Apoptosis in human embryo development: 2. Cerebellum

We analysed the spatial and temporal distribution of apoptosis in human cerebellum development, during embryonic and fetal periods. Cerebella excised from two human embryos (8 weeks old) and eight fetuses (12-22 weeks old), were paraffin embedded and serially sectioned. Apoptotic cells were identified by propidium iodide staining, and TUNEL. In addition, immunohistochemistry for suicide receptor Fas(APO-1/CD95) was performed. We determined the distribution and percentage of apoptotic cells as well as Fas(APO-1/CD95)-positive cells in different regions and stages of development. Apoptotic cells were seen in both proliferative zones and postmitotic regions along the migratory pathways as well as in the developing cerebellar cortex in all examined stages. The Fas(APO-1/CD95) immunoreactivity was present in all examined stages in a small population of apoptotic cells: either neuroblasts or differentiated cells in postmitotic zones. These findings suggest that apoptosis drives the selection of the cells which are committed to differentiate during the early stages of cerebellar development. The differences between apoptotic cells distribution and Fas receptor expression suggest that cell selection is driven by different apoptotic pathways.