A mitochondrion as the structural basis of the formation of a cell-type-specific organelle in Dictyostelium development

The mitochondrion has been mainly given attention as a self-reproductive and respiratory organelle. We report here that the mitochondrion may participate in the formation of a cell-type-specific organelle, coupling with the Golgi complex. During the development of Dictyostelium discoideum, the two types of cells, i.e., the anterior prestalk cells and the posterior prespore cells form a polarized cell mass. Prespore differentiation is characterized by the presence of unique vacuoles named PSVs (prespore-specific vacuoles) in the cytoplasm. Thus the PSV is the most essential organelle to understand the structural basis of cell differention in this organism. In differentiating prespore cells, the mitochondrion exerts a remarkable transformation to form a sort of vacuole (M-vacuole). Using a PSV specific antibody, it was immunocytochemically shown that a PSV antigen (C-IO) is localized in the M-vacuole as well as in the lining membrane of PSV. Interestingly, the C-10 antigen was also noticed in the Golgi cisternae that had fused with M-vacuole. Based on these findings, we propose here a promising model which suggests how both mitochondria and Golgi cisternae may be coordinately involved in the PSV formation. This model will provide a new aspect of mitochondrial functions in cell differentiation.