Mitochondria in mammalian cells are visualized as a network or as filaments that 
undergo continuous changes in shape and in localization within the cells. These 
changes are a consequence of the activity of different processes such as 
mitochondrial fusion and fission, and mitochondrial remodelling. In all, these 
processes are referred to as mitochondrial dynamics, and relevant questions, 
still unexplained, are why cells require such an active dynamics, or why 
mitochondria move to specific cellular regions. In this review we will summarize 
some of the biological functions assigned to the proteins identified as 
participating in mitochondrial fusion, namely mitofusin 1, mitofusin 2 and OPA1. 
In addition to the capacity of these proteins to promote fusion, mitofusin 2 or 
OPA1 regulate mitochondrial metabolism and loss-of-function reduces oxygen 
consumption and the capacity to oxidize substrates. We propose that 
mitochondrial fusion proteins operate as integrators of signals so they regulate 
both mitochondrial fusion and metabolism.