Discontinuities in the PSM

Experiments which have been interpreted as proving that somitogenesis clock oscillations are cell-autonomous consist in cutting the PSM transversally, and observing that oscillations continue in both halves for up to two cycles (Palmeirim et al., 1997, McGrew et al., 1998, Forsberg et al., 1998). Within the framework of the Lunatic fringe secretion model, these experiments can be modelled as introducing at some time a coupling boundary in the chain of oscillators, across which oscillators do not influence each other. Simulations have been performed (see Movie 2), which show that the oscillatory pattern is essentially unaffected for many cycles after the introduction of the boundary (see Figure 5 for a snapshot 4 cycles after the introduction of the boundary). The disruption becomes larger with time, but current experimental data does not allow verification of whether this actually happens, as tissues were fixed after at most two cycles of oscillation.

Figure 5: 2 cycles after the introduction of the coupling boundary at cell 150, the disruption of the pattern is minimal. An anomaly is only observed at times when the wave of expression reaches the coupling boundary. Abscissae correspond to cell number in the PSM (anterior is to the left, posterior to the right), and ordinates to L-fringe expression levels (in arbitrary units).

Movie 2: Simulation of the L-fng secretion model, with a coupling boundary introduced at the start of the movie, at cell 150. The pattern disruption is minimal, but grows with time.

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