RoL: Evolution of multicellular individuality

人类是由许多细胞组成的，但数十亿年来，地球上的生命都是由单细胞生物组成的，它们的身体是一个单细胞。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个尚未解决的主要问题。回答这个问题将有助于科学家了解地球生命的一个更熟悉的特征，即其层次结构。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作用的组织层次。在进化过程中，每一个层次都是从一组较低层次的单位中产生的。细胞群是如何进化成一个新的多细胞个体的，这是这个提议所要解决的基本问题。研究人员通过测试进化转型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，即应激反应有助于细胞群的起源以及这些细胞群中出现的特殊类型细胞的起源。他们将在volvocine绿色藻类中测试这一假设，volvocine藻类是一种生物谱系，从单细胞到多细胞个体跨越层次水平。验证这一假设将有助于科学家更好地了解人类疾病。例如，癌症在人体中的演变是研究中研究的过程的逆转。癌细胞已经停止与多细胞组中的其他细胞合作，并恢复了在单细胞水平上进化的能力。换句话说，癌症是一种疾病，其中个体性从多细胞群体的水平回到细胞水平。该项目将培训本科生和研究生，还将制定课程，更好地向中学生教授与复杂生物体进化有关的概念。拟议的工作将通过开发高通量表型分析和细胞群成像的方法来提供社会效益，这些方法可能有助于医学诊断。自然选择的进化需要个体水平上适应性的遗传变异。在个体的进化转变过程中，例如多细胞个体的进化，适应性必须从细胞水平重新映射到多细胞个体的新水平。以前的研究表明，压力反应可以是在向多细胞个体过渡期间重组适应性的主要动力。在这项工作中，研究了多细胞个体性的两个基本标准：群体不可分割性和体细胞劳动分工。研究人员已经表明，这两个个性标准对具有中等复杂性和个性水平的物种的压力做出了反应。研究人员还将检查表型和潜在的遗传反应，以影响群体形成和新细胞类型的起源。应用系统发育方法重建可塑性体细胞的进化历史，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，专性细胞分化是否在实验室群体中进化。最后，研究人员将通过利用基因表达分析和基因敲除的实验来确定这些应激反应的遗传基础，以了解基因选择在多细胞起源中所起的作用。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值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.