The Rheb-mTORC1 Coordinates Cell Cycle Progression and Endoreplication in Bombyx mori

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• The mechanistic target of the Rapamycin complex 1 (mTORC1) signaling pathway is crucial for cell growth and proliferation.
• Previous studies indicated mTORC1 activation enhances silk protein synthesis and silk gland size in Bombyx mori.
• Understanding mTORC1's role in silk gland development is key to improving silkworm yields.

Purpose of the Study:

• To investigate the molecular mechanism by which mTORC1 regulates silk gland cell growth and development.
• To elucidate the role of mTORC1 in controlling cell proliferation and endoreplication in Bombyx mori.
• To identify molecular targets for enhancing silk production in silkworms.

Main Methods:

• Utilized rapamycin to inhibit mTORC1 activity in Bombyx mori embryonic (BmE) cells and silk gland cells.
• Overexpressed Ras homolog enriched in brain (Rheb) to activate the mTORC1 pathway.
• Assessed cell proliferation, endoreplication, cell cycle progression (CyclinB, CyclinE levels), and DNA content.

Main Results:

• mTORC1 inhibition with rapamycin decreased BmE cell proliferation and silk gland cell endoreplication.
• Inhibition led to reduced CyclinB and CyclinE protein levels and DNA content, arresting the cell cycle at G2/M.
• Rheb overexpression significantly increased BmE cell proliferation and silk gland cell endoreplication, elevating DNA content.

Conclusions:

• mTORC1 activation is essential for promoting silk gland cell proliferation and endoreplication in Bombyx mori.
• This study clarifies the molecular basis for mTORC1's positive effect on silk protein synthesis and gland length.
• Findings provide novel molecular targets for breeding high-yield Bombyx mori varieties.