Ultrastructural Observations on DMBA-Induced Dermal Hyperpigmentation and Blue Nevus-Like Tumors in the Mongolian Gerbil 1

Abstract

Summary

Electron microscopic observations were made on the dermal hypepigmentation and blue nevus-like tumors induced in the dorsal trunk skin of Mongolian gerbils by DMBA. Hyperpigmented dermis was also examined in gerbils treated with DMBA and croton oil.

The dermal hyperpigmentation was characterized by numerous melanin-bearing melanocytes and macrophages. Some of the dermal melanocytes were loaded with fully melanized (Stage IV) melanosomes, whereas others contained both mature melanosomes and immature ones (Stages I-III). Some dermal melanocytes displayed giant melanosomes (“mac-romelanosomes”) along with melanosomes of normal size. Finally, occasional dermal melanocytes exhibited typical Stages I-III melanosomes as well as round Stage I-like melanosomes in which melanin deposition occurred prematurely on the vesicular and filamentous matrices. The macrophages of hyperpigmented dermis contained groups of melanosomes segregated within membrane-limited secondary lysosomes.

Paralleling the diversity in melanosome formation within the dermis, examination of DMBA-induced blue nevus-like tumors indicated that melanosomes were formed (1) in the standard manner with melanin deposited on a matrix of aligned filaments within a membrane-limited vacuole, and (2) by melanin deposition on a disorganized matrix of nonaligned filaments and/or mi-crovesicular bodies within a membrane-limited vacuole. Melanosomes formed via both pathways were subsequently grouped within autophagosomes and degraded therein.