Meningioma: current updates on genetics, classification, and mouse modeling

Meningiomas, the most common primary brain tumors in adults, are often benign and curable by surgical resection. However, a subset is of higher grade, shows aggressive growth behavior as well as brain invasion, and often recurs even after several rounds of surgery. Increasing evidence suggests that tumor classification and grading primarily based on histopathology do not always accurately predict tumor aggressiveness and recurrence behavior. The underlying biology of aggressive treatment-resistant meningiomas and the impact of specific genetic aberrations present in these high-grade tumors is still only insufficiently understood. Therefore, an in-depth research into the biology of this tumor type is warranted. More recent studies based on large-scale molecular data such as whole exome/genome sequencing, DNA methylation sequencing, and RNA sequencing have provided new insights into the biology of meningiomas and have revealed new risk factors and prognostic subtypes. The most common genetic aberration in meningiomas is functional loss of NF2 and occurs in both low- and high-grade meningiomas, whereas NF2-wildtype meningiomas are enriched for recurrent mutations in TRAF7, KLF4, AKT1, PI3KCA, and SMO and are more frequently benign. Most meningioma mouse models are based on patient-derived xenografts and only recently have new genetically engineered mouse models of meningioma been developed that will aid in the systematic evaluation of specific mutations found in meningioma and their impact on tumor behavior. In this article, we review recent advances in the understanding of meningioma biology and classification and highlight the most common genetic mutations, as well as discuss new genetically engineered mouse models of meningioma.

Oncogenic Events Dictate the Types and Locations of Gynecological Malignancies Originating from Krt8+ Mesothelial and Müllerian-Derived Epithelial Cells

Simple Summary

Ovarian and uterine cancers are the most common gynecological malignancies in women. The early detection, prevention, and treatment of these gynecological cancers can benefit from a better understanding of how tumor-initiating cells in them are formed from their corresponding target cell populations in the female reproductive system. To study this, we utilized a genetic approach in mice to introduce driver mutations commonly found in these cancers to Keratin 8 positive (K8⁺) mesothelial and epithelial cells in the ovary, fallopian tube, and uterus. We found that p53-loss appears to preferentially affect K8⁺ epithelial cells, leading to the development of uterine and ovarian malignancies, whereas PTEN-loss may preferentially affect mesothelial cells, leading to the development of ovarian endometrioid malignancies or adenoma on the fallopian tube surface. Collectively, our data suggest that oncogenic driver mutations may dominantly determine the locations and types of gynecological malignancies developed from K8⁺ mesothelial and epithelial cells in the female reproductive system.

Abstract

Ovarian and uterine cancers are the most prevalent types of gynecological malignancies originating from mesothelial and/or Müllerian-derived epithelial cells. Recent genomic studies have identified common mutations in them that affect signaling pathways such as p53, PTEN/PI3K, RAS, and WNT pathways. However, how these mutations and their corresponding deregulated pathways affect gynecological cancer development from their cells-of-origin remains largely elusive. To address this, we performed the intrabursal injection of Cre-expressing adenovirus under the control of Krt8 promoter (Ad-K8-Cre) to mice carrying combinations of various conditional alleles for cancer genes. We found that Ad-K8-Cre specifically targeted mesothelial cells, including ovarian surface epithelial (OSE) cells (mainly the LGR5⁺ subset of OSE cells) and mesothelial cells lining the fallopian tube (FT) serosa; the injected Ad-K8-Cre also targeted Müllerian-derived epithelial cells, including FT epithelial cells and uterine endometrial epithelial cells. The loss of p53 may preferentially affect Müllerian-derived epithelial cells, leading to the development of uterine and ovarian malignancies, whereas PTEN-loss may preferentially affect mesothelial cells, leading to the development of ovarian endometrioid malignancies (upon KRAS-activation or APC-loss) or adenoma on the FT surface (upon DICER-loss). Overall, our data suggest that different Krt8⁺ mesothelial and epithelial cell types in the female reproductive system may have different sensitivities toward oncogenic mutations and, as a result, oncogenic events may dominantly determine the locations and types of the gynecological malignancies developed from them.

A predicted deleterious allele of the essential meiosis gene MND1, present in ~ 3% of East Asians, does not disrupt reproduction in mice

Infertility is a major health problem affecting ~15% of couples worldwide. Except for cases involving readily detectable chromosome aberrations, confident identification of a causative genetic defect is problematic. Despite the advent of genome sequencing for diagnostic purposes, the preponderance of segregating genetic variants complicates identification of culprit genetic alleles or mutations. Many algorithms have been developed to predict the effects of 'variants of unknown significance', typically single nucleotide polymorphisms (SNPs), but these predictions are not sufficiently accurate for clinical action. As part of a project to identify population variants that impact fertility, we have been generating clustered regularly interspaced short palindromic repeats-Cas9 edited mouse models of suspect SNPs in genes that are known to be required for fertility in mice. Here, we present data on a non-synonymous (amino acid altering) SNP (rs140107488) in the meiosis gene Mnd1, which is predicted bioinformatically to be deleterious to protein function. We report that when modeled in mice, this allele (MND1K85M), which is present at an allele frequency of ~ 3% in East Asians, has no discernable effect upon fertility, fecundity or gametogenesis, although it may cause sex skewing of progeny from homozygous males. In sum, assuming the mouse model accurately reflects the impact of this variant in humans, rs140107488 appears to be a benign allele that can be eliminated or de-prioritized in clinical genomic analyses of infertility patients.