Since this approach provides only very limited conclusions about the causesof the observed phenomena, a new strategy has emerged, the so-called “upstreamanalysis" that allows us to identify the causes of the changes in expression. This strategy consists of two main stages: (1) analysis of the promoters and enhancers of the identified DEG to determine the transcription factors involved in the process; (2) reconstruction of signaling paths that activate these transcription factors and identify the main regulators at the top of such paths.