets born and number of piglets weaned were similar to results for numbers born alive. No significant dominance effect was found for prolificacy traits. For litter weight at weaning, no significant additive effect was observed at the ESR locus, but a significant negative dominance effect (-1.5 kg) was estimated averaged across parities (litters of AB sows were similar to litters of BB sows for this trait). No pleiotropic effect of the ESR polymorphism on average daily gain or lean meat percentage was found.

Piglet and placental traits at term in relation to the estrogen receptor genotype in gilts

Liveborn piglets from gilts with estrogen receptor (ESR) genotype AA (95 AA-AA and 91 AA-AB piglets), AB (88 AB-AA, 118 AB-AB, and 37 AB-BB piglets), and BB (97 BB-AB and 89 BB-BB piglets) were compared after farrowing, to examine whether piglet ESR genotype (ESRp) nested within maternal ESR genotype (ESRm) affected placental traits at term, piglet birth weight, and growth until weaning. Furthermore, the relation of birth weight to various placental traits and the relations between placental traits were evaluated relative to ESR genotype. For this study, 62 Large White x Meishan F2 crossbred gilts (18 AA, 24 AB, and 20 BB) were used. The gilts belonged to a population in which the A allele is favorable for litter size. ESRp nested within ESRm did not affect placental length, weight, surface area and number of areolae. ESRp nested within ESRm affected amnion weight (AA-AA amnions were heavier than AA-AB, AB-AA and BB-AB amnions), placental weight after including placental surface area in the model (AA-AB placentae were lighter than AA-AA, AB-BB and BB-AB placentae), placental efficiency calculated as birth weight divided by placental weight (AB-AA placentae were less efficient than AA-AB placentae), and the relations of birth weight to placental weight and birth weight to number of areolae. The found differences imply an interaction of maternal and fetal ESR genotype on placental traits (especially weight and number of areolae) during fetal development. Furthermore, the found effects on placental and amnion weight might be the result of a difference in thickness or vascularization or both. The favorable ESR allele for litter size, i.e. the A allele, appears to be the unfavorable allele for pre-weaning piglet growth. Therefore, further research on ESR in relation to vascularization, weight and thickness of placentae. uterine size, endometrial gland development, and piglet growth is recommended.

The effect of estrogen receptor genotype on litter size and placental traits at term in F2 crossbred gilts

The effect of estrogen receptor (ESR) genotype (two alleles, A and B) on litter size of 275 Large White x Meishan F2 crossbred gilts (73 AA, 126 AB and 76 BB gilts) was tested. In addition, for 63 of these gilts (18 AA, 24 AB, and 21 BB) the effect of ESR genotype on average placental traits at term was tested, since individual placental information was available for 88% of the 628 liveborn piglets. Without affecting average birth weight of the piglets, ESR genotype significantly affected litter size, i.e. AB gilts had larger litters than BB gilts (P < 0.05). Total number born was 11.38+/-0.38, 11.88+/-0.28, and 10.68+/-0.35, while number born alive was 10.45+/-0.39, 11.07+/-0.29, and 9.85+/-0.36 for AA, AB and BB gilts, respectively. Since the B allele in previous research was associated with largest litters, the hypothesis that ESR is a marker rather than the major gene itself is discussed. Average placental length, surface area, and weight including and excluding amnion were not affected by ESR genotype. However, placentae of AB gilts had a significantly lower number of areolae per placenta than BB gilts and had a lower number of areolae/cm2 placenta than AA and BB gilts. Number of areolae was 8945+/-663, 7240+/-619, and 9694+/-633, for AA, AB and BB gilts, respectively. Although the reason for the low number of areolae on placentae in AB gilts is not yet known, the results suggest that the ESR linked major gene for litter size might be involved in the development and activity of endometrial glands.

Fetal and placental traits at day 35 of pregnancy in relation to the estrogen receptor genotype in pigs

Fetuses from gilts with estrogen receptor (ESR) genotype AA (AA-AA and AA-AB) and BB (BB-AB and BB-BB) were compared at Day 35/36 of pregnancy, to examine whether fetal ESR genotype nested within maternal ESR genotype would affect fetal traits. Furthermore the relation of fetal body weight and fetal heart weight to various placental traits were evaluated relative to ESR genotype. Fetal and placental weight and length, and implantation surface area were not affected by fetal ESR genotype nested within maternal ESR genotype. Fetal weight was related similarly to placental length, placental weight, and implantation surface area: up to a certain threshold value (40 cm, 40 g and 250 cm2, respectively), an increase in the trait was associated with an increase of fetal weight. Thereafter, fetal weight did not change anymore. Thus, at Day 35/36 of pregnancy porcine fetuses seem to have a maximum growth potential. The percentage of AA-AA fetuses that had not reached this maximum growth potential was larger than of the other three genotype combinations studied, and therefore a higher subsequent fetal mortality may be expected in this group. Hearts of AA-AB fetuses were significantly heavier than those of BB-AB and BB-BB fetuses and tended to be heavier than those of AA-AA fetuses. The reason for this hypertrophy is unclear, but might be related to a difference in placental vascularity. Heart weight of fetuses from BB gilts increased with fetal weight, while heart weights of fetuses from AA gilts did not. Heart weight increased with an increase of placental length and implantation surface area up to 51 cm and 437 cm2, respectively, and thereafter decreased again. For BB-AB fetuses a similar relation was found between heart weight and placental weight, while heart weight of the other three genotype combinations remained unaffected as placental weight increased. The fetus and placenta are continuously changing during early pregnancy, therefore different mechanisms may change the demands for cardiac output. However, keeping in mind that placental size and blood volume are relatively large, placental vascularity and vascular development may play a major role. Therefore, further research on heart size, placental size and vascularity, relative to ESR genotype, is recommended.

Periovulatory hormone profiles and components of litter size in gilts with different estrogen receptor (ESR) genotypes

Estrus, endocrine changes during the periovulatory period, and components of litter size at Day 35/36 of pregnancy were studied in gilts with estrogen receptor genotype AA (AA gilts) or BB (BB gilts), in which the B allele is associated with a larger litter size. Neither estrus length nor estrous cycle length was affected by estrogen receptor genotype. No differences in periovulatory plasma LH, estrogen or progesterone profiles between the AA and BB gilts were detected. Furthermore, temporal aspects of these profiles were not different for both genotypes. Although the B allele is associated with a larger litter size, no differences in number of corpora lutea or number and percentage of vital Day 35/36 embryos were found in this study. This indicates that the difference in litter size is not due to differences in oocyte maturation, fertilization, implantation or embryonic survival, but is likely caused by a difference in fetal survival. Thus, uterine capacity might be different for both genotypes. The available uterine space per embryo seems to be the same for both genotypes, as is endometrial folding of uterine surface area. However, a difference in placental size was found. Embryos of BB gilts had significantly longer placentae than embryos of AA gilts. These results suggest a higher chance for placental insufficiency in AA gilts, leading to the expected higher fetal mortality compared with the BB gilts. The difference in placental size might have been related to a difference in the timing of embryonic mortality.

The estrogen receptor locus is associated with a major gene influencing litter size in pigs

Identification of individual major genes affecting quantitative traits in livestock species has been limited to date. By using a candidate gene approach and a divergent breed cross involving the Chinese Meishan pig, we have shown that a specific allele of the estrogen receptor (ER) locus is associated with increased litter size. Female pigs from synthetic lines with a 50% Meishan background that were homozygous for this beneficial allele produced 2.3 more pigs in first parities and 1.5 more pigs averaged over all parities than females from the same synthetic lines and homozygous for the undesirable allele. This beneficial ER allele was also found in pigs with Large White breed ancestory. Analysis of females with Large White breed background showed an advantage for females homozygous for the beneficial allele as compared to females homozygous for the other allele of more than 1 total pig born. Analyses of growth performance test records detected no significant unfavorable associations of the beneficial allele with growth and developmental traits. Mapping of the ER gene demonstrated that the closest known genes or markers were 3 centimorgans from ER. To our knowledge, one of these, superoxide dismutase gene (SOD2), was mapped for the first time in the pig. Analysis of ER and these linked markers indicated that ER is the best predictor of litter size differences. Introgression of the beneficial allele into commercial pig breeding lines, in which the allele was not present, and marker-assisted selection for the beneficial allele in lines with Meishan and Large White background have begun.

The PiGMaP consortium linkage map of the pig (Sus scrofa)

A linkage map of the porcine genome has been developed by segregation analysis of 239 genetic markers. Eighty-one of these markers correspond to known genes. Linkage groups have been assigned to all 18 autosomes plus the X Chromosome (Chr). As 69 of the markers on the linkage map have also been mapped physically (by others), there is significant integration of linkage and physical map data. Six informative markers failed to show linkage to these maps. As in other species, the genetic map of the heterogametic sex (male) was significantly shorter (approximately 16.5 Morgans) than the genetic map of the homogametic sex (female) (approximately 21.5 Morgans). The sex-averaged genetic map of the pig was estimated to be approximately 18 Morgans in length. Mapping information for 61 Type I loci (genes) enhances the contribution of the pig gene map to comparative gene mapping. Because the linkage map incorporates both highly polymorphic Type II loci, predominantly microsatellites, and Type I loci, it will be useful both for large experiments to map quantitative trait loci and for the subsequent isolation of trait genes following a comparative and candidate gene approach.