Stem cells are the providers of new cell types that are critical to the development of the normal embryo, and the disruption of their control can lead to cancer. My lab studies the fundamental mechanisms of stem cell function and differentiation in a model system that carries out an asymmetric, stem cell-like cell division that yields two unique daughter cells of different cell fate.

We are asking how the densely packed cellular space is organized to enable control of complex biochemical reactions in space and time and how this organization drives cell function. The discovery of liquid-liquid phase separation in living cells has provided a powerful framework to explain dynamic cellular processes. Our current goal is to design an entirely new method of drug delivery to normal and malfunctioning human cells. We have discovered that viscous, liquid membraneless organelles (MLO’s) in a bacterial cell provide a novel means of dynamically organizing the cytoplasm, thereby enabling the selective sequestration of signaling protein pathways. We have shown that MLO’s serve as selective signaling hubs that coordinate differential readout of the genome upon asymmetric cell division. A key constituent of the Caulobacter MLO is the PopZ protein, which has a canonical integral disordered region (IDR) that we have shown is critical for phase separation.

Our ability to rationally manipulate the material properties of the PopZ MLO provides an exciting opportunity to use PopZ as a biologically-orthogonal platform for engineering synthetic MLOs in human cells. We found that PopZ phase separates in human cells and the material properties and client cargo of the engineered PopZ MLO are maintained, making PopZ amenable for rational design. We further designed a set of localization tags that allow us to direct the PopZ to specific cellular addresses in human cells, such as actin filaments, lipid droplets, or the plasma membrane. By fusing PopZ to a GFP nanobody, we created a ‘NanoPop’ cassette that drives phase separation and can recruit GFP tagged proteins to the PopZ MLOs, enabling therapeutic applications, such as toxin sequestration or drug delivery in specifically targeted cells. We have also engineered an inducible degron cassette to clear the human cell of the PopZ MLO. We have recently filed a patent for this work applied to oncogenic cells in collaboration with Aaron Gitler and Steven Boeynaems at Stanford. Multiple collaborators are now using our NanoPop system to manipulate cells.