Transcriptional activity and mRNA processing are often impaired in myonuclei at the myotendinous junctions of <i>lmna</i>-null mice.

<p>Representative images of wild-type (WT) <i>lmna^+/+</i> EDL myofibres immunostained for acetyl-histone H3 (red) and counter-stained with DAPI (white), with merged images (<b>a–c</b>). Myonuclei at the myotendinous junction (MTJ) in WT myofibres have near homogeneous acetyl-histone H3 immunostaining, as observed along the myofibre, indicating similar levels of transcriptional activity. By contrast, immunostaining of <i>lmna</i>^−/− EDL myofibres revealed that myonuclei at the myotendinous junctions clearly had varying acetyl-histone H3 levels, indicating heterogeneous transcriptional activity, ranging from virtually inactive (background levels – arrow in <b>d–f</b>), to hyperacetylated, myonuclei (<b>d–f</b>). WT myonuclei also exhibit regular and homogeneous PABPN1 immunostaining at the myotendinous junction (<b>g–i</b>). In myonuclei at the myotendinous junctions of <i>lmna</i>^−/− EDL however, varying PABPN1 levels are observed, with many being virtually unstained (<b>j–l</b> - arrows), indicating an impairment of mRNA processing and maturation. Scale bar 50 µm.