Comparative Serum Challenges Show Divergent Patterns of Gene Expression and Open Chromatin in Human and Chimpanzee.


Humans experience higher rates of age-associated diseases than our closest living evolutionary relatives, chimpanzees. Environmental factors can explain many of these increases in disease risk, but species-specific genetic changes can also play a role. Alleles that confer increased disease susceptibility later in life can persist in a population in the absence of selective pressure if those changes confer positive adaptation early in life. One age-associated disease that disproportionately affects humans compared with chimpanzees is epithelial cancer. Here, we explored genetic differences between humans and chimpanzees in a well-defined experimental assay that mimics gene expression changes that happen during cancer progression: A fibroblast serum challenge. We used this assay with fibroblasts isolated from humans and chimpanzees to explore species-specific differences in gene expression and chromatin state with RNA-Seq and DNase-Seq. Our data reveal that human fibroblasts increase expression of genes associated with wound healing and cancer pathways; in contrast, chimpanzee gene expression changes are not concentrated around particular functional categories. Chromatin accessibility dramatically increases in human fibroblasts, yet decreases in chimpanzee cells during the serum response. Many regions of opening and closing chromatin are in close proximity to genes encoding transcription factors or genes involved in wound healing processes, further supporting the link between changes in activity of regulatory elements and changes in gene expression. Together, these expression and open chromatin data show that humans and chimpanzees have dramatically different responses to the same physiological stressor, and how a core physiological process can evolve quickly over relatively short evolutionary time scales.






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Publication Info

Pizzollo, Jason, William J Nielsen, Yoichiro Shibata, Alexias Safi, Gregory E Crawford, Gregory A Wray and Courtney C Babbitt (2018). Comparative Serum Challenges Show Divergent Patterns of Gene Expression and Open Chromatin in Human and Chimpanzee. Genome biology and evolution, 10(3). 10.1093/gbe/evy041 Retrieved from

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Gregory E. Crawford

Professor in Pediatrics

My primary research interest is understanding how the genome is regulated.  The human genome contains approximately 25,000 genes, which are encoded in ~2% of the genome. The overarching goal of my research program is to identify and characterize how these genes are turned on and off in different cell types, tissues, development states, environmental responses, diseases, and individuals. By understanding where all gene regulatory elements are located, how they work to regulate gene expression, and how non-coding variants within these regions affect function, my research program can address a number of important basic and clinical questions.


Gregory Allan Wray

Professor of Biology

I study the evolution of genes and genomes with the broad aim of understanding the origins of biological diversity. My approach focuses on changes in the expression of genes using both empirical and computational approaches and spans scales of biological organization from single nucleotides through gene networks to entire genomes. At the finer end of this spectrum of scale, I am focusing on understanding the functional consequences and fitness components of specific genetic variants within regulatory sequences of several genes associated with ecologically relevant traits. At the other end of the scale, I am developing molecular and analytical methods to detect changes in gene function throughout entire genomes, including statistical frameworks for detecting natural selection on regulatory elements and empirical approaches to identify functional variation in transcriptional regulation. At intermediate scales, I am investigating functional variation within a dense gene network in the context of wild populations and natural perturbations. My research leverages the advantages of several different model systems, but primarily focuses on sea urchins and primates (including humans).

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