The genetic self

Protoplasma, Feb 2018

Peter Nick

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The genetic self

Protoplasma The genetic self Peter Nick 0 Handling Editor: Peter Nick 0 0 Molekulare Zellbiologie, Botanisches Institut, Karlsruher Institut für Technologie, Molecular Cell Biology, Botanical Institute, Karlsruhe Institute of Technology , Karlsruhe , Germany Life is sustained in a subtle balance between reproduction and innovation. The elegant mechanism, by which a nucleotide strand induces a mirror image of itself, along with the ability of all cells to split into symmetrical copies of themselves, efficiently amplifies that what has been proven to be successful. Reproduction is a conservative business, though-if it were not accompanied by ongoing change, life would never have made it beyond some germinal states. Sophisticated processes, such as sexuality, meiosis, or transposons, actively increase variation and have been powerful driving forces for biological innovation. These considerations lead to the question, how these obviously antagonistic activities are integrated into a functional genetic self. The alternative that there is not such a thing as genetic integrity would imply that genetic damages just proceed and in case that the result is not any longer viable will be eliminated by selection. Although the impact of selection should not be denied here, it is clear on the other hand that most organisms actively maintain their genetic self by constraining or repairing genetic perturbances, or by eliminating damaged cells by apoptotic cell death. One of the many indications of an actively maintained genetic identity is the observation that mutations in germ cells are orders of magnitude more rare than in somatic cells. Thus, while individuals age, species remain forever young (Seidel 2015). But what happens with the genetic self, either when organisms lack a clear separation of soma and germ line, or when they propagate clonally (either as part of their natural development or in consequence of human manipulation)? Three contributions to the current issue highlight different aspects of the genetic self in animals and plants. - The genetic self of prokaryotes is circular—the DNA is forming a ring. In contrast, eukaryotic DNA is organised in linear units, which is probably tribute to the larger amounts of information that have to be processed and copied, but makes it more difficult to defend genetic integrity. In fact, double-strand breaks can lead to a situation, where smaller fragments of DNA are religated into small ring chromosomes. These are the topic of a review by Pristyazhnyuk and Menzorov (2018) in the current issue. Even if this genetic material is not lost during mitosis, such ring chromosomes can lead to drastic consequences for genetic integrity, because they are followed by considerable rearrangements of the remaining chromosomes. The authors address the causes for this phenomenon, the biological responses evoked by ring chromosomes, the medical implications of ring chromosomes, and the clinical aspects of ring chromosome syndromes. They also discuss the interesting possibility, whether the genetic reshuffling triggered by the presence of artificial ring chromosomes might be therapeutically exploited to cure large chromosomal aberrations. While the genetic self is challenged to a certain extent during each event of sexual propagation, hybridisation between two species represents a very drastic perturbation of genetic identity. While in animals such events lead to early abortion of the hybrid, hybridisation is a common event in plant evolution, giving rise to numerous novel species that often are even more successful than their parents. A contribution by Majka et al. (2018) deals with hybrids from two forage grasses, Festuca pratensis × Lolium perenne. Since the parental species harbour complementary traits, these hybrids are of economic relevance. The parental species are sufficiently different, such that genome reorganisation can be followed using fluorescent in situ probes. Virulent hotspots for reshuffling are fragile sites that had been linked with the 35S rDNA regions, which was also found for one of the parental species, Lolium perenne (Rocha et al. 2015) . This would mean that due to their functionality, certain regions of the genome are more prone for breakage. In their contribution, the authors now show that not the 35S rDNA regions, but a different type of fragile sites, the interstitial telomeric sequences, account for most rearrangements taking place in these What can we extract from these three glimpses into genetic integrity? Despite the specificities of the respective models and phenomena, a genome seems to be more than the mere sum of its genes, but exhibits certain holistic properties that are actively maintained, repaired, and restored. The intellectual challenge of a genetic self is to be seen in the question, how the information on the target situation is stored and relayed in a situation, where genetic integrity is perturbed. In case of single-strand repair, the answer is evident—the integrity comes from the template provided by the antisense strand and the chemical rules of base pairing. In case of supergenic organisation within a genome, there is no evident template. While there might be structural components, such as the pairing of entire chromosomes in the synaptonemal complex during the first meiotic prophase, the genetic self might also be Bembodied^ in cybernetic processes rather than in static structures. Compliance with ethical standards Conflict of interest The author declares that there is no conflict of interest. Majka J , Zwierzykowski Z , Majka M , Kosmala A ( 2018 ) Karyotype reshufflings of Festuca pratensis × Lolium perenne hybrids . Protoplasma, current issue Mamedes-Rodrigues T , Batista D Vieira N , Matos E , Fernandes D , Nunes-Nesi A , Cruz C , Viccini L , Nogueira F , Otoni WC ( 2018 ) Regenerative potential, metabolic profile, and genetic stability of Brachypodium distachyon embryogenic calli as affected by successive subcultures . Protoplasma, current issue Pristyazhnyuk I , Menzorov A ( 2018 ) Ring chromosomes: from formation to clinical potential. Protoplasma, current issue Rocha LC , Bustamante Fde O , Silveira RA , Torres GA , Mittelmann A , Techio VH ( 2015 ) Functional repetitive sequences and fragile sites in chromosomes of Lolium perenne L . Protoplasma 252 : 451 - 460 Seidel GE ( 2015 ) Maintaining integrity of germline DNA: individuals age, species do not . Reprod Fertil Dev 27 : 865 - 871


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Peter Nick. The genetic self, Protoplasma, 2018, 437-438, DOI: 10.1007/s00709-018-1229-x