PDF(Pubmed)
Abstract：
BACKGROUND: The tunicates form a group of filter-feeding marine animals closely related to vertebrates. They share with them a number of features such as a notochord and a dorsal neural tube in the tadpole larvae of ascidians, one of the three groups that make tunicates. However, a number of typical chordate characters have been lost in different branches of tunicates, a diverse and fast-evolving phylum. Consequently, the tunic, a sort of exoskeleton made of extracellular material including cellulose secreted by the epidermis, is the unifying character defining the tunicate phylum. In the larva of ascidians, the tunic differentiates in the tail into a median fin (with dorsal and ventral extended blades) and a caudal fin.
RESULTS: Here we have performed experiments in the ascidian Phallusia mammillata to address the molecular control of tunic 3D morphogenesis. We have demonstrated that the tail epidermis medio-lateral patterning essential for peripheral nervous system specification also controls tunic elongation into fins. More specifically, when tail epidermis midline identity was abolished by BMP signaling inhibition, or CRISPR/Cas9 inactivation of the transcription factor coding genes Msx or Klf1/2/4/17, median fin did not form. We postulated that this genetic program should regulate effectors of tunic secretion. We thus analyzed the expression and regulation in different ascidian species of two genes acquired by horizontal gene transfer (HGT) from bacteria, CesA coding for a cellulose synthase and Gh6 coding for a cellulase. We have uncovered an unexpected dynamic history of these genes in tunicates and high levels of variability in gene expression and regulation among ascidians. Although, in Phallusia, Gh6 has a regionalized expression in the epidermis compatible with an involvement in fin elongation, our functional studies indicate a minor function during caudal fin formation only.
CONCLUSIONS: Our study constitutes an important step in the study of the integration of HGT-acquired genes into developmental networks and a cellulose-based morphogenesis of extracellular material in animals.
RESULTS: Here we have performed experiments in the ascidian Phallusia mammillata to address the molecular control of tunic 3D morphogenesis. We have demonstrated that the tail epidermis medio-lateral patterning essential for peripheral nervous system specification also controls tunic elongation into fins. More specifically, when tail epidermis midline identity was abolished by BMP signaling inhibition, or CRISPR/Cas9 inactivation of the transcription factor coding genes Msx or Klf1/2/4/17, median fin did not form. We postulated that this genetic program should regulate effectors of tunic secretion. We thus analyzed the expression and regulation in different ascidian species of two genes acquired by horizontal gene transfer (HGT) from bacteria, CesA coding for a cellulose synthase and Gh6 coding for a cellulase. We have uncovered an unexpected dynamic history of these genes in tunicates and high levels of variability in gene expression and regulation among ascidians. Although, in Phallusia, Gh6 has a regionalized expression in the epidermis compatible with an involvement in fin elongation, our functional studies indicate a minor function during caudal fin formation only.
CONCLUSIONS: Our study constitutes an important step in the study of the integration of HGT-acquired genes into developmental networks and a cellulose-based morphogenesis of extracellular material in animals.
摘要：
背景：被膜形成一组与脊椎动物密切相关的滤食海洋动物。它们与它们共享许多特征，例如海鞘的t幼虫中的脊索和背侧神经管，做外衣的三个小组之一。然而,在被膜的不同分支中丢失了许多典型的脊索字符，一个多样化和快速进化的门。因此,外衣,一种由表皮分泌的纤维素组成的外骨骼，是定义被膜门的统一特征。在海鞘的幼虫中，外衣在尾巴中分为正鳍（具有背侧和腹侧延伸的叶片）和尾鳍。
结果：在这里，我们在海鞘Phallusia哺乳动物中进行了实验，以解决外衣3D形态发生的分子控制。我们已经证明，对于周围神经系统规格必不可少的尾部表皮中外侧图案也可以控制外衣向鳍的伸长。更具体地说,当尾表皮中线身份被BMP信号抑制废除时，或CRISPR/Cas9失活的转录因子编码基因Msx或Klf1/2/4/17，中位鳍没有形成。我们推测该遗传程序应调节外衣分泌的效应子。因此，我们分析了通过水平基因转移（HGT）从细菌中获得的两个基因在不同海鞘物种中的表达和调控，CesA编码纤维素合酶和Gh6编码纤维素酶。我们已经发现了这些基因在被膜中的出乎意料的动态历史，以及海鞘中基因表达和调节的高度变异性。虽然,在Phallusia,Gh6在表皮中具有区域性表达，与鳍伸长有关，我们的功能研究表明，仅在尾鳍形成过程中具有较小的功能。
结论：我们的研究是将HGT获得的基因整合到发育网络和基于纤维素的动物细胞外物质形态发生的研究中的重要一步。
结果：在这里，我们在海鞘Phallusia哺乳动物中进行了实验，以解决外衣3D形态发生的分子控制。我们已经证明，对于周围神经系统规格必不可少的尾部表皮中外侧图案也可以控制外衣向鳍的伸长。更具体地说,当尾表皮中线身份被BMP信号抑制废除时，或CRISPR/Cas9失活的转录因子编码基因Msx或Klf1/2/4/17，中位鳍没有形成。我们推测该遗传程序应调节外衣分泌的效应子。因此，我们分析了通过水平基因转移（HGT）从细菌中获得的两个基因在不同海鞘物种中的表达和调控，CesA编码纤维素合酶和Gh6编码纤维素酶。我们已经发现了这些基因在被膜中的出乎意料的动态历史，以及海鞘中基因表达和调节的高度变异性。虽然,在Phallusia,Gh6在表皮中具有区域性表达，与鳍伸长有关，我们的功能研究表明，仅在尾鳍形成过程中具有较小的功能。
结论：我们的研究是将HGT获得的基因整合到发育网络和基于纤维素的动物细胞外物质形态发生的研究中的重要一步。
