Biocompatibility of a genetically encoded calcium indicator in a transgenic mouse model

Engineering efforts of genetically encoded calcium indicators predominantly focused on enhancing fluorescence changes, but how indicator expression affects the physiology of host organisms is often overlooked. Here, we demonstrate biocompatibility and widespread functional expression of the genetically encoded calcium indicator TN-XXL in a transgenic mouse model. To validate the model and characterize potential effects of indicator expression we assessed both indicator function and a variety of host parameters, such as anatomy, physiology, behaviour and gene expression profiles in these mice. We also demonstrate the usefulness of primary cells and organ explants prepared from these mice for imaging applications. Although we find mild signatures of indicator expression that may be further reduced in future sensor generations, the 'green' indicator mice generated provide a well-characterized resource of primary cells and tissues for in vitro and in vivo calcium imaging applications. Calcium-sensing fluorescent proteins such as TN-XXL are valuable tools for studying cellular function but, when expressed in mice, may affect animal physiology and behaviour. The authors of this paper create transgenic mice expressing TN-XXL and show that long-term expression of TN-XXL is tolerated well.