Institute of Developmental Biology, University of Cologne, Germany.
Dev Biol. 2012 Sep 15;369(2):235-48. doi: 10.1016/j.ydbio.2012.06.023. Epub 2012 Jul 6.
Hemicentin 1 (Hmcn1) and Hemicentin 2 (Hmcn2) belong to the fibulin family of extracellular matrix (ECM) proteins that play pivotal roles during development and homeostasis of a variety of vertebrate tissues. Recently, we have shown that mutations in zebrafish Hmcn1, also called Fibulin 6, lead to massive fin blistering, similar to the defects caused by the Fraser syndrome gene Fras1. In contrast, the role of Hmcn2 during vertebrate development has thus far been uncharacterized. In zebrafish, hmcn2, like fibulin 1 (fbln1), another member of the fibulin family, is predominantly expressed in fin mesenchymal cells and developing somites, contrasting the strict epithelial expression of hmcn1. While antisense morpholino oligonucleotide (MO)-based knockdown of hmcn2 did not yield any discernable defects, hmcn2/fbln1 double knockdown fish displayed blistering in the trunk, pointing to an essential contribution of these proteins from mesodermal sources for proper epidermal-dermal junction formation. In contrast, and unlike hmcn1 mutants, epidermal-dermal junctions in the fin folds of hmcn2/fbln1 double knockdown fish were only moderately affected. Instead, they displayed impaired migration of fin mesenchymal cells into the fin folds, pointing to a crucial role of Hmcn2 and Fbln1 to remodel the ECM of the fin fold interepidermal space, which is a prerequisite for fibroblast ingrowth. TEM analyses suggest that this ECM remodeling occurs at the level of actinotrichia, the collageneous migration substrate of mesenchymal cells, and at the level of cross fibers, which resemble mammalian microfibers. This work provides first insights into the role of Hmcn2 during vertebrate development, identifying it as an evolutionary conserved protein that acts in functional redundancy with Fbln1C and/or Fbln1D isoforms to regulate tissue adhesion and cell migration, while extending the current knowledge of the functions of vertebrate Fbln1.
半钙黏蛋白 1（Hmcn1）和半钙黏蛋白 2（Hmcn2）属于细胞外基质（ECM）蛋白的纤维结合蛋白家族，在多种脊椎动物组织的发育和稳态中发挥关键作用。最近，我们发现，斑马鱼 Hmcn1（也称为纤维结合蛋白 6）的突变会导致大量鳍泡状，类似于 Fraser 综合征基因 Fras1 引起的缺陷。相比之下，Hmcn2 在脊椎动物发育过程中的作用迄今为止尚未确定。在斑马鱼中，hmcn2 与纤维结合蛋白 1（fbln1）一样，是纤维结合蛋白家族的另一个成员，主要在鳍间充质细胞和发育中的体节中表达，与 hmcn1 的严格上皮表达形成对比。虽然 hmcn2 的反义 寡核苷酸（MO）基敲低没有产生任何明显的缺陷，但 hmcn2/fbln1 双敲低鱼显示出躯干起泡，表明这些蛋白质从中胚层来源对适当的表皮-真皮连接形成有重要贡献。相比之下，与 hmcn1 突变体不同，hmcn2/fbln1 双敲低鱼鳍褶中的表皮-真皮连接仅受到中度影响。相反，它们显示出鳍间充质细胞向鳍褶迁移受损，这表明 Hmcn2 和 Fbln1 在重塑鳍褶间表皮空间的 ECM 中起着关键作用，这是成纤维细胞向内生长的前提。TEM 分析表明，这种 ECM 重塑发生在动纤毛水平，即间充质细胞的胶原迁移基质，以及在交叉纤维水平，其类似于哺乳动物的微纤维。这项工作首次提供了关于 Hmcn2 在脊椎动物发育过程中的作用的见解，确定它是一种进化保守的蛋白质，与 Fbln1C 和/或 Fbln1D 同工型一起发挥功能冗余作用，以调节组织粘附和细胞迁移，同时扩展了对脊椎动物 Fbln1 功能的现有认识。
