Developmental Biology, Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
Orthodontics, Department of Oral and Maxillofacial Diseases, University of Helsinki, Helsinki, Finland.
Sci Rep. 2017 Sep 21;7(1):12063. doi: 10.1038/s41598-017-12352-0.
Ectothermal reptiles have internal pigmentation, which is not seen in endothermal birds and mammals. Here we show that the development of the dorsal neural tube-derived melanoblasts in turtle Trachemys scripta is regulated by similar mechanisms as in other amniotes, but significantly later in development, during the second phase of turtle trunk neural crest emigration. The development of melanoblasts coincided with a morphological change in the dorsal neural tube between stages mature G15 and G16. The melanoblasts delaminated and gathered in the carapacial staging area above the neural tube at G16, and differentiated into pigment-forming melanocytes during in vitro culture. The Mitf-positive melanoblasts were not restricted to the dorsolateral pathway as in birds and mammals but were also present medially through the somites similarly to ectothermal anamniotes. This matched a lack of environmental barrier dorsal and lateral to neural tube and the somites that is normally formed by PNA-binding proteins that block entry to medial pathways. PNA-binding proteins may also participate in the patterning of the carapacial pigmentation as both the migratory neural crest cells and pigment localized only to PNA-free areas.
变温爬行动物具有内在色素沉着，而温血鸟类和哺乳动物则没有。在这里，我们表明，龟鳖 Trachemys scripta 背部神经管衍生的黑素细胞前体的发育受类似机制调控，但在发育后期，即龟鳖躯干神经嵴迁移的第二阶段。黑素细胞前体的发育与 G15 期和 G16 期之间成熟阶段的背部神经管形态变化相吻合。黑素细胞前体在 G16 时从神经管分离并聚集在神经管上方的甲壳形成区域，并在体外培养过程中分化为形成色素的黑素细胞。Mitf 阳性的黑素细胞前体不仅局限于鸟类和哺乳动物的背外侧途径，而且也像变温无羊膜动物一样通过体节存在于中间。这与神经管和体节通常由阻止进入中间途径的 PNA 结合蛋白形成的缺乏环境屏障背侧和侧部相对应。PNA 结合蛋白也可能参与甲壳色素形成的模式形成，因为迁移的神经嵴细胞和定位仅在 PNA 无区域的色素均参与其中。
