Thy1 transgenic mice expressing the red fluorescent calcium indicator jRGECO1a for neuronal population imaging in vivo

Calcium imaging is commonly used to measure the neural activity of large groups of neurons in mice. Genetically encoded calcium indicators (GECIs) can be delivered for this purpose using non-invasive genetic methods. Compared to viral gene transfer, transgenic targeting of GECIs provides stable long-term expression and obviates the need for invasive viral injections. Transgenic mice expressing the green GECI GCaMP6 are already widely used. Here we present the generation and characterization of transgenic mice expressing the sensitive red GECI jRGECO1a, driven by the Thy1 promoter. Four transgenic lines with different expression patterns showed sufficiently high expression for cellular in vivo imaging. We used two-photon microscopy to characterize visual responses of individual neurons in the visual cortex in vivo. The signal-to-noise ratio in transgenic mice was comparable to, or better than, mice transduced with adeno-associated virus. In addition, we show that Thy1-jRGECO1a transgenic mice are useful for transcranial population imaging and functional mapping using widefield fluorescence microscopy. We also demonstrate imaging of visual responses in retinal ganglion cells in vitro. Thy1-jRGECO1a transgenic mice are therefore a useful addition to the toolbox for imaging activity in intact neural networks.

钙成像（Calcium imaging）是检测小鼠体内大量神经元集群神经活动的常用技术手段。基因编码钙指示剂（Genetically Encoded Calcium Indicators, GECIs）可通过非侵入性遗传学方法递送，用于此类神经活动检测。相较于病毒基因转导策略，靶向GECIs的转基因方法可实现稳定的长期表达，且无需进行侵入性病毒注射。表达绿色GECI GCaMP6的转基因小鼠已得到广泛应用。本研究报道了由Thy1启动子（Thy1 promoter）驱动、表达敏感性红色GECI jRGECO1a的转基因小鼠的构建与表征。本研究共获得4种具有不同表达谱的转基因品系，其表达水平足以支持细胞级活体成像实验。我们借助双光子显微镜（two-photon microscopy）对活体小鼠视觉皮层内单个神经元的视觉响应进行了表征分析。该转基因小鼠的信噪比可与腺相关病毒（adeno-associated virus）转导的小鼠相当，甚至更优。此外，我们证实Thy1-jRGECO1a转基因小鼠可用于经颅神经元集群成像以及基于宽场荧光显微镜（widefield fluorescence microscopy）的功能图谱绘制。我们还实现了体外环境下视网膜神经节细胞（retinal ganglion cells）视觉响应的成像观测。综上，Thy1-jRGECO1a转基因小鼠可为完整神经网络活动成像的研究工具库增添极具价值的新选择。