Abstract
BackgroundDevelopment of the placenta during the late first trimester is critical to ensure normal growth and development of the fetus. Developmental differences in this window such as sex-specific variation are implicated in later placental disease states, yet gene expression at this time is poorly understood.MethodsRNA-sequencing was performed to characterize the transcriptome of 39 first trimester human placentas using chorionic villi following genetic testing (17 females, 22 males). Gene enrichment analysis was performed to find enriched canonical pathways and gene ontologies in the first trimester. DESeq2 was used to find sexually dimorphic gene expression. Patient demographics were analyzed for sex differences in fetal weight at time of chorionic villus sampling and birth.ResultsRNA-sequencing analyses detected 14,250 expressed genes, with chromosome 19 contributing the greatest proportion (973/2852, 34.1% of chromosome 19 genes) and Y chromosome contributing the least (16/568, 2.8%). Several placenta-enriched genes as well as histone-coding genes were identified to be unique to the first trimester and common to both sexes. Further, we identified 58 genes with significantly different expression between males and females: 25 X-linked, 15 Y-linked, and 18 autosomal genes. Genes that escape X inactivation were highly represented (59.1%) among X-linked genes upregulated in females. Many genes differentially expressed by sex consisted of X/Y gene pairs, suggesting that dosage compensation plays a role in sex differences. These X/Y pairs had roles in parallel, ancient canonical pathways important for eukaryotic cell growth and survival: chromatin modification, transcription, splicing, and translation.ConclusionsThis study is the first characterization of the late first trimester placenta transcriptome, highlighting similarities and differences among the sexes in ongoing human pregnancies resulting in live births. Sexual dimorphism may contribute to pregnancy outcomes, including fetal growth and birth weight, which was seen in our cohort, with males significantly heavier than females at birth. This transcriptome provides a basis for development of early diagnostic tests of placental function that can indicate overall pregnancy heath, fetal-maternal health, and long-term adult health.
Highlights
Development of the placenta during the late first trimester is critical to ensure normal growth and development of the fetus
Placentation in the first trimester can impact fetal growth, and abnormal placentation can lead to more pronounced effects complicating pregnancy including intrauterine growth restriction (IUGR) which results in very low birth weight infants, a sexually dimorphic outcome [1,2,3,4]
Identification of a transcriptome signature from late first trimester human placenta To identify the transcriptional profile of the late first trimester human placenta, RNA sequencing was performed on chorionic villi from 39 singleton pregnancies (17 female and 22 male samples)
Summary
Development of the placenta during the late first trimester is critical to ensure normal growth and development of the fetus Developmental differences in this window such as sex-specific variation are implicated in later placental disease states, yet gene expression at this time is poorly understood. The process of placentation occurs throughout the first trimester of pregnancy, whereby the outer cells of the blastocyst (the trophoblast cells) invade the maternal tissue and develop into the placenta. It is a highly regulated state of active cell proliferation, cell migration, and cell differentiation [5]. Placentation requires multiple factors, including maternal immune tolerance, various growth factors, fetal-maternal communication via chemical signaling, and a receptive maternal decidua that allows extravillous trophoblast cells to invade the maternal circulatory system and access maternal nutrients throughout pregnancy [5, 10,11,12,13]
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