Gonadoinhibitory effects of Neb-colloostatin and Neb-TMOF on ovarian development in the mealworm, Tenebrio molitor L.

The gonadostatic action of the peptides Neb-colloostatin (SIVPLGLPVPIGPIVVGPR) and Neb-TMOF (NPTNLH) from Neobellieria bullata was studied in female mealworm Tenebrio molitor. Both peptides potently inhibit ovarian development and terminal oocyte maturation of mated females during their first reproductive cycle. Injection of 4 mug of Neb-colloostatin or Neb-TMOFNeb-TMOF reduced, at day 4 of the cycle, the size of the terminal oocytes to about half or one third of the normal size in saline-injected controls. In addition, follicular patency was arrested. The injections of Neb-colloostatin and Neb-TMOF also caused a delay to the first ovulation and oviposition as well as a reduction of the number of eggs by about 50% in the first 3 days of the oviposition period. At 4 days after adult emergence, none of the peptides had caused significant changes in protein concentration or composition of the haemolymph. However, both peptides reduced total protein content in ovaries and induced qualitative changes in ovarian protein patterns. Electrophoretic analyses indicated that Neb-colloostatin and Neb-TMOF caused a loss of two proteins (150, 180 kDa) and a drastic reduction of 4 others (39, 43, 47, 130 kDa), which are the most abundant ones in ovaries of control females. On the other hand, they increased the concentration of 2 other polypeptides (65, 70 kDa), which normally occur in insignificant quantities in ovaries. Our results indicate that both peptides have a very similar mode of action despite the differences in their amino acid sequence. They seem to interfere with vitellogenin production by the fat body as well as with vitellogen uptake by the oocytes through modification of patency.