Development and Evolution of Vertebrates, CNRS-UPMC-UMR 7150, Station Biologique, Roscoff, France.
J Anat. 2013 Jan;222(1):56-66. doi: 10.1111/j.1469-7580.2012.01552.x. Epub 2012 Aug 20.
In the past few years, the small spotted dogfish has become the primary model for analyses of early development in chondrichthyans. Its phylogenetic position makes it an ideal outgroup to reconstruct the ancestral gnathostome state by comparisons with established vertebrate model organisms. It is also a suitable model to address the molecular bases of lineage-specific diversifications such as the rise of extraembryonic tissues, as it is endowed with a distinct extraembryonic yolk sac and yolk duct ensuring exchanges between the embryo and a large undivided vitelline mass. Experimental or functional approaches such as cell marking or in ovo pharmacological treatments are emerging in this species, but recent analyses of early development in this species have primarily concentrated on molecular descriptions. These data show the dogfish embryo exhibits early polarities reflecting the dorso-ventral axis of amphibians and teleosts at early blastula stages and an atypical anamniote molecular pattern during gastrulation, independently of the presence of extraembryonic tissues. They also highlight unexpected relationships with amniotes, with a strikingly similar Nodal-dependent regional pattern in the extraembryonic endoderm. In this species, extraembryonic cell fates seem to be determined by differential cell behaviors, which lead to cell allocation in extraembryonic and embryonic tissues, rather than by cell regional identity. We suggest that this may exemplify an early evolutionary step in the rise of extraembryonic tissues, possibly related to quantitative differences in the signaling activities, which shape the early embryo. These results highlight the conservation across gnathostomes of a highly constrained core genetic program controlling early patterning. This conservation may be obscured in some lineages by taxa-specific diversifications such as specializations of extraembryonic nutritive tissues.
在过去的几年中，小斑狗鲨已成为分析软骨鱼类早期发育的主要模式生物。其系统发育位置使其成为通过与已建立的脊椎动物模式生物进行比较来重建祖先天那肛动物状态的理想外群。它也是解决谱系特异性多样化的分子基础的合适模型，例如额外胚外组织的出现，因为它具有独特的额外胚外卵黄囊和卵黄管，可确保胚胎与未分裂的大量卵黄质之间的交换。在这种物种中，实验或功能方法（例如细胞标记或胚胎内药物处理）正在出现，但最近对该物种早期发育的分析主要集中在分子描述上。这些数据表明，狗鲨胚胎在早期囊胚阶段表现出反映两栖动物和硬骨鱼背腹轴的早期极性，并且在原肠胚形成过程中表现出非典型的无羊膜动物分子模式，而与额外胚外组织的存在无关。它们还突出了与羊膜动物的意外关系，在额外胚外内胚层中具有惊人相似的 Nodal 依赖性区域模式。在该物种中，额外胚外细胞命运似乎是由差异细胞行为决定的，这些行为导致额外胚外和胚胎组织中的细胞分配，而不是由细胞区域身份决定的。我们认为，这可能代表了额外胚外组织出现的早期进化步骤，可能与塑造早期胚胎的信号转导活性的定量差异有关。这些结果突出了控制早期模式形成的高度约束的核心遗传程序在颌类动物中的保守性。这种保守性可能会被一些谱系特有的多样化所掩盖，例如额外胚外营养组织的特化。
