Brunet Thibaut, Fischer Antje Hl, Steinmetz Patrick Rh, Lauri Antonella, Bertucci Paola, Arendt Detlev
Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
Elife. 2016 Dec 1;5:e19607. doi: 10.7554/eLife.19607.
The dichotomy between smooth and striated myocytes is fundamental for bilaterian musculature, but its evolutionary origin is unsolved. In particular, interrelationships of visceral smooth muscles remain unclear. Absent in fly and nematode, they have not yet been characterized molecularly outside vertebrates. Here, we characterize expression profile, ultrastructure, contractility and innervation of the musculature in the marine annelid and identify smooth muscles around the midgut, hindgut and heart that resemble their vertebrate counterparts in molecular fingerprint, contraction speed and nervous control. Our data suggest that both visceral smooth and somatic striated myocytes were present in the protostome-deuterostome ancestor and that smooth myocytes later co-opted the striated contractile module repeatedly - for example, in vertebrate heart evolution. During these smooth-to-striated myocyte conversions, the core regulatory complex of transcription factors conveying myocyte identity remained unchanged, reflecting a general principle in cell type evolution.
平滑肌细胞和横纹肌细胞之间的二分法是两侧对称动物肌肉组织的基础，但其进化起源尚未解决。特别是，内脏平滑肌之间的相互关系仍不清楚。果蝇和线虫中没有内脏平滑肌，在脊椎动物之外它们尚未在分子层面得到表征。在这里，我们描述了海洋环节动物肌肉组织的表达谱、超微结构、收缩性和神经支配，并识别出中肠、后肠和心脏周围的平滑肌，这些平滑肌在分子指纹、收缩速度和神经控制方面与它们的脊椎动物对应物相似。我们的数据表明，内脏平滑肌细胞和体壁横纹肌细胞在原口动物 - 后口动物的祖先中就已存在，并且平滑肌细胞后来多次采用了横纹肌收缩模块——例如，在脊椎动物心脏进化过程中。在这些从平滑肌细胞到横纹肌细胞的转变过程中，传达肌细胞身份的转录因子的核心调节复合体保持不变，这反映了细胞类型进化中的一个普遍原则。
