Data on nonbilaterian animals (sponges, cnidarians, and ctenophores) have suggested that Antennapedia (ANTP) class homeobox genes played a crucial role in the early diversification of animal body plans. Estimates of ancestral gene diversity within this important class of developmental regulators have been mostly based on recent analyses of the complete genome of a demosponge species, leading to the proposal that all ANTP families found in nonsponges animals (eumetazoans) derived from an ancestral "proto-NK" six-gene cluster. However, a single sponge species cannot reveal ancestral metazoan traits, in particular because lineage-specific gene duplications or losses are likely to have occurred during the long history of the Porifera. We thus looked for ANTP genes by degenerate polymerase chain reaction search in five species belonging to the Homoscleromorpha, a sponge lineage recently phylogenetically classified outside demosponges and characterized by unique histological features. We identified new genes of the ANTP class called HomoNK. Our phylogenetic analyses placed HomoNK (without significant support) close to the NK6 and NK7 families of cnidarian and bilaterian ANTP genes and did not recover the monophyly of the proposed "proto-NK" cluster. Our expression analyses of the HomoNK gene OlobNK in adult Oscarella lobularis showed that this gene is a strict marker of choanocytes, the most typical sponge cell type characterized by an apical flagellum surrounded by a collar of microvilli. These results are discussed in the light of the predominant neurosensory expression of NK6 and NK7 genes in bilaterians and of the recent proposal that choanocytes could be the sponge homologs of sensory cells.

中文翻译：

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NK同源盒基因在同硬质海绵中具有鼻突细胞特异性表达。

关于非双侧动物（海绵、刺胞动物和栉水母）的数据表明触角足 (ANTP) 类同源盒基因在动物身体计划的早期多样化中发挥了关键作用。对这一重要发育调节因子类别中祖先基因多样性的估计主要基于最近对一种海绵物种的完整基因组的分析，导致在非海绵动物（真后生动物）中发现的所有 ANTP 家族都来自祖先的“原始”。 NK”六基因簇。然而，单一的海绵物种不能揭示祖先的后生动物特征，特别是因为在 Porifera 的悠久历史中可能发生了谱系特异性基因重复或丢失。因此，我们通过简并聚合酶链反应搜索在属于 Homoscleromorpha 的五个物种中寻找 ANTP 基因，Homoscleromorpha 是一种海绵谱系，最近在系统发育学上分类为非海绵体，并具有独特的组织学特征。我们鉴定了名为 HomoNK 的 ANTP 类的新基因。我们的系统发育分析将 HomoNK（没有显着支持）置于接近刺胞动物和双边 ANTP 基因的 NK6 和 NK7 家族，并且没有恢复提议的“原始 NK”簇的单系。我们对成年小叶奥斯卡拉 (Oscarella lobularis) 中的 HomoNK 基因 OlobNK 的表达分析表明，该基因是脊骨细胞的严格标记，这是最典型的海绵细胞类型，其特征是顶端鞭毛被微绒毛圈包围。