Hierarchical modular structure in gene coexpression networks

Network module (community) structure has been a hot research topic in recent years. Many methods have been proposed for module detection and identification. Hierarchical structure of modules is shown to exist in different kinds of biological networks. Compared to the module identification methods, less research is done on the hierarchical structure of modules. In this paper, we propose a method for constructing the hierarchical modular structure in networks based on the extended random graph model. Statistical tests are applied to test the hierarchical relations between different modules. We give both artificial networks and real data examples to illustrate the performance of our approach. Application of the proposed method to yeast gene co-expression network shows that it does have a hierarchical modular structure with the modules on different levels corresponding to different gene functions.