Organelle degradation during the lens and erythroid differentiation is independent of autophagy

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Abstract

Autophagy is a bulk degradation system within cells through which cytoplasmic components are degraded within lysosomes. Primary roles of autophagy are starvation adaptation and intracellular protein quality control. In contrast to the ubiquitin–proteasome system, autophagy can also degrade organelles. Here we examined a possible role of autophagy in organelle degradation during lens and erythroid differentiation. We observed that autophagy occurs in embryonic lens cells. However, organelle degradation in lens and erythroid cells occurred normally in autophagy-deficient Atg5−/− mice. Our data suggest that degradation system(s) other than autophagy play major roles in organelle degradation during these processes.

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Materials and methods

Mice. Atg5+/− and Atg5−/− mice on the C57BL/6 background have been described previously [7]. Atg5+/− mice were crossed with green fluorescent protein (GFP)-fused LC3 transgenic mice [6] to produce Atg5−/− mice expressing GFP-LC3 (GFP-LC3 Atg5−/−). For caesarian delivery, pregnant mothers were injected on 17.5 and 18.5 dpc with 2 mg progesterone (Luteum Injection, Teikoku Hormone, Tokyo) to delay birth; neonates were obtained at 19.5 dpc. To prolong the survival of Atg5−/− neonates, artificial milk

Results and discussion

Since the organelle free zone (OFZ) in the lens is created between 17.5 dpc and birth, we first determined the occurrence of autophagy at this stage. LC3, a mammalian homolog of yeast Atg8, localizes to autophagosome membranes as a phosphatidylethanolamine (PE)-conjugated form [27], [28]. Taking this advantage, we have developed an autophagy-indicator mouse model, in which GFP-LC3 is systemically expressed [6]. Using these mice, autophagosomes can be detected as GFP-positive dots [29]. In lens

Acknowledgments

This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The authors thank the Yamada Science Foundation and the Cell Science Research Foundation for their financial support. This work was performed under the NIBB Cooperative Research Program. The authors declare that they have no competing financial interests.

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