Collaborative Research: 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（平滑肌和交叉横纹肌和骨骼肌）从任何入门文本中都是众所周知的，但很少有生物学家熟悉斜横纹肌。斜纹肌细胞在软体动物中很常见，至少在17门动物中都有，但斜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，斜纹允许在非常大的肌肉长度范围内输出相对较高的力。然而，最近的研究表明，斜横纹肌的收缩特性和活动长度范围是非常不同的，即使在同一动物的肌肉中也是如此。该项目将研究不同动物斜横纹肌的收缩特性和活动长度范围。这项研究可能会揭示肌肉结构和功能的基本新原理，否则这些原理仍然是模糊的，并为这种纤维类型的功能多样性和进化提供新的见解。该项目将为本科生提供机会，特别是第一代大学生和来自代表性不足背景的学生，以获得生理学，生物力学和科学传播方面的经验。该项目将与缅因州州立水族馆探索中心合作，为K-12学生和公众开发项目。该项目还将通过与北卡罗来纳大学科学与教学学士学位教育（UNC- best）计划的合作，影响中学教育，该计划为生物学本科专业学生提供获得北卡罗来纳州中学教师执照的机会。虽然斜横纹肌存在于至少17个动物门中，但这种条纹模式的功能意义尚不清楚。早期的研究表明，斜横纹肌比横横纹肌能在更宽的肌肉长度范围内输出更高的力。然而，最近的研究表明，许多斜横纹肌不能承受如此大的活动范围，相反，这个参数有相当大的变化。因此，目前的理解不能作为斜纹的功能意义的一般解释。这项研究的目的是测试一个新的模型，该模型基于对肌丝阵列几何形状的数学分析，该模型表明，斜纹的进化是为了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错开角度（即肌丝错开程度）来调节，错开越大，操作范围越广。测量长度-力特性、体内肌肉激活和长度变化以及肌纤维超微结构将用于测试模型预测并评估斜纹的功能意义。本文的初步研究将集中在Doryteuthis pealeii鱿鱼的肌丝交错和肌肉的长度-力关系上，这些肌肉在功能和操作长度范围上有很大的不同。此外，我们还将研究具有相似作用的肌肉以及在双边动物多样性范围内的特定类群之间的长度-力关系，从而确定斜横纹肌的结构和功能趋同。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.