Yan Zhu

The cell cycle is a fundamental biological process indispensable for life, and its orderly progression is governed by a complex signaling network. Although the p38 MAPK pathway plays important roles in regulating cell proliferation across metazoans, its mechanistic role in insect cell cycle progression remains poorly characterized, particularly in species with endoreplication systems. Here, we investigated the function and mechanism of Bombyx mori p38 MAPK (Bmp38 MAPK) in cell cycle regulation using the silkworm silk gland as a specialized endoreplication model. We found that the p38 MAPK is evolutionarily conserved from insects to mammals and exhibits both cytoplasmic and nuclear localization, with its expression peaking during the G1 phase. Overexpression of Bmp38 MAPK induced cell cycle arrest at both G1/S and G2/M phases and suppressed cell proliferation, whereas Bmp38 MAPK knockdown alleviated G1/S arrest and enhanced proliferation. Mechanistically, Bmp38 MAPK increased BmCyclin B expression while reducing the expression of BmCyclin E, BmCDK2 and BmCDK1. Protein interaction assays further confirmed interactions between Bmp38 MAPK and BmCDK2, BmCyclin E and BmCyclin B. Notably, Bmp38 MAPK significantly inhibited DNA synthesis in silk gland cells, suggesting that Bmp38 MAPK contributes to the regulation of endoreplication. These findings reveal a possible role for p38 MAPK in insect cell cycle control and provide potential mechanistic insights into the regulation of endoreplication in the silkworm silk gland.

Baculoviruses, the largest studied insect viruses, are highly pathogenic to host insects. Bombyx mori nucleopolyhedrovirus (BmNPV) is the main cause of nuclear polyhedrosis of silkworm, a viral disease that causes significant economic losses to the sericulture industry. The anti-BmNPV mechanism of the silkworm has not yet been characterized. Carboxypeptidase is an enzyme that is involved in virtually all life activities of animals and plants. Studies have shown that the carboxypeptidase family is related to insect immunity. There are few reports on the role of carboxypeptidase in the defense of silkworms against pathogen invasion. In this study, we identified the homologous gene Bombyx mori metal carboxypeptidases12 (BmMCP12) related to mammalian carboxypeptidase A2 (CPA2) and found that BmMCP12 had a Zn-pept domain. The BmMCP12 gene was primarily located in the cytoplasm and was highly expressed in the midgut of silkworms, and the expression level in BmN-SWU1 cells was upregulated after infection with BmNPV. After overexpression of the BmMCP12 gene, quantitative real-time (qRT)-PCR and Western blots showed that BmMCP12 could inhibit BmNPV replication, whereas knockout of the gene had the opposite effect. In addition, we constructed transgenic silkworm strains with a knockout of BmMCP12, and the transgenic strains had reduced resistance to BmNPV. These findings deepen the functional study of silkworm carboxypeptidase and provide a new target for BmNPV disease prevention in silkworms.

Temperature is an important factor in the growth, development, survival, and reproduction of organisms. The high-temperature resistance mechanism of insects may be significant for use in the prevention and control of insect pests. The silkworm, Bombyx mori, is an important Lepidoptera model species for studies on pest control in agriculture and forestry. We identified a gene in B. mori, the B. mori singed (Bmsn) gene, which is involved in the high-temperature resistance of silkworms. Sn proteins are highly conserved among species in many taxonomic groups. The overexpression of the Bmsn gene promoted the proliferation of silkworm cells, reduced oxidation, and reduced the accumulation of reactive oxygen species under stress. Interfering with the Bmsn gene had the opposite result. We constructed a transgenic B. mori strain that overexpressed the Bmsn gene. The physiological traits of the transgenic strain were significantly improved, and it had stronger high-temperature resistance. The Bmsn gene is involved in the process by which fat bodies respond to high-temperature stress. These findings provide insights into the mechanism of high-temperature resistance of insects and offer a new perspective on agricultural and forestry pest control.