text: As PACs consist of a light sensor and an enzyme in a single protein, they can be expressed in other species and cell types to manipulate cAMP levels with light. When bPAC is expressed in mouse sperm, blue light illumination speeds up the swimming of transgenic sperm cells and aids fertilization. When expressed in neurons, illumination changes the branching pattern of growing axons. PAC has been used in mice to clarify the function of neurons in the hypothalamus, which use cAMP signaling to control mating behavior. Expression of PAC together with K-specific cyclic-nucleotide-gated ion channels (CNGs) has been used to hyperpolarize neurons at very low light levels, which prevents them from firing action potentials.