Presence of Filterable and Nonfilterable Cell-Free mRNA in Amniotic Fluid

Abstract

Much current research focuses on the properties and clinical applications of circulating nucleic acids (1). The recent discovery of cell-free RNA in the plasma and serum of cancer patients has generated considerable interest (2)(3)(4)(5)(6). Circulating RNA is surprisingly stable, and Ng et al. (7) recently showed that a considerable proportion of plasma mRNA species is particle associated and thus possibly protected from nuclease degradation (8). Fetal-derived mRNA has also been found in the plasma and serum of pregnant women (9)(10)(11) and in amniotic fluid (12), and has many potential clinical applications (13)(14). Amniotic fluid is routinely collected during amniocentesis for fetal chromosome analysis or fetal lung maturity studies. However, little is known regarding the biology of circulating fetal mRNA or fetal mRNA in amniotic fluid. In this report, we explore whether cell-free fetal nucleic acids in amniotic fluid have properties similar to circulating DNA and mRNA. Expanding on the work of Ng et al. (7), we hypothesized that cell-free fetal mRNA in amniotic fluid might be present in a particle-associated form and could thus be filterable, whereas the non-particle–associated form of DNA would be present in such high concentrations that there would be no significant reduction in its quantity by filtration. Additionally, we wished to compare the quantities of nucleic acids in amniotic fluid containing cells with the quantities in filtered and unfiltered cell-free supernatant. We hypothesized that whole amniotic fluid containing amniocytes would contain a significantly larger amount of DNA and RNA than cell-free amniotic fluid. This study was performed with Institutional Review Board approval from Tufts-New England Medical Center. Seven amniotic fluid samples with a minimum volume of 3 mL each were obtained from women undergoing scheduled amniocenteses. One sample originated from a woman …