Wu Jiahn-Chun, Sung Hsin-Ching, Chung Tun-Hui, DePhilip Robert M
Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, Taipei 10018, Taiwan.
J Cell Biochem. 2002;84(4):717-24. doi: 10.1002/jcb.10092.
Costameres, vinculin-containing structures found in skeletal and cardiac muscle, are thought to anchor the Z-discs of the peripheral myofibrils to the sarcolemma. Several lines of evidence indicate that two different sets of costameres, integrin- and N-cadherin-based, are present in cardiac muscles. In this study, immunoblot analysis was used to study the expression of N-cadherin, alpha-catenin, beta-catenin, vinculin, talin, and laminin in rat cardiac muscles at embryonic days 15 and 19, the day of birth (postnatal day 0), postnatal weeks 1, 2, 3, and 4, and in the adult. Double immunofluorescence microscopy was performed to study the spatial and temporal distribution of these two sets of costameres in rat cardiomyocytes. Costameric staining for N-cadherin, codistributed with beta-catenin, was strong from embryonic day 15 up to postnatal week 2, gradually decreased after postnatal week 3, and was undetectable at postnatal week 4 and in the adult. Confocal microscopy showed that N-cadherin colocalized with alpha-actinin at cortical myofibrils. Double-labeling of beta-catenin and talin indicated the coexistence of N-cadherin/catenin- and integrin/talin-based costameres in rat cardiac muscle. Although beta-catenin and vinculin were co-localized at the costamere of cardiomyocytes from embryonic day 15 to postnatal week 3, staining for beta-catenin or talin was mutually exclusive at all stages examined. These results demonstrate the simultaneous, but mutually exclusive, existence of N-cadherin/catenin- and integrin/talin-based costameres in rat cardiomyocytes between late embryonic stages and postnatal week 3, while only integrin/talin-based costameres were found in adult rats. The N-cadherin/catenin-based costameres in rat cardiac muscles may play a role in myofibrillogenesis similar to that of their counterparts in cultured cardiomyocytes.
肌联蛋白结构存在于骨骼肌和心肌中，含有纽蛋白，被认为可将外周肌原纤维的Z盘锚定在肌膜上。有几条证据表明，心肌中存在两种不同类型的肌联蛋白结构，分别基于整合素和N-钙黏蛋白。在本研究中，采用免疫印迹分析来研究大鼠心肌在胚胎第15天和第19天、出生当天（出生后第0天）、出生后第1、2、3和4周以及成年期时N-钙黏蛋白、α-连环蛋白、β-连环蛋白、纽蛋白、踝蛋白和层粘连蛋白的表达。进行双重免疫荧光显微镜检查以研究这两种肌联蛋白结构在大鼠心肌细胞中的空间和时间分布。N-钙黏蛋白的肌联蛋白染色与β-连环蛋白共分布，从胚胎第15天到出生后第2周都很强，出生后第3周后逐渐减少，在出生后第4周和成年期无法检测到。共聚焦显微镜显示，N-钙黏蛋白与α-辅肌动蛋白在皮质肌原纤维中共定位。β-连环蛋白和踝蛋白的双重标记表明，大鼠心肌中存在基于N-钙黏蛋白/连环蛋白和整合素/踝蛋白的肌联蛋白结构。尽管从胚胎第15天到出生后第3周，β-连环蛋白和纽蛋白在心肌细胞的肌联蛋白处共定位，但在所有检查阶段，β-连环蛋白或踝蛋白的染色是相互排斥的。这些结果表明，在胚胎后期和出生后第3周之间，大鼠心肌细胞中同时存在但相互排斥的基于N-钙黏蛋白/连环蛋白和整合素/踝蛋白的肌联蛋白结构，而在成年大鼠中仅发现基于整合素/踝蛋白的肌联蛋白结构。大鼠心肌中基于N-钙黏蛋白/连环蛋白的肌联蛋白结构可能在肌原纤维形成中发挥作用，类似于它们在培养心肌细胞中的对应物。
