Compositions and methods for altering cell activity and function by expressing a light-activated ion pump polypeptide in a cell and contacting the cell with light that activates the expressed light-activated ion pump polypeptide. In some aspects of the invention, a light-activated ion pump polypeptide is a modified haloarcula halorhodopsin polypeptide, for example, a modified Halo 57 polypeptide.

Compositions and methods for altering cell activity and function by expressing a light-activated ion pump polypeptide in a cell and contacting the cell with light that activates the expressed light-activated ion pump polypeptide. In some aspects of the invention, a light-activated ion pump polypeptide is a modified haloarcula halorhodopsin polypeptide, for example, a modified Halo 57 polypeptide.

The present invention provides an isolated nucleic acid molecule comprising, or consisting of, the nucleic acid sequence of SEQ ID NO:1, or of a nucleic acid sequence of at least 700 bp having at least 80% identity to said sequence of SEQ ID NO:1, wherein said isolated nucleic acid molecule leads to the specific expression in layer 2/3 of mouse cortex of an exogenous gene in a particular population of EGR2-positive cells when a nucleic acid sequence coding for said exogenous gene is operatively linked to said isolated nucleic acid molecule, said particular population of EGR2-positive cells being characterized in that it also expresses ACTA2, ADORA3 and MYH11.

The present invention provides an isolated nucleic acid molecule comprising, or consisting of, the nucleic acid sequence of SEQ ID NO:1, or of a nucleic acid sequence of at least 700 bp having at least 80% identity to said sequence of SEQ ID NO:1, wherein said isolated nucleic acid molecule leads to the specific expression in layer 2/3 of mouse cortex of an exogenous gene in a particular population of EGR2-positive cells when a nucleic acid sequence coding for said exogenous gene is operatively linked to said isolated nucleic acid molecule, said particular population of EGR2-positive cells being characterized in that it also expresses ACTA2, ADORA3 and MYH11.

Provided herein are a voltage indicator and a method of measuring voltage. The voltage indicator includes a membrane-localized voltage-sensitive protein coupled to a capture protein. The method of measuring voltage includes administering a voltage indicator including a membrane-localized voltage-sensitive protein coupled to a capture protein, and determining changes in fluorescence of a small-molecule fluorescent dye captured by the capture protein.

Provided herein are a voltage indicator and a method of measuring voltage. The voltage indicator includes a membrane-localized voltage-sensitive protein coupled to a capture protein. The method of measuring voltage includes administering a voltage indicator including a membrane-localized voltage-sensitive protein coupled to a capture protein, and determining changes in fluorescence of a small-molecule fluorescent dye captured by the capture protein.