Mon, 8 March 2004 004:12 Peter F. wrote: "CNCabej" <[email protected]> wrote > I would rather say that there is one integrated control > system, with the CNS as > its controller that is limited by genes (G), as well by > numerous external and > internal stimuli. >I think that what you are expounding fits in somewhere at >the center of the most interesting and fascinating of all >fields of scientific inquiry. >(It makes me salivate without being able to chew and >swallow - but I still love it from a distance.< If this is really so (and I believe it is), is it not paradoxical that people here in sbe are showing so little interest for "the most interesting and fascinating of all fields of scientific inquiry"? I wonder whether you have an explantion. >However, even if the notion and embryonic theory of "the >histone code" might currently not catalyze conceptual >clarity or inspire further insight, I still think it is >generally so relevant to what is discussed here that you >ought to have at least given it a mention. >If only for sake of a good (comprehensively spread- >out) measure. "The histone code", if you mean the remodelling of the chromatin by acetylation/deacetylation of histones, is an essential part of the integrated control system, but it was not mentioned here because of lack of space. In principle, the expression of all housekeeping genes is related to that remodelling. The integrated (epigenetic) system of control is a hierarchic system where the chromatine represents a downstream element in the system. In a very simplified scheme upstream the chromatine are signal transduction pathways<---- membrane receptors <---- their respective extracellular signals (protein hormones, growth factors, secreted proteins, neurotransmitters etc.)<--- hormones of the target endocrine glands<--- pituitary stimulating hormones <--- hypothalamic releasing hormones <---- brain chemical signals <---processing of the internal/external stimuli. Downstream the chromatine ("the histone code") are transcription factors and genes. The epigenetic system of control, with the CNS as its controller, controls the function of all housekeeping genes, genes whose differential expression determines the type of the cell (even the so-called cell-cell interactions are interactions at the level of downstream elements of signal cascades ultimately originating in the CNS). The function of the integrated system of control, with the CNS as its controller, is to maintain the inexorably eroding metazoan structure at all the different levels of organization. This implies that the system 1)is in possession of information on the "normal" physiological and morphological state. 2) does monitor the state of the system (based on the pervasive presence of the neural tissue thoughout the animal body). 3) processes the input and by comparing with the set points it establishes detects deviations from the norm. 4) sends messages (in the form of signal cascades) to affected parts for restoring the normal state. Being in possession of information for the normal structure the integrated system is at the same time the epigenetic system of heredity as it is demonstrated by the fact that it regulates and controls 5. The formation of the egg and sperm cells 6. The placement of maternal cytoplasmic factors in the egg cell. 7. The early embryonic development (which is regulated not by zygotic genes, but by maternal cytoplasmic factors) up to the phylotypic stage, when a functioning CNS first arises. 8.The postphylotypic development, including the post-natal development (the All the above suggest that the genetic system of heredity, which is responsible for most of the hereditary characters in unicellulars, in metazoans is subordinate to the epigenetic system of heredity. If this is really so, how can one determine whether the evolution of genes is the cause or a consequence of evolution? Mary Jane West-Eberhard in her recently published book presents some curious arguments that genes in her expression are "followers not leaders" in evolution. While examples of inherited changes in morphology without changes in genes are known, does any one know an example of how a mutation in a gene brought about an advantageous morphological change in metazoans? If not, with H.F. Nijhout we all have to admit that genes do no more than producing chemicals (RNA and proteins).