Phoronids, rhynchonelliform and linguliform brachiopods show striking similarities in their embryonic fate maps, in particular in their axis specification and regionalization. However, although brachiopod development has been studied in detail and demonstrated embryonic patterning as a causal factor of the gastrulation mode (protostomy vs deuterostomy), molecular descriptions are still missing in phoronids. To understand whether phoronids display underlying embryonic molecular mechanisms similar to those of brachiopods, here we report the expression patterns of anterior (otx, gsc, six3/6, nk2.1), posterior (cdx, bra) and endomesodermal (foxA, gata4/5/6, twist) markers during the development of the protostomic phoronid Phoronopsis harmeri. The transcription factors foxA, gata4/5/6 and cdx show conserved expression in patterning the development and regionalization of the phoronid embryonic gut, with foxA expressed in the presumptive foregut, gata4/5/6 demarcating the midgut and cdx confined to the hindgut. Furthermore, six3/6, usually a well-conserved anterior marker, shows a remarkably dynamic expression, demarcating not only the apical organ and the oral ectoderm, but also clusters of cells of the developing midgut and the anterior mesoderm, similar to what has been reported for brachiopods, bryozoans and some deuterostome Bilateria. Surprisingly, brachyury, a transcription factor often associated with gastrulation movements and mouth and hindgut development, seems not to be involved with these patterning events in phoronids. Our description and comparison of gene expression patterns with other studied Bilateria reveals that the timing of axis determination and cell fate distribution of the phoronid shows highest similarity to that of rhynchonelliform brachiopods, which is likely related to their shared protostomic mode of development. Despite these similarities, the phoronid Ph. harmeri also shows particularities in its development, which hint to divergences in the arrangement of gene regulatory networks responsible for germ layer formation and axis specification.

中文翻译：

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PhoronopsisHarmereri 发育过程中的分子模式揭示了与 rhynchonelliform 腕足类动物的相似之处

Phoronids、rhynchonelliform 和舌形腕足类动物在它们的胚胎命运图谱中显示出惊人的相似之处，特别是在它们的轴规范和区域化方面。然而，尽管腕足动物发育已被详细研究并证明胚胎模式是原肠胚形成模式（原生造口术与后造口术）的一个因果因素，但在 phoronids 中仍然缺少分子描述。为了了解 phoronids 是否显示出与腕足类动物相似的潜在胚胎分子机制，在这里我们报告了前部 (otx、gsc、six3/6、nk2.1)、后部 (cdx、bra) 和内胚层 (foxA、gata4/) 的表达模式。 5/6，扭曲）在原生动物 phoronid PhoronopsisHarmereri 发育过程中的标记。转录因子foxA，gata4/5/6 和 cdx 在 phoronid 胚胎肠道的发育和区域化模式中表现出保守的表达，foxA 在假定的前肠中表达，gata4/5/6 划分中肠和 cdx 仅限于后肠。此外，通常是保存良好的前部标记的 Six3/6 显示出非常动态的表达，不仅区分了顶端器官和口腔外胚层，而且还区分了发育中的中肠和前中胚层的细胞簇，类似于已经报道了腕足动物、苔藓虫和一些氘核动物。令人惊讶的是，brachyury 是一种通常与原肠运动以及口腔和后肠发育相关的转录因子，似乎与 phoronids 中的这些模式事件无关。我们对基因表达模式与其他研究的 Bilateria 的描述和比较表明，phoronid 的轴确定时间和细胞命运分布与 rhynchonelliform 腕足动物的相似性最高，这可能与它们共同的原生发育模式有关。尽管有这些相似之处，phoronid Ph.harmeri 在其发展中也表现出特殊性，这暗示了负责胚层形成和轴规范的基因调控网络的排列存在差异。