Functional analysis of 30K proteins during silk gland degeneration by a caspase‐dependent pathway in Bombyx

Abstract

The 30K proteins are involved with important functions in the growth and development of Bombyx mori. In this study, the synthesis and regulation of 30K proteins were examined during the degeneration of Bombyx silk glands. On day 3 of the fifth instar, the protein level of 30Kc19 was low, whereas the silk proteins were rapidly synthesized. However, synthesis and accumulation of the 30Kc19 protein significantly increased at the prepupal stage and on day 1 of the pupal stage. At this stage, the silk gland cells were filled with 30Kc19 and genomic DNA. Moreover, the transcript levels of the 30K-encoding genes, including 30Kc6, 30Kc12, 30Kc19 and 30Kc23 were up-regulated during the degeneration of the Bombyx silk glands. During the time that the levels of the 30Kc19 protein were significantly up-regulated, it is notable that the transcript levels of the BmAtg8, BmAtg6 and BmDronc genes dramatically increased to regulate the programmed cell death of this gland. On day 1 of the pupal stage, intense fragmentation of genomic DNA occurred in the silk gland cells, and the putative active form of caspase was detected in the cytoplasm, showing the complete degradation of the silk glands in one day. In conclusion, the 30K proteins are synthesized in high concentrations, while proteolysis mediates silk gland degeneration in Bombyx by a caspase-dependent pathway. We propose that the 30K proteins may be nutrients and energy vectors to be absorbed by the developing tissues of pupae or moths.

Targeting and retention enhancement of quantum dots decorated with amino acids in an invertebrate model organism

“…For the sake of contrast tissue morphology, the target tissue silk glands and the non-targeted tissue of fat body were isolated on ice and fixed in 4% paraformaldehyde. Then the tissues were made of paraffin sections and were further stained by Hematoxylin and Eosin (HE) (Beyotime, Jiangsu, China) performed as described by Ji et al (2013) 19 .…”

“…The synthesized silk proteins in silk gland are more than 30% body weight of the organism. A silk gland synthesizes 6 × 10 9 fibroin proteins per second, which is more than 60 times faster than the rate of a human liver cell synthesizing serum albumin 19 20 . In this study, in order to improve delivery to an assumed target organ- SG, single amino acids, which are needed in large amounts during protein synthesis in SG of the silkworm, were linked to the QDs under investigation.…”

A Molecular View of Autophagy in Lepidoptera

“…In particular, BmATG1 , BmATG5 , BmATG6 , and BmATG8 were expressed in peritracheal athrocytes and gonads [31, 32]. A striking upregulation of various ATG genes during fifth larval instar and metamorphosis of this insect has also been observed in the larval midgut epithelium [32, 33], silk gland [29, 34, 35], and fat body [28, 32]. In fat body it has also been demonstrated that 20E levels affect the expression of these genes in vivo , confirming that the ecdysone titer in the hemolymph is linked to the induction of the autophagic program in the larval organs [28].…”

Role of BmDredd during Apoptosis of Silk Gland in Silkworm, Bombyx mori

“…The economic importance of silkworms is dependent on the functionality of the silk gland (SG), a specialized organ that synthesizes silk proteins in the silkworm. The SG undergoes rapid development during the fifth instar larvae with the genomic DNA content in SG cells increasing 200–400000 times through the process of endomitosis [9, 10]. Consequently, the SG becomes the largest organ in silkworm abdominal cavity until the wandering stage.…”