This paper addresses two examples of MOOCs aimed at developing mathematics teachers' professional learning. The programme, named "Math MOOC UniTO," was developed under the guidance of the three authors, in collaboration with some researcher-teachers from the University of Turin. This paper analyses the development of teachers' learning while attending the virtual environment of a MOOC, where all resources are available online and where peer interactions take place in asynchronous mode thanks to specific communication message boards. To analyse the data, two theoretical lenses were considered, namely, Meta-Didactical Transposition and Connectivism. The first lens allowed us to describe teachers' improvements at macro-level (praxeologies) and micro-level (agents); the second lens made possible the utmost consideration of the network of knowledge (learning is interpreted in the light of how nodes and connections within the network are determined dynamically). Using these theoretical lenses, we observed two different teachers' learning processes, namely, one that evolved dramatically because of the interventions (we call it an explosion), the other less proactively (we call it linear). We discuss them, presenting two different emblematic examples of data.