Increase of 30K protein in identified motoneurons by hemolymph results in inhibition of programmed cell death in silkworm, Bombyx mori (Lepidoptera, Bombycidae)

This study demonstrates that a 30K protein was gradually synthesized in primary-cultured motoneurons from the accessory planta retractor (APR) of the 6th abdominal ganglion (APR6) in silkworm ventral ganglia through stimulation of hemolymph. An increase in 30K protein synthesis resulted in an inhibition of programmed cell death (PCD) of APR6 motoneurons. The 30K protein was gradually synthesized from the 30Kc6 gene of identified APR6s in day-6 4th instars to day-9 5th instar larvae, but synthesis of the 30K protein ceased in isolated APR6s of day-1 pupa, which normally begin to undergo PCD. When pupal APR6s were treated with larval hemolymph, however, the 30K protein was synthesized suggesting the existence of an anti-PCD factor in the larval hemolymph. An increase of 30K protein within the APR6s was confirmed by antiserum made against the recombinant 30K protein that originated from the APR 30Kc6 gene. Larval APR6, in which PCD was induced with 20-hydroxyecdysone (20E) added to the primary culture, exhibited some PCD characteristics of shrinkage of cell bodies, axonal fragmentation and loss of mitochondrial function. These results provide new insights on the survival or PCD of insect motoneurons through stimulation of hemolymph.