The Involvement of Different Mobile LINE Copies of Blood Plasma and Extrachromosomal DNA of Liver Cells in Systemic Adaptive Response

A new biodosimetric method: branched DNA-based quantitative detection of B1 DNA in mouse plasma

A simple and accurate method for measuring the biological effects of radiation is of increasing importance, especially in mass casualty scenarios. We have therefore developed a new biodosimetric technique targeting circulating B1 DNA in mouse plasma by branched DNA signal amplification for rapid quantification of plasma DNA. This technology targets repetitive elements of the B1 retrotransposon in the mouse genome, followed by signal amplification using Panomics Quantigene 2.0 reagents. Evaluation was conducted concerning precision, accuracy and linearity. Plasma samples were collected from mice 0-24 h after 0-10 Gy total body irradiation (TBI). The average inter- and intra-assay coefficients of variance were 8.7% and 12.3%, respectively. The average recovery rate of spiked DNA into plasma was 89.5%. This assay revealed that when BALB/c and NIH Swiss mice were exposed to 6 Gy TBI, plasma B1 DNA levels increased significantly at 3 h post-TBI, peaked at 9 h and gradually returned toward baseline levels in 24 h. A dose-dependent change in plasma DNA was observed at 9 h post-TBI; the dose-response relation was monotonic, exhibiting linearity for BALB/c mice from 3 to 6 Gy (r = 0.993) and NIH Swiss mice from 3 to 7 Gy (r = 0.98). This branched DNA-based assay is reliable, accurate and sensitive in detecting plasma B1 DNA quantitatively. A radiation dose-correlated increase in plasma B1 DNA was demonstrated in BALB/c and NIH Swiss mice in the dose range from 3 to 6 Gy, suggesting that plasma B1 DNA has potential as a biomarker for radiation biological effect.

Retrotransposons, reverse transcriptase and the genesis of new genetic information

Spermatozoa of virtually all species can take up exogenous DNA or RNA molecules and internalize them into nuclei. A sperm endogenous reverse transcriptase activity can reverse-transcribe the internalized molecules in cDNA copies: exogenous RNA is reverse-transcribed in a one-step reaction, whereas DNA is first transcribed into RNA and subsequently reverse-transcribed. In either case, the newly synthesized cDNAs are delivered from sperm cells to oocytes at fertilization and are further propagated throughout embryogenesis and in tissues of adult animals. The reverse-transcribed sequences are underrepresented (below 1 copy/genome), mosaic distributed in tissues of adult individuals, transmitted in a non-Mendelian fashion from founders to F1 progeny, transcriptionally competent, variably expressed in different tissues and temporally transient, as they progressively disappear in aged animals. Based on these features, the reverse-transcribed sequences behave as extrachromosomal, biologically active retrogenes and induce novel phenotypic traits in animals. This RT-dependent mechanism, presumably originating from LINE-1 retroelements, generates transcriptionally competent retrogenes in sperm cells. These data strengthen the emerging view of a novel transgenerational genetics as the source of a continuous flow of novel epigenetic and phenotypic traits, independent from those associated to chromosomes. The distinctive features of this retrotransposon-based phenomenon share analogies with a recently discovered form of RNA-mediated inheritance, compatible with a Lamarckian-type adaptation.