CARBOHYDRATE METABOLISM IN THE EGGS OF THE SILKWORM, BOMBYX MORI. II. ANAEROBIOSIS AND POLYOL FORMATION

Shifts in the carbohydrate, polyol, and amino acid pools during rapid cold-hardening and diapause-associated cold-hardening in flesh flies (Sarcophaga crassipalpis): a metabolomic comparison

Flesh flies can enhance their cold hardiness by entering a photoperiod-induced pupal diapause or by a temperature-induced rapid cold-hardening process. To determine whether the same or different metabolites are involved in these two responses, derivatized polar extracts from flesh flies subjected to these treatments were examined using gas chromatography-mass spectrophotometry (GC-MS). This metabolomic approach demonstrated that levels of metabolites involved in glycolysis (glycerol, glucose, alanine, pyruvate) were elevated by both treatments. Metabolites elevated uniquely in response to rapid cold-hardening include glutamine, cystathionine, sorbitol, and urea while levels of beta-alanine, ornithine, trehalose, and mannose levels were reduced. Rapid cold-hardening also uniquely perturbed the urea cycle. In addition to the elevated metabolites shared with rapid cold-hardening, leucine concentrations were uniquely elevated during diapause while levels of a number of other amino acids were reduced. Pools of two aerobic metabolic intermediates, fumarate and citrate, were reduced during diapause, indicating a reduction of Krebs cycle activity. Principal component analysis demonstrated that rapid cold-hardening and diapause are metabolically distinct from their untreated, non-diapausing counterparts. We discuss the possible contribution of each altered metabolite in enhancing the overall cold hardiness of the organism, as well as the efficacy of GC-MS metabolomics for investigating insect physiological systems.

Effect of anoxia on diapause termination in eggs of the false melon beetle, Atrachya menetriesi

The effect of anoxia on diapause development in the leaf beetle Atrachya menetriesi was investigated to elucidate the role of oxygen in regulation of egg diapause. While anoxia alone had no effect on diapause termination, it decreased diapause intensity before chilling. Such an effect reached a maximum level when anoxia lasted for about 10 days. Anoxia applied during the pre-diapause stage also reduced diapause intensity. On the other hand, anoxia terminated diapause when the diapause intensity had been lowered by sufficient duration of chilling (50 days at 7.5 degrees C). The effect of anoxia was temperature dependent; the larger effect was elicited when anoxia was combined with a higher temperature. A 50-day chilling caused more than 20% of eggs to terminate diapause upon transfer to warm conditions. However, when this chilling period was interrupted on the 20th day by a 5-day exposure to a high temperature of 20, 25 or 30 degrees C, the effect of the former chilling was cancelled partially or completely, suggesting that warming reversed diapause development. This reversing effect of a high temperature, however, was not manifested when the warming was combined with anoxia. The results suggest that anoxia inhibits diapause reversal and facilitates a certain process of diapause development. The sequence of exposure to anoxia and chilling is not important.

Temperature-dependent activation of ERK/MAPK in yolk cells and its role in embryonic diapause termination in the silkworm Bombyx mori

The silkworm Bombyx mori requires 2-3 months of low temperature (5 degrees C) to terminate embryonic diapause. The molecular mechanisms, however, are unknown. Extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) is temperature-dependently activated in the yolk cells of diapausing eggs after 45 days at 5 degrees C, coincident with the acquisition of developmental competence of the embryos at 25 degrees C. Yolk cell granulation and dissociation also begin in diapause eggs incubated at 5 degrees C for 45 days. We used dechorionated egg culture as a model system of diapause termination and observed that both yolk cell dissociation and embryonic development are inhibited by MAPK-ERK kinase (MEK) inhibitor U0126. Therefore, we suggest that ERK in yolk cells has a role in regulating changes in yolk morphology and termination of embryonic diapause in B. mori.

Oxygen consumption in relation to sorbitol utilization at the termination of diapause in eggs of the silkworm, Bombyx mori

Rates of oxygen consumption were followed throughout the entire period of diapause in eggs of Bombyx mori. In non-diapause eggs at 25 degrees C, O(2) uptake was divisible into three phases, corresponding to morphogenetic processes. In diapause eggs at 25 degrees C, O(2) uptake showed a peak (100 &mgr;l/g eggs/h) at 1 day and then suddenly dropped to reach a level of 8-10 &mgr;l/g eggs/h at 10 days and thereafter. To break diapause, eggs were exposed to 5 degrees C for varying periods. When O(2) uptake was measured at 5 degrees C, it remained at 6 &mgr;l/g eggs/h. When eggs were chilled for increasing periods and O(2) uptake was measured immediately after warming to 25 degrees C, the rates increased after a lag phase. In HCl-treated eggs, O(2) uptake increased immediately after acid-treatment. In all cases, highly increasing O(2) uptake at 25 degrees C coincided with termination of diapause. These results were discussed in relation to sorbitol utilization at the termination of diapause.

Oxygen permeability of the chorion in relation to diapause termination in Bombyx eggs

Oxygen permeability of the chorion of the silkworm, Bombyx mori, was measured in relation to embryonic diapause. It did not change appreciably when the eggs were freed from diapause by being kept under long chilling. This finding suggests that the increase in oxygen permeability of the chorion is not a pre-requisite for the termination of the diapause and resynthesis of glycogen from 2 polyols.