Fig. 7

Ultrastructural analysis of differentiated AS reveals a multilayer organization with different cell types and an organized extracellular matrix. A Elongated cells with few rounded mitochondria, extensive endoplasmic reticulum with distended cisternae and cytoplasmic vesicles (asterisk) likely correspond to undifferentiated preadipocytes. B Small lipid droplets towards the cellular poles of putative preadipocytes. 2 µm bar in A and B. C Adipocytes in advanced differentiation stages are characterized by glycogen granules near the lipid droplets, rounded cell shape, and displacement of the nucleus towards the cellular periphery. 10 µm scale bar. D Terminally differentiated adipocytes are characterized by a single giant lipid droplet and a “ring-shaped” cytoplasm surrounding it, with a crescent moon-shaped nucleus on the one side of the lipid droplet. 5 µm scale bar. E The contact zone between plasma membranes of two adjacent adipocytes shows abundant and well-defined individual caveolae and caveolae/clusters known as rosettes. Frame magnification in E showing 3 individual caveolae (black arrow) and two rosettes (white asterisk). F The extracellular matrix in the adjacent zone to the adipocyte shown in panel (D) shows thick and banded fibers with a parallel arrangement, interspersed by thinner fibers with a looser disposition. 1 µm scale bar in E and F. G-–H Towards the center of AS is abundant ECM with a loose appearance, with thin and dispersed fibers (G) intertwined with thicker and banded fibers (H). 500 nm scale bar in G and H. N, nucleus; ER, endoplasmic reticulum; M, Mitochondrion; LD, lipid droplet; G, Golgi complex; Gly, glycogen; ECM, extracellular matrix