| Abstract: | Haematological information on steel (Sl) mice is limited largely to Sl/Sld mice of Bar Harbor stock (WC.B6 F1). Therefore, two Harwell alleles, SlgbH and Slcon, were investigated. In the steady state both heterozygotes were modestly anaemic, homozygous Slcon and compound Slcon/SlgbH more so. On perturbation by X-irradiation Slcon/SlgbH showed a decrease in median lethal dose (MLD)--6.5 Gy, Slcon/+ and Slcon/Slcon slightly less change (7.5 Gy) compared with +/+, 8 Gy. In recovery from sublethal doses single heterozygotes, double heterozygotes with Wv, and compounds showed no delay in restoration of the count of red blood corpuscles (RBC) such as that seen in typical W mice (e.g. Wv/+, W/Wv). Effects on Slcon/Slcon and Slcon/SlgbH differ from those reported for Sl/Sld in that they show normal growth of spleen colonies when used as lethally irradiated recipients of bone marrow, they support growth of implanted bone marrow to form radiation chimaeras. When Harwell steel mice are donors of bone marrow to lethally irradiated +/+ mice the chimaeras ultimately are not anaemic; when lethally irradiated Harwell steel mice are recipients of +/+ marrow they remain macrocytically anaemic. One deduces that, for normal development and production of normal RBC in the steady state, the erythron requires intrinsic factors determined by wild type alleles at the W locus and extrinsic factors determined by wild type alleles at the Sl locus. Mutant alleles at either locus may determine macrocytosis. Two mutant alleles at either locus are still more deleterious, often lethal. Whereas mutant W alleles may also influence the pluripotent haematopoietic stem cell (HSC) leading to reduced MLD on X-irradiation, a similarly reduced MLD for Sl mutants may represent an increased need for and consumption of products of the haematopoietic stem cells rather than truly increased radiosensitivity, since the Do for spleen colony-forming units is the same for Slcon/SlgbH as +/+ mice. |
