Maternal blood transcriptome reflects fetal maturation at the end of the organogenesis in cattle.
In cattle, harnessing information from the maternal blood to predict fetal health and development is attractive yet scarcely explored. We hypothesised that variations in fetal growth at the end of the organogenesis period impact on the molecular profile of fetal organs and is reflected in the maternal blood transcriptome. The objectives were to determine the transcriptomic modifications in maternal blood and in fetal liver, gonads, and heart according to fetal weight and to model a molecular signature based on the fetal organs allowing the prediction of fetal weight from the maternal blood transcriptome. In addition to a contemporaneous maternal blood sample, organ samples were collected from 10 male fetuses at day 42 day of gestation for RNA-sequencing. Fetal weight ranged from 1.25 to 1.69 gr (mean 1.44 ± 0.15 gr). Data were analysed through co-expression cluster analysis to identify biologically relevant genes dynamically changing according to fetal weight in each fetal organ and in maternal blood. Results revealed clusters of genes, the expression of which was positively correlated with fetal weight, and which enriched ontological terms involved in the organ functionality. For the heart, the 1346 co-expressed genes were involved in energy generation and protein synthesis. For the gonads, the 1042 co-expressed genes enriched seminiferous tubule development. The 459 co-expressed genes identified in the liver were associated with lipid synthesis and metabolism. Finally, the cluster of 571 co-expressed genes determined in maternal blood enriched oxidative phosphorylation and thermogenesis. The expression patterns of the common genes between the clusters in each fetal organ and the cluster in maternal blood were employed to construct a predictive regression model of fetal weight. The data from the fetal organs were used to train the model, and the data from the maternal blood were used to test it. The best prediction was achieved when the model was trained with the 35 common genes between heart and maternal blood (root mean square error=0.04, R-square=0.93). In conclusion, linking transcriptomic information from maternal blood with that from the fetal heart unveils maternal blood as a sensor of fetal development. Overall design: We used an asynchronous embryo transfer model to stimulate fetal growth physiologically, as demonstrated in our previous study (PMID: 36739669). Heifers were randomly assigned to one of the two groups: those receiving a Day 7 embryo on Day 7 of the cycle (synchronous; ET_D7, n=23) and those transferred a Day 7 embryo on Day 9 of the cycle (asynchronous; ET_D9, n=33). The synchronisation protocol was started two days earlier for heifers in the ET_D9 group, such that ET was done on the same day for both groups. Blood samples were collected in Tempus Tubes (Thermofisher Scientific, Waltham, MA USA) from pregnant heifers (n=25) on Day 42 of gestation, following which they were slaughtered in a commercial abattoir. The reproductive tract was recovered and held on ice until processing for sample collection, which was done in the first 30 min after slaughter. The pregnant uterine horn was opened along the major curvature to expose and retrieve the fetal membranes. Once the fetus was isolated, the liver, heart and gonads were dissected, placed in individual RNAse-free tubes and snap-frozen in liquid nitrogen. Blood and fetal organ samples were stored at -80 °C until processing for RNAseq. Samples corresponding to 10 male fetuses (equally derived from heifers in the ET_D7 and ET_D9 groups) were employed in the current study.