The ups and downs of p53 regulation in hematopoietic stem cells.

Hematopoietic stem cells provide an indispensible source for replenishing the blood with all its constituents throughout the organism's lifetime. Mice with a compromised hematopoietic stem cell compartment cannot survive. p53, a major tumor suppressor gene, has been implicated in regulation of hematopoiesis. In particular, p53 plays a role in homeostasis by regulating HSC quiescence and self renewal. We recently utilized a hypomorphic p53(515C) allele in conjunction with Mdm2, a negative regulator of p53 to gain insights into the role of p53 in hematopoietic regulation. Our analyses revealed that p53(515C/515C) Mdm2(-/-) double mutant mice die soon after birth due to hematopoietic failure. Further mechanistic studies revealed that in the absence of Mdm2, ROS induced postnatal p53 activity depletes hematopoietic stem cells, progenitors and differentiated cells.