Collaborative Proposal: RUI: Obliquely striated muscle: A soft-bodied invertebrate solution for tuning length-force properties to meet functional demands?

三种类型的肌肉细胞（平滑肌和横纹肌）是众所周知的任何介绍性文本，但很少有生物学家熟悉斜横纹肌。 斜横纹肌细胞在软体动物中很常见，至少存在于17个门的成员中，但斜横纹对这种重要肌肉类型的功能和性能的影响尚不清楚。 几十年来，人们一直认为斜条纹允许在非常大的肌肉长度范围内输出相对较高的力量。 然而，最近的工作表明，斜横纹肌的收缩特性和工作长度范围是非常不同的，即使在同一个体动物的肌肉。 该项目将研究不同动物斜横纹肌的收缩特性和工作长度范围。 这项研究可能揭示肌肉结构和功能的基本新原理，否则这些原理将仍然模糊不清，并为这种纤维类型的功能多样性和进化提供新的见解。 该项目将为本科生，特别是第一代大学生和来自代表性不足背景的学生提供机会，以获得生理学，生物力学和科学传播方面的经验。 该项目将与缅因州国家水族馆探索中心合作，为K-12学生和公众开发项目。 该项目还将通过与科学与教学学士学位教育（UNC-BEST）计划的合作影响中学教育，该计划为本科生物学专业的学生提供获得北卡罗来纳州中学教师执照的机会。 早期的研究表明，斜条纹允许高力量输出超过更广泛的肌肉长度比可能在横纹肌。 然而，最近的工作表明，许多斜横纹肌不能这样宽的操作范围，相反，在这个参数有相当大的变化。 因此，目前的理解不能作为斜条纹的功能意义的一般性解释。 这项研究的目的是测试一种新的模型，该模型基于对肌丝阵列几何形状的数学分析，这表明斜条纹的进化允许调整具有流体静力骨骼的动物的长度-力关系。 该模型预测长度-力关系可以通过改变交错角（即，肌丝的交错程度），更大的交错导致更宽的操作范围。 测量的长度-力特性，在体内肌肉激活和长度的变化，和肌纤维超微结构将被用来测试模型的预测和评估斜条纹的功能意义。 初步调查将集中在鱿鱼Doryteuthis pealeii的肌肉，在功能和操作长度范围内变化很大的肌丝交错和长度-力的关系。 此外，肌肉具有相似的作用和长度-力量之间的关系选择类群，跨越范围的两侧多样性将进行研究，从而确定结构和功能的收敛在斜纹肌。这个奖项反映了NSF的法定使命，并已被认为是值得支持的，通过评估使用基金会的智力价值和更广泛的影响审查标准。

Three types of muscle cells (smooth and the cross-striated cardiac and skeletal muscles) are well known from any introductory text, yet few biologists are familiar with obliquely striated muscles. Obliquely striated muscle cells are common in soft-bodied animals, occurring in members of at least 17 phyla, yet the implications of oblique striation for the function and performance of this important muscle type are unknown. It has been assumed for decades that oblique striation permits relatively high force output over an extraordinary range of muscle lengths. Recent work, however, suggests that the contractile properties and operating length ranges of obliquely striated muscles are very diverse, even among muscles within the same individual animal. The project will investigate the contractile properties and operating length ranges of obliquely striated muscles from diverse animals. This research is likely to reveal fundamental new principles of the structure and function of muscle that would otherwise remain obscure, and provide new insight into the diversity of function and the evolution of this fiber type. The project will provide opportunities for undergraduates, especially first-generation college students and those from underrepresented backgrounds, to gain experience in physiology, biomechanics, and science communication. In partnership with the Maine State Aquarium Discovery Center, the project will develop programs for K-12 students and the general public. The project will also impact secondary education through collaboration with the UNC Baccalaureate Education in Science and Teaching (UNC-BEST) program, which offers undergraduate Biology majors opportunities to obtain licensure as a secondary school teacher in North Carolina.Although obliquely striated muscle occurs in at least 17 animal phyla, the functional implications of this striation pattern remain unclear. Early studies suggested that oblique striation allows high force output over a much wider range of muscle lengths than possible in cross-striated muscle. Recent work, however, shows that many obliquely striated muscles are incapable of such wide operating ranges and instead, there is considerable variation in this parameter. The current understanding thus fails as a general explanation for the functional significance of oblique striation. The goal of the investigation is to test a new model, based on mathematical analysis of the geometry of the myofilament array, which suggests that oblique striation evolved to allow adjustment of the length-force relationship in animals with hydrostatic skeletons. The model predicts that the length-force relationship can be adjusted by altering the stagger angle (i.e., the degree of stagger of the myofilaments), with greater stagger resulting in a wider operating range. Measurements of length-force properties, in vivo muscle activation and length changes, and muscle fiber ultrastructure will be used to test the model predictions and assess the functional significance of oblique striation. The initial investigation will focus on the myofilament stagger and the length-force relationship of muscles in the squid Doryteuthis pealeii that vary widely in function and operating length range. In addition, muscles with similar roles and length-force relationships among select taxa that span the range of Bilaterian diversity will be studied, thus identifying structural and functional convergence in obliquely striated muscles.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.