Using CRISPR knock-in of fluorescent tags to examine isoform-specific expression of EGL-19 in C. elegans

L-type voltage-gated calcium channels (VGCCs) regulate calcium influx and excitation-contraction coupling in many types of muscle cells. Thus, VGCC mutations can cause skeletal and cardiac muscle diseases in humans, such as Duchenne muscular dystrophy and Timothy syndrome. To better understand the genetics and native expression of VGCCs, we have chosen to use the microscopic roundworm, C. elegans . The egl-19 locus is the sole L-type VGCC gene and it encodes three distinct isoforms (a, b, and c). Isoform c is curious because the protein is truncated, lacking the transmembrane domains that form the physical calcium channel. In this study, we have characterized egl-19 expression using CRISPR/Cas9 genome editing to 'knock-in' fluorescent tags of differing colors, allowing us to distinguish the expression pattern of each isoform. Not surprisingly, we found that EGL-19 is expressed in all types of muscle. In addition, we provide evidence that the truncated c isoform is expressed. Finally, although we find evidence that specific isoforms can have unique subcellular distributions, we also observed some expression patterns that appear to be artifacts. Overall, our results show interesting patterns of egl-19 expression, but also highlight the need for caution when interpreting expression of reporter genes even when they represent endogenous tags.