melanosome

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melanosome

[mə′lan·ə‚sōm]
(cell and molecular biology)
An organelle which contains melanin and in which tyrosinase activity is not demonstrable.
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The process requires genes committed to the synthesis and the assemblage of the proteins that form the walls of the pre-melanosomes, the synthesis of the different tyrosinases, the chaperoning of tyrosinases to the pre-melanosome, and the transfer of the melanosomes to the keratinocytes.
Silencing of GPNMB by siRNA inhibits the formation of melanosomes in melanocytes in a MITF-independent fashion.
"There's a complex interaction that occurs between the melanocytes and the keratinocytes, where they phagocytize the ends and take up the melanosomes," said Dr.
Immunolabelling for Melan-A was performed to identify melanocytes while melanosomes were immunostained using the HMB45 antibody.
Using powerful microscopes, the scientists detected within the feathers the remnants of organelles called melanosomes responsible for pigmentation.
By means of the tyrosinase enzyme in the melanosomes, first dopaquinone and then melanin occurs.
Histopathological studies have confirmed that energy from sunlight is absorbed into melanosomes of the retinal pigment epithelium, which can lead to solar retinopathy with thermal and photochemical damage to the photoreceptor cells and retinal pigment epithelium [2].
The origin of BT from neuroectodermal cells was also based on ultrastructural findings of mature membrane-bound melanosomes, suggesting melanin synthesis rather than phagocytosis, and on S100 positivity [19, 21].
The electron microscopy study revealed the presence of cells containing electron-dense granules, whose ultrastructural features corresponded to premelanosomes and melanosomes. Premelanosomes and melanosomes were identified in pigmented cells, pinealocytes, and interstitial cells.
Melanin synthesis is a tightly regulated process whereby potentially cytotoxic intermediates [85] polymerize onto structural protein fibrils in melanosomes and the specialized pigmented organelle in melanocytes.
Inside the keratinocytes, distributed in the hoof epidermal layer, an expressive number of melanosomes, rich in melanin was observed (Figs.
4) revealed irregularly placed giant melanosomes, consistent with CHS.