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cone cells

also: cone photoreceptors. Cone cells are retinal photoreceptor cells (visual cells) that transduce light signals into electrical responses. These cells are concentrated in the center of the retina. Cone cells project from the outer retinal surface into a carbohydrate-rich interphotoreceptor matrix.

Cone cells and other major cell types composing the neural retina (Jeon et al, 1998) arise from a pool of multipotent neuroepithelial progenitor cells and their development requires extrinsic signals (Cepko et al, 1996; Turner and Cepko, 1987; Holt et al, 1988; Wetts and Fraser, 1988; Belliveau and Cepko, 1999). Subsets of retinal progenitors have been shown to display temporally regulated and distinct biases in the fates of their progeny (Alexiades and Cepko, 1997).

These photoreceptor cells form synapses with sensor neurons (bipolar cells) that link to other specialized neurons (horizontal cells, amacrine cells) that form a lateral network within different parts of the retina and are involved in processing visual information. Major links are established to other sensor neurons (ganglion cells), the axon bundles of which form the optic nerve.

Unlike images produced by rod cells, images produced by cone cells are sharp and clear and in color. Cone cells are used for vision in bright light. Cone cells possess a non-motile cilium that contains light-sensitive pigments. There are three different types of cone cells in humans that differ in their light-sensitive pigments. These pigments have different specral maxima: S-cone cells are sensitive to short wavelengths (424 nm maximum) and contain a blue-sensitive pigment. M-cone cells are sensitive to medium wavelengths (530 nm maximum) and contain a green-sensitive pigment. L-cone cells are sensitive to longer wavelengths and contain a red-absorbing pigment (560 nm maximum) (Nathans et al, 1986; Oprian et al, 1991; Calkins, 2001). Additional types of cone cells with light-sensitive pigments that have different spectral maxima are found in some other species. Cone cells frequently show a mosaic-like distribution (Fei, 2003; Raven and Reese, 2003). Non-random distribution patterns of colour cones have been found in several species (Szel et al, 1996). Variations in the rations of different types of cone cells are abserved also (Hagstrom et al, 1998). The integration of impulses from different types of cone cells provides colour vision (Dacey, 2000; Lennie, 2000; Gegenfurtner and Kiper, 2003).

Nishida et al (2003) have shown that the transcription factor Otx2 is essential for retinal photoreceptor cell fate determination. Otx2-deficiency converts differentiating photoreceptor cells to amacrine-like neurons and transactivates the cone-rod homeobox gene Crx, which is required for terminal differentiation and maintenance of photoreceptor cells. Retroviral gene transfer of Otx2 steers retinal progenitor cells toward becoming photoreceptors.

For related information see also: Cell types.

LAST MODIFIED: September 2006

See REFERENCES for entry cone cells

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