Genomics · us
From a Single Reference to an Eight-Strain Map: The Brown Rat Pangenome Fills Blind Spots in Disease Models
The first telomere-to-telomere brown rat assembly, combined with eight commonly used laboratory strains, incorporates sequences and genes missing from previous reference genomes. It could improve the ability to pinpoint disease-associated variants, but there is still some way to go before it can be shown that these models better predict human responses.
Laboratory rats underpin a substantial amount of research into cardiovascular, kidney, and metabolic diseases, but interpreting their genetic differences has long relied on a reference genome that cannot possibly encompass every strain. A research team has now used the stroke-prone spontaneously hypertensive rat (SHRSP) to create a new, highly complete assembly and integrated eight laboratory strains into a graphical pangenome, aiming to reveal genetic variants that previously fell outside the reference coordinates.
The team said the new assembly adds approximately 7% more sequence than the existing reference and identifies more than 60 genes that could not previously be resolved. A “telomere-to-telomere” assembly aims to read the sequence continuously between the two ends of a chromosome, particularly filling gaps in centromeres, repetitive sequences, and other regions that are difficult to assemble using conventional short-read technologies. These regions are also often where structural variants such as large insertions, deletions, and duplications are found.
The work integrates PacBio HiFi, Oxford Nanopore ultra-long reads, and Hi-C data. The related doctoral thesis reports an overall Merqury quality value of 65.0, with 15 of the 22 chromosomes assembled without gaps. This also serves as a reminder that “telomere-to-telomere genome” describes the overall construction goal and principal results of the resource; it does not mean that every chromosome has been assembled completely without gaps.
The pangenome, meanwhile, no longer requires all data to be fitted into a single linear sequence. Using the SHRSP assembly as the backbone, the researchers incorporated SHR-B2, Dahl salt-resistant rats, F344, Brown Norway, Lyon hypertensive rats, Lyon normotensive rats, and Wistar Kyoto rats through Minigraph-Cactus. These strains have different disease predispositions and physiological characteristics. A graphical representation can preserve strain-specific sequence paths, reducing the alignment bias caused by using only a single reference genome.
The practical value may emerge first in structural variant analysis. If a variant affecting blood pressure, kidney function, or stroke risk lies in a region that was previously missing or misplaced, the new resource could help researchers relocate candidate genes and compare different strains more precisely. However, a more complete map will not by itself automatically make animal models more closely resemble human disease. Candidate variants still require validation through expression, functional, and physiological experiments, and improvements in assembly will not eliminate cross-species differences.
The assembly, Liftoff and BRAKER3 gene annotations, Iso-Seq data, pangenome graph, and structural variant files have been deposited in public databases, allowing other teams to reproduce the analyses. At this stage, this represents an infrastructure advance: it increases the resolution of genetic research in laboratory rats and provides tools for re-examining existing disease models. Whether it can truly improve the reproducibility of preclinical research and its ability to translate to humans remains to be answered by subsequent studies.