Epigenetics Comes of Age

The Dogma of the Genetic Program

Half a century ago we learned genes contain information for protein biosynthesis and that information is encoded in the form of the triplet code, according to which specific sequences of three nucleotides code for a specific amino acid. This is verified in thousands of organisms and by extrapolation we believe (or consider highly probable) that this is a universal code in the living world. The discovery of the autoregulatory systems of protein biosynthesis in microrganisms such as E. coli led to an idea, soon to become textbook knowledge, that the genome contains the full program of development of these unicellular microorganisms. Simultaneously this assumption was extended to the world of multicellulars so that it is still commonplace to speak of “genetic programs” of development of multicellular organisms.Is this extrapolation justified or is it an expression of human shortsightness and overestimation of the validity of the knowledge of his time? Even if the genome would have been verified to have the complete information for building a unicellular, which it has not, to extend the concept of genetic programs from unicellulars to multicellulars is methodologically wrong. A unicellular’s building blocks are molecules, macromolecules and supracellular structures composed of molecules of one or more types. Among these molecules proteins are essential and they are synthesized according to genetic information contained in the genome of unicellulars. Other molecules are products of the activity of proteins and others come from the environment. Now, almost two centuries after Schwann and Schleiden we forget that the building blocks and the determination of animal morphology and physioloogy are cells, billions and trillions of cells of tens of hundreds of different types.  Nevertheless, we still speak of genetic programs determining the development of animal morphology although no one has ever tried to show where, beyond the genetic information for protein biosynthesis, may this program be encoded let alone to present a model of how the genetic information for protein biosynthesis could determine the form, function and number of cells. Indeed, no one has elaborated on what other type of information, beyond the genetic information, may genome contain. No one has even tried to speculate how the information contained in the genome could determine the spatial arrangement of billions/trillions of cells in those intricate combinations that produce the diversity of morphologies and physiology of multicellular organisms. If there is a genetic program one would expect that at least the gene expression and synthesis of proteins according to the triplet code would be genetically determined by the genome. Ample and ever increasing evidence shows that gene expression is mostly extracellularly, epigenetically controlled and regulated, especially in multicellulars.But let’s suppose that a still unknown information is contained somewhere in the genome may be discovered sometime in the future. Would it resolve the enigma of the source of information for erecting multicellular structures of the size and complexity we see in extant metazoans?Any illusion on such a possibility will disappear when it will be confronted with some facts of individual development. So, e.g. during the individual development, during the intrauterine life, many mammal species, including humans, form hardly imaginable large number of specific connections. Obviously, not only tens of thousands of genes but even the whole amount of a few billion nucleotides in the genome of these species (a few billions) is negligible as a source of information for determining the huge amount of quadrillions of neural connections.So, the idea of genetic programs will not rise to the level of a testable hypothesis but will remain a dogma as long as its adherents do not resolve both the above problems:-          The qualitative inappropriateness of the genetic triplet code as a source of information for determining positional information for patterns of spatial arrangement of cells of various types in  the process of molding animal morphology.

-          The quantitative insufficiency of genetic information for determining the huge amount of information used for erecting the structure of these species.

What supprorts the survival of a dogma that for more than half a century has been impossible to be proven?

This entry was posted on Saturday, May 15th, 2010 at 4:29 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.