MicroRNAs and Robustness in Biological Regulatory Networks. A Generic Approach with Applications at Different Levels: Physiologic, Metabolic, and Genetic - Systems Biology of Metabolic and Signaling Networks - page 71

1.0

0.95

0.90

0.9

0.85

0.8 0.80

0.75

0.7

0.70

0.65

0.6

0.60

0.55

0.5

0.50

0.45

0.4

0.40

0.35

0.3

0.30

0.25

0.2

0.20

0.1 0.15

0.10

0.0

0.05

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.00

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70

a = 0.1

0.2

b = 0.2

0.05

a =
c =

0.2
0.5

b =
d =

0.5
0.02

c = d =

Fig. 4.6 Representation of the trajectories of a Lotka-Volterra system showing a collection of
non-limit cycles ( in blue ) organized around a center ( in red ) for different values of the parameters
a , b , c , d ( http://www.medownloads.com/download-Lotka-Volterra-146411.htm )

attractor having an important Attraction Basin Relative Size (ABRS) in sequential
updating mode when miRNA 159 is absent, and 4 periodic attractors when miRNA
159 is active and inhibits E2F (cf. Fig. 4.7 ).

4.4 MicroRNAs, MitomiRs, and ChloromiRs

4.4.1 Role of MicroRNAs in the General Architecture
of Genetic Regulatory Networks

The microRNAs are parts of the nuclear genome which pertains to the noncoding
genome. They have a partly unspecific role of inhibition, preventing the weakest
part of the genetic regulatory networks to be expressed and hence the appearance of
a too large number of attractors in these networks, i.e., forcing the network to have
only few possible behaviors for fulfilling a precise function. MicroRNAs play an
important role in both specific and nonspecific inhibition in many circumstances of
the cell life, like chromatin clock control and have a big influence on many
metabolic systems. We will first recall the origin of the microRNAs especially
those acting on or pertaining to the mitochondrial (resp. chloroplast) genome called
mitomiRs (resp. chloromiRs) (Bandiera et al. 2011 , 2013 ; Demongeot et al. 2013a ,
b , c ) and second present successively their role in controlling the energy system
[and more generally homeostasis (Bernard 1865 ; Cannon 1932 )], the chromatin
clock, the morphogenesis and cell cycle, the immunologic system, and finally their
possible influence in cancerogenesis and in robustness maintenance. For example,