Figure 1

Some vertices at the periphery of a regulatory network (the places where signals start or get their targets) can be rather significant. A: The topological impact of start-point S1 is bigger than that of start-point S2. Both, white and gray vertices are on some path beginning in S1, while S2 is limited on the gray ones. B: The topological significance of end-point T1 is bigger than that of end-point T2 because of being reachable from all gray and white vertices. However, in terms of betweenness centrality, all of them are attributed with zero values which fail to reflect the individual connectedness of such input/output elements within the whole network.