1 Department of Mathematics, University of York , York YO10 5DD , UK.
2 Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford , Oxford OX2 6GG , UK.
J R Soc Interface. 2019 Mar 29;16(152):20180668. doi: 10.1098/rsif.2018.0668.
Eukaryotic flagellar swimming is driven by a slender motile unit, the axoneme, which possesses an internal structure that is essentially conserved in a tremendous diversity of sperm. Mammalian sperm, however, which are internal fertilizers, also exhibit distinctive accessory structures that further dress the axoneme and alter its mechanical response. This raises the following two fundamental questions. What is the functional significance of these structures? How do they affect the flagellar waveform and ultimately cell swimming? Hence we build on previous work to develop a mathematical mechanical model of a virtual human sperm to examine the impact of mammalian sperm accessory structures on flagellar dynamics and motility. Our findings demonstrate that the accessory structures reinforce the flagellum, preventing waveform compression and symmetry-breaking buckling instabilities when the viscosity of the surrounding medium is increased. This is in agreement with previous observations of internal and external fertilizers, such as human and sea urchin spermatozoa. In turn, possession of accessory structures entails that the progressive motion during a flagellar beat cycle can be enhanced as viscosity is increased within physiological bounds. Hence the flagella of internal fertilizers, complete with accessory structures, are predicted to be advantageous in viscous physiological media compared with watery media for the fundamental role of delivering a genetic payload to the egg.
真核鞭毛的游动是由一个细长的运动单位——轴丝驱动的，轴丝具有一种内部结构，这种结构在极大的精子多样性中基本保持一致。然而，作为内部受精的哺乳动物精子，还表现出独特的附属结构，进一步修饰轴丝并改变其机械响应。这就提出了以下两个基本问题。这些结构的功能意义是什么？它们如何影响鞭毛的波形，最终影响细胞的游动？因此，我们在前人的工作基础上，构建了一个虚拟人类精子的数学力学模型，以研究哺乳动物精子附属结构对鞭毛动力学和运动的影响。我们的研究结果表明，当周围介质的粘度增加时，附属结构会增强鞭毛的强度，防止波形压缩和对称破缺的屈曲不稳定性。这与内部和外部受精剂（如人类和海胆精子）的先前观察结果一致。反过来，由于在生理范围内增加粘度可以增强鞭毛在一个拍打周期中的渐进运动，因此，在粘性生理介质中，带有附属结构的内部受精剂的鞭毛比在水介质中更具优势，因为其基本功能是将遗传有效负载传递给卵子。
