Figure 8

A summary of the modes of regulation encountered in the IRCSs and their parent strains. Blue marks the B6 chromosome segments while yellow marks the SEG chromosome segments. The blue arrows represent a B6 expression level, while the yellow arrows represent a SEG expression level. Red arrows correspond to expression levels that are different from the parent strains. The white arrows symbolize the interaction of trans-factors (octagons) on cis-regulatory elements, themselves located either on the same or on other chromosomes. (a, b) Parent strains B6 and SEG. (c) Representation of the interaction of an SEG trans-factor acting on the B6 genome. In the IRCSs, since the M. spretus segments account for less than 2% of the genome, this case is supposed to occur relatively rarely, but can probably explain the dysregulation of genes located in the B6 background. This dysregulation can be mediated either by an activating or inhibiting factor, the effect of these factors being detectable if the expression level is different from B6. (d) Interaction of a trans-factor of B6 origin on a M. spretus segment, resulting in a B6-like expression level. This type of regulation includes genes of class 1 (Figure 9). (e) Interaction of a trans-factor of B6 origin on a M. spretus segment, resulting in a SEG-like expression level (that is, the expression level is dictated by the cis-elements of M. spretus origin). This type of regulation includes genes of class 3 (Figures 9 and 10). (f) Interaction of a trans-factor of B6 origin on a M. spretus segment, resulting in a novel expression level. This type of regulation includes genes of class 2 (Figure 9).