Abstract
The cabbage armyworm, Mamestra brassicae, enters diapause in the early pupal stage. Pupal diapause is induced by rearing the larvae under short day lengths. We previously demonstrated that feeding Dopa during last larval instar induces pupal diapause even under long day lengths. In order to elucidate the mechanism by which pupal diapause is induced after experiencing short day lengths or fed Dopa under long day lengths, we analyzed gene expression in the brain of M. brassicae larvae under both of these conditions using a subtractive hybridization technique. After the secondary screen, 49 clones and 28 clones were identified as short day length or Dopa-feeding specific clones, respectively. All of these genes were sequenced and, using the base sequences of these clones, primers were synthesized. To confirm the genes enhanced specifically by these conditions, quantitative real-time PCR was carried out. This quantitative PCR analysis identified 15 and 1 clone whose expression was enhanced by the short day length conditions or Dopa-feeding, respectively. Among these clones, the gene with a high level of identity to receptor for activated protein kinase C (RACK) from Heliothis virescens is the most dramatically up-regulated under both conditions.
Highlights
Insect diapause is characterized by developmental or reproductive arrest and a decrease in metabolic rate
The cabbage armyworm, Mamestra brassicae, has the capacity to enter diapause in the pupal stage: Larvae reared under short day lengths (SD) at 22°C metamor phose into diapausing pupae, whereas those maintained under long day lengths (LD) at 22°C develop into nondiapausing pupae (Kimura & Masaki, 1992, 1993)
These results indicate that the increase in dopamine concentrations in hemolymph and nervous system should contribute to the induction of diapause
Summary
Insect diapause is characterized by developmental or reproductive arrest and a decrease in metabolic rate. Prior studies indicate that dopamine concentrations are elevated in the hemolymph and central nervous system of diapause-destined M. brassicae pupae reared under SD (Noguchi & Hayakawa, 1997). Dopamine concentrations were higher in the hemolymph and central nervous system of the Dopa-fed insects than in non-diapausing control insects around the time of pupal ecdysis (Noguchi & Hayakawa, 1997). These results indicate that the increase in dopamine concentrations in hemolymph and nervous system should contribute to the induction of diapause. We know that these two stimuli affect the larval brain during similar stages and induce diapause
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