PHYSIOLOGICAL APPROACHES TO INCREASE THE EFFICIENCY OF PORK PRODUCTION THROUGH IMPROVED NUTRITIONAL AND REPRODUCTIVE COMPETENCE
Location: Reproduction Research
Title: Impact of Selection for Uterine Capacity on the Placental Transcriptome
Submitted to: Pig Reproduction National Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 22, 2008
Publication Date: June 4, 2009
Citation: Freking, B.A., Miles, J.R., Bischoff, S.R., Tsai, S., Hardison, N., Xia, Y., Nonneman, D.J., Vallet, J.L., Piedrahita, J.A. 2009. Impact of Selection for Uterine Capacity on the Placental Transcriptome [Abstract]. In: Control of Pig Reproduction VIII (H. Rodriguez-Martinez, J.L. Vallet and A.J. Ziecik, eds.) Journal of Reproduction and Fertility Supplement. 66:207-208.
Direct single trait selection for 11 generations resulted in a 1.6 pig advantage for uterine capacity (UC) while average birth and placental weights at term remained unchanged. A serial slaughter experiment conducted throughout gestation determined the critical time period for the line difference in litter size was already established between d 25 and 45 of gestation and generated direct evidence of differential relative growth rates for placental tissues at these times. Our objective was to gain insight into placental transcriptional changes during this critical stage of gestation and identify genetic loci impacted by quantitative selection for uterine capacity.
Thirty gilts each from the UC and control (CO) lines were subjected to unilateral hysterectomy-ovariectomy at approximately 160 d of age and mated within line at approximately 280 d. Gilts were slaughtered at d 25, 30, or 40 of gestation. Fetal and placental tissues were obtained from each live embryo. Two male and two female embryos closest to the litter mean for placental weight were chosen to represent each litter sampled (n = 3 litters per line and time point combination). Placental tissues were pooled within litter and total RNA was extracted. Samples were labeled and hybridized to Affymetrix porcine array chips (n = 18) using the manufacturer's suggested protocols. Signal intensities were normalized using GC content Robust Multi-array Average (GCRMA) on the probe level data. Two-way ANOVA (two lines and three stages) was performed. Threshold values were set at a minimum of 1.5-fold difference and the false discovery rate was set to P < 0.05 (Benjamini and Hochberg algorithm). Less stringent two-way comparisons (t-tests) were also conducted between lines within each gestation stage. A gene by gene linear mixed model of probe intensity variation from 11 probes per gene target was also investigated to identify line x probe interactions. An interaction was declared significant when Prob t < 0.0064 and would indicate a putative coding region polymorphism associated with line within that probe.
A total of 4,171 targets on the array exceeded P value and threshold limits for the main effect of stage (2,230 up-regulated and 1,839 down-regulated from d 25 to d 40). Analysis of probe x line data yielded a large number (5,617) of putative transcribed SNP between the lines, with an overlap of 762 targets where day effects were significantly different in the two-way ANOVA. Two targets, LIM domain and actin-binding protein 1 (LIMA1) and a hypothetical protein LOC51524 (transmembrane protein 138) approached significance for main effect of line (P < 0.08). Both loci were validated as differentially expressed by QPCR (P < 0.05). Both genes are predicted to play roles in cell migration, suggesting participation in placental folded bilayer formation. Two-way comparisons within time points indicated increased expression occurred more frequently than decreased expression in the UC line and revealed the importance of pathways such as integrin signaling pathway (calpains, collagen, fibronectin) and lipid metabolism (adiponectin receptors). These analytical approaches identified both expression and polymorphism differences to pursue for identification of loci contributing to uterine capacity.