Brain Metabolic DNA Is Reverse Transcribed in Cytoplasm: Evidence by Immunofluorescence Analysis

In a previous study (Mol Neurobiol 55:7476-7486, 2017), newly synthesized brain metabolic DNA (BMD) from rat subcellular fractions has been shown to behave as a DNA-RNA hybrid when analyzed in cesium gradients at early [3H] thymidine incorporation times but to assume the double-stranded configuration at later times. Conversely, BMD from purified nuclei displayed the dsDNA configuration even at early incorporation times. The results were interpreted to support the BMD origin by reverse transcription in the cytoplasm and its later acquisition of the double-stranded configuration before the partial transfer to the nuclei. This interpretation has now been confirmed by immunofluorescence analyses of newly synthesized BrdU-labeled BMD from the mouse brain that demonstrates its cytoplasmic localization and colocalization with DNA-RNA hybrids. In addition, BrdU-labeled BMD has been shown to colocalize with astroglial anti-GFAP antibodies and with presynaptic anti-synaptophysin antibodies.