Collaborative Research: Convergent extension in a dynamically patterned epithelium

为了使胚胎从受精卵发育成成人，细胞必须以协调有序的方式伸长。像延伸身体轴线这样的基本过程，或者像在肾脏内部生长小管尖端这样的特殊过程，都需要伸长。这项研究将研究粉甲虫Tribolium在胚胎形成重复部分的整个过程中的伸长过程，这些重复部分被称为节段，构成其身体的前/后轴。尽管这显然是一个无缝的过程，但之前的研究表明，随着身体的伸长，分割速度会减慢，然后加快。与这种速率的切换相对应，细胞在伸长的早期和后期表现不同。这项工作将建立在这些初步观察的基础上，首先，仔细描述细胞团如何伸长的开关，其次，研究它是如何控制的。这种在逐渐伸长的身体轴线上组织伸长的不连续或切换是不寻常的，可能为伸长的新机制提供洞察。这项研究是一所第一类研究型大学和一所教学学院之间的合作努力。这项工作的一个主要影响是严格培训本科生进行跨学科研究，将伸长的计算机建模与甲虫胚胎的动手实验操作相结合。师范学院的本科生通过现场参观和广泛的在线互动与研究机构建立联系。这项工作背后的假设是，伸长的Tribolium胚胎代表着在胚胎伸长的早期和后期在两种收敛延伸机制之间转换的组织。基于初步数据，提出了一个在Tribolium中的伸长模型，其中前部细胞经历类似于果蝇胚胎延伸中的有序插入，而后部细胞在伸长的后部受到组织水平边界的指引，相对于相邻细胞以不那么有序的方式移动。这项工作将实验方法与计算模型结合起来，以检验这些假设。它结合了对突变胚胎的实时成像，这对不同的延长模型产生了不同的影响，并在计算机建模中提供了对Tribolium延长的机械见解。这项研究强调了Tribolium作为一种新的伸长模型。它将促进对独特的遗传和细胞机制的基本了解，这些机制有助于Tribolium逐渐延长的体轴中组织延长的不连续变化。计算模型和实验之间提出的动态反馈将提高对上游调控网络如何转化为塑造形态发生的离散细胞行为的理解。这项工作还可以与研究得很好的昆虫模型果蝇和脊椎动物进行比较，后者也是逐渐伸长的。这样的比较可以确定伸长的可变机制和保守机制，提供关于驱动形态发生的基本过程的进化的信息。此外，该项目将生成RNA序列数据、基因工具以及对整个社区有用的胚胎和组织伸长模型。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

For an embryo to develop from a fertilized egg into an adult, cells must elongate in a coordinated and orderly manner. Elongation is required for processes as basic as extending the body axis or as specific as growing the tips of tubules inside of kidneys. This research will examine the process of elongation in the flour beetle, Tribolium, throughout the time that the embryo is forming the repeated parts, called segments, which make up its anterior/posterior body axis. Although an apparently seamless process, previous work showed that segmentation slows down, then speeds up as the body elongates. Corresponding to this switch in rate, cells behave differently during early and late elongation stages. This work will build on those preliminary observations and, first, carefully describe the switch in how clusters of cells elongate and, second, investigate how it is controlled. This kind of discontinuity or switch in tissue elongation in a progressively elongating body axis is unusual and likely to provide insight into novel mechanisms of elongation. The research is a collaborative effort between a type 1 research university and a teaching college. A major impact of this work is to rigorously train undergraduates in interdisciplinary research, combining computer modeling of elongation with hands-on experimental manipulations of the beetle embryo. Undergraduates from the teaching college are linked to the research institution through both on-site visits and extensive online interactions. The hypothesis underlying this work is that the elongating Tribolium embryo represents a tissue that transitions between two mechanisms of convergent extension during early and late stages of embryo elongation. Based on preliminary data, a model of elongation in Tribolium is proposed in which anterior cells undergo ordered intercalation analogous to what is known in Drosophila embryo extension, while posterior cells move in a less orderly fashion relative to neighbors, directed by tissue-level boundaries in the elongating posterior. The work integrates experimental approaches with computational models to test these hypotheses. It combines live imaging of mutant embryos, that differentially affect the alternate models of elongation, with in silico modeling to provide mechanistic insights into Tribolium elongation. This research highlights Tribolium as a new model of elongation. It will develop a basic understanding of the unique genetic and cellular mechanisms that contribute to the discontinuous changes in tissue elongation in Tribolium's progressively elongating body axis. The proposed dynamic feedback between computational models and experiments will improve understanding of how upstream regulatory networks translate into discrete cell behaviors shaping morphogenesis. This work will also allow comparisons to the well-studied insect model, Drosophila, as well as vertebrates, which also elongate progressively. Such comparisons can identify variable versus conserved mechanisms of elongation, providing information about the evolution of fundamental processes that drive morphogenesis. Additionally, the project will generate RNA Seq data, genetic tools, and models of embryo and tissue elongation useful to the community at large.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.