RUI: Investigating tardigrade development to unravel the evolution of animal body plans

传统上很难研究动物身体的进化，因为它们的起源是在一个化石极其稀少的古代时期。发育生物学和基因组学技术的最新进展现在提供了另一种方法来重建产生动物身体计划的进化步骤。对水熊(迟发性)发育的研究可能对研究身体平面进化的两个重要主题--分割和微型化--特别有用。分割是动物的一个共同特征。这个项目将研究迟缓发育，以重建现代动物中存在的分段机制起源所依据的进化步骤。小型化已经在几个动物谱系中独立进化，包括迟滞谱系，但人们对小型化的发育基础知之甚少。本项目旨在确定紧凑型迟滞体表的发育起源，并确定小型化对控制迟滞肠道发育的发育机制的影响。这项工作的结果可能揭示支持微型化的一般发展原则。该项目将为11名本科生提供培训。一个关键的目标是为来自代表性不足群体的学生提供生物学方面的培训。对迟滞的研究也为促进公共科学宣传提供了一个极好的机会。该项目利用研究活动来提高佛罗里达州杰克逊维尔的公众科学素养。最近对HOX基因的一项研究表明，迟滞的身体计划是由躯干中部节段的丢失进化而来的。这一结果引发了几个问题。(1)躯干中段缺失的发育基础是什么？在许多双侧动物中，在躯干中段发育之前，典型的Wnt信号通路和该通路的抑制剂之间的拮抗相互作用指定了体轴的前部和后部。这项工作将测试这种机制是否如预测的那样指定迟滞的整个体轴，如果迟滞只是失去了生长躯干中部区域的能力。(2)迟滞动物中的其余节段是否与节肢动物中已发现的节段机制相同？为了解决这个问题，实验将测试节肢动物中指定节段边界的节段极性基因网络是否也指定迟滞中的节段边界。这项研究的结果将阐明在泛节肢动物系统发育中，这个网络在指定节段边界方面发挥了什么作用。(3)躯干中部节段的缺失对肠道(体轴的未分段部分)有何影响？为了解决这个问题，这项工作将确定在其他双边动物发育过程中形成肠道模式的机制在迟滞中的差异程度。实验将利用RNA干扰来干扰基因功能，并利用原位杂交来表征延缓的样例Hypsibius发育过程中的基因表达模式。这项研究将提供对细分和二次简化演变的发展基础的洞察。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。

The evolution of animal body plans has traditionally been difficult to study because their origins lie in an ancient period for which fossils are extremely rare. Recent advances in developmental biology and genomics techniques now provide alternative methods to reconstruct the evolutionary steps that gave rise to animal body plans. Studies of water bear (Tardigrade) development may be especially informative for investigating two important themes of body plan evolution—segmentation and miniaturization. Segmentation is a common characteristic of animals. This project will investigate tardigrade development in order to reconstruct the evolutionary steps that underlie the origins of the segmentation mechanisms that are present in modern animals. Miniaturization has evolved independently in several animal lineages, including in the tardigrade lineage, but very little is known about the developmental underpinnings of miniaturization. This project aims to identify the developmental origins of the compact tardigrade body plan, and to determine the consequences of miniaturization on the developmental mechanisms that control development of the tardigrade gut. Results of this work may reveal general developmental principles that underlie miniaturization. This project will provide training to eleven undergraduate students. A key aim is to provide training to students from underrepresented groups in biology. Research on tardigrades also provides an excellent opportunity to foster public science outreach. This project uses research activities to enhance public science literacy in Jacksonville, FL. A recent study of Hox genes revealed that the tardigrade body plan evolved by the loss of mid-trunk segments. This result raises several questions. (1) What is the developmental basis for the loss of mid-trunk segments? In many bilaterians, before growth of a mid-trunk region, antagonistic interactions between the canonical Wnt signaling pathway and inhibitors of this pathway specify anterior and posterior regions of the body axis. This work will test whether this mechanism specifies the entire body axis of a tardigrade, as predicted if tardigrades simply lost the ability to grow a mid-trunk region. (2) Do the remaining segments in tardigrades develop by the same segmentation mechanisms that have been identified in arthropods? To address this question, experiments will test whether the segment polarity gene network that specifies segment boundaries in arthropods also specifies segment boundaries in tardigrades. Results of this study will illuminate where in panarthropod phylogeny this network evolved a role in specifying segment boundaries. (3) What was the impact of the loss of mid-trunk segments on the gut, an unsegmented part of the body axis? To address this question, this work will determine the extent to which mechanisms that pattern the gut during development in other bilaterians have diverged in tardigrades. Experiments will utilize RNA interference to disrupt gene function and situ hybridization to characterize gene expression patterns during development of the tardigrade Hypsibius exemplaris. This research will provide insight into developmental underpinnings of the evolution of segmentation and secondary simplification.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.