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Mature spermatozoa are permeable to foreign DNA and RNA molecules. Here I propose a model, whereby extrachromosomal genetic information, mostly encoded in the form of RNA in somatic cells, can cross the Weismann barrier and reach epididymal spermatozoa. LINE-1 retrotransposon-derived reverse transcriptase (RT) can play key roles in the process by expanding the RNA-encoded information. Retrotransposon-encoded RT is stored in mature gametes, is highly expressed in early embryos and undifferentiated cells, and becomes downregulated in differentiated cells. In turn, RT plays a role in developmental control, as its inhibition arrests developmental progression of early embryos with globally altered transcriptomic profiles. Thus, sperm cells act as recipients, and transgenerational vectors of somatically derived genetic information which they pass to the next generation with the potential to modify the fate of the developing embryos.

// Alberto Gualtieri 1 , Federica Andreola 2 , Ilaria Sciamanna 1 , Paola Sinibaldi-Vallebona 3 , Annalucia Serafino 2 and Corrado Spadafora 1 1 Istituto Superiore di Sanita, Rome, Italy; 2 Institute of Translational Pharmacology, CNR, Rome, Italy; 3 Department of Experimental Medicine and Surgery - University of Rome “Tor Vergata”, Rome, Italy. Correspondence: Corrado Spadafora, email: // Keywords : LINE-1 retrotransposons; SINE retrotransposons; reverse transcriptase; copy number amplification; breast cancer progression Received : July 17, 2013 Accepted : August 7, 2013 Published : August 9, 2013 Abstract In higher eukaryotic genomes, Long Interspersed Nuclear Element 1 (LINE-1) retrotransposons and endogenous retroviruses represent large families of repeated elements encoding reverse transcriptase (RT) proteins. Short Interspersed Nuclear Element B1 (SINE B1) retrotrasposons do not encode RT, but use LINE-1-derived RT for their retrotransposition. We previously showed that many cancer types have an abundant endogenous RT activity. Inhibition of that activity, by either RNA interference-dependent silencing of active LINE-1 elements or by RT inhibitory drugs, reduced proliferation and promoted differentiation in cancer cells, indicating that LINE-1-encoded RT is required for tumor progression. Using MMTV-PyVT transgenic mice as a well-defined model of breast cancer progression, we now report that both LINE-1 and SINE B1 retrotransposons are up-regulated at a very early stage of tumorigenesis; LINE-1-encoded RT product and enzymatic activity were detected in tumor tissues as early as stage 1, preceding the widespread appearance of histological alterations and specific cancer markers, and further increased in later progression stages, while neither was present in non-pathological breast tissues. Importantly, both LINE-1 and SINE B1 retrotransposon families undergo copy number amplification during tumor progression. These findings therefore indicate that RT activity is distinctive of breast cancer cells and that, furthermore, LINE-1 and SINE B1 undergo copy number amplification during cancer progression.

// Ilaria Sciamanna 1 , Alberto Gualtieri 1,5 , Cristina Cossetti 1,5 , Emanuele Felice Osimo 1 , Manuela Ferracin 2 , Gianfranco Macchia 1 , Eleonora Arico 1 , Gianni Prosseda 3 , Patrizia Vitullo 1 , Tom Misteli 4 and Corrado Spadafora 1 1 Istituto Superiore di Sanita, Viale Regina Elena 299, Rome, Italy. 2 Laboratory for Technologies of Advanced Therapies (LTTA) and Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy. 3 Department of Biology and Biotechnology “Charles Darwin”, Sapienza University, Rome, Italy. 4 National Cancer Institute, NIH, Bethesda MD, USA. 5 Department of Experimental Medicine and Surgery - University of Rome “Tor Vergata”, Rome, Italy. Correspondence: Corrado Spadafora, email: // Keywords : LINE-1 retrotransposons, reverse transcriptase, transcriptome, miRNAs, DNA:RNA hybrids, cancer genome, reverse transcriptase inhibitor. Received : September 11, 2013 Accepted : October 12, 2013 Published : October 14, 2013 Abstract LINE-1 elements make up the most abundant retrotransposon family in the human genome. Full-length LINE-1 elements encode a reverse transcriptase (RT) activity required for their own retrotranpsosition as well as that of non-autonomous Alu elements. LINE-1 are poorly expressed in normal cells and abundantly in cancer cells. Decreasing RT activity in cancer cells, by either LINE-1-specific RNA interference, or by RT inhibitory drugs, was previously found to reduce proliferation and promote differentiation and to antagonize tumor growth in animal models. Here we have investigated how RT exerts these global regulatory functions. We report that the RT inhibitor efavirenz (EFV) selectively downregulates proliferation of transformed cell lines, while exerting only mild effects on non-transformed cells; this differential sensitivity matches a differential RT abundance, which is high in the former and undetectable in the latter. Using CsCl density gradients, we selectively identify Alu and LINE-1 containing DNA:RNA hybrid molecules in cancer but not in normal cells. Remarkably, hybrid molecules fail to form in tumor cells treated with EFV under the same conditions that repress proliferation and induce the reprogramming of expression profiles of coding genes, microRNAs (miRNAs) and ultraconserved regions (UCRs). The RT-sensitive miRNAs and UCRs are significantly associated with Alu sequences. The results suggest that LINE-1-encoded RT governs the balance between single-stranded and double-stranded RNA production. In cancer cells the abundant RT reverse-transcribes retroelement-derived mRNAs forming RNA:DNA hybrids. We propose that this impairs the formation of double-stranded RNAs and the ensuing production of small regulatory RNAs, with a direct impact on gene expression. RT inhibition restores the ‘normal’ small RNA profile and the regulatory networks that depend on them. Thus, the retrotransposon-encoded RT drives a previously unrecognized mechanism crucial to the transformed state in tumor cells.