Polymorphic inverted repeats near coding genes impact chromatin topology and phenotypic traits in Arabidopsis thaliana.

Transposons are mobile elements that are commonly silenced to protect eukaryotic genome integrity. In plants, transposable element (TE)-derived inverted repeats (IRs) are commonly found near genes, where they affect host gene expression. However, the molecular mechanisms of such regulation are unclear in most cases. Expression of these IRs is associated with production of 24-nt small RNAs, methylation of the IRs, and drastic changes in local 3D chromatin organization. Notably, many of these IRs differ between Arabidopsis thaliana accessions, causing variation in short-range chromatin interactions and gene expression. CRISPR-Cas9-mediated disruption of two IRs leads to a switch in genome topology and gene expression with phenotypic consequences. Our data show that insertion of an IR near a gene provides an anchor point for chromatin interactions that profoundly impact the activity of neighboring loci. This turns IRs into powerful evolutionary agents that can contribute to rapid adaptation.

Analysis of tRNA abstract shapes of precursor/derivative amino acids in Archaea.

Wong's theory of the genetic code's origin states that because of historical constraints, codon assignment depends on the relation between precursor and derivative amino acids, a result of the coevolutionary process between amino acids' biosynthetic pathways and tRNAs. Based on arguments supporting the assumption that natural selection favors more stable and thus functionally constrained structures, we tested whether precursor and derivative tRNAs are equally evolved by measuring their structural parameters, thermostability and molecular plasticity. We also estimated the extent to which precursor and derivative tRNAs differ within Archaea. We used Archaea sequences of both precursor and derivative tRNAs in order to examine the plastic repertoires or sets of suboptimal structures at a defined free energy interval. We grouped secondary structures according to their helix nesting and adjacency using abstract shapes analysis. This clustering enabled us to infer a consensus sequence for all shapes that fit the clover leaf secondary structure [Giegerich, R., et al., Nucleic Acids Res 2004; 32 (16): 4843-51.]. This consensus sequence was then folded in order to retrieve a set of suboptimal structures. For each pair of precursor and derivative tRNAs, we compared these plastic repertoires based on the number of secondary structures, the thermostability of the minimum free energy structure and two structural parameters (base pair propensity (P) and mean length of helical stem structures (S)), which were measured for every representative secondary structure [Schultes, E.A., et al., J Mol Evol 1999; 49 (1): 76-83.]. We found that derivative tRNAs have fewer numbers of shapes, higher thermostability and more stable parameters than precursor tRNAs, a fact in full agreement with Wong's coevolution theory of the genetic code.

Epigenetics and genetic determinism

This paper posits that the gene-centered viewpoint of the organism (gene-centrism) is not enough to explain biological complexity. Organisms are not completely determined by their genomes; rather, living beings can be seen as interpreters or intentional systems. Epigenetics is the framework that allows the avoidance of gene-centrism and permits the emergence of a more holistic standpoint where determination and novelty can coexist, as shown with examples taken from developmental biology and macromolecules folding. In summary, as P. Medawar and J. Medawar wrote: "Genetics proposes; epigenetics disposes."

O presente trabalho afirma que a visão geneticista do organismo (genecentrismo) não é suficiente para explicar a complexidade biológica. Os organismos não são completamente determinados por seus genomas; ou melhor, os seres vivos podem ser vistos como intérpretes ou sistemas intencionais. A epigenética é o arcabouço que ajuda a evitar o genecentrismo e permite a emergência de uma posição mais holística, em que determinismo e inovação podem coexistir, conforme demonstrado a partir de exemplos retirados da biologia do desenvolvimento e da estrutura das macromoléculas. Em resumo, como P. Medawar e J. Medawar escreveram: "A genética propõe e a epigenética dispõe".