Differential Gene Expression in Ovaries of Pregnant Pigs with High and Low Prolificacy Levels and Identification of Candidate Genes for Litter Size

Abstract

Previous results from a genome scan in an F(2) Iberian × Meishan pig intercross showed several chromosome regions associated with litter size traits in this species. In order to identify candidate genes underlying these quantitative trait loci (QTL), we performed an ovary gene expression analysis during the sow's pregnancy. F(2) sows were ranked by their estimated breeding values for prolificacy: six sows with the highest estimated breeding value (EBV) (i.e., high prolificacy) and six sows with the lowest EBV (low prolificacy) were selected. Samples were hybridized using an Affymetrix GeneChip porcine genome array. Statistical analysis with a mixed model approach identified 221 differentially expressed probes, representing 189 genes. These genes were functionally annotated in order to identify genetic pathways overrepresented in this list. Among the functional groups most represented was, in first position, immune system response activation against external stimulus. The second group consisted of integrated genes that regulate maternal homeostasis by complement and coagulation cascades. A third group was involved in lipid and fatty acid enzymes of metabolic processes, which participate in the steroidogenesis pathway. In order to identify powerful candidate genes for prolificacy, the second approach of this study was to merge microarray data with the QTL positional information affecting litter size, previously detected in the same experimental cross. As a result, we have identified 27 differentially expressed genes colocalizing with QTL for litter size traits, which fulfill the biological, positional, and functional criteria.

Differential Gene Expression in Uterine Endometrium During Implantation in Pigs1

“…In addition, the expression of litter size cannot be measured until the age of sexual maturity. However, these biological constraints can be potentially ameliorated by a better knowledge of the genetic regulation of litter size [3].…”

“…We expect that these differences in gene expression patterns to help identify candidate genes that contribute to differences in litter size. There have been some expression studies carried out in pigs looking at changes in endometria [14][15][16][17][18], ovaries [3], and placentas [19], and genes differently expressed at one stage of pregnancy have been identified. Furthermore, important biological processes and pathways were identified.…”

Secreted Phosphoprotein 1 Expression in Endometrium and Placental Tissues of Hyperprolific Large White and Meishan Gilts1

“…Recently, an association of a genetic polymorphism of the SPP1 gene with body weight and growth and other economically valuable traits was found in an F 2 Landrace 3 Jeji (Korea) Black pig population [18]. SPP1 has also been shown to improve development of porcine embryos in vitro [19], have reduced ovarian expression in prolific pig breeds [20], be a key component of the biochemical cascade that enables the porcine trophoblast to attach to the endometrium [21][22][23], mediate conceptus growth [24], influence fetal/placental development in pigs [24][25][26] and humans [25], and play an important physiological role in embryo implantation and placentation [27][28][29]. Indeed, SPP1 has recently been identified as a key molecule in facilitating conceptus-uterine interactions in mammals [30].…”

Proteomic analysis of reproduction proteins involved in litter size from porcine placenta

“…1,5) However, few studies have used proteomic analyses to assess placental litter size. Six proteins were predominantly identified in the SLSG including prenylcysteine oxidase-like, phosphoglycerate kinase (PGK) 1-like, ubiquitin carboxyl-terminal hydrolase 16-like isoform 2, calpain small subunit 1, 2-oxoglutarate dehydrogenase, and cytosolic nonspecific dipeptidase.…”

“…The Chinese Meishan has an average litter size of 14.3 piglets due to greater uterine capacity, whereas Iberian has an average litter size of seven. 1) The litter size in Berkshire is about 8.9. 2) Pig breeds have been highly divergent for more than 150,000 years, so it is possible to improve a highly reproductive pig breeding line with prolificacy-related genes.…”