Transgenic Studies
Section: Section of Gene Function and Regulation
Transgenic Approaches to the Development of a Model of Alveolar Rhabdomyosarcoma
Rhabdomyosarcomas (RMS) are a family of paediatric soft-tissue tumours which are apparently of the skeletal muscle lineage. Two subtypes of RMS, with distinct clinical presentations, have been categorised based on histological characteristics: embryonic and alveolar rhabdomyosarcoma (ERMS and ARMS).
Two unique translocations, t(2;13) and t(1;13), have been shown to be involved in most ARMS cases. The t(2;13) translocation is more frequent being found in over 70% of histologically diagnosed ARMS. It gives rise to a fusion gene that results from the juxtaposition of the Pax3 gene, encoding a member of the paired box-containing transcription factor family, with the FoxO1 (or FKHR) gene, encoding a member of the forkhead family of transcription factors. The t(1;13) translocation found in a smaller number of ARMS cases results in the generation of a similar fusion gene involving Pax7 and FoxO1.
In both cases, the fusion gene is thought to be under the transcriptional control of the respective Pax regulatory sequences. The resulting fusion protein contains the N-terminal region of the Pax protein, including intact paired box and homeodomain DNA-binding elements, and the C-terminal transactivation domain of FoxO1. Because the forkhead DNA-binding domain of FoxO1 is truncated in the fusion gene it has been proposed that the oncogenic activity of Pax3/7-FoxO1 is a result of the disregulation of Pax3/7-specific target genes.
ARMS tumours express a battery of muscle-specific markers; however, the cell type of origin of these sarcomas is not known. Although a myogenic origin is possible, disregulation of Pax3 or Pax7 target genes in non-myogenic cells may result in the activation of the myogenic programme in another cell type. Indeed, ectopic expression of Pax3 in the lateral plate mesoderm of chick embryos induces the expression of the myogenic regulatory factors Myf5, Myogenin and MyoD. Moreover, there are cells, such as myofibroblasts (kidney mesangial cells and liver stellate cells), which express sarcomeric proteins and other skeletal muscle markers but do not have a skeletal muscle origin.
Our objective is to set the bases for the generation of a transgenic-based animal model for ARMS. We are investigating the regulation of Pax gene expression and the pathological function of the FoxO1 protein. This work is providing background knowledge for the generation of an animal model based on the strengths of Cre-mediated homologous recombination in vivo coupled with the ability to drive transgene expression in a cell type-specific manner.
External funding: Cancer Research UK
In the Section of Gene Function and Regulation
