Previous work by Tapscott's lab (Snider, et al., 2010) showed that the DUX4 gene is normally expressed in germline cells of the human testes and is not normally expressed in other tissues in the adult, whereas in both FSHD1 and FSHD2 small amounts of DUX4 are expressed in muscle cells. In a new study recently published in the journal Developmental Cell, the research group identified genes that are regulated by DUX4 and detected the expression of these genes in FSHD muscle, "providing direct support for the model that misexpression of DUX4 is a causal factor for FSHD." This publication demonstrates that the low levels of DUX4 expressed in FSHD muscle has a domino effect, activating many genes. This allows for the identification of several biomarkers to track the progress of FSHD, and to determine the efficacy of treatment. In addition, the genes regulated by DUX4 suggest several mechanisms for the loss of muscle strength in FSHD and these can be tested as candidate targets for new therapies.
This study corroborates earlier observations that two forms of facioscapulohumeral muscular dystrophy, D4Z4 contraction-dependent FSHD1 and D4Z4 contraction-independent FSHD2, are unified by the relative relaxation of the D4Z4 chromatin structure and somatic transcriptional derepression of DUX4 (Lemmers, et al., 2010; Snider, et al., 2010), leading to the activation of germ line and early stem cell programs in skeletal muscle of individuals with FSHD. This study makes DUX4 and DUX4-reponsive genes and pathways direct targets for therapeutic intervention.
This is a major turning point, both identifying how DUX4 damages muscle in FSHD as the basis for developing therapies, and also a providing a set of biomarkers to easily determine if candidate therapies are actually working.
Refer to the Developmental Cell article.