Bao and Xu BMC Genomics 2011, 12:224 http://www.biomedcentral.com/1471-2164/12/224 R E S E A R C H A R T I C L E Open Access Identification of gene expression changes associated with the initiation of diapause in the brain of the cotton bollworm, Helicoverpa armigera Bin Bao and Wei-Hua Xu* Abstract Background: Diapause, a state of arrested development accompanied by a marked decrease of metabolic rate, helps insects to overcome unfavorable seasons. Helicoverpa armigera (Har) undergoes pupal diapause, but the molecular mechanism of diapause initiation is unclear. Using suppression subtractive hybridization (SSH), we investigated differentially expressed genes in diapause- and nondiapause-destined pupal brains at diapause initiation. Results: We constructed two SSH libraries (forward, F and reverse, R) to isolate genes that are up-regulated or down-regulated at diapause initiation. We obtained 194 unique sequences in the F library and 115 unique sequences in the R library. Further, genes expression at the mRNA and protein level in diapause- and nondiapause- destined pupal brains were confirmed by RT-PCR, Northern blot or Western blot analysis. Finally, we classified the genes and predicted their possible roles at diapause initiation. Conclusion: Differentially expressed genes at pupal diapause initiation are possibly involved in the regulation of metabolism, energy, stress resistance, signaling pathways, cell cycle, transcription and translation. Background Environmental changes are an obvious source of stress for an organism. Insects inhabiting variable environ- ments employ a number of adaptations to survive adverse conditions. Developmental arrest, called dia- pause in insects, is one evolutionary adaptation utilized to endure unfavorable conditions [1]. As a strategy for surviving unfavorable environmental conditions, dia- pause can occur in various developmental stages includ- ing egg, larva, pupa or adult, resulting in a programmed arrest of development coupled with other physiological changes [2]. Diapause is a dynamic process consisting of several successive phases: pre-diapause, diapause, and post-diapause, and each phase may comprise some sub- phases, e.g., the diapause phase is divided into diapause initiation, maintenance, and termination [3]. The * Correspondence: xuweihua@mail.sysu.edu.cn State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, China hormonal regulation of diapause has been well defined, but the molecular mechanism of diapause is unclear. Using pulse labeling combined with 2-dimensional elec- trophoresis and elimination hybridization, changes in protein synthesis [4] and gene expression [5] were firstly identified in the diapausing pupal brain of Sarcophaga crassipalpis, suggesting that diapause is a unique devel- opmental pathway rather than a simple shutdown of gene expression [6]. Suppression subtractive hybridiza- tion (SSH) has been used to evaluate diapause-specific gene expression in Culex pipiens [7] and S. crassipalpis [8]. Recently, a systemic investigation of transcript pro- filing of nondiapause and diapause pupae has been con- ducted using microarray technique in S. crassipalpis [9]. In addition, proteomic method has been used to identify differentially expressed proteins in the brains of S. cras- sipalpis [10] and Helicoverpa armigera [11]. Many genes and proteins related to diapause have been identified, but differentially expressed genes during diapause initia- tion are rarely reported [6]. It is yet unknown why © 2011 Bao and Xu; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.