Epigenetic learning in non-neural organisms

Epigenetic learning in non-neural organisms
SIMONA GINSBURG, and EVA JABLONKA
J. Biosci. 33(4), October 2008
http://www.ias.ac.in/jbiosci/gins68.pdf

A pretty interesting paper. A good starting point is the definition of Epigenetics.

Definition of learning in the paper:

We therefore say that simple forms of learning occurred when:
(i) One or more inputs (e.g. external sensory stimuli or the organism’s own behaviours) start a reaction that leads to a behavioural response.

(ii) The input-response relations are memorized. By “memorized” we mean that some physical traces of the reaction persist. The organism is no longer in its initial (pre-input) state, but when the input has gone it does not go on exhibiting the behavioural response. It is the threshold for responding to the input that has been changed as a result of the past response.

(iii) The memorized relations can be recalled upon later exposure to one or more of the inputs. The response appears more readily or with less exposure to these inputs.

Mechanisms:

The autocatalytic mechanisms underlying cell memory and cell heredity are called epigenetic inheritance systems (EISs). Jablonka and Lamb (2005, 2007a, b) distinguished four types of epigenetic control mechanisms, all based on autocatalysis, that lead to epigenetic inheritance (the transmission from mother cell to daughter cell of variations that are not the result of DNA differences) and cell memory (the persistence in non-dividing cells of variations that are not the result of DNA differences):

(i) Self-sustaining feedback loops
(ii) Structural inheritance
(iii) Chromatin marking
(iv) RNA-mediated inheritance


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