Ultrastructural studies on tumours and cell cultures of the Harding--Passey mouse melanoma.

Abstract

SUMMARY Ultrastructural studies have been carried out on tumours and monolayers of cells of the transplantable Harding-Passey mouse melanoma, grown in tissue culture. Tumours were found to consist of melanin-producing, melanin-producing-and-containing and melanin-containing cells. Melanosomal complexes found in melanin-containing cells appeared to arise by fusion of solitary melanosomes either with each other or with lysosomes. Melanophages, previously regarded as macrophages which have migrated into the tumour, are probably altered and older melanoma cells. Melanosomal complexes contained in these cells have formed by autophagocytosis. Tissue culture studies support this view. Melanoma cells grown in vitro were invariably found to contain melanosomal complexes as well as solitary melanosomes, and older cells in culture contained numerous melanosomal complexes. Virus-like particles resembling immature C-type virus particles were found in all the tumours examined and were especially abundant in cultured cells. These particles were found in the cisternae of rough endoplasmic rcticulum. The significance of these virus particles is still a matter for speculation.