Transcriptome sequencing and estimation of DNA methylation level in the subsocial wood-feeding cockroach Cryptocercus punctulatus (Blattodea: Cryptocercidae)

The wood-feeding cockroach genus Cryptocercus is a subsocial and sister group of the eusocial cockroaches, i.e., termites. Although Cryptocercus is a key taxon for understanding the evolution of eusociality in the Blattodea (cockroaches and termites), few genetic resources are available for comparative genetic analyses. In this study, we conducted transcriptome sequencing of Cryptocercus punctulatus Scudder using next-generation sequencing technology to generate a massive genetic resource. By transcriptome sequencing and subsequent de novo transcriptome assembly, we obtained 132,191 contigs. The assembled transcriptome contained almost all of the conserved core eukaryote or insect genes. Furthermore, juvenile hormone- and DNA methylation-related genes that are considered to be key genes for the caste polyphenism in eusocial insects, were identified from the transcriptome assembly. In addition, the ratio of the observed (O) cytosine-phosphate-guanine (CpG) content to the expected (E) one (CpG O/E), which is a proxy for the DNA methylation level, was calculated for coding regions extracted from the assembly. The CpG O/E values were less than 1 in most of the coding regions, and the frequency distribution of the CpG O/E values was bimodal rather than unimodal. These results indicate that most C. punctulatus genes are involved in DNA methylation.