Enhanced Myc Expression in Silkworm Silk Gland Promotes DNA Replication and Silk Production.

Wenliang Qian,Yuting Wu,Daojun Cheng,Hao Li,Yan Yang,Zheng Li,Xuechuan He

doi:10.3390/insects12040361

Abstract

Simple SummaryBased on a transgenic approach, enhancing Myc expression in the silkworm posterior silk gland (PSG), which was driven by the promoter of the fibroin heavy chain (FibH) gene, was performed for investigating the biological functions of Myc in silk gland. Enhanced Myc expression elevated the cocoon size. This elevation might be resulted from the increasing of FibH expression and DNA content in the PSG cells by promoting the transcription of the genes that are involved in DNA replication.Silkworm is an economically important insect that synthetizes silk proteins for silk production in silk gland, and silk gland cells undergo endoreplication during larval period. Transcription factor Myc is essential for cell growth and proliferation. Although silkworm Myc gene has been identified previously, its biological functions in silkworm silk gland are still largely unknown. In this study, we examined whether enhanced Myc expression in silk gland could facilitate cell growth and silk production. Based on a transgenic approach, Myc was driven by the promoter of the fibroin heavy chain (FibH) gene to be successfully overexpressed in posterior silk gland. Enhanced Myc expression in the PSG elevated FibH expression by about 20% compared to the control, and also increased the weight and shell rate of the cocoon shell. Further investigation confirmed that Myc overexpression increased nucleus size and DNA content of the PSG cells by promoting the transcription of the genes involved in DNA replication. Therefore, we conclude that enhanced Myc expression promotes DNA replication and silk protein expression in endoreplicating silk gland cells, which subsequently raises silk yield.

Highlights

The silkworm (Bombyx mori) is an economically important insect that synthesizes silk proteins for silk production in the silk gland
Based on the full-length sequence of silkworm Myc gene, we cloned the opening reading frame of the Myc gene and constructed recombinant Myc overexpression plasmid driven by fibroin heavy chain (FibH) promoter, which is activated in the PSG (Figure 1A)
These results indicate that Myc was overexpressed in the PSG of transgenic silkworm

Summary

Introduction

The silkworm (Bombyx mori) is an economically important insect that synthesizes silk proteins for silk production in the silk gland. The silk gland comprises three parts, namely, anterior (ASG), middle (MSG), and posterior (PSG). Cell numbers in the silk gland are determined by mitosis during the late embryonic stage [1]. Silk gland cells stop the mitotic cell cycle and enter into endoreplication. 17–19 rounds of endoreplicating cell cycles, called the endocycle, the DNA content in each cell can be increased by about 400,000 times, which results in a dendritic nucleus [2,3,4]. As is well known, endoreplicating cells generally undergo multiple rounds of genome

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