Abstract
In termites, division of labor among castes, categories of individuals that perform specialized tasks, increases colony-level productivity and is the key to their ecological success. Although molecular studies on caste polymorphism have been performed in termites, we are far from a comprehensive understanding of the molecular basis of this phenomenon. To facilitate future molecular studies, we aimed to construct expressed sequence tag (EST) libraries covering wide ranges of gene repertoires in three representative termite species, Hodotermopsis sjostedti , Reticulitermessperatus and Nasutitermestakasagoensis . We generated normalized cDNA libraries from whole bodies, except for guts containing microbes, of almost all castes, sexes and developmental stages and sequenced them with the 454 GS FLX titanium system. We obtained >1.2 million quality-filtered reads yielding >400 million bases for each of the three species. Isotigs, which are analogous to individual transcripts, and singletons were produced by assembling the reads and annotated using public databases. Genes related to juvenile hormone, which plays crucial roles in caste differentiation of termites, were identified from the EST libraries by BLAST search. To explore the potential for DNA methylation, which plays an important role in caste differentiation of honeybees, tBLASTn searches for DNA methyltransferases (dnmt1, dnmt2 and dnmt3) and methyl-CpG binding domain (mbd) were performed against the EST libraries. All four of these genes were found in the H . sjostedti library, while all except dnmt3 were found in R . speratus and N . takasagoensis . The ratio of the observed to the expected CpG content (CpG O/E), which is a proxy for DNA methylation level, was calculated for the coding sequences predicted from the isotigs and singletons. In all of the three species, the majority of coding sequences showed depletion of CpG O/E (less than 1), and the distributions of CpG O/E were bimodal, suggesting the presence of DNA methylation.
Highlights
Termites, one of the major social insect groups, live in colonies and construct complex societies with highly sophisticated division of labor among castes, which show distinctive behavior and morphology for their specialized tasks [1,2]
We extracted total RNA from 18, 26, and 25 categories of individuals that were classified based on caste/sex/developmental stage in Hodotermopsis sjostedti, Reticulitermes speratus, and Nasutitermes takasagoensis, respectively (Tables S1-S3)
All of the reads obtained have been deposited in the DDBJ Sequence Read Archive (DRA) database under accession numbers DRA000538 and DRA001044 for H. sjostedti, DRA001045 for R. speratus, and DRA001046 for N. takasagoensis
Summary
One of the major social insect groups, live in colonies and construct complex societies with highly sophisticated division of labor among castes, which show distinctive behavior and morphology for their specialized tasks [1,2]. A significant number of studies that focused on differential gene expression among castes and among individuals in the course of caste differentiation have been reported in termites Miura & Scharf [4]) These studies successfully identified genes with caste-specific or -biased expressions, and up- or downregulated genes during caste differentiation. Termites are represented by more than 2600 extant species [5] and exhibit considerable diversity in morphology and behavior of castes and caste developmental pathways [6]. To facilitate gene expression analyses in termites, it is important to construct expressed sequence tag (EST) libraries, which are used as an information source for gene discovery, gene structure identification, and so on [7,8,9,10]
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