Surface properties of human melanoma cells

The morphology of the amelanotic Greene melanoma

Pieces of amelanotic Greene melanoma were transplanted onto the iris surface of rabbit eyes, where they started to grow rapidly after a dormant period of four to five days. Light microscopically, the melanoma cells appeared round or polygonal and contained large, lightly staining nuclei and prominent nucleoli. Electron microscopy revealed rather electron translucent nuclei containing only a small rim of heterochromatin immediately subjacent to the nuclear envelope. The very prominent, reticulated nucleoli frequently lay close to the nuclear surface. The cytoplasm of the cells showed a well developed Golgi field which contained myriad vesicles of different shape and density and cross-striated, membrane-bound organelles of early melanin synthesis. The mitochondria were short and the smooth-surfaced endoplasmic reticulum was inconspicuous. The rough-surface endoplasmic reticulum was sparse and exhibited predominantly short segments. Like other very active cells, the melanoma cells contained a multitude of ribosomes. Melanoma cells which were not completely surrounded by other cells exhibited numerous processes at the free cell surface and, directly subjacent to these, a layer of very electron dense cytoplasm, indicating that these cells may possess a certain amount of motility. Many light and electron microscopical aspects of the amelanotic Greene melanoma are identical or similar to human uveal melanomas, especially of the epithelioid variety. On morphological grounds it is therefore possible to suspect a close biological relationship of these tumors. Thus, the use of the Greene amelanotic melanoma as a model for study of diagnostic and therapeutic problems in ophthalmology may be considered adequate.

Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. III. Melanin pigment and melanogenesis in experimental neurogenic tumors: a reappraisal of the histogenesis of pigmented nerve sheath tumors

Four melanin pigment-containing intracranial tumors were found in three Long-Evans rats in the course of experimental oncogenesis by transplacental ethylnitrosourea (ENU). One of them was a leptomeningeal melanoma. Aside from the presence of scattered melanin-pigmented cells, the other three had the typical histological features of ENU-induced malignant nerve sheath tumors. Two of the three tumors were studied by electron microscopy and in tissue and organ culture systems. One of them demonstrated progressive melanogenesis in vitro; the other failed to produce more melanin and showed increasing differentiation, with a Schwannoma-like pattern by light microscopy. Melanosomes and premelanosomes were identified in both tumors by electron microscopy; the other fine structural features were those of malignant Schwannomas. These observations are relevant to the controversy on the histogenesis of pigmented nerve sheath tumors occasionally encountered in man and on the relationship of these tumors to pigmented nevi. The findings in the present study support the view of Masson that neoplastic nerve sheath cells are capable of melanogenesis.