FSHD-like Disease Models
DUX4 (double homeobox 4) gene
The primary mediator of FSHD pathology is aberrant expression of the DUX4 (double homeobox 4) gene located in the distal D4Z4 repeat unit of FSHD-permissive 4qA chromosomes. The full-length DUX4 protein, DUX4-fl, encodes a transcription factor that activates expression of several hundred protein-coding genes and ncRNAs, and its expression leads to rapid apoptosis (programmed cell death) in many somatic cells. Still, little is known about the actual DUX4-mediated pathogenic mechanism in FSHD or its normal role in human development. This is largely due to the fact that DUX4 is specific to old world primates and therefore not found in traditional model organisms such as mice and flies. Thus, there are no natural animal models of FSHD and these must be created by inserting the human DUX4 gene into the genome of the organism of interest.
We are engineering human cellular models, including iPSC models, and animal models of FSHD (mouse, Drosophila, and mini-pig) to gain insight into the developmental aspects of FSHD and to provide tools for therapeutic development and pre-clinical testing. These models are based on aberrant expression of DUX4-fl. Importantly, despite being a human transcription factor, even low levels of DUX4-fl in human, murine, fish, and amphibian somatic cells result in apoptosis, and DUX4 expression in early vertebrate development greatly disrupts myogenesis (Figure 4). These extremely sensitive and potentially pathogenic responses to very low levels of DUX4-fl create problems for generating transgenic animal models since "leaky" expression from transgenes, even under the designated "OFF" conditions, often leads to embryonic lethality.
We have overcome the lethal transgene leakiness and successfully generated a variety of DUX4-based animal models, including Drosophila (above), mouse models (below) and are in the process of engineering mini-pig models. Each model has unique strengths and serves a different purpose as we aim to understand mechanisms of DUX4-fl pathogenesis. In addition, these models are useful for developing and testing therapeutic strategies targeting DUX4-fl regulation, expression, and function.
Recently, we have successfully developed a series of phenotypic FSHD-like mouse models based on controllable expression of DUX4-fl. These mice are proving quite informative for understanding DUX4-mediated pathology. In addition, these mouse models serve as wonderful tools for preclinical testing our various FSHD therapeutic approaches. Importantly, these mice are available to the entire FSHD research community.
Learn more about our FSHD-like mouse models here:
A cre-inducible DUX4 transgenic mouse model for investigating facioscapulohumeral muscular dystrophy