Okayama University, Research Core for Interdisciplinary Sciences (RCIS), 3-1-1 Tsushimanaka, Kitaku, Okayama City 700-8530, Japan.
Dev Biol. 2013 Sep 1;381(1):213-26. doi: 10.1016/j.ydbio.2013.05.010. Epub 2013 Jun 13.
Urodele amphibians can regenerate their limbs. During limb regeneration, dermal fibroblasts are transformed into undifferentiated cells called blastema cells. These dermis-blastema cells show multipotency. Such so-called endogenous reprogramming of cell differentiation is one of the main targets of amphibian limb regeneration studies. It is well recognized that nerve presence controls the initiation of limb regeneration. Accordingly, nerve factors have been sought in amphibian limb regeneration. To investigate it, a relatively new study system called the accessory limb model (ALM) was developed. Using ALM, two signaling cascades (Fgf and Gdf5 signaling) came under focus. In the present study, Growth and differentiation factor-5 (Gdf5) application to wounded skin initiated limb regeneration responses and resulted in induction of a blastema-like structure in the absence of a nerve. However, the Gdf5-induced structure showed defects as a regeneration blastema, such as absence of detectable Prrx1 expression by in situ hybridization. The defects could be remedied by additional Fibroblasts growth factor (Fgf) inputs. These two inputs (Gdf5 and Fgfs) were sufficient to substitute for the nerve functions in the induction of limb regeneration. Indeed, Fgf2, Fgf8, and Gdf5 applications with the contralateral skin graft resulted in limb formation without nerve supply. Furthermore, acquisition of cartilage differentiation potential of dermal fibroblasts was tested in an in vivo and in vitro combination assay. Dermal fibroblasts cultured with Gdf5 were difficult to participate in cartilage formation when the cultured cells were grafted into cartilage forming region. In contrast, dermal fibroblasts cultured with Fgf2 and Fgf8 became easier to participate into cartilage formation in the same procedure. These results contribute to our understanding of molecular mechanisms of the early phase of amphibian limb regeneration.
有尾两栖动物可以再生肢体。在肢体再生过程中，真皮成纤维细胞转变为未分化的细胞，称为芽基细胞。这些真皮-芽基细胞显示出多能性。这种所谓的细胞分化的内源性重编程是两栖动物肢体再生研究的主要目标之一。人们普遍认识到，神经的存在控制着肢体再生的启动。因此，在两栖动物肢体再生中寻找神经因子。为了研究这一点，开发了一种称为附加肢体模型（ALM）的相对较新的研究系统。利用 ALM，两个信号级联（Fgf 和 Gdf5 信号）成为焦点。在本研究中，生长分化因子 5（Gdf5）应用于受伤的皮肤引发了肢体再生反应，并导致在没有神经的情况下诱导出芽基样结构。然而，Gdf5 诱导的结构显示出作为再生芽基的缺陷，例如原位杂交检测不到可检测的 Prrx1 表达。通过额外的成纤维细胞生长因子（Fgf）输入可以弥补这些缺陷。这两个输入（Gdf5 和 Fgfs）足以替代神经在诱导肢体再生中的功能。事实上，应用 Fgf2、Fgf8 和 Gdf5 并结合对侧皮肤移植导致在没有神经供应的情况下形成肢体。此外，还在体内和体外联合测定中测试了真皮成纤维细胞获得软骨分化潜能。当培养细胞移植到软骨形成区域时，用 Gdf5 培养的真皮成纤维细胞很难参与软骨形成。相比之下，用 Fgf2 和 Fgf8 培养的真皮成纤维细胞在相同的过程中更容易参与软骨形成。这些结果有助于我们理解两栖动物肢体再生早期阶段的分子机制。
