RUI: Developmental Biology of Turtle Shell Formation

斯科特·F吉尔伯特提案#IOS-0748508 RUI：龟壳形成的发育生物学龟壳是一种进化上的新奇，由两个主要部分组成，即上甲壳和下腹甲。“使海龟成为海龟”的是肋骨迁移到背部皮肤的真皮中，而不是它们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鉴定肋骨分泌的导致皮肤变成骨骼的分子。我们预计肋骨分泌称为骨形态发生蛋白（BMPs）的蛋白质，并且骨形成的时间由这些BMPs和存在于真皮中的BMPs抑制剂之间的相互作用调节。形成胸甲的细胞起源于一种叫做躯干神经嵴的胚胎结构。在任何其他现存的物种上都没有发现躯干神经嵴产生骨骼。然而，颅神经嵴通常构成面骨。如果躯干神经嵴细胞失去了Hox基因的表达，它们同时获得了形成骨骼的能力。Hox基因表达似乎抑制神经嵴细胞形成骨骼的能力。因此，该项目的另一个主要目标是测试一个假设，即在海龟胚胎中，神经嵴细胞的群体产生较晚，失去了Hox表达，并迁移形成了腹侧骨。如果这些假设得到证实，这项研究就可以解释海龟是如何得到它的壳的这个“古老”问题。它将为一个新的解剖结构如何在化石记录中如此迅速地进化的问题提供一个解决方案，它也将提供一个容易理解的例子，说明进化是如何产生新结构的。 它将由本科生完成，并应使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.