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.
Sciamanna
Ilaria
I
Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy.
Vitullo
Patrizia
P
Curatolo
Angela
A
Spadafora
Corrado
C
D000220:Adaptation, Biological / Q000235:genetics; D000818:Animals; D019143:Evolution, Molecular; D005796:Genes; D014644:Genetic Variation / Q000235:genetics; D008297:Male; D051379:Mice; D008954:Models, Biological; D012194:RNA-Directed DNA Polymerase / Q000502:physiology*; D018626:Retroelements / Q000502:physiology*; D013094:Spermatozoa / Q000378:metabolism / Q000502:physiology
D018626:Retroelements; D012194:RNA-Directed DNA Polymerase