| Summary: | 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 <i>Myc</i> gene has been identified previously, its biological functions in silkworm silk gland are still largely unknown. In this study, we examined whether enhanced <i>Myc</i> expression in silk gland could facilitate cell growth and silk production. Based on a transgenic approach, <i>Myc</i> was driven by the promoter of the fibroin heavy chain (<i>FibH</i>) gene to be successfully overexpressed in posterior silk gland. Enhanced <i>Myc</i> expression in the PSG elevated <i>FibH</i> expression by about 20% compared to the control, and also increased the weight and shell rate of the cocoon shell. Further investigation confirmed that <i>Myc</i> 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 <i>Myc</i> expression promotes DNA replication and silk protein expression in endoreplicating silk gland cells, which subsequently raises silk yield.
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