Department of Biochemistry and Biophysics, Programs in Developmental and Stem Cell Biology, Genetics and Human Genetics, Cardiovascular Research Institute, University of California, San Francisco, 1550 4th St, Room 384, San Francisco, CA 94158, USA.
Dev Biol. 2012 Dec 1;372(1):111-9. doi: 10.1016/j.ydbio.2012.07.015. Epub 2012 Jul 25.
scotch tape (sco) is a zebrafish cardiac mutant initially proposed to exhibit a reduced amount of cardiac jelly, the extracellular matrix between the myocardial and endocardial layers. We analyzed sco(te382) mutant hearts in detail using both selective plane illumination microscopy (SPIM) and transmission electron microscopy (TEM), and observed a fascinating endocardial defect. Time-lapse SPIM imaging of wild-type and mutant embryos revealed significant and dynamic gaps between endocardial cells during development. Although these gaps close in wild-type animals, they fail to close in the mutants, ultimately leading to a near complete absence of endocardial cells in the atrial chamber by the heart looping stage. TEM analyses confirm the presence of gaps between endocardial cells in sco mutants, allowing the apparent leakage of cardiac jelly into the lumen. High-resolution mapping places the sco(te382) mutation within the fbn2b locus, which encodes the extracellular matrix protein Fibrillin 2b (OMIM ID: 121050). Complementation and further phenotypic analyses confirm that sco is allelic to puff daddy(gw1) (pfd(gw1)), a null mutant in fbn2b, and that sco(te382) is a hypomorphic allele of fbn2b. fbn2b belongs to a family of genes responsible for the assembly of microfibrils throughout development, and is essential for microfibril structural integrity. In sco(te382) mutants, Fbn2b is disabled by a missense mutation in a highly conserved cbEGF domain, which likely interferes with protein folding. Integrating data obtained from microscopy and molecular biology, we posit that this mutation impacts the rigidity of Fbn2b, imparting a structural defect that weakens endocardial adhesion thereby resulting in perforated endocardium.
透明胶带（scotch tape，sco）是一种斑马鱼心脏突变体，最初被提出是因为其心脏果冻（心肌层和心内膜层之间的细胞外基质）含量减少。我们使用选择性平面照明显微镜（selective plane illumination microscopy，SPIM）和透射电子显微镜（transmission electron microscopy，TEM）对 sco(te382)突变体心脏进行了详细分析，观察到一个迷人的心内膜缺陷。野生型和突变型胚胎的延时 SPIM 成像显示，在发育过程中心内膜细胞之间存在显著且动态的间隙。尽管这些间隙在野生型动物中会闭合，但在突变体中却无法闭合，最终导致心房腔中的心内膜细胞几乎完全缺失，在心脏环化阶段。TEM 分析证实 sco 突变体中心内膜细胞之间存在间隙，允许心脏果冻明显渗漏到管腔中。高分辨率图谱将 sco(te382)突变定位在 fbn2b 基因座内，该基因座编码细胞外基质蛋白 Fibrillin 2b（OMIM ID：121050）。互补和进一步的表型分析证实，sco 与 puff daddy(gw1)（pfd(gw1)）等位，即 fbn2b 的 null 突变体，并且 sco(te382)是 fbn2b 的一个功能获得性突变体。fbn2b 属于一组基因家族，负责在整个发育过程中组装微纤维，对于微纤维结构的完整性至关重要。在 sco(te382)突变体中，Fbn2b 由于 cbEGF 结构域的高度保守错义突变而失活，该突变可能干扰了蛋白质折叠。整合显微镜和分子生物学获得的数据，我们假设该突变影响了 Fbn2b 的刚性，导致心内膜黏附的结构缺陷，从而导致心内膜穿孔。
