Department of Ecology and Evolutionary Biology, UCLA, 621 Young Drive South, Los Angeles, CA 90095-1606, USA.
Evol Dev. 2010 Jul-Aug;12(4):404-15. doi: 10.1111/j.1525-142X.2010.00427.x.
In Cnidaria, the medusae of Scyphozoa and its sister-group Cubozoa uniquely possess rhopalia at their bell margin. These sensory centers coordinate behavior and development. We used fluorescent in situ hybridization and confocal microscopy to examine mRNA expression patterns in Aurelia sp.1 (Cnidaria, Scyphozoa) during early medusa formation, while simultaneously visualizing the developing nervous system by immunofluorescence. The genes investigated include AurOtx1, and the POU genes, AurPit1, and AurBrn3, homologs of genes known to function in cephalar neural organization and sensory cell differentiation across Bilateria. Our results show that AurOtx1 expression defines the major part of the oral neuroectodermal domain of the rhopalium, within which distinct populations of AurBrn3- and AurPit1-expressing sensory cells develop. Thus, despite the unique attributes of rhopalial evolution, we suggest that the rhopalial nervous system of scyphozoan medusae involves similar patterns of differential expression of genes that function in bilaterian cephalic structure and neuroendocrine system development. We propose that rhopalia evolved from preexisting sensory structures that developed distinct populations of sensory cells differentially expressing POU genes within Otx oral-neuroectodermal domains. This implies some commonality of developmental genetic functions involving these genes in the still poorly constrained common ancestor of bilaterians and cnidarians.
在刺胞动物门中，水母纲的水螅体及其姐妹类群立方水母纲在其钟形边缘独特地拥有触须。这些感觉中心协调行为和发育。我们使用荧光原位杂交和共聚焦显微镜来研究 Aurelia sp.1（刺胞动物门、水母纲）在早期水母形成过程中的 mRNA 表达模式，同时通过免疫荧光观察正在发育的神经系统。研究的基因包括 AurOtx1，以及 POU 基因 AurPit1 和 AurBrn3，这些基因在两侧对称动物的头区神经组织和感觉细胞分化中具有功能。我们的结果表明，AurOtx1 的表达定义了触须的口腔神经外胚层域的主要部分，在该部分中，AurBrn3 和 AurPit1 表达的感觉细胞群体发育。因此，尽管触须的进化具有独特的特征，但我们认为，水母纲水母的触须神经系统涉及到在两侧对称动物的头区结构和神经内分泌系统发育中具有功能的基因的相似的差异表达模式。我们提出，触须是从具有不同感觉细胞群体的原始感觉结构进化而来的，这些感觉细胞在 Otx 口腔神经外胚层域中差异表达 POU 基因。这意味着在两侧对称动物和刺胞动物的尚未充分约束的共同祖先中，涉及这些基因的发育遗传功能具有一定的共性。
