Transgene expression of the mhChR2::YFP fusion protein is directed to GABAergic interneuronal populations by the mouse vesicular GABA transporter (VGAT or Slc32a1) promoter/enhancer regions on the BAC transgene. The mhChR2::YFP fusion protein is composed of a mammalian codon-optimized Chlamydomonas reinhardtii-derived channelrhodopsin-2 that was modified to harbor a gain-of-function H134R substitution (mhChR2; also called hChR2-H134R) fused in-frame with an enhanced yellow fluorescent protein (EYFP). The mhChR2 is designed to cause larger stationary photocurrents compared to ChR2. The bacterial opsins are retinal-binding proteins that provide light-dependent ion transport and sensory functions to a family of halophilic bacteria; and this mhChR2 functions as a blue light-driven cation channel that depolarizes the cell and causes action potentials. As such, illuminating mhChR2-expressing neurons with blue light (450-490 nm) leads to rapid and reversible photostimulation of action potential firing/neural activity in these cells. EYFP expression is visible by direct fluorescence (epifluorescence microscope). VGAT-mhChR2-YFP mice derived from founder line 8 exhibit strong EYFP expression in olfactory bulb (glomerular and mitral cell layers), thalamic reticular nucleus, superior colliculus, inferior colliculus, brainstem, and molecular layer of cerebellum. Moderate EYFP expression is found in cortex, hippocampus, thalamus, and granule cell layer of olfactory bulb. GAD67 co-staining shows the mhChR2-EYFP expressing neurons are GABAergic interneurons. High EYFP fluorescence is also observed for gray matter in transverse section of the spinal cord. (J:171570)
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