Ultrastructural Research And Electron Microscopic Enzymo-Cytochemistry On The Apoptosis And Cell Differentiation During Dictyostelium Discoideum Development

Amoebae of the cellular slime mould Dictyostelium discoideum multiplies by binary fission under favorable conditions, once starving or depleting their food source, up to several hundred thousand amoeboid cells will undergo differentiation and morphogenesis during its multicellular development. The whole process of multi cellular development can be divided into four portions: aggregation, cell mound, slug and the fruiting body. The cell differentiation leads to two main types of cells: prespore cell and prestalk cell. The spores cell is viable, so it can germinate and give rise to amoebae that complete the life cycle, while the prestalk cell is destined to go apoptosis for differentiating the stalk cell during the development. Although some changes in ultrastructure during the multicellular development such as food vacuoles and cellulose shell of stalk cell are observed before, the exact morphological characters during the cell differentiation and apoptosis, such as mitochondrion, autophagic vacuoles, nucleus and prespore cell vacuoles, remain unknown.To understand relationship between the morphological traits of the apoptosis andcell differentiation during Dictyostelium discoideum development, electronmicroscopy and DAPI staining are applied. The result showed that the crista nearbyouter membrane of the mitochondria was disrupted by a small vacuole that appears inmitochondria of the majority of cell at mound stage. The cristae were eliminatedgradually while the small vacuole grew bigger. Finally, the mitochondrion vacuolatedwas enclosed with monomembrane. These results suggest that the prespore cellvacuoles is resulted from the disruption of cristea in mitochondrion, and thisendoautophagy occurring at organelle level has something to do with thedifferentiation of prespore cell. In prestalk cell, several autophagic vacuoles hademerged, the mitochondria engulfed by autophagic vacuoles kept their cristae intact atfirst. When the differentiation went further, these autophagic vacuoles fused into a bigone. At this stage the cristae of some mitochondria commenced to disrupt in the formof endoautophagy just like in prespore cell mentioned above. Only the mitochondriawith cristae disrupted were engulfed by autophagic vacuoles, the other mitochondriawhose critae keep intact were no longer engulfed until development complete. Duringthe culmination stage, the nucleus changed a lot and did not remain structural integrityany more, some high electronic spots of condensed chromatin appeared in the nucleus.The nucleolus diminished gradually, but the karyotheca kept intact. The autophagicvacuoles continued to engulf organelles such as mitochondria, eventually, karyotheca...