BackgroundAnalysis of lymphocyte cell lines revealed substantial differences in the expression of mRNA and microRNA (miRNA) among human populations. The extent of such population-associated differences in actual human tissues remains largely unexplored. The placenta is one of the few solid human tissues that can be collected in substantial numbers in a controlled manner, enabling quantitative analysis of transient biomolecules such as RNA transcripts. Here, we analyzed microRNA (miRNA) expression in human placental samples derived from 36 individuals representing four genetically distinct human populations: African Americans, European-Americans, South Asians, and East Asians. All samples were collected at the same hospital following a unified protocol, thus minimizing potential biases that might influence the results.ResultsSequence analysis of the miRNA fraction yielded 938 annotated and 70 novel miRNA transcripts expressed in the placenta. Of them, 82 (9%) of annotated and 11 (16%) of novel miRNAs displayed quantitative expression differences among populations, generally reflecting reported genetic and mRNA-expression-based distances. Several co-expressed miRNA clusters stood out from the rest of the population-associated differences in terms of miRNA evolutionary age, tissue-specificity, and disease-association characteristics. Among three non-environmental influenced demographic parameters, the second largest contributor to miRNA expression variation after population was the sex of the newborn, with 32 miRNAs (3% of detected) exhibiting significant expression differences depending on whether the newborn was male or female. Male-associated miRNAs were evolutionarily younger and correlated inversely with the expression of target mRNA involved in neuron-related functions. In contrast, both male and female-associated miRNAs appeared to mediate different types of hormonal responses. Demographic factors further affected reported imprinted expression of 66 placental miRNAs: the imprinting strength correlated with the mother’s weight, but not height. ConclusionsOur results showed that among 12 assessed demographic variables, population affiliation and fetal sex had a substantial influence on miRNA expression variation among human placental samples. The effect of newborn-sex-associated miRNA differences further led to expression inhibition of the target genes clustering in specific functional pathways. By contrast, population-driven miRNA differences might mainly represent neutral changes with minimal functional impacts.

Background Lipids contained in milk are an essential source of energy and structural materials for a growing infant. Furthermore, lipids' long-chain unsaturated fatty acid residues can directly participate in infant tissue formation. Here, we used untargeted mass spectrometric measurements to assess milk lipid composition in seven mammalian species: humans, two macaque species, cows, goats, yaks, and pigs.Results Analysis of the main milk lipid class, triacylglycerides, revealed species-specific quantitative differences in the composition of fatty acid residues for each of seven species. Overall, differences in milk lipid composition reflect evolutionary distances among species, with each species group demonstrating specific lipidome features. Among them, human milk contained more medium and long-chain unsaturated fatty acids compared to other species, while pig milk was the most distinct, featuring the highest proportion of long-chain polyunsaturated fatty acids. ConclusionsWe show that milk lipidome composition is dynamic across mammalian species, changed extensively in pigs, and contains features particular to humans.

Background Lipids contained in breast milk are an essential source of energy and structural materials for a growing infant. Furthermore, lipids’ long-chain unsaturated fatty acid residues can directly participate in infant tissue formation. Here, we used untargeted mass spectrometric measurements to assess breast milk lipid composition in seven mammalian species: humans, two macaque species, cows, goats, yaks, and pigs.Results Analysis of the main milk lipid class, triacylglycerides, revealed species-specific differences in the composition of fatty acid residues for each of seven species. While human milk showed more medium and long-chain unsaturated fatty acids, pig milk composition was the most distinct, featuring the highest proportion of long-chain polyunsaturated fatty acids. Conclusions We show that breast milk lipidome composition is dynamic across mammalian species, changed extensively in pigs, and contains features particular to humans.