Center for Integrative Genomics and Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA.
BMC Biol. 2010 Jan 18;8:4. doi: 10.1186/1741-7007-8-4.
LIM homeobox (Lhx) transcription factors are unique to the animal lineage and have patterning roles during embryonic development in flies, nematodes and vertebrates, with a conserved role in specifying neuronal identity. Though genes of this family have been reported in a sponge and a cnidarian, the expression patterns and functions of the Lhx family during development in non-bilaterian phyla are not known.
We identified Lhx genes in two cnidarians and a placozoan and report the expression of Lhx genes during embryonic development in Nematostella and the demosponge Amphimedon. Members of the six major LIM homeobox subfamilies are represented in the genomes of the starlet sea anemone, Nematostella vectensis, and the placozoan Trichoplax adhaerens. The hydrozoan cnidarian, Hydra magnipapillata, has retained four of the six Lhx subfamilies, but apparently lost two others. Only three subfamilies are represented in the haplosclerid demosponge Amphimedon queenslandica. A tandem cluster of three Lhx genes of different subfamilies and a gene containing two LIM domains in the genome of T. adhaerens (an animal without any neurons) indicates that Lhx subfamilies were generated by tandem duplication. This tandem cluster in Trichoplax is likely a remnant of the original chromosomal context in which Lhx subfamilies first appeared. Three of the six Trichoplax Lhx genes are expressed in animals in laboratory culture, as are all Lhx genes in Hydra. Expression patterns of Nematostella Lhx genes correlate with neural territories in larval and juvenile polyp stages. In the aneural demosponge, A. queenslandica, the three Lhx genes are expressed widely during development, including in cells that are associated with the larval photosensory ring.
The Lhx family expanded and diversified early in animal evolution, with all six subfamilies already diverged prior to the cnidarian-placozoan-bilaterian last common ancestor. In Nematostella, Lhx gene expression is correlated with neural territories in larval and juvenile polyp stages. This pattern is consistent with a possible role in patterning the Nematostella nervous system. We propose a scenario in which Lhx genes play a homologous role in neural patterning across eumetazoans.
LIM 同源盒（Lhx）转录因子是动物谱系所特有的，在果蝇、线虫和脊椎动物的胚胎发育中具有模式形成作用，在指定神经元身份方面具有保守作用。尽管在海绵动物和刺胞动物中已经报道了该家族的基因，但在非双侧动物门中，Lhx 家族在发育过程中的表达模式和功能尚不清楚。
我们在两种刺胞动物和一种扁盘动物中鉴定了 Lhx 基因，并报告了在 Nematostella 和 demosponge Amphimedon 胚胎发育过程中 Lhx 基因的表达。在 starlet 海葵 Nematostella vectensis 和扁盘动物 Trichoplax adhaerens 的基因组中，存在六个主要 LIM 同源盒亚家族的成员。水螅刺胞动物 Hydra magnipapillata 保留了六个 Lhx 亚家族中的四个，但显然失去了另外两个。haplosclerid 多孔动物 Amphimedon queenslandica 只代表了三个亚家族。在 T. adhaerens（一种没有任何神经元的动物）的基因组中，存在一个不同亚家族的三个 Lhx 基因的串联簇和一个含有两个 LIM 结构域的基因，表明 Lhx 亚家族是通过串联重复产生的。在 Trichoplax 中，这个串联簇可能是 Lhx 亚家族首次出现时原始染色体结构的残余。在实验室培养的动物中，六个 Trichoplax Lhx 基因中有三个表达，而 Hydra 中的所有 Lhx 基因都表达。Nematostella Lhx 基因的表达模式与幼虫和幼年息肉阶段的神经区域相关。在无神经的多孔动物 A. queenslandica 中，三个 Lhx 基因在发育过程中广泛表达，包括与幼虫光感觉环相关的细胞中表达。
Lhx 家族在动物进化的早期就已经扩张和多样化，在刺胞动物-扁盘动物-双侧动物的最后共同祖先出现之前，所有六个亚家族已经分化。在 Nematostella 中，Lhx 基因的表达与幼虫和幼年息肉阶段的神经区域相关。这种模式与在 Nematostella 神经系统中进行模式形成的可能作用一致。我们提出了一个假设，即 Lhx 基因在后生动物的神经模式形成中发挥同源作用。
Zotero 插件
