Bao Z Z, Lakonishok M, Kaufman S, Horwitz A F
Department of Biochemistry, University of Illinois at Urbana-Champaign IL 61801.
J Cell Sci. 1993 Oct;106 ( Pt 2):579-89. doi: 10.1242/jcs.106.2.579.
Immunization against a 70 kDa band that co-purifies with skeletal muscle integrins has resulted in an antibody directed against the avain alpha 7 integrin subunit. The specificity of the antibody was established by patterns of tissue staining and cross-reactivity with antibodies directed against the cytoplasmic domain of the rat alpha 7 cytoplasmic domain. On sections of adult skeletal muscle the alpha 7 integrin was enriched in the myotendinous junction (MTJ). This localization was unique as neither the alpha 1, alpha 3, alpha 5, alpha 6 and alpha v subunit localizes in the myotendinous junction. The distribution of the alpha 7 subunit in the MTJ was examined during embryonic development. alpha 7 expression in the junction is first apparent around embryo day 14 and is almost exclusively at the developing MTJ at this stage. alpha 3 is expressed with distinctive punctate staining around the junctional area in earlier embryos (11-day). The time of appearance of the alpha 7 subunit in the MTJ correlates with the insertion of myofibrils into subsarcolemmal densities and folding of the junctional membrane, suggesting a role of the alpha 7 integrin in this process. Vinculin is present throughout development of the myotendinous junction, suggesting that the alpha 7 integrin recognizes a preformed cytoskeletal structure. The presence of the alpha 7 subunit in the myotendinous junction and the alpha 5 subunit in the adhesion plaque demonstrates a molecular difference between these two adherens junctions. It also points to possible origins of junctional specificity on muscle. Differences between these two junctions were developed further using an antibody against phosphotyrosine (PY20). Phosphotyrosine is thought to participate in the organization and stabilization of adhesions. The focal adhesion and the neuromuscular junction, but not the MTJ, contained proteins phosphorylated on tyrosine.
针对与骨骼肌整合素共纯化的一条70 kDa条带进行免疫，已产生一种针对鸡α7整合素亚基的抗体。该抗体的特异性通过组织染色模式以及与针对大鼠α7胞质结构域的抗体的交叉反应来确定。在成年骨骼肌切片上，α7整合素在肌腱连接点（MTJ）处富集。这种定位是独特的，因为α1、α3、α5、α6和αv亚基均不在肌腱连接点处定位。在胚胎发育过程中检查了α7亚基在MTJ中的分布。α7在连接点的表达在胚胎第14天左右首次明显出现，并且在此阶段几乎仅在发育中的MTJ处表达。α3在早期胚胎（11天）的连接区域周围以独特的点状染色表达。α7亚基在MTJ中出现的时间与肌原纤维插入肌膜下致密物以及连接膜折叠相关，表明α7整合素在该过程中起作用。纽蛋白在肌腱连接点的整个发育过程中都存在，这表明α7整合素识别一种预先形成的细胞骨架结构。α7亚基在肌腱连接点中的存在以及α5亚基在黏附斑中的存在表明这两种黏附连接之间存在分子差异。这也指出了肌肉上连接特异性的可能起源。使用抗磷酸酪氨酸（PY20）抗体进一步研究了这两种连接之间的差异。磷酸酪氨酸被认为参与黏附的组织和稳定。粘着斑和神经肌肉接头，但不是MTJ，含有酪氨酸磷酸化的蛋白质。
