Tissue-specific transcriptomics in the field cricket Teleogryllus oceanicus

Abstract

Field crickets (family Gryllidae) frequently are used in studies of behavioral genetics, sexual selection, and sexual conflict, but there have been no studies of transcriptomic differences among different tissue types. We evaluated transcriptome variation among testis, accessory gland, and the remaining whole-body preparations from males of the field cricket, Teleogryllus oceanicus. Non-normalized cDNA libraries from each tissue were sequenced on the Roche 454 platform, and a master assembly was constructed using testis, accessory gland, and whole-body preparations. A total of 940,200 reads were assembled into 41,962 contigs, to which 36,856 singletons (reads not assembled into a contig) were added to provide a total of 78,818 sequences used in annotation analysis. A total of 59,072 sequences (75%) were unique to one of the three tissues. Testis tissue had the greatest proportion of tissue-specific sequences (62.6%), followed by general body (56.43%) and accessory gland tissue (44.16%). We tested the hypothesis that tissues expressing gene products expected to evolve rapidly as a result of sexual selection--testis and accessory gland--would yield a smaller proportion of BLASTx matches to homologous genes in the model organism Drosophila melanogaster compared with whole-body tissue. Uniquely expressed sequences in both testis and accessory gland showed a significantly lower rate of matching to annotated D. melanogaster genes compared with those from general body tissue. These results correspond with empirical evidence that genes expressed in testis and accessory gland tissue are rapidly evolving targets of selection.

Keywords: Teleogryllus oceanicus; field cricket; gryllid; reference transcriptome; tissue-specific transcriptome.

Figure 1

Distribution of sequences among tissues. The distribution of all sequences (contigs and singletons) mapping to each tissue is shown on the left, and the distribution of sequences from each tissue with successful BLASTx hits is shown on the right.

Figure 2

Histogram of contig lengths. Only contigs <4000 bp are shown. The data have a long tail with no peaks reaching 10,718 bp.

Figure 3

Species matches to tissue-specific sequences (contigs and singletons). The percentages indicate the top BLASTx matches for each species category.

Figure 4

The proportion of tissue-specific sequences (contigs and singletons) with a BLASTx match to Drosophila melanogaster proteins in FlyBase. Column widths are proportional to the total number of sequences. Tissues that were significantly different do not share a small letter: both testis and accessory gland sequences showed a lower proportion of matches to D. melanogaster genes compared with general body tissue and also were significantly different from one another (see Results section for details).