Physiological effectors regulating gene expression of the hypertrehalosemic hormone in the cockroach, Blaberus discoidalis

Abstract

Dot blot hybridization and northern blot hybridization analyses were used to elucidate the physiological factors regulating transcript levels of the hypertrehalosemic hormone (Bld-HrTH) in the corpora cardiaca (CC) of Blaberus discoidalis. Using northern blot hybridization analysis the CC, ventral nerve cord, fat body, and brain were tested to determine if Bld-HrTH was produced solely in the CC or if there were other sites of synthesis. The CC was the only tissue in which Bld-HrTH MRNA was detected. The size of the Bld-HrTH message was determined to be approximately 0.5 kb. Initial studies using dot blot hybridization analysis focused on the effects of age, gender, and sex on Bld-HrTH MRNA content This baseline data was used to target the appropriate stage for analyzing various aspects of feeding with emphasis on the role of glucose and trehalose in Bld-HrTH regulation. For both males and females, the highest content of Bld-HrTH MRNA was found immediately after the adult molt. Bld-HrTH MRNA was high in females between days 0 through 4 but declined by approximately 75% by day 10, where it remained through day 30. In males, the trend was similar, but the Bld-HrTH MRNA content declined by about 50% between days 0 and 4. Mating had no effect on Bld-HrTH MRNA content in female CC. Starvation for 10 days, but not dehydration, increased Bld-HrTH MRNA content 1.8-fold in females. Bld-HrTH MRNA content in males, however, did not appear to be affected by starvation. The mechanical aspects of chewing and neural stimuli by stretch receptors of the foregut did not affect Bld-HrTH MRNA content. Feeding following starvation down-regulated Bld-HrTH transcripts by 30% after 48 hours; but injections of glucose or trehalose, carbohydrate-rich agar cubes given ad lib., and glucose solutions given ad lib. in starved females did not significantly affect Bld-HrTH MRNA content. These studies demonstrate that regulation of Bld-HrTH is influenced by age, gender and feeding Reproduction, water intake, the presence of circulating carbohydrates within the hemocoel, and carbohydrates passing through the gut do not appear to play a significant role in Bld-HrTH MRNA content. Based on the data presented in these studies, regulation of Bld-HrT'H in relation to feeding is nutritionally based but is not influenced by glucose or trehalose. A biosynthetic model relating Bld-HrTH gene expression to trehalose utilization in the cells has been proposed.