  Two different types of directed networks are investigated, transcriptional
regulation networks and neural networks. The directed network structure are
studied and also shown to reflect the different processes taking place on the
networks. The distribution of influence, identified as the the number of
downstream vertices, are used as a tool for investigating random vertex
removal. In the transcriptional regulation networks we observe that only a
small number of vertices have a large influence. The small influences of most
vertices limit the effect of a random removal to in most cases only a small
fraction of vertices in the network. The neural network has a rather different
topology with respect to the influence, which are large for most vertices. To
further investigate the effect of vertex removal we simulate the biological
processes taking place on the networks. Opposed to the presumpted large effect
of random vertex removal in the neural network, the high density of edges in
conjunction with the dynamics used makes the change in the state of the system
to be highly localized around the removed vertex.
