Miller Huang

Neuroblastoma and MYCN

Neuroblastoma, the most common extracranial solid tumor of childhood, is thought to originate from undifferentiated neural crest cells. Amplification of the MYC family member, MYCN, is found in ∼25% of cases and correlates with high-risk disease and poor prognosis. Currently, amplification of MYCN remains the best-characterized genetic marker of risk in neuroblastoma. This article reviews roles for MYCN in neuroblastoma and highlights recent identification of other driver mutations. Strategies to target MYCN at the level of protein stability and transcription are also reviewed.

Isolation of single-base genome-edited human iPS cells without antibiotic selection.

Precise editing of human genomes in pluripotent stem cells by homology-driven repair of targeted nuclease–induced cleavage has been hindered by the difficulty of isolating rare clones. We developed an efficient method to capture rare mutational events, enabling isolation of mutant lines with single-base substitutions without antibiotic selection. This method facilitates efficient induction or reversion of mutations associated with human disease in isogenic human induced pluripotent stem cells.

Glial Progenitors as Targets for Transformation in Glioma

Glioma is the most common primary malignant brain tumor and arises throughout the central nervous system. Recent focus on stem-like glioma cells has implicated neural stem cells (NSCs), a minor precursor population restricted to germinal zones, as a potential source of gliomas. In this review, we focus on the relationship between oligodendrocyte progenitor cells (OPCs), the largest population of cycling glial progenitors in the postnatal brain, and gliomagenesis. OPCs can give rise to gliomas, with signaling pathways associated with NSCs also playing key roles during OPC lineage development. Gliomas can also undergo a switch from progenitor- to stem-like phenotype after therapy, consistent with an OPC-origin even for stem-like gliomas. Future in-depth studies of OPC biology may shed light on the etiology of OPC-derived gliomas and reveal new therapeutic avenues.

Generating trunk neural crest from human pluripotent stem cells

Neural crest cells (NCC) are stem cells that generate different lineages, including neuroendocrine, melanocytic, cartilage, and bone. The differentiation potential of NCC varies according to the level from which cells emerge along the neural tube. For example, only anterior “cranial” NCC form craniofacial bone, whereas solely posterior “trunk” NCC contribute to sympathoadrenal cells. Importantly, the isolation of human fetal NCC carries ethical and scientific challenges, as NCC induction typically occur before pregnancy is detectable. As a result, current knowledge of NCC biology derives primarily from non-human organisms. Important differences between human and non-human NCC, such as expression of HNK1 in human but not mouse NCC, suggest a need to study human NCC directly. Here, we demonstrate that current protocols to differentiate human pluripotent stem cells (PSC) to NCC are biased toward cranial NCC. Addition of retinoic acid drove trunk-related markers and HOX genes characteristic of a posterior identity. Subsequent treatment with bone morphogenetic proteins (BMPs) enhanced differentiation to sympathoadrenal cells. Our approach provides methodology for detailed studies of human NCC, and clarifies roles for retinoids and BMPs in the differentiation of human PSC to trunk NCC and to sympathoadrenal lineages.

Imaging-based chemical screening reveals activity-dependent neural differentiation of pluripotent stem cells

Mammalian pluripotent stem cells (PSCs) represent an important venue for understanding basic principles regulating tissue-specific differentiation and discovering new tools that may facilitate clinical applications. Mechanisms that direct neural differentiation of PSCs involve growth factor signaling and transcription regulation. However, it is unknown whether and how electrical activity influences this process. Here we report a high throughput imaging-based screen, which uncovers that selamectin, an anti-helminthic therapeutic compound with reported activity on invertebrate glutamate-gated chloride channels, promotes neural differentiation of PSCs. We show that selamectin’s pro-neurogenic activity is mediated by γ2-containing GABAA receptors in subsets of neural rosette progenitors, accompanied by increased proneural and lineage-specific transcription factor expression and cell cycle exit. In vivo, selamectin promotes neurogenesis in developing zebrafish. Our results establish a chemical screening platform that reveals activity-dependent neural differentiation from PSCs. Compounds identified in this and future screening might prove therapeutically beneficial for treating neurodevelopmental or neurodegenerative disorders. DOI: http://dx.doi.org/10.7554/eLife.00508.001

G34, Another Connection between MYCN and a Pediatric Tumor

Recurrent mutations in H3F3A at K27 and G34 are frequent in pediatric glioblastoma, but it is unclear how these mutations promote tumorigenesis. In this issue of Cancer Discovery, Bjerke and colleagues identify mutations at G34 in H3F3A that result in elevated expression of MYCN as a potential mechanism in gliomagenesis.

Abstract 3230: Human stem cell-based model of MYCN-driven neuroblastoma

Neuroblastoma (NB), a disease of neural crest (NC) origin, is the most common extracranial solid tumor in childhood. High-risk NB patients represent the subgroup with the worst prognosis and frequently harbor amplification of MYCN. Due to its biochemical structure as a transcription factor, MYCN has been difficult to target directly with small molecules. Alternatively, identification of cooperating partners of MYCN-induced tumorigenesis can reveal a more therapeutically viable target, such as anaplastic lymphoma kinase (ALK). While genetically engineered mouse models (GEMMs) of NB driven by MYCN and ALK exist, recent studies have found significant differences between mouse models of disease and the human tumors they are intended to represent. In support of this, mouse and human NC cells differ in development and marker expression, and the genetic requirement for transformation of human cells has been shown to be more complex than mouse cells, suggesting that a human cell-based NB model would be more relevant. To develop a human cell-based model of NB, we started with a normal human induced pluripotent stem (iPS) cell line derived integration-free from a healthy adult and transduced empty vector, ALK F1174L (active mutant), doxycycline-inducible MYCN (DOX-MYCN), or ALK F1174L/DOX-MYCN. These iPS cells were differentiated towards NC cells and subsequently implanted orthotopically into renal capsules of mice fed on dox chow. Within 3 months, 60% of mice developed tumors with ALK F1174L/DOX-MYCN, 10% with DOX-MYCN, and 0% with both empty vector and ALK F1174L alone. Tumors were transplantable and demonstrated histologic characteristics consistent with NB, including morphology and expression markers. Thus, we are demonstrating the first, to our knowledge, human stem cell-based model of NB. We are using this system to further investigate similarities and differences with GEMMs of NB, test and establish novel candidate drivers of NB, and evaluate potential therapeutic options. Citation Format: Miller Huang, Lauren K. McHenry, Matthew L. Miller, Grace E. Kim, Branden S. Moriarity, Yuichiro Miyaoka, Marianne E. Bronner, David A. Largaespada, Bruce R. Conklin, Hanlee P. Ji, John M. Maris, Katherine K. Matthay, William A. Weiss. Human stem cell-based model of MYCN-driven neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3230. doi:10.1158/1538-7445.AM2015-3230