Three Dimensional Image Analysis Applying Various Serial Section Techniques on Study of Melanin Transfer in Human Skin

Abstract

In the basal layer of the epidermis, there are melanocytes that produce melanin. Main function of melanin is to prevent UV-induced damage of keratinocytes by filtering out harmful UV radiation. Melanosomes containing melanin are organelle transferred from melanocytes to neighboring keratinocytes. However the mechanism of melanosome transfer is not fully understood. The study of the mechanism is necessary to understand the hyper or hypo-pigmentary disorders. Three possible mechanisms of melanosome transfer have been reported: (1) direct inoculation of melanosomes into keratinocytes via keratinocyte-melanocyte membrane fusions through nanotubular filopodia, (2) release of individual melanosomes from melanocytes and their uptake by keratinocytes via phagocytosis, (3) partial cytophagocytosis of melanocyte dendrite tips containing melanosomes by keratinocytes, (4) coupled exocytosis of the melanin by melanocytes and subsequent endocytosis by keratinocytes. But those results were studied in different system such as cell culture, mouse skin and so on. In order to know which mechanism moves melanin from melanocyte to keratinocyte in human, we tried to use biopsy tissue of human skin.Structural studies using 2D images show limitations in understanding the structure of cellular organelle. To cope with the difficulty, over the last few years the 3D reconstruction techniques using electron microscopes have been developed at extremely high speed as the related equipments develop. In this study, 3D structure was reconstructed from newly developed serial section techniques. The serial section showed the detail of melanin transfer from melanocyte to keratinocyte in human skin. Our result will help to unravel the mechanisms behind a wide range of human pigmentary disease (This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning(2015R1C1A1A02037153).