Abstract
BackgroundLitter size in pigs is a major factor affecting the profitability in the pig industry. The peri-implantation window in pigs is characterized by the coordinated interactions between the maternal uterine endometrium and the rapidly elongating conceptuses and represents a period of time during which a large percentage of the developing conceptuses are lost. However, the gene expression and regulatory networks in the endometrium contributing to the establishment of the maternal: placental interface remain poorly understood.ResultsWe characterized the endometrial gene expression profile during the peri-implantation stage of development by comparing two breeds that demonstrate very different reproductive efficiencies. We employed the porcine Affymetrix GeneChip® to assay the transcriptomic profiles of genes expressed in the uterine endometrium obtained from Meishan and Yorkshire gilts (n = 4 for each breed) on day 12 of gestation (M12 and Y12, respectively). Total of 17,076 probesets were identified as "present" in at least two arrays. A mixed model-based statistical analysis predicted a total of 2,656 (q < 0.1) transcripts as differentially expressed between Meishan and Yorkshire pigs. Eighteen differentially expressed transcripts of interest were validated by quantitative real-time PCR. Gene ontology (GO) annotation revealed that the known functions of the differentially expressed genes were involved in a series of important biological processes relevant to early pregnancy establishment in the pig.ConclusionsThe results identified endometrial gene expression profiles of two breeds differing in litter size and identified candidate genes that are related to known physiological pathways related to reproductive prolificacy. These findings provide a deeper understanding of molecular pathways differing between two breeds at the critical peri-implantation stage of pregnancy, which can be utilized to better understand the events contributing to pregnancy establishment in the pig.
Highlights
Litter size in pigs is a major factor affecting the profitability in the pig industry
If the signal of a transcript from at least two of the four biological replicates were called “present” by the Affymetrix algorithm, we considered this transcript expressed in the endometrium
14,951 transcripts were identified in Meishan day 12 (M12) endometrium, and 14,558 transcripts were detected in Yorkshire day 12 (Y12) endometrium
Summary
Litter size in pigs is a major factor affecting the profitability in the pig industry. Pig litter size, which can be impacted by multiple factors including ovulation rate, embryonic survival, uterine capacity and fetal survival, is one of the most important economic traits affecting trait values may accelerate genetic improvement. It is well established that prenatal mortality can be a major determinant of litter size in pigs [5,9,10]. Events in conceptus development, including rapid trophoblastic elongation and successful establishment of the fetal: maternal interface, play a key part in determining litter size. The timing of endometrial exposure to estrogen is critical as specific molecular cues associated with uterine receptivity occur simultaneously with conceptus estrogen synthesis and abnormal exposure to estrogen prior to day 12 results in compromised pregnancy establishment [13,14,15]
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