97 MAGNITUDE AND SPECIFICITY OF EFFECTS OF MATERNAL AND PATERNAL GENOMES ON THE FETO-PLACENTAL UNIT
Authors: Xiang R. , Estrella C. A. S. , Fitzsimmons C. J. , Kruk Z. A. , Thomsen D. A. , Rutley D. L. , Kind K. L. , Roberts C. T. , Hiendleder S. 
Published: December 2014

The placenta, a major determinant of fetal growth in eutherians, facilitates maternal-fetal cross talk and mediates programming of postnatal phenotype via genetic and epigenetic mechanisms. However, magnitude and specificity of effects of maternal and paternal genomes on placental and fetal phenotype and their relationships are unclear. Using an outbred bovine intra-species model with well-defined Bos taurus taurus and Bos taurus indicus maternal and paternal genetics, we generated purebred and reciprocal cross fetuses (Animal Ethics No. S-094-2005) to dissect and quantify effects of parental genomes, fetal sex, and nongenetic maternal effects (maternal weight and post-conception maternal weight gain) on 41 gross and histomorphological feto-placental parameters. Analysis of data from 73 fetuses recovered at midgestation (Day 153) with general linear models (Xiang et al. 2014 JBMR http://dx.doi.org/10.1002/jbmr.2263) using the GLM procedure of R version 22.14 (R Development Core Team, Vienna, Austria) revealed that maternal and paternal genome combined explained the highest proportion of variation (47.2–99.5%) in 30 investigated parameters with significant (P < 0.05–0.0001) models. Fetal sex accounted for up to 32.2% (P < 0.05–0.0001) and nongenetic maternal effects for up to 25.1% (P < 0.05–0.001) of variation in 11 and 14 parameters, respectively. Partitioning of parental (epi)genome variation showed that the maternal genome predominantly contributed to variation in gross (80.3–95.7%; P < 0.05–0.0001) and histomorphological (51.5–82.1%; P < 0.05–0.0001) placental parameters, fetal weight (54.1%; P < 0.0001), and fetal organ weights (43.7–73.1%; P < 0.05–0.0001), whereas the paternal genome predominantly contributed to fetal fluids weight (73.0%; P < 0.001), umbilical cord weight (73.9%; P < 0.05) and length (73.2%; P < 0.01), and placental (69.6%; P < 0.05) and umbilical cord (83.2%; P < 0.0001) efficiency. Our finding that the maternal genome determined placental phenotype (i.e. nutrient source) and the paternal genome determined umbilical cord and fetal fluid phenotype (i.e. nutrient flow) is in line with predicted expression patterns of genomic imprinting effects by both maternal-offspring coadaptation (Wolf and Hager 2006 PLoS Biol. 4, e380) and conflict-of-interest (Moore and Haig 1991 Trends Genet 7, 45–49) hypotheses in the feto-placental unit. Furthermore, there were 4 maternal genome determined relationships between placental weights and umbilical cord phenotype (P < 0.05–0.0001) and 28 paternal genome and/or fetal sex-determined relationships between fetus-, organ- and fetal fluid weights and umbilical cord phenotype (P < 0.05–0.0001). The finding of specific relationships between placenta and fetus merging in clusters differentiated by maternal and paternal genome effects suggests the existence of (epi)genetic-regulated morphological modules within the feto-placental unit.Funded by the JS Davies Bequest.