Detection of pre-DMS in bone marrow MKs. (A) View of a 100-µm-thick BM section with immunofluorescence staining as indicated on the figure. The different stages of development of the DMS (pre-, intermediate, and late) are identified by the anti-GPIbβ antibody. Bar, 20 µm. (B) Higher-magnification confocal image of a typical stage I MK showing GPIbβ at the cell periphery and the pre-DMS (arrow) connected to and located just beneath the cell surface, between the nuclear lobes (see supplemental Movie 3 for the complete Z-stack analysis). Bar, 10 µm. (C) Representative TEM image of the pre-DMS. Note the well-defined boundary, the precise localization in the perinuclear region (arrow) between the nuclear lobes, and the connection with the cell surface (arrowhead). Bar, 2 µm (D) 3D reconstruction from an FIB/SEM analysis of the pre-DMS (orange) in a bilobulated immature MK. Note that the pre-DMS is precisely positioned between the 2 lobes of the nucleus and is already branched at this early stage of development. The arrowhead indicates a connection with the cell surface.