ACE2 and COVID-19: Mouse models for COVID-19 that allow the analysis of breathing regulation are more complicated to develop, not only because the animal experiments are hindered by the need of laboratories with high biosafety levels, but because the spike proteins of SARS-CoV and SARS-CoV2 have a much lower binding affinity to the murine ACE2 than to its human homolog (Lutz et al., 2020).