Regulators of stem cell proliferation in the haemopoietic tissues of W/Wv and SI/SId mice

The presence of CFU-S proliferation stimulatory and inhibitory activities in the bone marrow and spleens of normal mice (+/+) and mice with mutations affecting the proliferative behaviour of stem cells (S1/S1^d and W/W^v) has been investigated.S1/S1^d and +/+ bone marrow and spleen contain virtually no detectable stimulator but the corresponding tissues from W/W^v mice are both strongly stimulatory. SI/SI^d marrow in particular, but also +/+ marrow are strongly inhibitory whilst +/+ spleen, S1/SI^d spleen, W/W^v marrow and W/W^v spleen all contain inhibitory activity but at a lower specific activity.The data are compatible with studies of cell and tissue grafts that have indicated an intrinsic haemopoietic stem cell defect in W/W^v mice and an extrinsic, microenvironmental defect in SI/SI^d mice. It is suggested that they are also compatible with defective regulatory interactions between stem cells and regulator-producing cells and that the W and S1 loci may code for products involved in the production of, or response to, CFU-S proliferation regulators.