User:J. C. Martinez-Garcia/Notebook/HMS Activities/2008/12/19

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The Jablonka and Ginsburg paper
Eva jablonka send me the following paper:


 * S. Ginsburg, E. Jablonka (2008): Epigenetic learning in non-neural organisms [[Media:GJepigenetic memory08.pdf]]. J. Biosci. 33(4).

The paper is very interesting and its main topic concerns a proposal of a plausible biological mechanism underlying cell memory as a support of learning in non neural organisms. The proposed mechanism supposes that cell memory can be (in a non exclusive way) instantiated by chromatin marking. Based on a general concept of learning (1. One or more inputs atart a reaction that leads to a behavioral response; 2. The input-response relations are memorized, i.e. some physical traces of the reaction persist; 3. the memorized relations can be recalled upon later exposure to one or more of the inputs, the response appears then more readily or with less exposure to these inputs), the paper propose then five toy models based on chromatin marking:
 * 1) Constant memory and output.
 * 2) Memory with decay.
 * 3) Decay with a threshold.
 * 4) memory with delayed output (priming).
 * 5) Memory with cumulative marking and assimilation.

In order to illustrate how these toy models can support learning, the authors provided fours simple examples:
 * 1) Sensitization: decay with threshold and recall.
 * 2) Habituation: inhibitory modifications and recall.
 * 3) Pseudo-conditioning sensitization linked to a generally amplifying input.
 * 4) Associative activation.

In order to contribute to the discussion concerning cell learning, teh authors proposed two new concepts:


 * 1) Epigenetic engram : representation of a past input on the system, i.e. a cellular structure of activity that acts as a memory trace, and is remnant or specific modification of an originally induced epigenetic mark or structure.
 * 2) Epigentic recall : the facilitated reconstruction of a previously induced phenotypic response, based on persistent epigenetic engrams.

At the end of the paper they propose some possible expansion of the epigenetics research program:


 * 1) Study the nature and extent of the mark and gene expression (memory span).
 * 2) What happens when the marks in generation are faithfully inherited (non-matching effect in the subsequent generation)? Effects of mark deprivation on the development of offspring.
 * 3) Distinguish between cases of learning and cases of a constant response that seems like learning.
 * 4) Sensitization and habituation in cell lineages within a multi-cellular organism during development.
 * 5) Instantiation of patters of interactions/communications between cells in multi-cellular organisms which have not neural system (like the plants).
 * 6) Experiments on memory and learning in Tricoplax.
 * 7) Molecular basis of responses in plants associated to habituation and sensitization.
 * 8) Study active protists.

As far the evolutionary implications of their proposal, the authors argue that memory and learning improves fitness of organisms living in recurrently changing environments.

That is! I will continue with all these things tomorrow morning.


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