A new phenotype identification method with the fluorescent expression in cross-sectioned tails in Thy1-GCaMP6s transgenic mice

Purpose: Unless the phenotype of the transgenic mice is distinguishable, genotyping in each mouse is required prior to experiments. This study aimed to establish a new identification method for the phenotype in Thy1-GCaMP6s transgenic mice to reduce the cost and time. Methods: Tail biopsies (2 mm) were performed under general anesthe-sia with isoflurane in 3 to 4-week-old mice. Then, the resected tail was cut again with a sharp razor, and the cross-sections were observed with two-photon microscopy (excitation wavelength = 940 nm). The emitted light was split into green and red light by a dichroic mirror (570 nm) with bandpass filters (495-540 nm for green, 575-645 nm for red). Results: Two types of expressed fluorescent pattern were found in the tail tissue: the presence of green fluorescent structures (type 1) and the absence of the structures (type 2). Cortical imaging confirmed that type 1 expressed the cortical GCaMP6s, while type 2 did not. Conclusion: These results suggest that observation of the cross-sectioned tail in Thy1-GCaMP6s mice enabled to identify the phenotype within approximately 10 min/mouse, which reduces the cost and time for geno-typing.