Mouse model to understand the role of Dux4 in FSHD

Dandapat, Abhijit and Bosnakovski, Darko and Baltgalvis, Kristen and Hartweck, Lynn M. and Lonetree, Cara-lin and Nash, Nardine and Lowe, Dawn and Kyba, Michael (2011) Mouse model to understand the role of Dux4 in FSHD. In: ISSCR 9th Annual Meeting, 15-18 June 2011, Toronto, Ontario, Canada.

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FSHD is an autosomal dominant disease that affects 1:20000 individuals.
Mapping studies have associated the disease with a reduced number
(1-10) of the D4Z4 macrosatellite repeats from the usual ~100. These
repeats lie adjacent to the telomeres and are usually present in a highly
silenced epigenetic state. It is not clear which genes are affected or how
DNA methylation patterns affect the disease. Within the D4Z4 repeat is
an ORF encoding a putative transcription factor named Dux4, containing
two homeodomains. Although the function of Dux4 is unknown, the Dux4
homeodomains are similar to those of Pax7, a protein known to be involved
in muscle development, proliferation and differentiation. We have previously
reported that Dux4 is toxic when misexpressed at high levels in many
cell types, and blocks differentiation of myoblasts when expressed at low
levels, and competes with Pax7 for regulation of myogenic target genes.
To model Dux4 function in vivo, we made a Dux4-inducible mES cell line
by inserting a doxycycline-inducible Dux4 allele (iDux4+3’UTR) onto the X
chromosome at a euchromatic region (HPRT). High-level induction of the
Dux4 was toxic to mES cells but low-level Dux4 resulted in altered differentiation.
When iDux4+3’UTR mice where generated and bred, this allele
demonstrated leaky phenotypes in females, and male-specific lethality. Rare
live-born males were small and underdeveloped with abnormal skin and
defective sperm development and showed changes to muscle fibers, but
no overt muscle degeneration. However, mice died within 1 month, well
before the stage degeneration usually begins in FSHD. Dux4 protein could
be induced and observed in cultured primary cells, and we are evaluatingpups and embryos for Dux4 expression in vivo. Dux4 carrier females were
smaller and displayed the skin phenotype in transverse stripes. We hypothesize
that the 3’ UTR contains an enhancer which drives leaky expression in
some embryonic cell types and that X chromosome inactivation combined
with selective survival of XDUX4-inactive cells protects the females from the
lethality. To test for selectively biased X inactivation, we crossed Dux4 carrier
females with XGFP males. Upon FACS analysis of the GFP+ cells in XGFP/
X+ vs. XGFP/ XDux4 female progeny, we found that the latter had an elevated
frequency of GFP positive cells in most tissues, including the satellite
cell compartment of skeletal muscle, confirming our hypothesis of selective
XDUX4 inactivation. This mouse model suggests that Dux4 is a dominant
lethal gene even when expressed at very low levels and can cause a variety
of developmental defects in EBs and in embryo development.

Item Type: Conference or Workshop Item (Speech)
Subjects: Medical and Health Sciences > Basic medicine
Divisions: Faculty of Medical Science
Depositing User: Darko Bosnakovski
Date Deposited: 24 Jan 2014 12:13
Last Modified: 24 Oct 2014 10:59

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