Jan Willem Bek

Neuroblastoma is a childhood developmental cancer; however, its embryonic origins remain poorly understood. Moreover, in-depth studies of early tumor-driving events are limited because of the lack of appropriate models. Herein, we analyzed RNA sequencing data obtained from human neuroblastoma samples and found that loss of expression of trunk neural crest–enriched gene MOXD1 associates with advanced disease and worse outcome. Further, by using single-cell RNA sequencing data of human neuroblastoma cells and fetal adrenal glands and creating in vivo models of zebrafish, chick, and mouse, we show that MOXD1 is a determinate of tumor development. In addition, we found that MOXD1 expression is highly conserved and restricted to mesenchymal neuroblastoma cells and Schwann cell precursors during healthy development. Our findings identify MOXD1 as a lineage-restricted tumor-suppressor gene in neuroblastoma, potentiating further stratification of these tumors and development of novel therapeutic interventions.

Ovarian cancer (OC) is an umbrella term for cancerous malignancies affecting the ovaries, yet treatment options for all subtypes are predominantly derived from high-grade serous ovarian cancer, the largest subgroup. The concept of "functional precision medicine" involves gaining personalized insights on therapy choice, based on direct exposure of patient tissues to drugs. This especially holds promise for rare subtypes like low-grade serous ovarian cancer (LGSOC). This study aims to establish an in vivo model for LGSOC using zebrafish embryos, comparing treatment responses previously observed in mouse PDX models, cell lines and 3D tumor models. To address this goal, a well-characterized patient-derived LGSOC cell line with the KRAS mutation c.35 G>T (p.(Gly12Val)) was used. Fluorescently labeled tumor cells were injected into the perivitelline space of 2 days’ post-fertilization zebrafish embryos. At 1 day post-injection, xenografts were assessed for tumor size, followed by random allocation into treatment groups with trametinib, luminespib and trametinib + luminespib. Subsequently, xenografts were euthanized and analyzed for apoptosis and proliferation by confocal microscopy. Tumor cells formed compact tumor masses (n = 84) in vivo, with clear Ki67 staining, indicating proliferation. Zebrafish xenografts exhibited sensitivity to trametinib and luminespib, individually or combined, within a two-week period, establishing them as a rapid and complementary tool to existing in vitro and in vivo models for evaluating targeted therapies in LGSOC.

Ovarian cancer (OC) is an umbrella term for cancerous malignancies affecting the ovaries, yet treatment options for all subtypes are predominantly derived from high-grade serous ovarian cancer, the largest subgroup. The concept of "functional precision medicine" involves gaining personalized insights on therapy choice, based on direct exposure of patient tissues to drugs. This especially holds promise for rare subtypes like low-grade serous ovarian cancer (LGSOC). This study aims to establish an in vivo model for LGSOC using zebrafish embryos, comparing treatment responses previously observed in mouse PDX models, cell lines, and 3D tumor models. To address this goal, a well characterized patient-derived LGSOC cell line with the KRAS mutation c.35 G > T (p.(Gly12Val)) was used. Fluorescently labelled tumor cells were injected into the perivitelline space of 2 days post fertilization zebrafish embryos. At 1 day post-injection xenografts were as-sessed for tumor size, followed by random allocation into treatment groups with trametinib, luminespib, and trametinib + luminespib. Subsequently xenografts were euthanized and analysed for apoptosis and proliferation by confocal microscopy. Tumor cells formed compact tumor masses (n=84) in vivo and with clear Ki67 staining, indicating proliferation. Zebrafish xenografts exhibited sensitivity to trametinib and luminespib, individually or combined, within a two-week period, establishing them as a rapid and complementary tool to existing in vitro and in vivo models for evaluating targeted therapies in LGSOC.

SNARE proteins comprise a conserved protein family responsible for catalyzing membrane fusion during vesicle traffic. Syntaxin18 (STX18) is a poorly characterized endoplasmic reticulum (ER)-resident t-SNARE. Recently, together with TANGO1 and SLY1, its involvement was shown in ER to Golgi transport of collagen II during chondrogenesis. We report a fetus with a severe osteochondrodysplasia in whom we identified a homozygous substitution of the highly conserved p.Arg10 to Pro of STX18. CRISPR/Cas9-mediated Stx18 deficiency in zebrafish reveals a crucial role for Stx18 in cartilage and bone development. Furthermore, increased expression of multiple components of the Stx18 SNARE complex and of COPI and COPII proteins suggests that Stx18 deficiency impairs antero- and retrograde vesicular transport in the crispant stx18 zebrafish. Taken together, our studies highlight a new candidate gene for a recessive form of osteochondrodysplasia, thereby possibly broadening the SNAREopathy phenotypic spectrum and opening new doors toward future research avenues. © 2023 American Society for Bone and Mineral Research (ASBMR).

The ‘plant homeodomain zinc finger protein 6’ (PHF6) is affected by germline mutations in patients with cognitive disabilities and somatic mutations in acute T-cell leukemia (T-ALL). We and others previously obtained evidence for a key role of PHF6 in hematopoietic precursor cell self-renewal capacity and lineage commitment during differentiation, while recent work revealed a role in non-homologous end joining and G2 checkpoint recovery. In this study, we identified the ribonucleotide reductase subunit M2 (RRM2), as a novel PHF6 interacting protein by immunoprecipitation coupled mass spectrometry. We confirmed the PHF6-RRM2 interaction in different normal and malignant cellular background and mapped the interaction interface towards the first PHD domain of PHF6 through NanoBRET^™ based deletion mapping. We also demonstrated that PHF6 knockdown in neuroblastoma cells causes increased replicative stress and DNA damage. Furthermore, we show binding of PHF6 to the DNA-damage associated H3K56ac histone mark. In view of our recent finding of RRM2 as a MYCN co-dependency and target for synergistic CHK1 inhibition in neuroblastoma, we performed CUT&RUN mapping of H3K56ac and PHF6 genome-wide binding sites in neuroblastoma cells and next to a significant overlap of the two, we also found evidence for a functional crosstalk with established core regulatory circuitry transcription factors. Our data suggest that PHF6 is a component of the earlier proposed ‘replitase’, implicated in active regulation of RRM2 function during replication and DNA repair.

High-risk neuroblastoma, a pediatric tumor originating from the sympathetic nervous system, has a low mutation load but highly recurrent somatic DNA copy number variants. Previously, segmental gains and/or amplifications allowed identification of drivers for neuroblastoma development. Using this approach, combined with gene dosage impact on expression and survival, we identified ribonucleotide reductase subunit M2 (RRM2) as a candidate dependency factor further supported by growth inhibition upon in vitro knockdown and accelerated tumor formation in a neuroblastoma zebrafish model coexpressing human RRM2 with MYCN. Forced RRM2 induction alleviates excessive replicative stress induced by CHK1 inhibition, while high RRM2 expression in human neuroblastomas correlates with high CHK1 activity. MYCN-driven zebrafish tumors with RRM2 co-overexpression exhibit differentially expressed DNA repair genes in keeping with enhanced ATR-CHK1 signaling activity. In vitro, RRM2 inhibition enhances intrinsic replication stress checkpoint addiction. Last, combinatorial RRM2-CHK1 inhibition acts synergistic in high-risk neuroblastoma cell lines and patient-derived xenograft models, illustrating the therapeutic potential.

Proteoglycans are structurally and functionally diverse biomacromolecules found abundantly on cell membranes and in the extracellular matrix. They consist of a core protein linked to glycosaminoglycan chains via a tetrasaccharide linkage region. Here, we show that CRISPR/Cas9-mediatedb3galt6knock-out zebrafish, lacking galactosyltransferase II, which adds the third sugar in the linkage region, largely recapitulate the phenotypic abnormalities seen in human β3GalT6-deficiency disorders. These comprise craniofacial dysmorphism, generalized skeletal dysplasia, skin involvement and indications for muscle hypotonia. In-depth TEM analysis revealed disturbed collagen fibril organization as the most consistent ultrastructural characteristic throughout different affected tissues. Strikingly, despite a strong reduction in glycosaminoglycan content, as demonstrated by anion-exchange HPLC, subsequent LC-MS/MS analysis revealed a small amount of proteoglycans containing a unique linkage region consisting of only three sugars. This implies that formation of glycosaminoglycans with an immature linkage region is possible in a pathogenic context. Our study, therefore unveils a novel rescue mechanism for proteoglycan production in the absence of galactosyltransferase II, hereby opening new avenues for therapeutic intervention.

Genome‐wide association studies (GWAS) have improved our understanding of the genetic architecture of common, complex diseases such as osteoporosis. Nevertheless, to attribute functional skeletal contributions of candidate genes to osteoporosis‐related traits there is a need for efficient and cost‐effective in vivo functional testing. This can be achieved through CRISPR‐based reverse genetic screens, where phenotyping is traditionally performed in stable germline KO mutants. Recently it was shown that first‐generation (F0) mosaic mutant zebrafish (so‐called crispants) recapitulate the phenotype of germline KOs. To demonstrate feasibility of functional validation of osteoporosis candidate genes through crispant screening, we compared a crispant to a stable KO zebrafish model for the lrp5 gene. In humans, recessive loss‐of‐function mutations in LRP5, a co‐receptor in the Wnt signaling pathway, cause Osteoporosis‐pseudoglioma syndrome. In addition, several GWAS studies identified LRP5 as a major risk locus for osteoporosis‐related phenotypes. In this study, we showed that early stage lrp5 KO larvae display decreased notochord mineralization and malformations of the head cartilage. Quantitative micro‐computed tomography (microCT) scanning and mass‐spectrometry element analysis of the adult skeleton revealed decreased vertebral bone volume and bone mineralization, hallmark features of osteoporosis. Furthermore, regenerating fin tissue displayed reduced Wnt signaling activity in lrp5 KO adults. We next compared lrp5 mutants with crispants. Next‐generation sequencing analysis of adult crispant tissue revealed a mean out‐of‐frame mutation rate of 76%, resulting in strongly reduced levels of Lrp5 protein. These crispants generally showed a milder, but nonetheless highly comparable skeletal phenotype and a similarly reduced Wnt pathway response compared to lrp5 KO mutants. In conclusion, we show through faithful modeling of LRP5‐related primary osteoporosis, that crispant screening in zebrafish is a promising approach for rapid functional screening of osteoporosis candidate genes.

Proteoglycans are structurally and functionally diverse biomacromolecules found abundantly on cell membranes and in the extracellular matrix. They consist of a core protein linked to glycosaminoglycan chains via a tetrasaccharide linkage region. Here, we show that CRISPR/Cas9-mediated b3galt6 knock-out zebrafish, lacking galactosyltransferase II, which adds the third sugar in the linkage region, largely recapitulate the phenotypic abnormalities seen in human β3GalT6-deficiency disorders. These comprise craniofacial dysmorphism, generalized skeletal dysplasia, skin involvement and indications for muscle hypotonia. In-depth TEM analysis revealed disturbed collagen fibril organization as the most consistent ultrastructural characteristic throughout different affected tissues. Strikingly, despite a strong reduction in glycosaminoglycan content, as demonstrated by anion-exchange HPLC, subsequent LC-MS/MS analysis revealed a small amount of proteoglycans containing a unique linkage region consisting of only three sugars. This implies that formation of glycosaminoglycans with an immature linkage region is possible in a pathogenic context. Our study therefore unveils a novel rescue mechanism for proteoglycan production in the absence of galactosyltransferase II, hereby opening new avenues for therapeutic intervention.