The Zou lab aims to understand the relationship of stem cells and their physical niches, and to identify the molecules that regulate homeostasis of stem cells. Results from our laboratory demonstrate that the chemokine CXCL12 not only functions as the major chemoattractant for hematopoietic stem cells (HSCs) homing into the stem cell niche, but also regulates quiescence of HSCs. Our data further reveal a potential signaling circuit for regulating HSC quiescence that connects the signal from BM niche (CXCL12) with a HSC surface receptor (CXCR4) and a cell cycle regulator (p57KIP2). Current projects include investigating the role of p57kip2 in HSC quiescence using p57kip2 knockout mice and identification of the CXCR4 signaling components that regulate p57kip2 expression. Future studies will extend into other stem cells and cancer stem cells.