Notochord Differentiation in the Ascidian Ciona Intestinalis

这项研究的总体目标是利用海鞘动物广泛的谱系图谱和简单的胚胎发育，来描述脊索分化的调控途径。Ciona是一种简单的脊索动物，拥有很小的基因组(在大小上与线虫和果蝇的基因组相当)。这种简单性表明，所有脊索动物的共同特征，如脊索，可能由直接适用于脊椎动物系统的“精简”路径来指定。一个详细的脊索谱系已经被描述；在仅仅9次胚胎分裂之后，完全分化的脊索只有40个细胞(大约在受精后10-12小时)。莱文博士认为，Ciona已经做好了分子分析的准备，特别是在阐明发育途径方面。该项目的大部分工作将致力于建立卵裂球解聚试验，从而在详细谱系的背景下定义潜在有趣的调节蛋白的胚胎活动。这项测试将涉及向早期胚胎注射适当的mRNAs。在解聚分期胚胎后，将培养单独的、已定义的卵裂球，从而允许评估自主与非自主的调节相互作用。特别工作将集中在其他系统中涉及脊索发育的三种调控蛋白，包括Axis/Pintallavis、Floating Head/Xnot和brychyury/T。

The overall goal of the proposed study is to exploit the extensive lineage maps and simple embryonic development of the Ascidian, Ciona intestinalis, to characterize the regulatory pathway underlying notochord differentiation. Ciona is a simple chordate that possesses a small genome (comparable in size to the genomes of C. elegans and Drosophila). This simplicity suggests that common features of all chordates, such as the notochord, might be specified by "stripped down" pathways that are directly applicable to vertebrate systems. A detailed notochord lineage has been characterized; after just nine embryonic cleavages the fully differentiated notochord contains only forty cells (about 10-12 hours after fertilization). Dr. Levine believes that Ciona is well poised for molecular analyses, particularly the elucidation of developmental pathways. Much of the project's effort will be devoted to the establishment of a blastomere disaggregation assay, whereby the embryonic activities of potentially interesting regulatory proteins are defined within the context of detailed lineages. This assay will involve the microinjection of early embryos with appropriate mRNAs. Individual, defined blastomeres will be cultured after disaggregating staged embryos, thereby permitting an assessment of autonomous versus nonautonomous regulatory interactions. Special efforts will focus on three regulatory proteins that have been implicated in notochord development in other systems, including axial/pintallavis, floating head/Xnot, and brychyury/T.