Abstract: 【Aim】To explore the effects of bone morphogenetic protein (BMP) signal on the phagocytosis of Drosophila melanogaster plasmatocytes. 【Methods】The UAS-Gal4 system of D. melanogaster was used to specifically knock down BMP signal-related genes Dpp, Gbb, Tkv, Put, Med, Wit, Sax, Mad, Dad, Sal, Brk and Omb in plasmatocytes. The phagocytic indexes of plasmatocytes were calculated to analyze the phagocytic capacities of plasmatocytes after injecting non-pathogenic fluorescence-conjugated microspheres (FluoSphere Microspheres), pHrodo-labeled Gram-negative bacterium Escherichia coli (pHrodo-Escherichia coli) and pHrodo-labeled Gram-positive bacterium Staphylococcus aureus (pHrodo-Staphylococcus aureus) into the 3rd instar larva and adult of D. melanogaster. 【Results】 In the plasmatocytes of the 3rd instar larva of D. melanogaster, knocking down the expression of Dpp, Gbb, Tkv, Wit, Dad, Brk and Omb significantly reduced the phagocytic indexes to FluoSphere Microspheres, while knocking down Dpp, Gbb, Tkv, Wit, Dad and Brk significantly impaired the phagocytic capacity to pHrodo-Escherichia coli, compared with control group Cg>w¹¹¹⁸. In addition, the ability of plasmatocytes to phagocytize pHrodo-Staphylococcus aureus decreased obviously after knocking down Gbb compared with control group Cg>w¹¹¹⁸. Moreover, in adults, we found that the total phagocytic capacity of plasmatocytes decreased obviously upon knocking down Gbb and Dad, whereas after the knockdown of Put, the total phagocytic capacity of plasmatocytes increased. 【Conclusion】In the D. melanogaster larvae, Dpp, Gbb, Tkv, Wit, Dad, Brk and Omb positively regulate the phagocytosis of plasmatocytes. Dpp, Gbb, Tkv, Wit, Dad and Brk promote the phagocytosis of plasmatocytes to Gram-negative bacteria, while Gbb promotes the phagocytosis of plasmatocytes to Gram-positive bacteria. In the D. melanogaster adults, Gbb and Dad contribute to the phagocytosis of total plasmatocytes, while Put negatively regulates the phagocytosis of plasmatocytes.

Key words: Drosophila melanogaster, plasmatocytes, BMP signal, phagocytosis, FluoSphere Microspheres, pHrodo-Escherichia coli, pHrodo-Staphylococcus aureus