  Intact-organism imaging of Drosophila larvae reveals and quantifies
chromatin-aqueous phase separation. The chromatin can be organized near the
lamina layer of the nuclear envelope, conventionally fill the nucleus, be
organized centrally, or as a wetting droplet. These transitions are controlled
by changes in nuclear volume and the interaction of chromatin with the lamina
(part of the nuclear envelope) at the nuclear periphery. Using a simple
polymeric model that includes the key features of chromatin self-attraction and
its binding to the lamina, we demonstrate theoretically that it is the
competition of these two effects that determines the mode of chromatin
distribution. The qualitative trends as well as the compositional profiles
obtained in our simulations compare well with the observed intact-organism
imaging and quantification. Since the simulations contain only a small number
of physical variables we can identify the generic mechanisms underlying the
changes in the observed phase separations.
