Marked Changes in Lamellar Granule and Trans-Golgi Network Structure Occur During Epidermal Keratinocyte Differentiation.

Epidermal lamellar granules (LGs) transport various lipids, proteins and protein inhibitors from the trans-Golgi network (TGN) to the extracellular space, and play an important role in skin barrier formation. We elucidated the three-dimensional (3D) structure of LGs and the TGN in normal human skin by focused ion beam scanning electron microscopy (FIB-SEM). Reconstructed FIB-SEM 3D images revealed that the overall LG structure changed from vesicular to reticular within the second layer of the stratum granulosum. Furthermore, the TGN was well developed within this layer and spread through the cytoplasm with branched, tubular structures that connected to LGs. Our study reveals the unique overall 3D structure of LGs and the TGN within the cells of the epidermis, and provides the basis for an understanding of the skin barrier formation.