Borisenko Ilya, Adamski Marcin, Ereskovsky Alexander, Adamska Maja
Department of Embryology, Faculty of Biology, Saint-Petersburg State University, Saint-Petersburg, Russia.
Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway.
BMC Evol Biol. 2016 Jun 10;16(1):123. doi: 10.1186/s12862-016-0700-6.
Wnt proteins are secreted signalling molecules found in all animal phyla. In bilaterian animals, including humans, Wnt proteins play key roles in development, maintenance of homeostasis and regeneration. While Wnt gene repertoires and roles are strongly conserved between cnidarians and bilaterians, Wnt genes from basal metazoans (sponges, ctenophores, placozoans) are difficult or impossible to assign to the bilaterian + cnidarian orthologous groups. Moreover, dramatic differences in Wnt numbers among basal metazoan exist, with only three present in the genome of Amphimedon queenslandica, a demosponge, and 21 in the genome of Sycon ciliatum, a calcisponge. To gain insight into the ancestral Wnt repertoire and function, we have chosen to investigate Wnt genes in Halisarca dujardini, a demosponge with relatively well described development and regeneration, and a very distant phylogenetic relationship to Amphimedon.
Here we describe generation of a eukaryotic contamination-free transcriptome of Halisarca dujardini, and analysis of Wnt genes repertoire and expression in this species. We have identified ten Wnt genes, with only one orthologous to Amphimedon Wnt, and six appearing to be a result of a lineage specific expansion. Expression analysis carried out by in situ hybridization of adults and larvae revealed that two Halisarca Wnts are expressed in nested domains in the posterior half of the larvae, and six along the adult body axis, with two specific to the osculum. Strikingly, expression of one of the Wnt genes was elevated in the region undergoing regeneration.
Our results demonstrated that the three Poriferan lineages (Demospongiae, Calcarea and Homoloscleromorpha) are characterized by highly diverse Wnt gene repertoires which do not display higher similarity to each other than they do to the non-sponge (i.e. ctenophore, cnidarian and bilaterian) repertoires. This is in striking contrast to the uniform Wnt repertoires in Cnidarians and Bilaterians, suggesting that the Wnt family composition became "fixed" only in the last common ancestor of Cnidarians and Bilaterians. In contrast, expression of Wnt genes in the apical region of sponge adults and the posterior region of sponge larvae suggests conservation of the Wnt role in axial patterning across the animal kingdom.
Wnt蛋白是在所有动物门类中都能找到的分泌型信号分子。在包括人类在内的两侧对称动物中，Wnt蛋白在发育、体内平衡维持和再生过程中发挥关键作用。虽然刺胞动物和两侧对称动物之间的Wnt基因库和功能高度保守，但基础后生动物（海绵动物、栉水母、扁盘动物）的Wnt基因很难或无法归入两侧对称动物+刺胞动物的直系同源组。此外，基础后生动物的Wnt数量存在显著差异，在一种寻常海绵纲的昆士兰扁海绵基因组中只有3个Wnt基因，而在一种钙质海绵的纤毛偕老同穴基因组中有21个。为了深入了解Wnt基因库的祖先组成和功能，我们选择研究杜氏哈氏海绵中的Wnt基因，这是一种寻常海绵纲动物，其发育和再生过程已有相对充分的描述，并且与昆士兰扁海绵的系统发育关系非常远。
在此我们描述了杜氏哈氏海绵无真核生物污染转录组的构建，以及该物种中Wnt基因库和表达情况的分析。我们鉴定出了10个Wnt基因，其中只有1个与昆士兰扁海绵的Wnt直系同源，另外6个似乎是谱系特异性扩增的结果。通过对成体和幼虫进行原位杂交进行的表达分析表明，两个杜氏哈氏海绵Wnt基因在幼虫后半部的嵌套区域表达，6个沿成体身体轴表达，其中2个在出水口处特异性表达。引人注目的是，其中一个Wnt基因在再生区域的表达升高。
我们的结果表明，三个海绵动物谱系（寻常海绵纲、钙质海绵纲和同骨海绵纲）的特点是Wnt基因库高度多样，它们彼此之间的相似性并不高于它们与非海绵动物（即栉水母、刺胞动物和两侧对称动物）基因库的相似性。这与刺胞动物和两侧对称动物中统一的Wnt基因库形成了鲜明对比，表明Wnt家族组成仅在刺胞动物和两侧对称动物的最后一个共同祖先中才变得“固定”。相比之下，Wnt基因在海绵成体顶端区域和海绵幼虫后部区域的表达表明，Wnt在整个动物界轴向模式形成中的作用具有保守性。
Zotero 插件