Rough endoplasmic reticulum-associated tubular structures occurring in acute promyelocytic leukaemia

Intracytoplasmic tubular structures (TS) which have not yet been described were found electron microscopically in a large percentage (26.5%) of leukaemic cells from a 25-year-old female with acute promyelocytic leukaemia. The TS were bundles of tubules measuring about 90 nm in diameter and continuous with rough endoplasmic reticulum, the maximum of the TS attaining 3.0 micron in length and 0.53 micron in width. The TS were mostly solitary, occasionally 2 or 3 within a cell in a plane of sectioning and were usually located around the Golgi region. By three-dimensional observation with a goniometer stage, it was confirmed that the TS showed latticework of rings in cross sections and fascicular tubular arrays in longitudinal sections. In the latter, some tubules exhibited meshworks of polygonal vesicles measuring about 20 nm and cross striations of filamentous bristles with the periodicity of about 22 nm. The origin and nature of the TS are discussed.