Identification of PML Oncogenic Domains (PODs) in Human Megakaryocytes

Abstract

Megakaryocytes (Mks) are unique cells in the human body in that they carry a single and polyploid nucleus. It is therefore of interest to understand their nuclear ultrastructure. PML oncogenic domains (PODs) were described in several types of eukaryotic cells using human autoantibodies which recognize nuclear antigens with a specific speckled pattern (dots) in indirect immunofluorescence (IF). Two main antigens, PML and Sp 100, usually colocalize and concentrate in these nuclear subdomains. We investigated the presence of PODs using IF and immunoelectron microscopy (IEM) in cells from megakaryocytic lineage: the HEL cell line and human cultured Mks. Antibodies against PML, Sp100, and anti-nuclear dots were used in single and double labeling. PODs were identified in HEL cells and in human Mks, and their ultrastructure was characterized. We then used IF to quantify PODs within Mks and showed that their number increased proportionally to nuclear lobularity. In summary, we report the identification of PODs in human Mks at an ultrastructural level and an increase in PODs number in parallel with Mk ploidy. We show that endomitosis not only leads to DNA increase but also to the multiplication of at least one of the associated nuclear structures.