Title:
Physiological function of apoptosis in development and stress response

Masayuki Miura, Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo

Abstract:
Multicellular organisms evolved machineries to get rid of cells by apoptosis. In this study, we focused on evolutionally conserved caspase activating molecule apaf-1 to elucidate the in vivo roles of caspase activation and apoptosis in Drosophila and mouse.
We found hypomorphic mutant of apaf-1 is sensitive to this epidermal injury. Epidermal injury induced caspase activation within 30 min in gut, the tissue distant from injured site. apaf-1overexpression in gut fully rescued the injury-induced lethal phenotype of apaf-1 mutant. Moreover, wild type showed lethality by the injection of the hemolymph of pricked flies that caspase activity is inhibited in gut, suggesting the toxic factor was induced in the hemolymph after injury. These results suggest caspase activity is required in gut to regulate the systemic defense response in order to overcome tissue injury in vivo . We are currently conducting proteomics and metabolomics analysis of hemolymph of dpf-1 mutant to investigate the systemic factors that regulate physiological consequences of apoptosis defects.
In mammals, mice deficient for apaf-1 causes severe brain malformations such as brain ventricle compression and indented neuroepithelium, leading to the speculation that overgrowth of neuroepithelium occurs without apoptosis. However, we found that inhibition of apoptosis did not cause significant increases in total cell numbers of neuroepithelium. Instead, it led to incompletion of the cranial NTC, which is likely to end in severe brain malformation. Live-imaging analysis with the mouse embryos expressing SCAT3, a fluorescent indicator protein to monitor caspase-3 activation in living cells, revealed that preventing apoptosis by inhibition of caspases disturbed smooth morphological changes of developing neural plates and also reduced the speed of the cranial NTC. These results suggested that eliminating dying cells by apoptosis contributes to the smooth progression of NTC within a limited developmental time window.

References:
Miura, M.: Apoptotic and nonapoptotic caspase functions in animal development. Cold Spring Harb. Perspect. Biol. 4; doi: 10.1101/cshperspect. a008664, 2012

Yamaguchi, Y., Shinotsuka, N., Nonomura, K., Takemoto, K., Kuida, K., Yoshida, H., and Miura, M.: Live imaging of apoptosis in a novel transgenic mouse highlights its role in neural tube closure. J. Cell Biol. 195, 1047-1060, 2011

Kanda, H., Igaki, T., Okano, H., and Miura, M.: Conserved metabolic energy production pathways govern Eiger/TNF-induced non-apoptotic cell death. Proc. Natl. Acad. Sci. USA 108, 18977-18982, 2011

Koto, A., Kuranaga, E., and Miura, M.: Apoptosis ensures spacing pattern formation of Drosophilasensory organs. Current Biol.21, 278-287, 2011