Brown Daniel D, Davis Anna C, Conlon Frank L
Carolina Cardiovascular Biology Center, UNC-Chapel Hill, Chapel Hill, NC 27599-7126, USA.
Gene Expr Patterns. 2006 Oct;6(8):913-8. doi: 10.1016/j.modgep.2006.03.003. Epub 2006 Apr 21.
Titin proteins play an essential role in maintaining muscle function and structure. Recent work has implicated the involvement of the novex-3 titin isoform in sarcomere restructuring and disease. Unlike avian and mammalian systems, Xenopus laevis myogenesis is characterized by a wave of primary myogenesis followed by apoptosis of the primary muscles and formation of new muscles by secondary myogenesis. We show here that the Xenopus laevis novex-3 titin isoform (Xtn3) is developmentally expressed throughout the somites, heart, and primary muscles of the developing embryo. Downregulation of Xtn3 expression at tadpole stages appears to coincide with the change in myofiber composition from solely embryonic "fast" fiber types to myofibers containing both "fast" and "slow" fiber types. We demonstrate that Xtn3 is expressed early in the presomitic mesoderm and remains expressed in the somites, ventral myoblasts, and developing jaw muscles through late tailbud stage. Furthermore, we show that Xtn3 is expressed in the cardiac primordia prior to linear heart tube formation and remains expressed in the heart until tadpole stage, at which point it is downregulated in the heart except in discrete patches of cardiac cells. Finally, we demonstrate that Xtn3 transcripts are detectable in adult heart and muscle tissues.
肌联蛋白在维持肌肉功能和结构方面发挥着至关重要的作用。最近的研究表明，novex-3肌联蛋白异构体参与了肌节重构和疾病的发生。与鸟类和哺乳动物系统不同，非洲爪蟾的肌发生特点是一波原发性肌发生，随后原发性肌肉发生凋亡，继发性肌发生形成新的肌肉。我们在此表明，非洲爪蟾的novex-3肌联蛋白异构体（Xtn3）在发育中的胚胎的体节、心脏和原发性肌肉中呈发育性表达。蝌蚪阶段Xtn3表达的下调似乎与肌纤维组成从仅含胚胎型“快”纤维类型转变为同时含有“快”和“慢”纤维类型相一致。我们证明，Xtn3在体节中胚层早期表达，并在体节、腹侧成肌细胞和发育中的颌部肌肉中持续表达至晚期尾芽阶段。此外，我们表明，Xtn3在线性心脏管形成之前就在心脏原基中表达，并在心脏中持续表达至蝌蚪阶段，此时它在心脏中除了离散的心肌细胞斑块外均下调。最后，我们证明在成年心脏和肌肉组织中可检测到Xtn3转录本。
