Spry is downregulated by multiple viruses to elevate ERK signaling and ensure viral reproduction in silkworm

Area of Science:

• * Molecular biology
• * Virology
• * Entomology

Background:

• * Viral diseases pose a significant threat to silkworm (Bombyx mori) production, primarily caused by Bombyx mori nucleopolyhedrovirus (BmNPV), B. mori cytoplasmic polyhedrosis virus (BmCPV), and B. mori bidensovirus (BmBDV).
• * Viruses manipulate host cellular pathways for replication, but the specific pathways targeted by these three silkworm viruses remain largely unelucidated.
• * Spry proteins act as negative regulators upstream of the Extracellular signal-regulated kinase (ERK) pathway, a crucial signaling cascade involved in cellular processes.

Purpose of the Study:

• * To investigate whether BmNPV, BmCPV, and BmBDV coordinately regulate a common host cellular pathway in silkworms.
• * To determine the role of Bombyx mori Spry (BmSpry) in the silkworm's response to viral infections.
• * To elucidate the relationship between BmSpry, p-ERK levels, and viral proliferation in silkworms.

Main Methods:

• * Quantification of BmSpry expression and p-ERK levels in silkworm larvae following infection with BmNPV, BmCPV, and BmBDV.
• * Construction of a transgenic RNA interference (RNAi) vector targeting BmSpry for generating a Spry-knockdown silkworm line (Spry-I).
• * Microinjection of the RNAi vector into silkworm embryos to create the Spry-I transgenic line and subsequent validation of BmSpry knockdown.

Main Results:

• * Infection with each of the three viruses led to a significant decrease in BmSpry expression and a corresponding increase in p-ERK levels in silkworm larvae.
• * The Spry-I transgenic silkworms exhibited significantly reduced BmSpry expression compared to non-transgenic controls.
• * Spry-I larvae showed significantly higher viral loads and increased mortality rates when challenged with BmNPV, BmCPV, or BmBDV, alongside elevated p-ERK levels post-infection.

Conclusions:

• * Multiple classes of silkworm viruses, including BmNPV, BmCPV, and BmBDV, downregulate BmSpry expression.
• * The downregulation of BmSpry results in elevated p-ERK signaling.
• * This virus-induced modulation of the BmSpry/p-ERK pathway is crucial for facilitating viral reproduction and pathogenesis in silkworms.