Light-sensitive Motile Iridophores and Visual Pigments in the Neon Tetra, Paracheirodon innesi

Abstract

Although motile iridophores in the longitudinal stripes of neon tetra skin are under control of the sympathetic nervous system, they also respond to light directly and show circadian color changes. Using neon tetra skin, we found that the photoresponse of iridophores depends on light intensity, and that light near 500 nm is most effective. RT-PCR demonstrated the expression of mRNAs encoding rhodopsin and two kinds of cone opsins (Pi-green1 and Pi-green2) in neon tetra skin where the light-sensitive iridophores exist. These mRNAs are also expressed in the lateral eyes. The cone opsin genes, Pi-green1 and Pi-green2, show high similarity with the g101 and g103 genes of unique green cone opsins (belonging to the MWS/LWS group) of the blind Mexican cavefish. These results show that Pi-green1, Pi-green2, and/or rhodopsin may play important roles in the photoresponse of neon tetra iridophores, which are most sensitive to light near 500 nm.

Into the blue: Gene duplication and loss underlie color vision adaptations in a deep-sea chimaera, the elephant sharkCallorhinchus milii

“…LWS gene duplications have also been reported in a number of species of teleost fish (Yokoyama and Yokoyama 1990;Register et al 1994;Chinen et al 2003;Fuller et al 2004;Kasai and Oshima 2006;Matsumoto et al 2006;Weadick and Chang 2007), in Old World primates (Nathans et al 1986;Ibbotson et al 1992), and in a single species of New World primate, the howler monkey (Dulai et al 1999). In primates, the duplication is directly linked to the attainment of trichromacy, and the same may be the case for the elephant shark.…”

Visual phototransduction components in cephalopod chromatophores suggest dermal photoreception

“…However, extraocular photoreceptors can also express opsins identical to those in the retina and may potentially use visual phototransductive pathways. Examples of these include rhodopsin in the light organ and parolfactory vesicles of squids and cone opsins in the dermis of fish (Hara and Hara, 1980;Tong et al, 2009;Ban et al, 2005;Kasai and Oshima, 2006;Chen et al, 2013). Nile tilapia (Oreochromis niloticus) and neon tetra (Paracheirodon innesi) are particularly notable, because opsins identical to those in the retina play a role in initiating signals that result in expansion and contraction of pigment cells (chromatophores) or modulation of the color reflected from iridophores.…”

Functional characterisation of the chromatically antagonistic photosensitive mechanism of erythrophores in the tilapiaOreochromis niloticus

“…Like other photoreceptors, chromatophore photosensitivity is proposed to be associated with the expression of opsin-based photopigments within cells (Ban et al, 2005). Using molecular approaches, opsin expression has been identified in tissues containing chromatophores and in pigment cell lines (Miyashita et al, 2001;Kasai and Oshima, 2006;Im et al, 2007). However, some of these results have been obtained from tissues that may contain a mixture of different types of chromatophores.…”

“…By contrast, the aggregations and dispersion of red pigment (erythrosomes) of erythrophores are induced in different spectral ranges (Ban et al, 2005;Chen et al, 2013). Both visual and non-visual photopigments have been identified within isolated chromatophores and in tissues containing chromatophores (Provencio et al, 1998;Kasai and Oshima, 2006). Opsins are thought to initiate phototransduction by the regulation of intracellular cAMP level through G s and G i proteins, leading to pigment dispersion and aggregation, respectively (Ban et al, 2005).…”