We want to know whether multiple regulatory circuits in networks of genes-controllers represent a fine tuning system to specify the precise position in the embryo where the target gene is active or whether the regulatory inputs are redundant.
We have here a problem of structural stability of the self-regulated system with respect to perturbations that introduce a side regulatory pathway which increases the order of the system. Hence the system has been constructed in such a way that the appearance of a side pathway do not give rise to an instability of the original system.
My consideration exploits following essential characters of gene networks. Each gene-member of the network encodes peptide-product which function is activation or repression of another gene (so called, targeting gene). These transcription factors recognise specific sequences of DNA in regulatory domains of the targeting genes and tightly bind to the targeting sites. Given member of the network produces transcription factors that specifically activate or repress of other netters, and vice versa. Complex network of autoregulatory and cross-regulatory actions functionally connects the genes forming thereby gene networks and cascades. Result of action of the network or cascade is peculiar spatial pattern of activity (expression) of the network members. Down-activated members, in turn, switch on structural genes in appropriate time and place. We preferably assume the concentration-dependent action of the peptide-regulator on the targeting gene. Namely, at low concentrations it acts as activator, while at high concentrations it acts as repressor (See Jackle et al., 1992).
Complexification of the Genes-Controllers Nets: Biological Experience
Complexification of the Regulatory Nets: Theoretical Model
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