BACKGROUND NK genes are a group of homeobox transcription factors that are involved in various molecular pathways across bilaterians. They are typically divided into two subgroups, the NK cluster (NKC) and NK-linked genes (NKL). While the NKC genes have been studied in various bilaterians, corresponding data of many NKL genes are missing to date. To further investigate the ancestral roles of NK family genes, we analyzed the expression patterns of NKL genes in the onychophoran Euperipatoides rowelli. RESULTS The NKL gene complement of E. rowelli comprises eight genes, including BarH, Bari, Emx, Hhex, Nedx, NK2.1, vax and NK2.2, of which only NK2.2 was studied previously. Our data for the remaining seven NKL genes revealed expression in different structures associated with the developing nervous system in embryos of E. rowelli. While NK2.1 and vax are expressed in distinct medial regions of the developing protocerebrum early in development, BarH, Bari, Emx, Hhex and Nedx are expressed in late developmental stages, after all major structures of the nervous system have been established. Furthermore, BarH and Nedx are expressed in distinct mesodermal domains in the developing limbs. CONCLUSIONS Comparison of our expression data to those of other bilaterians revealed similar patterns of NK2.1, vax, BarH and Emx in various aspects of neural development, such as the formation of anterior neurosecretory cells mediated by a conserved molecular mechanism including NK2.1 and vax, and the development of the central and peripheral nervous system involving BarH and Emx. A conserved role in neural development has also been reported from NK2.2, suggesting that the NKL genes might have been primarily involved in neural development in the last common ancestor of bilaterians or at least nephrozoans (all bilaterians excluding xenacoelomorphs). The lack of comparative data for many of the remaining NKL genes, including Bari, Hhex and Nedx currently hampers further evolutionary conclusions. Hence, future studies should focus on the expression of these genes in other bilaterians, which would provide a basis for comparative studies and might help to better understand the role of NK genes in the diversification of bilaterians.

中文翻译：

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在灰指甲甲虫Euperipatoides rowelli（Peripatopsidae）中表达不属于NK簇的NK基因。

背景技术NK基因是一组同源异型框转录因子，其参与了跨生物分子的各种分子途径。它们通常分为两个亚组，即NK簇（NKC）和NK连锁基因（NKL）。虽然已经在各种双语者中研究了NKC基因，但迄今为止，许多NKL基因的相应数据都缺失。为了进一步研究NK家族基因的祖先作用，我们分析了甲壳虫Euperipatoides rowelli中NKL基因的表达模式。结果大肠埃希菌的NKL基因补体由八个基因组成，包括BarH，Bari，Emx，Hhex，Nedx，NK2.1，vax和NK2.2，以前仅研究了NK2.2。我们对其余七个NKL基因的数据揭示了在E. rowelli胚胎中与发育中的神经系统相关的不同结构中的表达。而NK2。1和vax在发育早期的大脑皮层的不同内侧区域表达，在神经系统的所有主要结构都建立之后，BarH，Bari，Emx，Hhex和Nedx在发育后期表达。此外，BarH和Nedx在发育中的肢体中以不同的中胚层结构域表达。结论我们的表达数据与其他双语者的表达数据进行比较，结果表明在神经发育的各个方面，NK2.1，vax，BarH和Emx的表达方式相似，例如由保守分子机制（包括NK2.1和vax，以及涉及BarH和Emx的中枢和周围神经系统的发育。NK2.2还报道了在神经发育中的保守作用，提示NKL基因可能主要参与了生物演化的最后一个共同祖先，至少是双边生物或至少是nezorozoans（所有xlatecoelomorphs）。目前缺少许多剩余的NKL基因的比较数据，包括Bari，Hhex和Nedx，这阻碍了进一步的进化结论。因此，未来的研究应侧重于这些基因在其他双语者中的表达，这将为比较研究提供基础，并可能有助于更好地理解NK基因在双语者多样化中的作用。Hhex和Nedx当前阻碍了进一步的进化结论。因此，未来的研究应侧重于这些基因在其他双语者中的表达，这将为比较研究提供基础，并可能有助于更好地理解NK基因在双语者多样化中的作用。Hhex和Nedx当前阻碍了进一步的进化结论。因此，未来的研究应侧重于这些基因在其他双语者中的表达，这将为比较研究提供基础，并可能有助于更好地理解NK基因在双语者多样化中的作用。