Biology subjects

Maass, K. K.

Publications and source records attributed to Maass, K. K..

5 recordsLinked to original sources

bioRxiv2026

Diverse Mechanisms of SMARCB1 Inactivation and Genome Maintenance Defects in Ultra-Rare Malignant Rhabdoid Tumors

Malignant rhabdoid tumors (MRTs) are extremely rare and highly aggressive pediatric cancers classically defined by biallelic loss of the SMARCB1 gene, with rare involvement of SMARCA4. However, the molecular mechanisms leading to this loss are not yet fully understood. MRTs occur predominantly in infants, with the highest incidence in children under one year of age. Clinically, they are characterized by early metastatic dissemination and dismal outcomes, with 5-year event-free survival rates below 20%. There are currently no curative therapies for these patients. Here, we performed integrated genomic, transcriptomic, and epigenomic profiling of 16 patient-derived MRT models including intracranial, renal, and soft tissue origins. While SMARCB1 deficiency was ubiquitous, we observed substantial heterogeneity in the mechanisms driving its inactivation. Only two tumors harbored detectable coding single-nucleotide variants in SMARCB1; the predominant mechanisms involved large-scale deletions and broad loss-of-heterozygosity (LOH) on chromosome 22, with extensive LOH in tumors lacking point mutations or focal deletions, consistent with allelic loss as a frequent "second hit." In contrast, SMARCA4 remained intact across all models, reinforcing the mutual exclusivity of SMARCB1 and SMARCA4 alterations. Structural analyses revealed extensive variation, including more than 400 events per tumor on average and candidate gene fusions such as AHI1:MYB, whereas alterations in TP53 and BRCA1/2 genes were infrequent. Transcriptomic and epigenomic profiling showed heterogeneity driven by tissue of origin, disease progression, and therapeutic response, with subtype-specific programs and epigenetic modulation of DNA repair and immune-related genes (SLFN11, MGMT, LIF) linked to treatment sensitivity. Collectively, our findings refine the molecular definition of MRTs, showing that while SMARCB1 loss remains the foundational driver, tumor behavior is further shaped by structural variation, impaired DNA repair pathways, and dynamic epigenetic landscapes. These integrated changes contribute to tumor heterogeneity, progression, and differential therapeutic vulnerabilities. Beyond advancing mechanistic understanding and identifying candidate biomarkers for patient stratification, our multi-omics dataset represents a valuable resource for the research community, supporting future studies and efforts to improve clinical management of this highly aggressive pediatric malignancy.

cancer biology↗

bioRxiv2024

Single-cell multidimensional profiling of tumor cell heterogeneity in supratentorial ependymomas

Supratentorial ependymomas are aggressive childhood brain cancers that retain features of neurodevelopmental cell types and segregate into molecularly and clinically distinct subgroups, suggesting different developmental roots. The developmental signatures as well as microenvironmental factors underlying aberrant cellular transformation and behavior across each supratentorial ependymoma subgroup are unknown. Here we integrated single cell- and spatial transcriptomics, as well as in vitro and in vivo live-cell imaging to define supratentorial ependymoma cell states, spatial organization, and dynamic behavior within the neural microenvironment. We find that individual tumor subgroups harbor two distinct progenitor-like cell states reminiscent of early human brain development and diverge in the extent of neuronal or ependymal differentiation. We further uncover several modes of spatial organization of these tumors, including a high order architecture influenced by mesenchymal and hypoxia signatures. Finally, we identify an unappreciated role for brain-resident cells in shifting supratentorial ependymoma cellular heterogeneity towards neuronal-like cells that co-opt immature neuronal morphology and invasion mechanisms. Collectively, these findings provide a multidimensional framework to integrate transcriptional and phenotypic characterization of tumor heterogeneity in supratentorial ependymoma and its potential clinical implications.

cancer biology↗

bioRxiv2022

Compartments in medulloblastoma with extensive nodularity are connected through differentiation along the granular precursor lineage

Medulloblastoma with extensive nodularity (MBEN) are cerebellar tumors with two histologically distinct compartments and varying disease course. In some children MBEN progresses, while others show spontaneous differentiation into more benign tumors. However, the mechanisms that control the tug-of-war between proliferation and differentiation are not well understood. Here, we dissected this process with a multi-modal single cell transcriptome analysis. We found that the internodular MBEN compartment comprised proliferating early cerebellar granular neuronal precursors (CGNP)-like tumor cells as well as stromal, vascular, and immune cells. In contrast, the nodular compartment consisted of postmitotic, neuronally differentiated MBEN cells. Both compartments were connected through an intermediate cell stage of actively migrating CGNPs. Furthermore, astrocyte-like tumor cells were identified that had branched off the main CGNP developmental trajectory. Cells with an astroglial phenotype were found in close proximity to migrating, late CGNP-like and postmitotic neuronally differentiated cells. Our study reveals how the spatial tissue organization is linked to the developmental trajectory of proliferating tumor cells through a migrating precursor stage into differentiated tumor cells with a more benign phenotype. We anticipate that our framework for integrating single nucleus RNA-sequencing and spatial transcriptomics will help to uncover intercompartmental interactions also in other cancers with varying histology.

cancer biology↗

bioRxiv2021

Single cell multi-omics analysis of chromothriptic medulloblastoma highlights genomic and transcriptomic consequences of genome instability

Chromothripsis is a form of genome instability, whereby a presumably single catastrophic event generates extensive genomic rearrangements of one or few chromosome(s). However, little is known about the heterogeneity of chromothripsis across different clones from the same tumor, as well as changes in response to treatment. We analyzed single-cell genomic and transcriptomic alterations linked with chromothripsis in human p53-deficient medulloblastoma (n=7). We reconstructed the order of somatic events, identified early alterations likely linked to chromothripsis and depicted the contribution of chromothripsis to malignancy. We characterized subclonal variation of chromothripsis and its effects on double-minute chromosomes, cancer drivers and putatively druggable targets. Furthermore, we highlighted the causative role and the fitness consequences of specific rearrangements in neural progenitors. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=85 SRC="FIGDIR/small/449944v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@9d30e4org.highwire.dtl.DTLVardef@1f4d34eorg.highwire.dtl.DTLVardef@5cd50corg.highwire.dtl.DTLVardef@a71a81_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2020

Establishment of a simplified preparation method for single-nucleus RNA-sequencing and its application to long-term frozen tumor tissues

Recent advances allowing the genomic analysis of individual cells from a bulk population have provided intriguing new insights into areas such as developmental processes and tumor heterogeneity. Most approaches to date, however, rely on the availability of fresh surgical specimens, thereby dramatically reducing the ability to profile particularly rare tissue types. Pediatric central nervous system tumors - the leading cause of childhood cancer deaths - represent one such example, where often only frozen rather than native material is available. Due to an increasing need for advanced techniques to understand the heterogeneity of these tumors, we optimized a method to isolate intact nuclei from long-term frozen pediatric glioma tissues. We performed a technical comparison between different single nucleus RNA-sequencing (snRNA-seq) systems using a patient-derived xenograft model as a test sample. Further, we applied the established nucleus isolation method to analyze frozen primary tissue from two pediatric central nervous system tumors - one pilocytic astrocytoma and one glioblastoma - allowing the identification of distinct tumor cell populations and infiltrating microglia. The results show that our fast, simple and low-cost nuclear isolation protocol provides intact nuclei, which can be used in both droplet-based 3 transcriptome amplification (10X Genomics) and plate-based whole transcriptome amplification (Fluidigm C1) single-cell sequencing platforms, thereby dramatically increasing the potential for application of such methods to rare entities.

cancer biology↗