Cellular mechanisms of heterogeneity in NF2-mutant schwannoma
Schwannomas are sporadic, usually benign tumors that develop predominately on spinal nerve roots and cranial nerves. Inactivation of NF2 in Schwann cells (SC) is the cause of nearly all schwannomas and mutations in additional genes are few if present at all.
Despite their genetic similarity, NF2-mutant schwannomas are characterized by significant variability, exhibiting diverse natural histories, growth rates, and clinical impact. However, it is unknown how this diversity, which can exist even between tumors in the same patient, arises.
In their study, Chiasson-MacKenzie et al first utilized phase contrast and confocal microscopy and quantitative real-time PCR to investigate NF2-mutant SC morphology, expression of cytoskeletal and signaling genes, and macropinocytosis. Together, these in vitro studies indicated that in the absence of NF2, external signals and auto and paracrine ligands drive SC to self-generate heterogeneous phenotypic states.
The authors next utilized HALO® to quantitatively analyze schwannoma heterogeneity in tissue, first scanning formalin-fixed paraffin-embedded human and mouse tissue on Vectra 3 and Polaris slide scanners, respectively. The FISH-IF module was used to quantify protein and mRNA and observe inter- and intratumor heterogeneity, while the Spatial Analysis module was leveraged to measure positive cell proximity to dorsal root ganglion (DRG) soma. A random forest classifier that was generated using the Tissue Classifier Add-on and trained to recognize tumor cells and exclude DRG soma was used throughout these analyses. The results supported the authors’ in vitro observations and provided insight into the distribution of heterogenous tumor cell populations in tissue and the development of self-generated heterogeneity early during schwannoma tumorigenesis.