Data from: Notch and Nodal control expression of a forkhead factor in the specification network of a multipotent progenitor population in sea urchin

Indirect development, where embryogenesis gives rise to a larval form, requires that some cells retain developmental potency until they contribute to the different tissues in the adult, including the germ line, in a later, post-embryonic phase. In sea urchins, the coelomic pouches are the major contributor to the adult but how coelomic pouch cells (CPCs) are specified during embryogenesis is unknown. We here identify the key signaling inputs into the CPC specification network and show the forkhead factor foxY is the first transcription factor specifically expressed in CPC progenitors. Through dissection of its cis-regulatory apparatus we determine that the foxY expression pattern is the result of two signaling inputs: First, Delta/Notch signaling activates foxY in CPC progenitors and, second, Nodal signaling restricts its expression to the left side, where the adult rudiment will form, through direct repression by the Nodal target pitx2. A third signal, Hedgehog, is required for coelomic pouch morphogenesis and institution of laterality but does not directly affect foxY transcription. Knockdown of foxY results in failure to form coelomic pouches and disrupts expression of virtually all transcription factors known to be expressed in this cell type. Our experiments place foxY at the top of the regulatory hierarchy underlying specification of a cell type maintaining developmental potency.间接发育（Indirect development）指胚胎发生过程中会生成幼虫形态，该发育模式要求部分细胞维持发育潜能，直至后续胚后阶段，参与成体个体包括生殖系在内的各类组织的形成。在海胆（sea urchins）中，体腔囊（coelomic pouches）是成体结构的主要贡献来源，但胚胎发生过程中体腔囊细胞（coelomic pouch cells, CPCs）的特化机制迄今仍不明晰。本研究明确了调控体腔囊细胞特化网络的关键信号输入，并证实叉头框转录因子foxY是首个在体腔囊细胞祖细胞中特异性表达的转录因子。通过剖析其顺式调控元件系统（cis-regulatory apparatus），我们发现foxY的表达模式由两类信号输入共同调控：其一，Delta/Notch信号通路在体腔囊细胞祖细胞中激活foxY的转录；其二，Nodal信号通路通过其下游靶基因pitx2的直接抑制作用，将foxY的表达范围限定在成体原基（adult rudiment）即将形成的左侧区域。第三种信号分子Hedgehog信号通路参与体腔囊的形态发生与左右不对称性的建立，但并不直接调控foxY的转录。敲低foxY基因会导致体腔囊无法正常形成，同时几乎所有已知在该细胞类型中表达的转录因子的表达均受到干扰。本研究实验结果证实，foxY位于维持发育潜能的细胞类型特化调控层级的顶端。