Abstract: 【Aim】 The fat body is the major site for metabolism and innate immunity in insects. ATG8 protein subcellular localization is one of the key biomarkers for autophagy, and nuclear shrinkage is one morphological characteristic of apoptosis. However, there is a lack of cellular observation of BmATG8 protein during molting and metamorphosis of Bombyx mori. This work aims to determine the spatiotemporal changes in BmATG8 subcellular localization and nuclear morphology in the fat body of B. mori and to explore their regulation by 20-hydroxyecdysone (20E). 【Methods】 By using immunofluorescent staining and Hoechst staining, the changes in BmATG8 localization and nuclear morphology in the fat body of B. mori during day 2 of the 4th instar larva to day 2 of the prepupa, after injection of 20E (10 μg/larva) in the fat body of the day 2 5th instar larvae, and in larvae at the wandering stage after RNAi of 20E receptor gene usp were detected, respectively. 【Results】 During larval molting and larval-pupal metamorphosis of B. mori, BmATG8 protein was highly expressed in the fat body, and meanwhile nuclear shrinkage occurred. The 20E treatment (10 μg/larva) induced BmATG8 expression and its cytoplastic localization as well as nuclear shrinkage at the normal feeding larval stage. RNAi of usp in B. mori larva at the wandering stage decreased the content of cytoplastic BmATG8 and alleviated the nuclear shrinkage in fat body. 【Conclusion】 BmATG8 not only exists in the cytosol of B. mori during the larval-pupal metamorphosis, but also is highly expressed at the larval molting stage, occurring simultaneously with the nuclear shrinkage. Moreover, cytoplastic localization of BmATG8 and nuclear shrinkage are regulated by 20E signaling. This study provides a foundation for further studying the function and regulatory mechanism of BmATG8 in the future.

Key words: Bombyx mori, BmATG8 protein, nuclear morphology, fat body, developmental change, 20-hydroxyecdysone