Effect Of Diapause-inducing Temperature And Photoperiod On The Expression Of Diapause-related Endocrine Genes In The Silkworm, Bombyx Mori

Bombyx mori is the model insect of Lepioloptera with diapausing during its egg stage. Diapause inducements are due to temperature and photoperiod in the incubation process of parental eggs. However, whether or not eggs at progeny enter into diapause depends on temperature after oviposition. This paper investigated the expression of diapause-related endocrine genes in Bombyx mori using the classic diapause-inducing incubation conditions, which contained prothoracicotropic hormone gene, diapause hormone and pheromone biosynthests activating neuropeptide gene, eclosion hormone gene and pituitary homeobox gene. The major results are as follows:1 Diapause-related endocrine genes had tissue specific expression charac-teristics in Bombyx moriGene microarray analysis displayed that four genes, containing Ptth,Dh-pban,Eh?and?Pitx, had issue specific expression characteristics during postembryonic stage. Ptth gene expression level in head is higher than any other tissues. Dh-pban gene expression level in head is the highest in all tissues, and then in posterior silk gland and Malpighian tubules. The expression in other tissues is very low. Expression level of Eh gene is highest in integument, and then in head. There is almost no expression in ovary. Pitx gene expression in the Malpighian tubules is the highest, followed by the midgut and the head, lower levels of other tissues, of which only traces of the blood volume in the expression.2 The temperature and photoperiod inducing diapause of offspring eggs up-regulated the expression level of Dh-pban geneEggs at progeny are completely diapause when parental eggs are under constant illumination at 25℃(25LL) incubation, and they are completely non-diapause under constant darkness at 15℃(15DD). The Dh-pban mRNA of eggs in 25LL stayed at a high level, but it was very low in 15LL. Under 25LL or 20LD, the Dh-pban level of parental eggs up-regulated in the late incubation stage, which indicated that B. mori would be sensitive to the external illumination and temperature after embryonic nervous developed. However, the mRNA level of Dh-pban was not oscillated with the periodic oscillation of incubation photoperiod and temperature. The Dh-pban expression level rose at 25℃during postembryonic developmental stage. In conclusion, the incubation temperature and photoperiod of parental eggs affected the diapause of offspring eggs, but Dh-pban was not the direct gene regulated by the zeitgebers.3 The effect of photoperiod and temperature on the expression of Eh and Pitx gene was different among different stagesThe Eh mRNA of eggs in 15DD stayed at a very low level. Under 25LL or 20LD, the Eh level of parental eggs up-regulated in the late incubation stage, which indicated that B. mori would be sensitive to the external illumination and temperature after embryonic nervous developed. In the offspring, Eh gene mRNA expression level is very low under 25LL, and in the diapause period in the embryo, the gene is almost not detected Eh mRNA. However under 15DD, the offspring Eh gene mRNA can be detected in the whole Embryonic stage.Under incubation environment of 25LL, 20LD, 15DD, Pitx mRNA can be detected in silkworm eggs, and under the conditions of 25LL Pitx gene expression is in general higher than 20LD and 15DD. In postembryonic period, Pitx mRNA level is in general higher under 25LL than 15DD. Under 25LL incubation environment, in offspring diapause eggs during the age of 12-24 h embryos, Pitx mRNA levels increased rapidly but then declined rapidly to the age of 72 h, eggs gradually into the diapause stage embryos. Pitx mRNA can not be detected. However under 15DD, the offspring Pitx mRNA can be detected in the whole Embryonic stage.