Comparative transcriptomics and gene expression in larval tiger salamander (Ambystoma tigrinum) gill and lung tissues as revealed by pyrosequencing.

Biologists are beginning to unravel the complexities of gene expression in model organisms by studying the transcriptome, the complement of genes that are transcribed in a given tissue. It is unclear, however, if findings from model systems apply to non-model organisms because of environmental effects on gene expression. Furthermore, there have been few efforts to quantify how transcriptome or gene expression varies across individuals and across tissues in natural environments. Herein, we describe transcriptomic profiling of gene expression in lung and gill tissue of three larval tiger salamanders. We do so with a hierarchical experimental design that captures variation in expression among genes, among tissues, and among individuals. Using 454 pyrosequencing, we produced high-quality sequence data of 59 megabases and assembled ~200,000 reads into 19,501 contigs. These contigs BLASTed to 3,599 transcripts, of which 721 were expressed in both tissues, 1,668 were unique to gill, and 1,210 unique to lung. Our data showed tissue-specific patterns in gene expression level with variation among transcripts and individuals. We identified genes and gene ontology terms related to respiration and compared their relative expression levels between gill and lung tissues. We also found evidence of exogenous genes associated with larval salamanders, and we identified ~1400 potential molecular markers (microsatellites and single nucleotide polymorphisms) that are associated with expressed genes. Given the tissue-specific differences we observed in transcriptomes, these data reinforce the idea that changes in gene expression serve as a primary mechanism underlying phenotypic plasticity.