Skip to main content
Premium Trial:

Request an Annual Quote

PNAS Papers Take on Polar Bear Evolution, Siberian Hamster Seasonality, and More

Researchers from Vanderbilt University, Clark University, and the University of Massachusetts detect diet- and environment-related copy number changes that have occurred during polar bear evolution. The team profiled copy number variants in three bear species using whole-genome sequences for 17 polar bears, nine brown bears, and two black bears. At the species level, the analysis pointed to copy number shifts and gene losses in the polar bear compared to the brown bear, from which it diverged less than 500,000 years ago. Those changes included polar bear-specific copy number losses affecting olfactory receptor genes, along with pared down copy numbers for fatty acid metabolism and salivary amylase enzyme genes. "These results suggest that natural selection shaped patterns of CNV in response to the transition from an omnivorous to primarily carnivorous diet during polar bear evolution," the authors note.

A team from the US and the UK presents a genomic and transcriptomic analysis of the Siberian hamster — a model animal that adjusts to dramatic seasonal changes in daylight and temperature with metabolic, hormonal, behavioral, and physical changes. The researchers put together a draft genome for the Siberian hamster, Phodopus sungorus, which they annotated with the help of hypothalamus transcriptome data. To explore the seasonal plasticity-related events spurred on by documented triiodothyronine thyroid hormone synthesis in the hamster's hypothalamus, meanwhile, they compared expression profiles in samples from adult male hamsters adapted to long or short photoperiods. Along with clues to specific seasonal responses, the authors suggest the genome and transcriptomes "may permit deeper understanding of the molecular signaling pathways that translate environmental cues into seasonal biological signals, which is relevant for understanding and mitigating the impact of seasonal disruption on health and well-being in human and non-human animals."

Researchers in Switzerland and France dig into the transcriptional organization and directionality of mammalian Hox genes, which are notorious for turning up in clusters in animals with bilateral symmetry. Using CRISPR-Cas9 gene editing, chromatin immunoprecipitation sequencing, and other approaches, the team engineered — and tracked the consequences of — targeted inversions and regulatory activity in the HoxD gene cluster in mice. From the transcriptional, regulatory, and functional patterns found in the edited animals, the authors suggest "enhanced organization of Hox clusters in vertebrates evolved in conjunction with the emergence of global gene regulation to optimize a coordinated response of selected subset of target genes."