Horizontal cells span across photoreceptors and summate inputs before synapsing onto photoreceptor cells. This mutation results in defective retinal pigment epithelium phagocytosis of photoreceptor outer segments. The rhodopsin gene encodes a principal protein of photoreceptor outer segments. Plants use four kinds of photoreceptors&colon; phytochrome, cryptochrome, a UV-B photoreceptor, and protochlorophyllide "a". This alters vertical transmission between photoreceptor, bipolar and ganglion cells. Postsynaptic structures differ for cochlear cells and photoreceptor cells. When light hits photoreceptive pigments within the photoreceptor cell, the pigment changes shape. When light hits a photoreceptive pigment within the photoreceptor cell, the pigment changes shape. One species may have six different opsin genes, but only express one spectrally distinct photoreceptor. The gene is expressed at the active zone of photoreceptor ribbon synapses. Guard cells contain phototropin proteins which are serine and threonine kinases with blue-light photoreceptor activity. Cone opsins, employed in color vision, are less-stable opsins located in the cone photoreceptor cells. OTX2 activity commits cells to the photoreceptor fate. Every rod or cone photoreceptor releases the same neurotransmitter, glutamate. This is generally followed by loss of cone photoreceptor cells.