Israel Oceanography and Limnological Research, National Institute of Oceanography, PO Box 8030, Haifa 31080, Israel.
Stanford Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford 94305-5323, CA, USA.
Cells. 2012 Dec 27;2(1):1-18. doi: 10.3390/cells2010001.
A number of challenges have hindered the development of a unified theory for metazoan regeneration. To describe the full range of complex regeneration phenomena in Animalia, we suggest that metazoans that regenerate missing body parts exhibit biological attributes that are tailored along a morpho-spatial regeneration continuum, illustrated in its polar scenarios by the USA "stars and stripes" flag. Type 1 organisms ("T1, 'stars'") are typical colonial organisms (but contain unitary taxa) that are able to regenerate "whole new stars", namely, whole bodies and colonial modules, through systemic induction and sometimes multiple regeneration foci (hollow regeneration spheres, resembling the blastula) that compete for dominance. They regenerate soma and germ constituents with pluripotent adult stem cells and exhibit somatic-embryogenesis mode of ontogeny. Type 2 organisms ("T2, 'stripes'") are capable of limited regeneration of somatic constituents via fate-restricted stem cells, and regenerate through centralized inductions that lead to a single regeneration front. T2 organisms are unitary and use preformistic mode of ontogeny. T1 and T2 organisms also differ in interpretation of what constitutes positional information. T2 organisms also execute alternative, less effective, regeneration designs (i.e., scar formation). We assigned 15 characteristics that distinguish between T1/T2 strategies: those involving specific regeneration features and those operating on biological features at the whole-organism level. Two model organisms are discussed, representing the two strategies of T1/T2 along the regeneration continuum, the Botrylloides whole body regeneration (T1) and the mouse digit-tip regeneration (T2) phenomena. The above working hypothesis also postulates that regeneration is a primeval attribute of metazoans. As specified, the "stars and stripes" paradigm allows various combinations of the biological features assigned to T1 and T2 regeneration strategies. It does not consider any concentration gradient or thresholds and does not refer to the "epimorphosis" and "morphallaxis" terms, regeneration types across phyla or across body plans. The "stars and stripes" paradigm also ignores, at this stage of analysis, cases of regeneration loss that may obscure biological trajectories. The main advantage of the "stars and stripes" paradigm is that it allows us to compare T1/T2 regeneration, as well as other modes of regeneration, through critical determining characteristics.
有许多挑战阻碍了后生动物再生的统一理论的发展。为了描述动物界中复杂的再生现象，我们建议，缺失身体部位的后生动物表现出的生物属性沿着形态空间再生连续体进行调整，用美国的“星条旗”来表示其极端情况。1 型生物（“T1，‘星’”）是典型的群体生物（但包含单一分类群），它们能够通过系统诱导和有时多个竞争主导地位的再生焦点（空心再生球体，类似于囊胚）来“全新生成星”，即全新的身体和群体模块。它们通过多能成体干细胞再生体细胞和生殖成分，并表现出体胚胎发生的个体发生模式。2 型生物（“T2，‘条纹’”）能够通过命运受限的干细胞有限地再生体细胞，并通过集中诱导来再生，导致单一再生前缘。T2 生物是单一的，使用预形成的个体发生模式。T1 和 T2 生物在对构成位置信息的解释上也存在差异。T2 生物也执行替代的、效果较差的再生设计（即疤痕形成）。我们分配了 15 个特征来区分 T1/T2 策略：涉及特定再生特征的特征和在整个生物体水平上操作的生物特征。讨论了两种模式生物，它们沿着再生连续体代表了 T1/T2 的两种策略，即 Botrylloides 整体再生（T1）和小鼠指尖再生（T2）现象。上述工作假设还假定再生是后生动物的原始属性。如前所述，“星条旗”范式允许将分配给 T1 和 T2 再生策略的生物特征进行各种组合。它不考虑任何浓度梯度或阈值，也不涉及“表皮发生”和“形态变化”术语、跨门或跨体计划的再生类型。“星条旗”范式也忽略了分析阶段可能掩盖生物轨迹的再生损失案例。“星条旗”范式的主要优点是，它允许我们通过关键决定特征来比较 T1/T2 再生以及其他再生模式。
