BACKGROUND The basic helix-loop-helix (bHLH) family of transcription factors is one of the largest superfamilies of regulatory transcription factors and is widely used in eukaryotic organisms. They play an essential role in a range of metabolic, physiological, and developmental processes, including the development of the nervous system (NS). These transcription factors have been studied in many metazoans, especially in vertebrates but also in early branching metazoan clades such as the cnidarians and sponges. However, currently very little is known about their expression in the most basally branching bilaterian group, the xenacoelomorphs. Recently, our laboratory has characterized the full complement of bHLH in the genome of two members of the Xenacoelomorpha, the xenoturbellid Xenoturbella bocki and the acoel Symsagittifera roscoffensis. Understanding the patterns of bHLH gene expression in members of this phylum (in space and time) provides critical new insights into the conserved roles of the bHLH and their putative specificities in this group. Our focus is on deciphering the specific roles that these genes have in the process of neurogenesis. RESULTS Here, we analyze the developmental expression of the whole complement of bHLH genes identified in the acoel S. roscoffensis. Based on their expression patterns, several members of bHLH class A appear to have specific conserved roles in neurogenesis, while other class A genes (as well as members of other classes) have likely taken on more generalized functions. All gene expression patterns are described in embryos and early juveniles. CONCLUSION Our results suggest that the main roles of the bHLH genes of S. roscoffensis are evolutionarily conserved, with a specific subset dedicated to patterning the nervous system: SrAscA, SrAscB, SrHes/Hey, SrNscl, SrSrebp, SrE12/E47 and SrOlig.

中文翻译：

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acoel S. roscoffensis 中转录调节因子 bHLH 家族的特征及其在神经发生中的推定作用。

背景技术转录因子的基本螺旋-环-螺旋(bHLH)家族是最大的调节转录因子超家族之一，广泛用于真核生物。它们在一系列代谢、生理和发育过程中发挥着重要作用，包括神经系统 (NS) 的发育。这些转录因子已在许多后生动物中进行了研究，特别是在脊椎动物中，但也在早期分支的后生动物进化枝中，如刺胞动物和海绵中。然而，目前对它们在最基部分枝的双侧动物群异种腔形体中的表达知之甚少。最近，我们的实验室在 Xenacoelomorpha 的两个成员的基因组中表征了 bHLH 的完整补体，即 xenoturbellid Xenoturbella bocki 和 acoel Symsagittifera roscoffensis。了解该门成员中 bHLH 基因表达的模式（在空间和时间上）为 bHLH 的保守作用及其在该组中的假定特异性提供了重要的新见解。我们的重点是破译这些基因在神经发生过程中的具体作用。结果 在这里，我们分析了在无花果 S. roscoffensis 中鉴定的整个 bHLH 基因的发育表达。根据它们的表达模式，bHLH A 类的几个成员似乎在神经发生中具有特定的保守作用，而其他 A 类基因（以及其他类的成员）可能具有更普遍的功能。所有基因表达模式都在胚胎和早期幼体中描述。结论 我们的研究结果表明，金黄色葡萄球菌 bHLH 基因的主要作用。