Model Suggests That Mammalian Sperm Cells Have Two Modes of Swimming (IMAGE)
Caption
A new mathematical model predicts that mammalian sperm cells have two distinct swimming modes. This prediction opens new questions about potential connections between sperm cells’ motor activity and their transitions to hyperactivation phases that may play an important role in fertilization. The finding is part of a larger effort to use math and fluid dynamics to describe how mammalian sperm move. The research is led by a team of engineers at the University of California San Diego. The new work was published in the journal Physical Review Fluids on 15 November, 2023.
Mammalian sperm cells propel themselves by beating their flagella back and forth thanks to chemically powered motors that drive waves along their flagella, which are threadlike appendages.
The researchers’ new model of a swimming sperm cell captures the interactions between its motor kinetics and changes in the shape (deformations) of the flagella as well as the movements of the head of the sperm cell. The model also accounts for the complex fluid mechanics around the sperm cell as it moves.
This new model predicts that the swimming speed of a mammalian sperm cell does not simply increase as its chemical motors’ activity increases. Instead, as the motor activity of a swimming sperm cell increases, this motor activity passes a threshold level at which point a second, distinct swimming mode emerges. It is this second mode that could potentially be linked to sperm hyperactivation.
In swimming mode one, the head of the mammalian sperm cell swings back and forth more than it does in swimming mode two. In swimming mode two, the wave-shaped beating of the flagellum is stronger than it is in swimming mode one. (See the related video for a visual side-by-side comparison of swimming modes one and two.)
Credit
UC San Diego / David Saintillan
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