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Genetic and epigenetic alterations are essential for the initiation and progression of human cancer. We previously reported that primary human medulloblastomas showed extensive cancer-specific CpG island DNA hypermethylation in critical developmental pathways. To determine whether genetically engineered mouse models (GEMMs) of medulloblastoma have comparable epigenetic changes, we assessed genome-wide DNA methylation in three mouse models of medulloblastoma. In contrast to human samples, very few loci with cancer-specific DNA hypermethylation were detected, and in almost all cases the degree of methylation was relatively modest compared with the dense hypermethylation in the human cancers. To determine if this finding was common to other GEMMs, we examined a Burkitt lymphoma and breast cancer model and did not detect promoter CpG island DNA hypermethylation, suggesting that human cancers and at least some GEMMs are fundamentally different with respect to this epigenetic modification. These findings provide an opportunity to both better understand the mechanism of aberrant DNA methylation in human cancer and construct better GEMMs to serve as preclinical platforms for therapy development.

Double homeobox 4 (DUX4) is a candidate disease gene for facioscapulohumeral dystrophy (FSHD), one of the most common muscular dystrophies characterized by progressive skeletal muscle degeneration. Despite great strides in understanding precise genetics of FSHD, the molecular pathophysiology of the disease remains unclear. One of the major limitations has been the availability of appropriate molecular tools to study DUX4 protein. In the present study, we report the development of five new monoclonal antibodies targeted against the N- and C-termini of human DUX4, and characterize their reactivity using Western blot and immunofluorescence staining. Additionally, we show that expression of the canonical full coding DUX4 induces cell death in human primary muscle cells, whereas the expression of a shorter splice form of DUX4 results in no such toxicity. Immunostaining with these new antibodies reveals a differential effect of two DUX4 isoforms on human muscle cells. These antibodies will provide an excellent tool for investigating the role of DUX4 in FSHD pathogenesis.

Rhabdomyosarcomas are characterized by expression of myogenic specification genes, such as MyoD and/or Myf5, and some muscle structural genes in a population of cells that continues to replicate. Because MyoD is sufficient to induce terminal differentiation in a variety of cell types, we have sought to determine the molecular mechanisms that prevent MyoD activity in human embryonal rhabdomyosarcoma cells. In this study, we show that a combination of inhibitory Musculin:E-protein complexes and a novel splice form of E2A compete with MyoD for the generation of active full-length E-protein:MyoD heterodimers. A forced heterodimer between MyoD and the full-length E12 robustly restores differentiation in rhabdomyosarcoma cells and broadly suppresses multiple inhibitory pathways. Our studies indicate that rhabdomyosarcomas represent an arrested progress through a normal transitional state that is regulated by the relative abundance of heterodimers between MyoD and the full-length E2A proteins. The demonstration that multiple inhibitory mechanisms can be suppressed and myogenic differentiation can be induced in the RD rhabdomyosarcomas by increasing the abundance of MyoD:E-protein heterodimers suggests a central integrating function that can be targeted to force differentiation in muscle cancer cells.

The basic helix-loop-helix (bHLH) transcription factor Myod directly regulates gene expression throughout the program of skeletal muscle differentiation. It is not known how a Myod-driven myogenic program is modulated to achieve muscle fiber-type-specific gene expression. Pbx homeodomain proteins mark promoters of a subset of Myod target genes,including myogenin (Myog); thus, Pbx proteins might modulate the program of myogenesis driven by Myod. By inhibiting Pbx function in zebrafish embryos, we show that Pbx proteins are required in order for Myod to induce the expression of a subset of muscle genes in the somites. In the absence of Pbx function, expression of myog and of fast-muscle genes is inhibited, whereas slow-muscle gene expression appears normal. By knocking down Pbx or Myod function in combination with another bHLH myogenic factor,Myf5, we show that Pbx is required for Myod to regulate fast-muscle, but not slow-muscle, development. Furthermore, we show that Sonic hedgehog requires Myod in order to induce both fast- and slow-muscle markers but requires Pbx only to induce fast-muscle markers. Our results reveal that Pbx proteins modulate Myod activity to drive fast-muscle gene expression, thus showing that homeodomain proteins can direct bHLH proteins to establish a specific cell-type identity.

Background Transplantation of myogenic stem cells possesses great potential for long-term repair of dystrophic muscle. In murine-to-murine transplantation experiments, CXCR4 expression marks a population of adult murine satellite cells with robust engraftment potential in mdx mice, and CXCR4-positive murine muscle-derived SP cells home more effectively to dystrophic muscle after intra-arterial delivery in mdx5cv mice. Together, these data suggest that CXCR4 plays an important role in donor cell engraftment. Therefore, we sought to translate these results to a clinically relevant canine-to-canine allogeneic transplant model for Duchenne muscular dystrophy (DMD) and determine if CXCR4 is important for donor cell engraftment. Methods In this study, we used a canine-to-murine xenotransplantation model to quantitatively compare canine muscle cell engraftment, and test the most effective cell population and modulating factor in a canine model of DMD using allogeneic transplantation experiments. Results We show that CXCR4 expressing cells are important for donor muscle cell engraftment, yet FACS sorted CXCR4-positive cells display decreased engraftment efficiency. However, diprotin A, a positive modulator of CXCR4-SDF-1 binding, significantly enhanced engraftment and stimulated sustained proliferation of donor cells in vivo. Furthermore, the canine-to-murine xenotransplantation model accurately predicted results in canine-to-canine muscle cell transplantation. Conclusions Therefore, these results establish the efficacy of diprotin A in stimulating muscle cell engraftment, and highlight the pre-clinical utility of a xenotransplantation model in assessing the relative efficacy of muscle stem cell populations.