Table of Contents
Definition
Chromatophores are referred to as pigment-containing cells or groups of cells that produce colour. They are present in various creatures, including fish, amphibians, reptiles, crabs, and cephalopods. Melanocytes are a kind of cells that are responsible for the colouration of mammals and birds. Other membrane expansions into the cytoplasm of some prokaryotes, such as cyanobacteria, are called chromatophores and contain pigments.
In ectothermic animals, chromophores are produced in the neural crest during embryonic development and play a significant role in imparting skin and eye colour. Erythrophores (red), xanthophores (yellow), iridophores (iridescent/reflective), leucophores (white), melanophores (black/brown), and cyanophores (blue) are the mature chromatophores that are divided into subclasses based on their colour (more accurately “hue”) under white light.
Several species can quickly alter their colour through systems that move pigment and reposition reflecting plates within chromatophores. Metachrosis, also known as physiological colour change, is the term used to describe this phenomenon, which is frequently used as a form of camouflage.
Classification
There are three different categories of chromatophores:
- Iridophores: These cells have reflective platelets, which alter how they are oriented to reflect various colours.
- Melanophores: The melanin that gives the skin its dark hues is found in these cells.
- Xanthophores: The carotenoids that give the skin its yellow and orange hues are found in these cells.
Erythrophores and Xanthophores
Chromatophores are classified as either erythrophores or xanthophores depending on whether they are predominantly composed of red/orange carotenoids or significant quantities of yellow pteridine pigments. The overall colour, however, relies on the ratio of red and yellow pigments when vesicles carrying carotenoids and pteridine are present in the same cell. Consequently, the difference between these chromatophores is not always evident.
Leucophores and Iridophores
Iridophores are chromatophores that reflect light utilising crystalline plates of guanine-based chemochromes also known as guanophores or guanochromes. They produce iridescent hues when lighted as a result of constructive light interference. Iridophores produce bright blue or green colours by utilising biochromes as coloured filters, which causes an optical phenomenon called Tyndall or Rayleigh scattering.
Leucophores, a related class of chromatophores, are primarily found in the tapetum lucidum of several fish. They use crystalline purines (usually guanine) to reflect light, like iridophores. Leucophores have more structured crystals than iridophores, which reduces diffraction. They emit a white shine when exposed to white light.
Melanophores
Because of its ability to absorb light, eumelanin, a kind of melanin found in melanophores, gives them their dark brown or black appearance. It is dispersed throughout the cell in vesicles called melanosomes.
To produce skin, hair, and eye colour, humans have just one type of pigment cell, melanocytes — the mammalian equivalent of melanophores. Melanophores are by far the most extensively researched chromatophore, partly because the cells are typically relatively simple to visualise due to their size and contrasting colour. However, the biology of melanophores and melanocytes differ from one another.
Cyanophores
Some bacteria and algae contain light-emitting organelles called cyanophores. They are in charge of providing these organisms with their characteristic blue-green hue. Phycobilins and phycoerythrin are the two types of proteins that make up cyanophores. The blue hue comes from phycobilins, whereas the red tint comes from phycoerythrin.
Functions & Applications
Animals have colour-changing pigment cells or chromophores in their skin. They serve as a means of communication, temperature regulation, and camouflage. Melanin, a pigment found in chromophores, absorbs light. The melanin is concentrated, and the pigment cells appear dark when constricted. The melanin is scattered when the cells grow, giving the cells a light appearance.
Chromatophores are often used in practical research. Zebrafish larvae, for example, are used to examine how chromatophores coordinate and communicate to produce the continuous horizontal striped pattern seen in adult fish. This is regarded as a helpful model system in the field of evolutionary developmental biology for understanding patterning.
Additionally, human conditions or diseases like albinism and melanoma have been modelled using chromatophore biology.
Chromatophores are also studied as a biomarker of blindness in cold-blooded species because animals with specific visual abnormalities cannot effectively adapt to light settings.
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