RoL: Evolution of multicellular individuality

人类是由许多细胞组成的，但在数十亿年的时间里，地球上的生命是由单细胞有机体组成的，这些生物体的身体就是一个细胞。单细胞生物为什么以及如何进化成多细胞个体是生物学中一大悬而未决的问题。回答这个问题将有助于科学家了解地球上生命最熟悉的特征之一，那就是它的等级结构。基因存在于染色体中，染色体存在于细胞中，细胞存在于多细胞生物中，多细胞生物存在于复杂的社会中。生命层次中的每一个层次都代表着自然选择可能发挥作用的一个组织层次。在进化过程中，这些级别中的每一个都是从一组较低级别的单位中产生的。一组细胞如何进化成一个新的多细胞个体是这一提议所要解决的基本问题。研究人员通过测试进化转变的一般理论来解决这个问题。研究人员提出了一个新的假设，即应激反应在细胞组的起源以及在这些组中出现的特殊类型的细胞的起源中起着重要作用。他们将在Volvocine绿藻中测试这一假设，Volvocine绿藻是一种跨越从单细胞到多细胞个体的层次结构的有机体谱系。验证这一假说将有助于科学家更好地了解人类疾病。例如，癌症在人体内的进化是研究中所研究的过程的逆转。癌细胞停止了与多细胞组中其他细胞的合作，并重新获得了在单细胞水平上进化的能力。换句话说，癌症是一种疾病，在这种疾病中，个体从多细胞群体的水平回到细胞水平。该项目将对本科生和研究生进行培训，并将开发课程，向中学生更好地教授与复杂有机体进化有关的概念。这项拟议的工作将通过开发高通量的细胞组表型和成像方法来提供社会效益，这可能有助于医学诊断。自然选择的进化需要个体水平上的适应性遗传变异。在个体的进化转变过程中，例如多细胞个体的进化，适应度必须从细胞水平重新映射到多细胞个体的新水平。先前的研究表明，在向多细胞个体转变的过程中，压力反应可能是健康重组的主要推动力。这项工作研究了多细胞个体的两个基本标准：群体的不可分离性和体细胞的分工。研究人员已经证明，这两个个性标准在中等复杂性和个性水平的物种中对压力做出反应。研究人员还将研究影响群体形成和新细胞类型起源的压力的表型和潜在遗传反应。应用系统发育学方法重建可塑性体细胞的进化史，将使研究人员能够确定体细胞的可塑性发育是在细胞分化所需的关键基因起源之前还是之后。此外，他们将使用实验进化来测试在他们的模型预测的条件下，实验室群体中的专性细胞分化是否进化。最后，研究人员将通过实验确定这些应激反应的遗传基础，利用基因表达分析和基因敲除来了解基因共选在多细胞起源中所起的作用。这一奖项反映了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。

Humans are made up of many cells, but for billions of years, life on earth consisted of unicellular organisms whose bodies were a single cell. Why and how unicellular organisms evolved into multicellular individuals is a major unsolved question in biology. Answering this question will help scientists understand one of the more familiar features of life on earth, which is its hierarchical structure. Genes exist in chromosomes, chromosomes exist in cells, cells exist in multicellular organisms, and multicellular organisms exist in complex societies. Each of these levels in the hierarchy of life represents a level of organization on which natural selection may act. During evolution, each one of these levels has arisen from a group of lower-level units. How did groups of cells evolve into a new multicellular individual is the basic question addressed by this proposal. The researchers approach this question by testing a general theory of evolutionary transitions. The researchers present a novel hypothesis that stress responses are instrumental in the origin of cell groups and in the origin of specialized types of cells that arise in these groups. They will test this hypothesis in the volvocine green algae, a lineage of organisms that span hierarchical levels from single cells to multicellular individuals. Testing this hypothesis will help the scientists to better understand human disease. For example, the evolution of cancer in a human body is the reversal of the processes studied in the research. A cancerous cell has stopped cooperating with other cells in the multicellular group and has regained its capacity to evolve at the single cell level. In other words, cancer is a disease in which individuality changes from the level of the multicellular group back to the level of the cell. The project will result in training of undergraduate and graduate students and also will develop curricula to better teach concepts related to the evolution of complex organisms to middle school students. The proposed work will provide societal benefits through the development of methods of high-throughput phenotyping and imaging of cell groups that may help with medical diagnosis.Evolution by natural selection requires heritable variation in fitness at the individual level. During evolutionary transitions in individuality, such as the evolution of multicellular individuals, fitness must be remapped from the cell level to the new level of the multicellular individual. Previous work has shown that stress responses can be a major impetus for the reorganization of fitness during the transition to multicellular individuality. There are two basic criteria of multicellular individuality investigated in the work: group inseparability and somatic cell division of labor. The researchers have shown that these two individuality criteria respond to stress in species with intermediate complexity and levels of individuality. The researchers also will examine the phenotypic and underlying genetic responses to stress that affect group formation and the origin of new cell types. The application of phylogenetic methods to reconstruct the evolutionary history of plastic somatic cells will allow the researchers to determine whether the plastic development of somatic cells preceded or followed the origin of key genes necessary for cellular differentiation. Furthermore, they will use experimental evolution to test whether obligate cellular differentiation evolves in lab populations under the conditions predicted by their models. Finally , the researchers will identify the genetic basis for these stress responses via experiments utilizing gene expression analyses and gene knockouts to understand the role played by gene co-option in the origin of multicellularity.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.