인슐린(insulin)과 insulin-like growth factor-1 (IGF-1)은 척추동물에서 대사, 생장, 수명 등의 여러 생리대사를 조절하는 중요한 호르몬 이다. 곤충에서도 IGF-1과 구조적으로 유사한 insulin-like peptide (ILP)들이 존재하며 이들이 곤충 생리 조절에 중요하게 관여함이 밝혀졌다. 이번 총설에서 곤충 ILP 및 초파리(Drosophila melanogaster) 유전체 분석을 통해 척추동물에 존재하는 인슐린 및 IGF-1 수용체 신호전달계와 유 사하다고 확인된 ILP 수용체 신호전달계에 대해 설명하고자 한다. 추가적으로, 곤충 체내의 영양 상태에 따라 조절되는 뇌에서의 ILP의 합성과 분비, ILP에 의한 대사의 생리적 조절에 대해 논한다. 또한 ILP가 생장, 발달, 생식, 휴면에 기여하는 바도 논의하고, 마지막으로 ILP 수용체 신 호전달계 제어를 통한 해충 방제에의 이용 가능성에 대해 제안하고자 한다.

Like vertebrate insulins, insulin-like peptides (ILPs) play crucial roles in controlling immature growth, adult lifespan, and plasma sugar level in some insects. An ILP gene (SeILP1) was predicted from a transcription database of Spodoptera exigua. SeILP1 encodes 95 amino acid sequence, which shares sequence homologies (33~83%) with other insects ILPs. The predicted B and A chains possess six cysteine residences. SeILP1 was expressed in all developmental stages of S. exigua. However, its expression was detected in fat body, gut and epidermis, but not in hemocytes. Its expression increased with feeding activity. Plasma trehalose levels of fifth instar larvae maintained at relatively stable concentration of 2.31±0.62 mM. However, starvation induced a significant increase of plasma trehalose level by more than two fold in 48 h, at which SeILP1 expression kept at a low level. RNA interference of SeILP1 induced a significant increase of plasma trehalose level. Interestingly, a bovine insulin decreased plasma trehalose level in a dose-dependent manner. These results indicate mat SeILP1 plays a role in suppressing plasma trehalose level in S. exigua.

Insulin in vertebrates plays a crucial role in maintaining homeostasis of blood sugar level. Insulin-like peptide (ILP) has been identified in insects, such as Drosophila melanogaster and Aedes aegypti. Plasma sugars and polyols of the diamondback moth, Plutella xylostella were separated by a Bio-LC. Among seven peaks, trehalose was the most predominant blood sugar and maintained at approximately 3.5 mM in the larval plasma. However, the feeding activity affected the plasma trehalose level, in which starvation significantly up-regulated the trehalose level. Analysis of ILP expression upon feeding indicated that feeding stimulated the gene expression of ILP. Interestingly, an injection of a vertebrate insulin significantly suppressed the hypertrehalosemia induced by starvation. These results suggest that ILP is a endocrine signal to down-regulate the plasma trehalose level in P. xylostella.