John Svaren, PhD – Slide of the Week

Title: CRISPR-Cas9 deletion of PMP22 super enhancer creates  a new model of hereditary neuropathy with liability to pressure palsies (HNPP)

Legend: (A) Morphometric analysis demonstrates axonal loss i thin section were taken from 3- to 5-month-old wild-type, Pmp22-SE+/− and Pmp22-SE−/− nerve.

Citation: Harrison Pantera, Bo Hu, Daniel Moiseev, Chris Dunham, Jibraan Rashid, John J. Moran, Kathleen Krentz, C. Dustin Rubinstein, Seongsik Won, Jun Li and John Svaren (2020). Pmp22 super-enhancer deletion causes tomaculaformation and conduction block in peripheral nerves. Human Molecular Genetics, 29(10):1689-1699

Abstract: Copy number variation of the peripheral nerve myelin gene Peripheral Myelin Protein 22 (PMP22) causes multiple forms of inherited peripheral neuropathy. The duplication of a 1.4 Mb segment surrounding this gene in chromosome 17p12 (c17p12) causes the most common form of Charcot-Marie-Tooth disease type 1A, whereas the reciprocal deletion of this gene causes a separate neuropathy termed hereditary neuropathy with liability to pressure palsies (HNPP). PMP22 is robustly induced in Schwann cells in early postnatal development, and several transcription factors and their cognate regulatory elements have been implicated in coordinating the gene’s proper expression. We previously found that a distal super-enhancer domain was important for Pmp22 expression in vitro, with particular impact on a Schwann cell-specific alternative promoter. Here, we investigate the consequences of deleting this super-enhancer in vivo. We find that loss of the super-enhancer in mice reduces Pmp22 expression throughout development and into adulthood, with greater impact on the Schwann cell-specific promoter. Additionally, these mice display tomacula
formed by excessive myelin folding, a pathological hallmark of HNPP, as have been previously observed in heterozygous Pmp22 mice as well as sural biopsies from patients with HNPP. Our findings demonstrate a mechanism by which smaller copy number variations, not including the Pmp22 gene, are sufficient to reduce gene expression and phenocopy a peripheral neuropathy caused by the HNPP-associated deletion encompassing PMP22.

About the Lab: The Svaren laboratory is focused on the transcriptional and epigenetic regulation of myelination. Myelin is a vital constituent of the nervous system that increases the speed of action potentials and also provides trophic support for the long axons that project from neurons. Their studies are centered on the myelin-producing cells of the peripheral nervous system, called Schwann cells. The Svaren lab has focused on elucidating regulation of gene networks during Schwann cell development and response to injury. They have also recently found a novel role of the polycomb repressive complex 2, an epigenetic regulator, in controlling the regenerative responses of Schwann cells after peripheral nerve injury.

Slide of the Week Archives