Who Lives and Who Dies

Abstract

Apoptosis is essential for normal development. Large numbers of cells are eliminated by apoptosis in early neural development and during the formation of neural connections. However, our understanding of this life-or-death decision is incomplete, because it is difficult to identify dying cells by conventional strategies. Live imaging is powerful for studying apoptosis, because it can trace a death-fated cell throughout its lifetime. The Drosophila sensory organ development is a convenient system for studying neural-cell selection via lateral inhibition. We recently showed that about 20% of the differentiating neuronal cells die during sensory organ development, which results in the characteristic spatial patterning of the sensory organs. The eliminated differentiating neurons expressed neurogenic genes and high levels of activated Notch. Thus, live imaging allowed us to document the role of apoptosis in neural progenitor selection, and revealed that Notch activation is the mechanism determining which cells die during sensory organ development.

This article refers to:

Acknowledgments

We thank E. Kuranaga for great contributions for this study, and all members of the Miura laboratory for technical support and helpful advice. We thank the University of Tokyo and Leica Microsystems Imaging Center (TLI) for imaging analysis.

Figures and Tables

Figure 1 Fine-tuning of neural cell number via programmed cell death. Neural cell number is adjusted via programmed cell death during both early neural cell-fate determination and post-mitotic neural wiring. (A) Our recent study revealed the function of programmed cell death in the selection of neural progenitors. Mis-specified SOP-like cells have characteristics intermediate between SOPs and epithelial cells. They are specifically eliminated by caspase-dependent cell death to ensure the correct sensory organ patterning. (B) Neurotrophic theory proposed the function of programmed cell death in neuronal wiring. Excess neurons compete for a limited amount of NGF provided by target tissues. Neurons that fail to bind enough of the survival factor die by programmed cell death, resulting in the proper innervation of targets.

Addendum to: