mRNA of placental origin is readily detectable in maternal plasma

Abstract

The discovery of circulating fetal nucleic acid in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis. Thus far, a gender- and polymorphism-independent fetal-specific target that can be used for prenatal screening and monitoring in all pregnant women has not been reported. In addition, the origin of such circulating nucleic acid has remained unclear. Here we provide direct evidence that the placenta is an important source of fetal nucleic acid release into maternal plasma by demonstrating that mRNA transcripts from placenta-expressed genes are readily detectable in maternal plasma. The surprising stability of such placental mRNA species in maternal plasma and their rapid clearance after delivery demonstrate that such circulating mRNA molecules are practical markers for clinical use. The measurement of such plasma mRNA markers has provided a gender-independent approach for noninvasive prenatal gene expression profiling and has opened up numerous research and diagnostic possibilities.

Figure 1

Stability of placenta-derived mRNA in maternal blood. Box plots of mRNA levels in maternal plasma before and after incubation of the blood sample at room temperature for 24 h. (A) hPL. (B) βhCG. (C) GAPDH. The lines inside the boxes denote the medians. The boxes mark the interval between the 25th and 75th percentiles. The whiskers denote the interval between the 10th and 90th percentiles. The filled circles mark the data points outside the 10th and 90th percentiles.

Figure 2

Particle-associated nature of placenta-derived mRNA in maternal plasma. Box plots show plasma mRNA levels of pregnant women after different pore-sized filtration treatments. (A) hPL. (B) βhCG. (C) GAPDH. The lines inside the boxes denote the medians. The boxes mark the interval between the 25th and 75th percentiles. The whiskers denote the interval between the 10th and 90th percentiles. The filled circles mark the data points outside the 10th and 90th percentiles.

Figure 3

Levels of placenta-derived mRNA in maternal plasma in normal pregnancy. (A) Box plot of hPL mRNA in maternal plasma and protein levels in maternal serum at various stages of gestation. (B) Box plot of βhCG mRNA in maternal plasma and hCG protein levels in maternal serum at various stages of gestation. The lines inside the boxes denote the medians. The boxes mark the interval between the 25th and 75th percentiles. The whiskers denote the interval between the 10th and 90th percentiles. The filled circles mark the data points outside the 10th and 90th percentiles. (C) Correlation between hPL mRNA in maternal plasma and protein levels in maternal serum. (D) Correlation between βhCG mRNA in maternal plasma and protein levels (IU, international units) in maternal serum.

Figure 4

Clearance of fetus-derived mRNA from maternal plasma after delivery. (A and B) Maternal plasma hPL mRNA levels (A) and maternal plasma GAPDH mRNA levels (B) before delivery and 24 h after delivery. The results of eight plasma samples are shown, and each line represents one plasma sample obtained from one subject. (C and D) Maternal plasma hPL mRNA levels (C) and maternal plasma GAPDH mRNA levels (D) before delivery and 2 h after delivery. The results of 13 plasma samples are shown, and each line represents one plasma sample obtained from one subject.