P06. Live-imaging analysis of apoptosis and caspase activation reveals that apoptosis is a facilitator of the neural tube closure

Abstract

Neural tube closure (NTC) is a fundamental process to construct the brain and the spinal cord in vertebrates. The neural plate develops bilateral neural folds, which in turn come into contact in the midline and fuse together to create the neural tube. Programmed cell death (PCD), especially apoptosis, is widely observed during the process. Several lines of evidence suggested that apoptosis is essential to complete cranial NTC. However, it is still unclear how apoptosis contributes to the completion of cranial NTC. To examine the relationship between dying cells and morphogenetic movement such as neural plate bending, fusion of neural ridge, and epithelial remodeling after the fusion, direct visualization of dying cells during NTC could be effective. We have conducted a live-imaging analysis of apoptosis during cranial NTC with the mouse embryo expressing SCAT3, a fluorescent indicator protein to monitor caspase-3 activation in living cells. In these embryos, caspase activation was observed in dying cells of the pre-fusion neural ridge, fusion point, and the post-fusion midline. Thus, this system allowed us to observe the dynamics of cranial NTC when caspase activation and apoptosis were inhibited. We found that the speed of closure tended to become slow under caspase-inhibited condition, suggesting that caspase activation and apoptosis contribute to the progression of neural tube closure within a limited developmental time window.