Growth-blocking peptide expressed in the insect nervous system--cloning and functional characterization

Area of Science:

• Insect Physiology
• Molecular Biology
• Biochemistry

Background:

• Growth-blocking peptide (GBP) is an insect biogenic peptide that inhibits lepidopteran larval growth and pupation.
• GBP gene transcription shows tissue-specific regulation, with distinct mRNA transcripts in fat body (0.8 kb) and brain central nervous system (CNS) (2.5 kb).

Purpose of the Study:

• To investigate the molecular mechanisms underlying tissue-specific GBP gene expression.
• To explore the impact of parasitization on GBP expression and its downstream effects in the insect brain CNS.

Main Methods:

• Isolation and sequencing of GBP cDNA from brain CNS.
• Sequence analysis of genomic GBP gene fragments.
• Ribonuclease protection assays to measure GBP mRNA levels.
• Measurement of GBP precursor and GBP concentrations.
• In vitro incubation of brain CNS with GBP to assess dopamine levels and protein synthesis.

Main Results:

• GBP cDNA from brain CNS is nearly identical to fat body cDNA but has a longer 5'-untranslated region.
• A specific sequence element (TGATAA) in the 5'-untranslated region of the genomic GBP gene may contribute to tissue-specific expression in the fat body.
• Parasitization significantly elevates GBP mRNA, precursor, and GBP concentrations in the brain CNS.
• GBP incubation increases brain CNS dopamine by enhancing dopa decarboxylase activity, potentially via increased cytoplasmic Ca2+.
• Elevated dopamine reduces methionine incorporation into brain CNS proteins.

Conclusions:

• The differential expression of GBP in insects is regulated by variations in the 5'-untranslated region and genomic elements.
• Parasitization triggers a neuroendocrine response involving GBP and dopamine in the insect brain CNS.
• GBP-induced dopamine elevation may serve as a mechanism to modulate host insect physiology during parasitization.