Role of Insect Neuropeptides and Juvenile Hormones in Silk Protein Biosynthesis

Abstract

Brain or the neurosecretory system in insects being the wider part of the central nervous system does play important role in the neuroendocrine regulation of biological activities controlling growth, development and reproduction. The brain also regulates the synthesis and the release of juvenile hormones (JH) by the corpora allata (CA). A large number of neuropeptides are being identified in invertebrates and are found to play important roles in controlling brain functions of insects and their behaviour. Insect neuropeptides and juvenile hormones (JH) play important roles in all aspects of insect development and reproduction. Juvenile Hormone Acid Methyltransferase (JHAMT) is found to be the key regulatory enzyme in juvenile hormone biosynthesis. The ability of corpora allata to synthesize juvenile hormone is controlled by stimulatory and inhibitory signals. These signals are mediated through neuropeptides or its analogues are either stimulatory (Allatotropin, and its analogues), synthetic analogues ( allatotropin analogue acetylated, ATAA and allatotropin analogue non acetylated, ATANA) or inhibitory (allatostatin, allatinhibin). It has been observed that the activities of the cellular ultra structure immediately after last larval moulting of the neuro secretory cells were very less compared to later part of the instar. Juvenile hormone and its analogues are found to cause various biochemical changes in the larval tissues. It also increases larval body weight, coccon weight and silk shell weight which is the result of secretion of more silk protein and lengthening of last instar. Similar observations are also shown by non-mulberry silkworm Philosamia ricini with JH-III. Juvenile hormones are found to inhibit silk gland function, prevent their degeneration and indirectly causing an increase in silk production. The practical application of these neuropeptides is also now undertaken by different groups for pest management as biocontrol agents. However, the molecular action and functional properties of these natural peptides are still a challenge to insect endocrinologists. In this paper, the role of neuropeptides and juvenile hormones with respect to silk protein biosynthesis in non-mulberry silkworms are being reviewed. doi: 10.5214/ans.0972.7531.2008.150404 Competing interests: None. Source of Funding: USEFI, DBT, DST, Ministry of Environment and Forests, Central Silk Board Received Date: 25 Sept 2008 Revised Date: 18 Oct 2008 Accepted Date: 30 Oct 2008