Comparative Histolab Padova and University of Bologna, Italy.
Histol Histopathol. 2019 Oct;34(10):1111-1120. doi: 10.14670/HH-18-123. Epub 2019 May 6.
The hypothesis here presented tries to explain why organ regeneration is present in fish and amphibians (anamniotes) but is absent in reptiles, birds and mammals (amniotes). Anamniotes possess complex life cycles including larvae and metamorphosis stages, the latter representing a physiological form of organ destruction and regeneration coded in their genome that can be reactivated in adults in the form of regeneration. Part of the genome for larvae and metamorphosis phases was likely lost in amniotes with the evolution of direct development, the potentiation of the immune system and the increase in complexity of the nervous system. These events consequently determined incapability for organ regeneration in extant amniotes with the exception of the lizard tail. This likely derives from the evolution of a mechanism of immunosuppression that allows the regeneration of the tail although the complete morphogenetic plane of tail embryogenesis is lost. The lizard model of imperfect but outstanding organ regeneration indicates the possibility to improve organ regeneration also in other amniotes. In fact, the induction of a blastema in the amputated lizard limb has stimulated the formation of short limbs containing cartilaginous bones of the femur, tibia and fibula, and these experiments foster some hope for future attempts to induce limb and digit regeneration also in mammals.
本文提出的假设试图解释为什么鱼类和两栖类（无羊膜动物）具有器官再生能力，而爬行类、鸟类和哺乳类（羊膜动物）则没有。无羊膜动物具有复杂的生命周期，包括幼虫和变态阶段，后者代表了其基因组中编码的一种生理性器官破坏和再生形式，可以在成体中以再生的形式重新激活。随着直接发育、免疫系统增强和神经系统复杂性增加的进化，部分幼虫和变态阶段的基因组可能在羊膜动物中丢失。这些事件导致了现存羊膜动物除了蜥蜴尾巴之外，都无法进行器官再生。这可能源于免疫抑制机制的进化，尽管尾巴胚胎发生的完整形态发生平面丢失了，但仍允许尾巴再生。蜥蜴不完全但突出的器官再生模型表明，在其他羊膜动物中也有可能改善器官再生。事实上，在截去的蜥蜴肢体中诱导芽基，刺激了含有股骨、胫骨和腓骨软骨骨的短肢的形成，这些实验为未来尝试在哺乳动物中诱导肢体和指（趾）再生提供了一些希望。
