Making maxillary barbels with a proximal-distal gradient of Wnt signals in matrix-bound mesenchymal cells.
Making maxillary barbels with a proximal-distal gradient of Wnt signals in matrix-bound mesenchymal cells.
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DOI：
10.1111/ede.12167
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发表时间：
2015-11
影响因子：
2.9
通讯作者：
LeClair EE
中科院分区：
文献类型：
--
作者：
Figueroa F;Singer SS;LeClair EE
一般细胞信号通路的个体发育部署使特定附属物的进化成为可能。许多鱼类、两栖动物和爬行动物都有被称为触须的独特皮肤附属物，在细胞和分子水平上对此知之甚少。在这项研究中，我们研究了与斑马鱼上颌骨触须相关的细胞排列、细胞分裂模式和基因表达谱。ZMB最早的细胞组织是上颌骨真皮内的间充质细胞内旋；没有上皮胎盘，也没有任何轴向拉长的上皮细胞，如所预期的顶端外胚层脊(AER)。随着ZMB的发育，处于S相的细胞最初随机分布于附件各处，逐渐过渡到集中在远端的增殖群。通过观察Wnt反应转基因报告系TCFsiam中ZMB的个体发育阶段，我们在这些发育中的附属物中发现了一层强荧光的间充质细胞层。利用体外培养技术对发育中的触须组织进行体外培养，我们将荧光标记与有丝分裂标记EDU共同定位于这些细胞。令人惊讶的是，TCF+细胞几乎没有增殖，这表明它是一个慢周期的亚群。ZMB的透射电子显微镜发现，TCF+细胞位于触须基质核心内的单层周围层中。在形态上，这些细胞类似于成纤维细胞或成骨细胞；除了它们与基质结合的位置外，它们还通过其煎饼状的细胞核、丰富的粗面内质网以及进入周围细胞外基质的细胞质延伸而被识别。综上所述，这些特征定义了斑马鱼中一种新的间充质细胞群，即“TCF+核心细胞”。提出了一种触须发育的工作模型，在该模型中，这些最小有丝分裂的中胚层细胞响应于外胚层来源的Wnt信号，沿着附属器近端-远端梯度分布，产生胶原质基质。这证明了脊椎动物附肢生长的一种新机制。相似的遗传信号和细胞行为可能是其他鱼类触须结构独立和重复进化的原因。
The evolution of specific appendages is made possible by the ontogenetic deployment of general cell signaling pathways. Many fishes, amphibians and reptiles have unique skin appendages known as barbels, which are poorly understood at the cellular and molecular level. In this study, we examine the cell arrangements, cell division patterns, and gene expression profiles associated with the zebrafish maxillary barbel, or ZMB. The earliest cellular organization of the ZMB is an internal whorl of mesenchymal cells in the dermis of the maxilla; there is no epithelial placode, nor any axially-elongated epithelial cells as expected of an apical ectodermal ridge (AER). As the ZMB develops, cells in S-phase are at first distributed randomly throughout the appendage, gradually transitioning to a proliferative population concentrated at the distal end. By observing ZMB ontogenetic stages in a Wnt-responsive transgenic reporter line, TCFsiam, we identified a strongly fluorescent mesenchymal cell layer within these developing appendages. Using an in vitro explant culture technique on developing barbel tissues, we co-localized the fluorescent label in these cells with the mitotic marker EdU. Surprisingly, TCF+ cells showed little proliferation, indicating a slow-cycling subpopulation. Transmission electron microscopy of the ZMB located the TCF+ cells in a single, circumferential layer within the barbel’s matrix core. Morphologically, these cells resemble fibroblasts or osteoblasts; in addition to their matrix-bound location, they are identified by their pancake-shaped nuclei, abundant rough endoplasmic reticulum, and cytoplasmic extensions into the surrounding extracellular matrix. Taken together, these features define a novel mesenchymal cell population in zebrafish, the ‘TCF+ core cells.’ A working model of barbel development is proposed, in which these minimally mitotic mesodermal cells produce collagenous matrix in response to ectodermally-derived Wnt signals deployed in a proximal-distal gradient along the appendage. This documents a novel mechanism of vertebrate appendage outgrowth. Similar genetic signals and cell behaviors may be responsible for the independent and repeated evolution of barbel structures in other fish species.