Diapause in a tropical oil-collecting bee: molecular basis unveiled by RNA-Seq

Abstract\ud \ud Background\ud Diapause is a natural phenomenon characterized by an arrest in development that ensures the survival of organisms under extreme environmental conditions. The process has been well documented in arthropods. However, its molecular basis has been mainly studied in species from temperate zones, leaving a knowledge gap of this phenomenon in tropical species. In the present study, the Neotropical and solitary bee Tetrapedia diversipes was employed as a model for investigating diapause in species from tropical zones. Being a bivoltine insect, Tetrapedia diversipes produce two generations of offspring per year. The first generation, normally born during the wet season, develops faster than individuals from the second generation, born after the dry season. Furthermore, it has been shown that the development of the progeny, of the second generation, is halted at the 5th larval instar, and remains in larval diapause during the dry season. Towards the goal of gaining a better understanding of the diapause phenomenon we compared the global gene expression pattern, in larvae, from both reproductive generations and during diapause. The results demonstrate that there are similarities in the observed gene expression patterns to those already described for temperate climate models, and also identify diapause-related genes that have not been previously reported in the literature.\ud \ud \ud Results\ud The RNA-Seq analysis identified 2275 differentially expressed transcripts, of which 1167 were annotated. Of these genes, during diapause, 352 were upregulated and 815 were downregulated. According to their biological functions, these genes were categorized into the following groups: cellular detoxification, cytoskeleton, cuticle, sterol and lipid metabolism, cell cycle, heat shock proteins, immune response, circadian clock, and epigenetic control.\ud \ud \ud Conclusion\ud Many of the identified genes have already been described as being related to diapause; however, new genes were discovered, for the first time, in this study. Among those, we highlight: Niemann-Pick type C1, NPC2 and Acyl-CoA binding protein homolog (all involved in ecdysteroid synthesis); RhoBTB2 and SASH1 (associated with cell cycle regulation) and Histone acetyltransferase KAT7 (related to epigenetic transcriptional regulation). The results presented here add important findings to the understanding of diapause in tropical species, thus increasing the comprehension of diapause-related molecular mechanisms.This work was supported by Coordenação de Aperfeiçoamento de Pessoal\ud de Nível Superior (CAPES) as a scholarship to PKFS, by Conselho Nacional de\ud Desenvolvimento Científico e Tecnológico (CNPq) as a research fellowship to\ud MCA, by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)\ud as a scholarship to NSA (2012/18531–0) and research grants to MCA (2010/\ud 50597–5 and 2013/12530–4). This work was developed in the Centro de\ud Pesquisa em Biodiversidade e Computação (BioComp) of the Universidade\ud de São Paulo (USP), supported by the USP Provost’s Office for Research. The\ud funding agencies had no role in the study design, sample collection, analysis\ud and interpretation of the data, and in writing the manuscript