RUI: Developmental Biology of Turtle Shell Formation

斯科特·F·吉尔伯特提案#iOS-0748508 Rui：龟甲形成的发育生物学龟甲是由两个主要部分组成的进化新奇事物，上甲壳和下盘甲层。“使乌龟成为乌龟”的是肋骨进入背部皮肤的真皮，而不是向下迁移形成肋骨笼。这项研究将使用细胞移植和基因标记技术来识别肋骨分泌的分子，这些分子会导致皮肤变成骨骼。我们认为肋骨分泌的蛋白质称为骨形态发生蛋白(BMPs)，骨形成的时机由这些BMPs和真皮中存在的BMPs抑制物之间的相互作用来调节。形成胎盘的细胞起源于一种名为躯干神经脊的胚胎结构。在其他现存物种中，还没有发现躯干神经脊能长出骨头。然而，颅神经脊通常会形成面部骨骼。如果主干神经脊细胞失去了HOX基因的表达，它们同时获得了形成骨骼的能力。HOX基因的表达似乎抑制了神经脊细胞成骨的能力。因此，这个项目的另一个主要目标是检验这样一个假设，即在海龟胚胎中，一群神经脊细胞产生得较晚，失去了其HOX表达，并迁移形成了胎盘骨骼。如果这些假设得到证实，这项研究将更深入地解释海龟是如何获得外壳这一“古老”问题的。它将为化石记录中一种新的解剖结构如何如此快速地进化的问题提供一个解决方案，也将提供一个易于理解的例子，说明进化是如何工作的，以制造新的结构。它将由本科生完成，应该让他们熟悉进化发育遗传学的基本技术。

Scott F. Gilbert Proposal #IOS-0748508 RUI: Developmental biology of turtle shell formationThe turtle shell is an evolutionary novelty composed of two main parts, the upper carapace and the lower plastron. What "makes a turtle a turtle" is the migration of the ribs into the dermis of the back skin rather than their migrating downward to form a rib cage. This study will use cell transplantation and gene labeling techniques to identify the molecules secreted by the ribs which cause the skin to turn into bone. We expect that the ribs are secreting proteins called Bone Morphogenetic Proteins (BMPs) and that the timing of bone formation is regulated by the interplay between these BMPs and inhibitors of BMPs that exist in the dermis. Cells forming the plastron originate in an embryonic structure called the trunk neural crest. The trunk neural crest has not been seen to produce bones on any other extant species. The cranial neural crest, however, usually makes facial bones. If trunk neural crest cells lose the expression of Hox genes, they simultaneously gain the ability to form skeleton. Hox gene expression appears to inhibit the ability of neural crest cells to form bone. So another major objective of this project is to test the hypothesis that in turtle embryos, a population of neural crest cells is produced late, loses its Hox expression, and migrates to form the plastron bones. If these hypotheses are validated, this research goes far in explaining the "age-old" question of how the turtle got its shell. It would provide a solution to the question of how a novel anatomical structure can evolve so quickly in the fossil record, and it would also provide a readily understood example how evolution works to make new structures. It will be done by undergraduates and should acquaint them with the basic techniques of evolutionary developmental genetics.