College of Agriculture and Life Sciences, Departments of Food Science, Cornell University, Ithaca, NY 14853.
College of Veterinary Medicine, Department of Biomedical sciences, Cornell University, Ithaca, NY 14853.
Proc Natl Acad Sci U S A. 2021 Nov 2;118(44). doi: 10.1073/pnas.2107500118.
Mammalian sperm migration within the complex and dynamic environment of the female reproductive tract toward the fertilization site requires navigational mechanisms, through which sperm respond to the tract environment and maintain the appropriate swimming behavior. In the oviduct (fallopian tube), sperm undergo a process called "hyperactivation," which involves switching from a nearly symmetrical, low-amplitude, and flagellar beating pattern to an asymmetrical, high-amplitude beating pattern that is required for fertilization in vivo. Here, exploring bovine sperm motion in high-aspect ratio microfluidic reservoirs as well as theoretical and computational modeling, we demonstrate that sperm hyperactivation, in response to pharmacological agonists, modulates sperm-sidewall interactions and thus navigation via physical boundaries. Prior to hyperactivation, sperm remained swimming along the sidewalls of the reservoirs; however, once hyperactivation caused the intrinsic curvature of sperm to exceed a critical value, swimming along the sidewalls was reduced. We further studied the effect of noise in the intrinsic curvature near the critical value and found that these nonthermal fluctuations yielded an interesting "Run-Stop" motion on the sidewall. Finally, we observed that hyperactivation produced a "pseudo-chemotaxis" behavior, in that sperm stayed longer within microfluidic chambers containing higher concentrations of hyperactivation agonists.
哺乳动物精子在雌性生殖道复杂而动态的环境中向受精部位迁移，需要导航机制，通过这些机制，精子对生殖道环境做出反应并保持适当的游动行为。在输卵管（输卵管）中，精子经历一个称为“超激活”的过程，其中涉及从几乎对称、低幅度和鞭毛拍打模式切换到不对称、高幅度拍打模式，这是体内受精所必需的。在这里，我们通过探索高宽比微流控储液器中的牛精子运动以及理论和计算建模，证明了精子超激活会调节精子侧壁相互作用，从而通过物理边界进行导航。在超激活之前，精子仍沿着储液器的侧壁游动；然而，一旦超激活导致精子的固有曲率超过临界值，沿侧壁的游动就会减少。我们进一步研究了固有曲率中噪声的影响接近临界值，并发现这些非热涨落在侧壁上产生了有趣的“跑停”运动。最后，我们观察到超激活产生了一种“假趋化性”行为，即在含有更高浓度超激活激动剂的微流控室内，精子停留的时间更长。
