Pol III binding in six mammals shows conservation among amino acid isotypes despite divergence among tRNA genes.

RNA polymerase III (Pol III) transcription of tRNA genes is essential for generating the tRNA adaptor molecules that link genetic sequence and protein translation. By mapping Pol III occupancy genome-wide in mouse, rat, human, macaque, dog and opossum livers, we found that Pol III binding to individual tRNA genes varies substantially in strength and location. However, when we took into account tRNA redundancies by grouping Pol III occupancy into 46 anticodon isoacceptor families or 21 amino acid-based isotype classes, we discovered strong conservation. Similarly, Pol III occupancy of amino acid isotypes is almost invariant among transcriptionally and evolutionarily diverse tissues in mouse. Thus, synthesis of functional tRNA isotypes has been highly constrained, although the usage of individual tRNA genes has evolved rapidly

Comparative transcriptomics in human and mouse

Cross-species comparisons of genomes, transcriptomes and gene regulation are now feasible at unprecedented resolution and throughput, enabling the comparison of human and mouse biology at the molecular level. Insights have been gained into the degree of conservation between human and mouse at the level of not only gene expression but also epigenetics and inter-individual variation. However, a number of limitations exist, including incomplete transcriptome characterization and difficulties in identifying orthologous phenotypes and cell types, which are beginning to be addressed by emerging technologies. Ultimately, these comparisons will help to identify the conditions under which the mouse is a suitable model of human physiology and disease, and optimize the use of animal models