Abstract:

Spermatogenesis in rodent seminiferous tubules exhibits characteristic dynamics with spatiotemporal periodicities called “seminiferous epithelial cycle” and “spermatogenic wave.” Although first described as early as 1871, the detailed dynamics, underlying mechanism, and biological significance of the “cycle” and “wave” remain largely unknown.

To tackle this issue, we have developed live imaging in vivo, enabling extended period of filming for about ten days; and ex vivo organ culture imaging for about a month, to observe an 8.6-day temporal periodicity in this phenomenon. Using mice carrying a transgene that illuminates germ cells in a specific phase of the cycle, we observed an exquisite spatiotemporal coordination of germ cells. Over larger time and space scales, such small-scale coordination composes a periodic, wave-like propagation along the seminiferous tubules. However, the cycle and wave do not show fully regular periodicity but include characteristic irregularities, including inconstant wave velocity, wave emergence resulting in bidirectional propagation, vanishment of collided waves, and even change of the wave pattern over the cycles. Nevertheless, we also observed an organ-scale, global order of the wave. Intriguingly, we found that a minimal mathematical model can explain such complex dynamics, suggesting the self-organizing nature of the cycle and wave. These analyses will throw light on the biophysical principles and the cellular and molecular mechanisms underpinning spermatogenesis as well as the homeostasis of other cycling organs.

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