In syllids (Annelida, Syllidae), the regenerative blastema was subject of many studies in the mid and late XXth century. This work on syllid regeneration showed that the blastema is developed by a process of dedifferentiation of cells near the wound, followed by their proliferation and redifferentiation (cells differentiate to the original cell type) or, in some specific cases, transdifferentiation (cells differentiate to a cell type different from the original). Up to date, participation of stem cells or pre-existing proliferative cells in the blastema development has never been observed in syllids. This study provides the first comprehensive description of Syllis malaquini’s regenerative capacity, including data on the cellular proliferation dynamics by using an EdU/BrdU labelling approach, in order to trace proliferative cells (S-phase cells) present before and after operation. Syllis malaquini can restore the anterior and posterior body from different cutting levels under experimental conditions, even from midbody fragments. Our results on cellular proliferation showed that S-phase cells present in the body before bisection do not significantly contribute to blastema development. However, in some specimens cut at the level of the proventricle, cells in S-phase located in the digestive tube before bisection participated in regeneration. Also, our results showed that nucleus shape allows to distinguish different types of blastemal cells as forming specific tissues. Additionally, simultaneous and sequential addition of segments seem to occur in anterior regeneration, while only sequential addition was observed in posterior regeneration. Remarkably, in contrast with previous studies in syllids, sexual reproduction was not induced during anterior regeneration of amputees lacking the proventricle, a foregut organ widely known to be involved in the stolonization control. Our findings led us to consider that although dedifferentiation and redifferentiation might be more common, proliferative cells present before injury can be involved in regenerative processes in syllids, at least in some cases. Also, we provide data for comparative studies on resegmentation as a process that differs between anterior and posterior regeneration; and on the controversial role of the proventricle in the reproduction of different syllid lineages.

中文翻译：

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Syllis malaquini（Syllidae，Annelida）再生过程中的细胞增殖动态

在节虫科（Annelida、Sylidae）中，再生芽基是二十世纪中后期许多研究的主题。这项关于皮瓣再生的工作表明，芽基是通过伤口附近细胞的去分化过程形成的，然后是它们的增殖和再分化（细胞分化为原始细胞类型），或者在某些特定情况下，转分化（细胞分化为原始细胞类型）。细胞类型与原始细胞类型不同）。迄今为止，从未在 syllids 中观察到干细胞或预先存在的增殖细胞参与胚基发育。这项研究首次全面描述了 Syllis malaquini 的再生能力，包括使用 EdU/BrdU 标记方法获得的细胞增殖动态数据，以追踪手术前后存在的增殖细胞（S 期细胞）。Syllis malaquini 可以在实验条件下从不同的切割水平，甚至从中体碎片恢复前体和后体。我们的细胞增殖结果表明，二分之前体内存在的 S 期细胞对胚基发育没有显着贡献。然而，在一些在腺胃水平切割的标本中，平分前位于消化管中的S期细胞参与了再生。此外，我们的结果表明，细胞核形状可以区分不同类型的胚细胞形成特定的组织。此外，在前部再生中似乎发生了节段的同时和顺序添加，而在后部再生中仅观察到顺序添加。值得注意的是，与之前对 sylids 的研究相比，在缺乏前肠的截肢者的前部再生过程中没有诱导有性生殖，前肠是众所周知的参与匍匐控制的前肠器官。我们的研究结果使我们考虑到，尽管去分化和再分化可能更常见，但损伤前存在的增殖细胞可能参与syllids的再生过程，至少在某些情况下是这样。此外，我们还提供了重新分割的比较研究数据，作为前路和后路再生之间不同的过程；以及腺胃在不同syllid谱系的繁殖中具有争议的作用。