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Fig. 4.8 The general architecture of a genetic regulatory network with up- and down-trees and
circuits, positive or negative, isolated, tangential, or intersecting
(1) the upper trees control the circuits, their genes sources being often microRNAs
and (2) the down-trees are controlled by the circuits until their final leaves, in
general genes responsible of the final differentiation of a cell lineage (cf. Fig. 4.8 ).
The mitomiRs are localized in the nuclear noncoding genome and inhibit key
genes involved in the energy system, like the ATPase or translocase genes, but they
could also be present in the noncoding part of the mitochondrial genome, targeting
the mitochondrial tRNAs, hence causing an unspecific inhibitory noise, which
leaves expressed only the attractors of the dynamics of certain circuits on which
this ubiquitous inhibition is compensated by a sufficient activation from the genes
preceding in the trees or circuits the mitomiR target. In Fig. 4.9 , we can see several
situations in which the microRNA can or cannot prevent the attractor to behave as a
periodic limit cycle. This last behavior (Fig. 4.9 , right) is observed if the absolute
value of the negative interaction weight related to the microRNA is less than the
value of the preceding positive interaction. In this case, the microRNA has no
influence on the network dynamics. This behavior is similar to the unspecific
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