Sequential steps of macroautophagy and chaperone-mediated autophagy are involved in the irreversible process of posterior silk gland histolysis during metamorphosis ofBombyx mori

Abstract

To elucidate the degradation process of the posterior silk gland during metamorphosis of the silkworm Bombyx mori, tissues collected on the 6th day after entering the 5th instar (V6), prior to spinning (PS), during spinning (SP) and after cocoon formation (CO) were used to analyze macroautophagy, chaperone-mediated autophagy (CMA) and the adenosine triphosphate (ATP)-dependent ubiquitin proteasome. Immediately after entering metamorphosis stage PS, the levels of ATP and phosphorylated p70S6 kinase protein decreased spontaneously and continued to decline at SP, followed by a notable restoration at CO. In contrast, phosphorylated AMPactivated protein kinase α (AMPKα) showed increases at SP and CO. Most of the Atg8 protein was converted to form II at all stages. The levels of ubiquitinated proteins were high at SP and CO, and low at PS. The proteasome activity was high at V6 and PS but low at SP and CO. In the isolated lysosome fractions, levels of Hsc70/Hsp70 protein began to increase at PS and continued to rise at SP and CO. The lysosomal cathepsin B/L activity showed a dramatic increase at CO. Our results clearly demonstrate that macroautophagy occurs before entering the metamorphosis stage and strongly suggest that the CMA pathway may play an important role in the histolysis of the posterior silk gland during metamorphosis.

More Than Skin Deep: Autophagy Is Vital for Skin Barrier Function

“…Traditionally, autophagy is orchestrated by the group of ATG proteins, which precisely control the autophagic process ( 11 , 19 ). The process kickstarts the formation of the pre-initiation complex, followed by generation of the phagophore, autophagosome, and autolysosome, leading to cargo degradation (Figure 1 B) ( 11 , 19 , 20 ). Mammalian target of rapamycin complex 1 inhibition leads to the induction of autophagy and assembles ULK1/2, ATG13, and FIP200 to form the pre-initiation complex at the phagophore (Figure 1 B).…”

Vacuolar protein sorting 4 is required for silkworm metamorphosis

“…Recent studies have shown that autophagy and apoptosis are induced prior to metamorphosis in the Drosophila fat body (Lindmo et al , ), silkworm posterior silk gland (Shiba et al , ), silkworm midgut (Franzetti et al , ) and fat body (Tian et al , ). We found that BmVps4 was also up‐regulated before metamorphosis, indicating a similarly early induction of the MVB pathway.…”

“…However, the physiological functions of MVB proteins in metamorphosis are rarely reported. During metamorphosis, larval tissues and organs are completely degraded or transformed into pupal or adult forms, and some adult‐specific tissues and organs are de novo formed from imaginal discs (Romanelli et al , , ; Shiba et al , ). The degradation process requires highly active autophagy and apoptosis, and the formation of tissues and organs requires active cell proliferation and differentiation.…”

Autophagy in skin barrier and immune‐related skin diseases

“…12 Sequentially, the process is initiated by the formation of the pre-initiation complex, developed by the elongation and completion of the autophagosome, and finished with the generation of autolysosome to degrade cargoes. 13,14 In general, the functional components involved in the process include the UNC-51-like kinase (ULK) complex, ATG5-ATG12-ATG16L1 conjugation systems, the Beclin 1 class III phosphatidylinositol 3-kinase (PI3K) complex, and the microtubule-associated protein 1 light chain 3 (LC3) conjugation systems (Figure 1). 15 The pre-initiation complex consists of ULK1, FIP200 (FAK family kinase-interacting protein of 200 kDa), ATG13, and ATG101.…”