A nonpigmented membrane-bound vesicle in a melanocyte that contains tyrosine and matures into the melanin-filled melanosome; prominent in melanocytes of albinos.
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106) HMB-45 (anti-gp100), a premelanosome marker, has been shown to mark the intraepidermal and superficial dermal components of melanocytic nevi, with the exception of diffuse dermal staining in blue nevi.
Similarly, Stone et al (16) detected HMB-45 and NK1-C3 immunoreactivity predominantly in epithelioid and spindle cells and premelanosome -like structures in epithelioid cells in 9 cases by electron microscopy.
Markers such as chromogranin A and gp100 (the target of antibody HMB-45) localize to granular structures within the cell and tumor cytoplasm, in dense core granules (chromogranin A) and premelanosomes (gp100), respectively.
The second population exhibits fine elongations, enclosed in basal membrane while the third population consists of dendritic cells containing melanosomes and premelanosomes.
The ink is a complex mixture of organelles, premelanosomes, melanosomes, granules, proteic material (enzymes), glucosamine, and phospholipids in suspension.
12) Electron microscopy may identify the presence of melanosomes or premelanosomes.
No melanosomes or melanosome-like structures have been identified, although premelanosomes were very occasionally seen in one case.
There were no recognizable lipid droplets, premelanosomes, fusiform densities, or micropinocytotic vesicles.
2) In 2 reported cases, transmission electron microscopy was used to identify melanosomes, premelanosomes, and discrete aggregates of intermediate filaments distending the cytoplasm.
Ultrastructurally, epithelioid cells in AML show evidence of melanogenesis by the presence of intracytoplasmic membrane-bound dense bodies, crystalloids, or granules consistent with premelanosomes (Figure 4).
Ultrastructurally, melanosomes and premelanosomes can be seen.