In vivo time-lapse imaging of cell proliferation and differentiation in the optic tectum of Xenopus laevis tadpoles

Neural progenitor cells (NPCs) are the highly polarized dividing stem cells of the developing brain that give rise to all neurons and glia. Early on, NPCs divide symmetrically and expand the pool of progenitor cells, but as development continues the NPCs begin to asymmetrically divide to produce neurons. The mechanisms that govern this irreversible commitment to neurogenesis are not fully understood, but in other stem cell populations the regulation of mitochondria and cell metabolism is key to controlling stem cell fate. Here we use timelapse 3D confocal microscopy to observe NPCs, their cellular progeny, and their mitochondria in the developing Xenopus tectum. Our results track individual NPCs over days and show that they contain abundant mitochondria that form complicated networks distributed throughout the cells. We find that NPCs preparing to divide shift mitochondria toward the cell body where they become asymmetrically distributed, suggesting that the cells control which progeny inherit mitochondria. This uneven distribution of mitochondria in cell preparing to divide led us to test the role that mitochondria play in cell division. We overexpressed the mitochondrial biogenesis master regulator, PGC-1a, which induced the NPCs to asymmetrically divide and produce neurons, while PGC-1a knockdown limited neurogenesis. Together these data suggest that the regulation of mitochondria by NPCs prior to cell division and their unequal inheritance during cell division, contributes to the fate of the newborn cells in the developing brain.