Melanosome

Source: Wikipedia, the free encyclopedia.
For the geological term, see
melanosome (geology)
.
7× speed timelapse video of fish melanophores responding to 200 uM adrenaline; the melanosomes retreat to the center of the star-shaped melanophore cells.
Fish and frog melanophores are cells that can change colour by dispersing or aggregating pigment-containing melanosomes.

A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotection in animal cells and tissues.

Melanosomes are synthesised in the skin in

retinal pigment epithelial (RPE) cells. In lower vertebrates, they are found in melanophores or chromatophores.[1][2]

Structure

Melanosomes are relatively large organelles, measuring up to 500

electron microscopy
, which varies according to the maturity of the melanosome, and for research purposes a numeric staging system is sometimes used.

Synthesis of melanin

Melanosomes are dependent for their pigment on certain enzymes, especially

light microscopy
it is known as a pre-melanosome.

Dysfunction or absence of the melanin-synthesising enzymes (in conditions such as Chédiak–Higashi syndrome) leads to various patterns of albinism.

Pseudopodia and tanning

In some melanocytes, the melanosomes remain static within the cell. In others the cell can extend its surface lengthwise as temporary projections known as pseudopodia, which carry melanosomes away from the center of the cell, thereby increasing the cell's effectiveness in absorbing light.

The pseudopodial process (aka the tanning process) happens slowly in dermal melanocytes in response to

ultraviolet light and to production of new melanosomes and increased donation of melanosomes to adjacent keratinocytes, which are typical skin surface cells. Donation occurs when some keratinocytes engulf the end of the melanocyte pseudopodia, which contain many melanosomes. Cytoplasmic dynein will carry the vesicles containing the melanin to the center of the cell, which causes melanosomes to sequester the keratinocyte's nucleus, providing optimal protection from UV rays. These changes are responsible for tanning of human skin after exposure to UV light or sunlight.[citation needed
]

In animals

In many species of fish, amphibians, crustaceans, and reptiles, melanosomes can be highly mobile within the cell in response to hormonal (or sometimes neural) control, which leads to visible changes in colour that are used for behavioural signaling or photoprotection.

Melanosomes found in certain fish species contain

photoprotective system works for the fish on a molecular level.[3]

Recently, melanosomes were found in spiders as well.[4]

The beautiful and rapid colour changes seen in many cephalopods such as octopuses and squid, are based on a different system, the chromatophore organ.[5][6]

In fossils

Recent (2008) discoveries by

Neogene periods (66 to 2 million years ago). The feathers contain preserved residues of carbon that were previously thought to be traces of bacteria that decomposed feather tissues; however these (residues) are in fact microscopic organic imprints of fossilized melanosomes. Some of these structures still maintain an iridescent color typical of feather and fur tissues. It is conjectured that these microscopic structures could be further studied to reveal the original colors and textures of softer tissues in fossils. "The discovery of ultra-structural detail in feather fossils opens up remarkable possibilities for the investigation of other features in soft-bodied fossils, like fur and even internal organs," said Derek Briggs of the Yale University study team.[7][8]

Melanosomes were used to discover the true colors of fossil

Beijing Museum of Natural History, Peking University, Yale University, the Peabody Museum of Natural History, the University of Akron, and the University of Texas at Austin.[9][10]

Melanosomes have also been found in fossils from Tupandactylus cf. imperator pteurosaurs in the Lower Cretaceous Crato Formation, in the Araripe Basin, in Brazil.[11]

Templating

Melanosomes are believed to template melanin polymerization by way of

Pmel17, which is present in abundant quantities in melanosomes.[12]

References

  1. ^
    PMID 19056669
    .
  2. PMID 17878918
    .
  3. S2CID 46220077
    .
  4. PMID 28566355
    .
  5. S2CID 17172396
    .
  6. ^ Wood, James; Jackson, Kelsie (2004). "How Cephalopods Change Color" (PDF). The Cephalopod Page. Retrieved 23 August 2016.
  7. ^ Andrea Thompson (2008-07-08). "Feather Fossils Could Yield Dinosaur Colors".
    LiveScience
    . Retrieved 2009-08-29.
  8. ^ "Ancient Bird Feathers Had Iridescent Glow". Fox News. 2009-08-26. Retrieved 2009-08-28.
  9. S2CID 206525132
    .
  10. ^ Jesus Diaz (8 February 2010). "The Real Colors of a Dinosaur Revealed for the First Time". Gizmodo. Gawker Media. Retrieved 8 January 2015..
  11. S2CID 248298392
    .
  12. PMID 16300414
    .

External links
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