Effect of exogenous hormones on transcription levels of pyridoxal 5′-phosphate biosynthetic enzymes in the silkworm (Bombyx mori)

Vitamin B6 includes 6 pyridine derivatives, among which pyridoxal 5′-phosphate is a coenzyme for over 140 enzymes. Animals acquire their vitamin B6 from food. Through a salvage pathway, pyridoxal 5′-phosphate is synthesized from pyridoxal, pyridoxine or pyridoxamine, in a series of reactions catalyzed by pyridoxal kinase and pyridoxine 5′-phosphate oxidase. The regulation of pyridoxal 5′-phospahte biosynthesis and pyridoxal 5′-phospahte homeostasis are at the center of study for vitamin B6 nutrition. How pyridoxal 5′-phosphate biosynthesis is regulated by hormones has not been reported so far. Our previous studies have shown that pyridoxal 5′-phosphate level in silkworm larva displays cyclic developmental changes. In the current study, effects of exogenous juvenile hormone and molting hormone on the transcription level of genes coding for the enzymes involved in the biosynthesis of pyridoxal 5′-phospahte were examined. Results show that pyridoxal kinase and pyridoxine 5′-phosphate oxidase are regulated at the transcription level by development and are responsive to hormones. Molting hormone stimulates the expression of genes coding for pyridoxal kinase and pyridoxine 5′-phosphate oxidase, and juvenile hormone appears to work against molting hormone. Whether pyridoxal 5′-phosphate biosynthesis is regulated by hormones in general is an important issue for further studies.