ACQUIRED TRAITS CAN BE INHERITED

IN LESS COMPLEX ANIMALS, ACQUIRED TRAITS ARE TRANSMITTED

From Quantamagazine

Since Mendel's time, we have accepted that the main means of information and transmission of biological information in complex organisms is mainly carried out by encrypted DNA. However, today, thanks to epigenetics we are learning that at least in less complex animals, certain adaptive responses are not necessarily transmitted to the new generations by gene sequences, that is, that some learned behaviors and certain physiological responses can be epigenetically inherited.  Lately, the:A. Weismann barrier (1892, "the traits acquired by the somatic cells of complex organisms -by exposure to the environment- are not transmitted to oocytes and sperm and from there to the next generation"), is losing its rigidity. Epigenetically speaking and according to Oded Rechavi (Tel Aviv University), the information learned by somatic tissues is communicated and incorporated into the germ line, by means of small RNA molecules and / or perhaps by hormone like-peptides, being the nervous system able to promote inheritable adaptive responses. Proposals that have required epigenetic researchers  to ask themselves: a) If learned adaptive behaviors can be passed on to the next generation, that would seem to eliminate the necessity for certain standard evolved changes to the genome. b) why not incorporate these adaptive changes to the genome so that they could be more stable? O. Rechavi, thinks in this regard arguing that, although more studies are lacking, it is real the existence of 2 inheritance mechanisms (RNA-DNA), being the DNA, the most recent. In 1950 R. Alexander Brink, achieved  under different environmental conditions, that corn plants with identical genomes, had different expressions in the form of heritable grains of different colors, inferring the existence of different production mechanisms: chemical modifications of proteins and DNA or  the existence of small RNA molecules that, when transiting to the germ cells, interacted with the DNA, affecting genetic regulation.   In another experiment, the germ cells producing sperm and oocytes of the C. elegans worm were marked with a green fluorescent protein and the neurons with red, proving that the adaptive responses learned by these worms caused changes in the neural system that induced changes in the germ cells, allowing the progeny of worms to exhibit the same adaptive behavior to cope  with  stress. Rechavi said that this was possible due to the emergence of small RNA-RNA transmitter molecules, which performed different functions from the usual peptide production. 10 years ago, at Columbia University, Rechavi showed that C. elegans virus-infected worms could defend themselves by generating small RNAs that neutralized viruses and that their subsequent progeny also produced these protective RNAs, even if they were not exposed to viruses (Cell, 2011), and that the stress could induce the production of small inheritable molecules of RNAs that helped adaptive response. In Cell (June 13,2019), Rechavi, investigated the inheritance of chemotaxis, concluding that, in these cases, the worms inherited siRNA molecules produced in their parents' neurons, adding Peter Sarkies, that the information mediated by the siRNAs could also be transmitted transgenerationally. According to Sarkies, C. elegans worms also have some ability to take double stranded RNA from the environment and use it to silence endogenous genes, inducing adaptive responses. In this regard and according to G. Bosco (Dartmouth College), it is necessary to answer certain questions: a) why does the neural signals reach the germ tissue and change the information contained in the oocyte? b) What need induces the brain to perform these actions in the germ tissue? c) If a worm ingesting an environmental chemist manages to change the epigenome of oocytes and spermatozoa, why can't we make our brain to generate a similar molecule? In a paper (2017/Nature Cell Biology), Burton exposed C. elegans worms to high levels of salt, inducing a state called osmotic stress, against which the worm's brain responded by secreting insulin-like peptides that changed  oocytes, inducing in them epigenetic changes, making the worm's progeny produce more protective glycerol against osmotic stress. For Burton, the hormone-like peptides secreted by worm brains induce epigenetic changes in oocyte-forming cells, further achieving that their progeny solves the problem of high environmental salt levels. A characteristic of the epigenetic inheritance is that it only lasts a few generations and then ceases, denominating it for that reason: adaptive plasticity.

GENETIC CODE

EXPANDED GENETIC CODE

From quantamagazine

In 1992, the mathematician E. Sathmary analyzed the consequences of adding or subtracting letters  to the current human genetic code, concluding that although it was possible to increase more characters, there was a risk that the added letters resemble each other, increasing the chances of a mismatch, shape distortion and increased DNA mutagenesis. In contrast, only 2 letters, restrict the emergence of complex bio-organisms. So, the existence of only 4 letters in our genetic code, represent a frozen character, restricted and optimal (fidelity and metabolic efficiency), induced by environmental conditions of the early Earth, where possibly the RNA performed simultaneously storing information and the catalytic work of  proteins. Now, the organic chemist Steven Benner (Foundation for Applied Molecular Evolution. Florida), after 30 years of experiments with artificial genetic codes has added two new letters (p and  z) to the  4  letters of our  genetic code. For Benner, the current DNA is a molecule that would work best, because nucleotides p and  z  align perfectly into  the present DNA, using the same bonds that links  two pairs of current letters, maintaining its natural shape and  because   DNA sequences that contained p and z letters do better than  traditional DNA. While the letter p carries a molecular structure which helps  folding phenomenon, the letter z carries a nitro group, which facilitates the  molecular bonding. According to Benner, an expanded genetic code could generate more combinations, more protein and/or eliminate the necessity of the latter. Instead the system: DNA-RNA-PROTEIN, life on other planets might be evolving with the system: DNA-RNA, capable of evolving faster and transmitting information in both directions. Benner adds that although the current genetic code produces 20 amino acids, a 6-letter code would produce 216  amino acids and billions of proteins, besides to  store far more genetic information. An RNA 6-letter code would do all the work of proteins catalyzing reactions better and produce more complex structures.

CÓDIGO GENÉTICO EXPANDIDO

En 1992, el matemático E. Sathmary analizo las  consecuencias de añadir o restar  letras al código genético humano actual, concluyendo que aunque  era posible incrementar  más caracteres,  existía el riesgo de que las letras añadidas se pareciesen mucho entre sí, incrementándose las posibilidades de un mal apareamiento, distorsión de la forma del DNA e incremento de la mutagénesis. Contrariamente, solo 2 letras,  restringirían  la emergencia de bio-organismos complejos. La existencia de  solo 4 letras en nuestro código genético, representaría un carácter helado, restringido y óptimo (fidelidad y eficiencia metabólica), inducido por  las condiciones  medioambientales de la Tierra primitiva, en las que posiblemente el RNA  realizaba  simultáneamente el almacenamiento   de  información y el trabajo catalítico de las proteínas. Ahora, el químico orgánico Steven Benner (Foundation for Applied Molecular Evolution. Florida),  tras  30 años de experimentos con códigos genéticos artificiales ha  añadido  2 nuevas letras (p y z), a las 4  básicas del  código genético humano. Para Benner, el DNA actual es una molécula que funcionaria mejor de ser perfeccionada, porque  los  nucleótidos p y z se acoplan  perfectamente al DNA actual, empleando los mismos enlaces que unen los 2 pares de letras actuales,  manteniendo su forma natural y porque las secuencias de DNA que contienen letras p y z evolucionan mejor  que el DNA tradicional. Mientras la  letra p porta una estructura molecular que ayuda al plegamiento proteico,  la letra z porta un grupo nitro, que facilita la unión molecular.  Según Benner,  un  código genético expandido generara más combinaciones, más proteínas y/o  prescindirá de estas últimas. En lugar del trío: DNA-RNA-PROTEINAS, la vida en otros planetas podría estar evolucionando con  el dúo: DNA-RNA, capaz de trasmitir  información en ambas direcciones, evolucionando más   rápido. Benner agrega,  que aunque el código genético actual produce  20 amino ácidos, un código de 6 letras produciría  216  amino ácidos y billones de  proteínas, además de almacenar muchísimo más información genética.   Un  RNA de 6 letras haría todo el trabajo de las proteínas, catalizando mejor las reacciones y produciendo estructuras más complejas.