Limiting-pool mechanism of size control of nucleoli in the C. elegans embryo

Cells contain organelles which maintain a dynamic yet coherent structure, but the mechanisms by which
these assemblies form and stably persist are not well understood. Here, we consider the assembly of
nucleoli in C. elegans embryo as a model-system for questions regarding the mechanisms controlling the
size of self-assembling structures within the cell. Recent experiments suggest that, in C. elegans early
embryo, nucleoli grow until the pool of its building blocks is depleted from the nucleoplasm. This is
known as the ‘limiting-pool’ mechanism.
In order to study experimental signatures of the limiting-pool mechanism, we consider a simple model
of the self-assembly of two spherical structures from a common pool of building blocks. Using theory
and simulations, we analyze the time series of the sizes of the spherical structures and make specific
predictions about their autocorrelation functions. We then compare these theoretical results to
fluorescence data from experiments that measure nucleoli size as a function of time in late stages of C.
elegans embryo development. This approach can be used in other experimental systems to
quantitatively test for the limiting-pool mechanism, and can be extended to other size-control
mechanisms.