Inducible MLL-AF9 Expression Drives an AML Program during Human Pluripotent Stem Cell-Derived Hematopoietic Differentiation.

A t(9;11)(p22;q23) translocation produces the MLL-AF9 fusion protein, which is found in up to 25% of de novo AML cases in children. Despite major advances, obtaining a comprehensive understanding of context-dependent MLL-AF9-mediated gene programs during early hematopoiesis is challenging. Here, we generated a human inducible pluripotent stem cell (hiPSC) model with a doxycycline dose-dependent MLL-AF9 expression. We exploited MLL-AF9 expression as an oncogenic hit to uncover epigenetic and transcriptomic effects on iPSC-derived hematopoietic development and the transformation into (pre-)leukemic states. In doing so, we observed a disruption in early myelomonocytic development. Accordingly, we identified gene profiles that were consistent with primary MLL-AF9 AML and uncovered high-confidence MLL-AF9-associated core genes that are faithfully represented in primary MLL-AF9 AML, including known and presently unknown factors. Using single-cell RNA-sequencing, we identified an increase of CD34 expressing early hematopoietic progenitor-like cell states as well as granulocyte-monocyte progenitor-like cells upon MLL-AF9 activation. Our system allows for careful chemically controlled and stepwise in vitro hiPSC-derived differentiation under serum-free and feeder-free conditions. For a disease that currently lacks effective precision medicine, our system provides a novel entry-point into exploring potential novel targets for personalized therapeutic strategies.

Underreported and unknown student harassment at the Faculty of Science.

Reports of sexual harassment at medical faculties throughout the world, including the Radboud University, raised the question how prevalent this is at the Faculty of Science. We performed a survey among students to assess their experiences with harassment. This questionnaire consisted of questions from the EGERA survey, a questionnaire held among staff of multiple European Universities. We found that 9% of the respondents had observed or experienced harassment at the Faculty. Hardly any of these cases were reported to one of the institutional services. Moreover, most students did not now any of the provided services. We therefore suggest raising awareness on harassment and to make students more familiar with the trust person.

CBFß-MYH11 interferes with megakaryocyte differentiation via modulating a gene program that includes GATA2 and KLF1.

The inv(16) acute myeloid leukemia-associated CBFß-MYH11 fusion is proposed to block normal myeloid differentiation, but whether this subtype of leukemia cells is poised for a unique cell lineage remains unclear. Here, we surveyed the functional consequences of CBFß-MYH11 in primary inv(16) patient blasts, upon expression during hematopoietic differentiation in vitro and upon knockdown in cell lines by multi-omics profiling. Our results reveal that primary inv(16) AML cells share common transcriptomic signatures and epigenetic determiners with megakaryocytes and erythrocytes. Using in vitro differentiation systems, we reveal that CBFß-MYH11 knockdown interferes with normal megakaryocyte maturation. Two pivotal regulators, GATA2 and KLF1, are identified to complementally occupy RUNX1-binding sites upon fusion protein knockdown, and overexpression of GATA2 partly induces a gene program involved in megakaryocyte-directed differentiation. Together, our findings suggest that in inv(16) leukemia, the CBFß-MYH11 fusion inhibits primed megakaryopoiesis by attenuating expression of GATA2/KLF1 and interfering with a balanced transcriptional program involving these two factors.

Obstructor-A is required for epithelial extracellular matrix dynamics, exoskeleton function, and tubulogenesis.

The epidermis and internal tubular organs, such as gut and lungs, are exposed to a hostile environment. They form an extracellular matrix to provide epithelial integrity and to prevent contact with pathogens and toxins. In arthropods, the cuticle protects, shapes, and enables the functioning of organs. During development, cuticle matrix is shielded from premature degradation; however, underlying molecular mechanisms are poorly understood. Previously, we identified the conserved obstructor multigene-family, which encodes chitin-binding proteins. Here we show that Obstructor-A is required for extracellular matrix dynamics in cuticle forming organs. Loss of obstructor-A causes severe defects during cuticle molting, wound protection, tube expansion and larval growth control. We found that Obstructor-A interacts and forms a core complex with the polysaccharide chitin, the cuticle modifier Knickkopf and the chitin deacetylase Serpentine. Knickkopf protects chitin from chitinase-dependent degradation and deacetylase enzymes ensure extracellular matrix maturation. We provide evidence that Obstructor-A is required to control the presence of Knickkopf and Serpentine in the extracellular matrix. We propose a model suggesting that Obstructor-A coordinates the core complex for extracellular matrix protection from premature degradation. This mechanism enables exoskeletal molting, tube expansion, and epithelial integrity. The evolutionary conservation suggests a common role of Obstructor-A and homologs in coordinating extracellular matrix protection in epithelial tissues of chitinous invertebrates.