BmEL-2 promotes triglyceride metabolism by regulating BmAGPATγ and BmFAF2 expression in Bombyx mori

Bombyx mori ELAV-like-1 (BmEL-1) and B. mori ELAV-like-2 (BmEL-2) are 2 members of the ELAV-like family of RNA-binding proteins. Mutations in Bmel-1 and Bmel-2 resulted in 5.8% and 28.5% decreases in larval weight on the 3rd day of the 5th instar larva (L5D3), respectively. Triglycerides (TG) are the most important energy resource and are the main component of neutral fat (NF) in animals. To investigate the role of Bmelav-like genes in the synthesis and decomposition of TG, transcriptomic, and metabolic analyses were performed on the whole bodies on the 1st day of the 2nd instar larvae (L2D1) and on fat bodies on L5D3 of Bmel-1^- and Bmel-2^- mutants, respectively. As compared with the control silkworm, differentially expressed genes generated in both mutants were mainly enriched in lysine degradation, fatty acid (FA) metabolism, and unsaturated FAs biosynthesis. The diglyceride and phosphatide contents were significantly lower in Bmel-1^- and Bmel-2^- fat bodies than those of the control group. Consistently, the NF content of both mutants' fat bodies were reduced by 50% and 60%, respectively. BmEL-2 positively regulates BmAGPATγ (B. mori 1-acyl-sn-glycerol-3-phosphate acyltransferase gamma, LOC101741736) and BmFaF2 (B. mori fatty acid synthetase-associated factor 2, LOC101739090) expression by binding to the specific regions of their 3' untranslated regions in BmN cells. This study suggests that BmEL-2 may be an important regulator of BmAGPATγ and BmFAF2 expression and thereby participates in TG metabolism in the silkworm fat body.