Haemopoietic stem cell proliferation in the bone marrow of S1/S1d mice

In marrow from Sl/Sld mice (but not +/+ mice) day 7 and day 8 CFU-S proliferate whilst day 10 and day 12 CFU-S exhibit negligible proliferation. Media conditioned by both +/+ and Sl/Sld marrow contains an inhibitor of CFU-S proliferation but day 8 CFU-S in +/+ and Sl/Sld marrow show marked dose-response differences to this factor. To inhibit the proliferation of Sl/Sld CFU-S required approximately ten times the concentration of inhibitor that inhibited the proliferation of +/+ CFU-S. Thus abnormally responsive day 8-CFU-S were shown to proliferate in an inhibitory environment. Abnormalities in Sl/Sld CFU-S function were also demonstrated in heterotopic transplantation experiments using +/+ and Sl/Sld donors and hosts to obtain ectopic bone marrow with various stromal (donor) and haemopoietic (host) combinations. Day 8 Sl/Sld CFU-S were seen to proliferate, irrespective of whether the stromal environment was derived from Sl/Sld or +/+ marrow. Sl/Sld mice are generally regarded as animals in which there is a genetically determined defect in haemopoiesis due to an abnormality in the haemopoietic environment. It is difficult, however, to attribute the abnormal CFU-S behaviour in these experiments to environmental factors and the results are consistent with mutation at the Sl locus affecting the responses of CFU-S to regulatory signals, i.e. the genetic defect is not confined to the stromal environment.     

Infertility due to growth arrest of ovarian follicles in Sl/Slt mice

Sl, Sld, and Slt are mutant alleles at the steel locus. All Sl/Sld and most Sl/Slt female mice are infertile, but the cause of the infertility is different. Germ cells are absent in Sl/Sld ovaries but present in Sl/Slt ovaries. The infertility of Sl/Slt female mice was attributed to the growth arrest of ovarian follicles, and the mechanism was analyzed by producing aggregation chimeras between Sl/Slt and +/+ embryos. Sl/Slt oocytes were ovulated and fertilized in Sl/Slt----+/+ chimeras. We investigated the origin of granulosa cells in the growing follicles and that of granulosa-derived luteal cells in the chimeras by using the electrophoretic pattern of phosphoglycerate kinase-1 and the histochemical activity of beta-glucuronidase as markers. Granulosa cells of Sl/Slt genotype developed and constituted pregnant corpora lutea in Sl/Slt----+/+ chimeras. Therefore, the growth arrest of Sl/Slt ovarian follicles may not be due to an intrinsic defect in granulosa cells but may instead be due to an intrinsic defect in ovarian stromal cells. This suggests that normal stromal cells are essential for the development of ovarian follicles.     

Regulation of haemopoietic stem-cell proliferation in mice carrying the Slj allele

We investigated a haemopoietic stromal defect, in mice heterozygous for the Sl^j allele, during haemopoietic stress induced by treatment with bacterial lipopolysaccharides (LPS) or lethal total body irradiation (TBI) and bone-marrow cell (BMC) reconstitution. Both treatments resulted in a comparable haemopoietic stem cell (CFU-s) proliferation in Sl^j/+ and +/+ haemopoietic organs. There was no difference in committed haemopoietic progenitor cell (BFU-e and CFU-G/M) kinetics after TBI and +/+ bone-marrow transplantation in Sl^j/+ and +/+ mice. the Sl^j/+ mice were deficient in their ability to support macroscopic spleen colony formation (65% of +/+ controls) as measured at 7 and 10 days after BMC transplantation. However, the Sl^j/+ spleen colonies contained the same number of BFU-E and CFU-G/M as colonies from +/+ spleens, while their CFU-s content was increased. On day 10 post-transplantation, the macroscopic ‘missing’ colonies could be detected at the microscopic level. These small colonies contained far fewer CFU-s than the macroscopic detectable colonies. Analysis of CFU-s proliferation-inducing activities in control and post-LPS sera revealed that Sl^j/+ mice are normal in their ability to produce and to respond to humoral stem-cell regulators. We postulate that Sl^j/+ mice have a normal number of splenic stromal ‘niches’ for colony formation. However, 35% of these niches is defective in its proliferative support.     

Presence of pluripotent haemopoietic precursors in vitro (CFU-mix) in haemopoietic tissues from mice of W/Wv genotype

Abstract. The presence or absence of haemopoietic precursors, which produce mixed colonies in vitro (CFU-mix) was examined in the bone marrow and spleen of (WB x C57BL/6) F1- W/W^v mice. Despite the failure of macroscopically evident colonyformation in the spleens of irradiated mice, haemopoietic cells of W/W^v mice did produce macroscopically-evident mixed colonies containing erythroid cells, macrophages, and often megakaryocytes, in culture medium. The size and constitution of mixed colonies derived from W/W^v mice were comparable to those of mixed colonies from congenic +/+ mice. The present results appear consistent with in vivo haemopoiesis in the W/W^v mice, which is obviously deficient, but sufficient for survival.     

Role of splenic stroma in the action of bacterial lipopolysaccharides on radiation mortality: a study in mice carrying the Slj allele

Abstract. Sl_j/+ mice display a slight macrocytic anaemia due to a defect in their haemopoietic organ stroma. They have a deficient endogenous spleen colony (CFU-end) formation following sublethal doses of gamma-radiation compared with their normal +/+ littermates, which is likely to be due to the low pre-irradiation CFU-S content of the Sl_j/+ spleen. CFU-S in these congenic mice do not differ in their sensitivity to gamma-irradiation or stem cell-activating factor. While injection of +/+ mice with 10 μg of lipopolysaccharide-W (LPS) one day prior to irradiation led to a substantial increase in their survival, the survival of Sl_j/+ mice was only slightly increased. Irradiation induced a similar dose-related reduction in the numbers of CFU-S in the spleen and femora of LPS-injected Sl_j/+ mice compared to similarly treated +/+ mice when measured directly after irradiation. At Day 9 after irradiation, injection of LPS led to a significantly higher CFU-end formation and higher numbers of CFU-S and nucleated cells in the Sl_j/+ spleens compared to LPS-injected +/+ mice. No such differences in the radioprotective effect of LPS were observed in the +/+ and Sl_j/+ mice with respect to the splenic and femoral ⁵⁹Fe-incorporation and the femoral CFU-S numbers at Day 9. These data strongly suggest a contribution by immigrating CFU-S to the CFU-S numbers and endogenous colony formation in at least the Sl_j/+ spleen after LPS injection and subsequent sublethal irradiation. The observations also imply that the splenic organ stroma may play a mediatory role in the radioprotective action of LPS. In addition, the data represent an extreme example of a lack of correlation between animal survival and haemopoietic parameters. Caution should be taken when applying endogenous colony counts as a means of screening potential anti-radiation drugs.     

Maintenance of granulopoiesis in long-term bone marrow cultures from W/Wv mice and effects of lipopolysaccharide on granulopoiesis in culture

Abstract. An attempt was made to establish long-term cultures of marrow cells from genetically anaemic W/W ^v mice. Two batches of horse sera were used. One batch of horse serum (HS-lot A) supported long-term maintenance (up to 20 weeks) of granulopoiesis in vitro. The number of suspension cells in W/W^v marrow culture was maintained at the same level as that in the control +/+ culture, but the number of granulocyte-macrophage progenitor cells (GM-CFC) and the ratio of immature to mature granulocytes were at a lower level than those in +/+ culture. These data suggest that haemopoietic progenitors in W/W^v cultures maintain a higher level of differentiation, and hence an increased self-renewal than those in +/+ cultures. Another batch of horse serum (HS-lot B) was less effective in the maintenance of the cultures, and the cultures deteriorated within 10 weeks. Addition of bacterial lipopolysaccharide (LPS) induced increased granulopoiesis in +/+ cultures, whereas such treatment resulted in the depletion of suspension cells in W/W^v cultures. The results suggest that haemopoietic cells of W/W^v mouse cannot cope with the strong stimulus for differentiation that occurs after the administration of LPS, although the cells can continue a moderately increased self-renewal and differentiation, as indicated by the results in the culture with HS-lot A.     

Regulation of haemopoietic stem-cell proliferation in mice carrying the Slj allele

We investigated a haemopoietic stromal defect, in mice heterozygous for the Slj allele, during haemopoietic stress induced by treatment with bacterial lipopolysaccharides (LPS) or lethal total body irradiation (TBI) and bone-marrow cell (BMC) reconstitution. Both treatments resulted in a comparable haemopoietic stem cell (CFU-s) proliferation in Slj/+ and +/+ haemopoietic organs. There was no difference in committed haemopoietic progenitor cell (BFU-e and CFU-G/M) kinetics after TBI and +/+ bone-marrow transplantation in Slj/+ and +/+ mice. The Slj/+ mice were deficient in their ability to support macroscopic spleen colony formation (65% of +/+ controls) as measured at 7 and 10 days after BMC transplantation. However, the Slj/+ spleen colonies contained the same number of BFU-E and CFU-G/M as colonies from +/+ spleens, while their CFU-s content was increased. On day 10 post-transplantation, the macroscopic 'missing' colonies could be detected at the microscopic level. These small colonies contained far fewer CFU-s than the macroscopic detectable colonies. Analysis of CFU-s proliferation-inducing activities in control and post-LPS sera revealed that Slj/+ mice are normal in their ability to produce and to respond to humoral stem-cell regulators. We postulate that Slj/+ mice have a normal number of splenic stromal 'niches' for colony formation. However, 35% of these niches is defective in its proliferative support.     

Haemopoietic stem cells: spleen colony-forming cells are normally actively proliferating

The haemopoietic stem cells forming spleen colonies (CFU-S) had on average 30 to 40% of cells engaged in the DNA synthesis in normal mice continuously over 4 years. A majority of experiments aimed at the suppression of the CFU-S proliferation, which included suppression of the T-lymphocytes by means of cyclosporin A or by adult thymectomy, administration of antibacterial and antifungal agents and maintainance of mice in a sterile environment, suppression of antibody-producing cells by a successive administration of the bacterial lipopolysaccharide and cyclophosphamide and attempts to increase the total number of CFU-S in the body through massive transfusions of bone marrow cells or by grafting plugs of the bone marrow under the kidney capsulae, have not been sufficiently effective. A transient suppression of CFU-S proliferation occurred during recovery of the haemopoietic tissue from damage caused by cyclophosphamide. The results support the view that changes in CFU-S numbers and in the proportion of them in DNA synthesis may be positively correlated when CFU-S numbers fluctuate physiologically about their normal values. The failure to manipulate the CFU-S proliferation rate easily suggests that proliferation of these cells may not be under a strong 'switch on - switch off' control.     

Haemopoietic stem cells: spleen colony-forming cells are normally actively proliferating

Abstract. The haemopoietic stem cells forming spleen colonies (CFU-S) had on average 30 to 40% of cells engaged in the DNA synthesis in normal mice continuously over 4 years. A majority of experiments aimed at the suppression of the CFU-S proliferation, which included suppression of the T-lymphocytes by means of cyclosporin A or by adult thymectomy, administration of antibacterial and antifungal agents and maintainance of mice in a sterile environment, suppression of antibody-producing cells by a successive administration of the bacterial lipopolysaccharide and cyclophosphamide and attempts to increase the total number of CFU-S in the body through massive transfusions of bone marrow cells or by grafting plugs of the bone marrow under the kidney capsulae, have not been sufficiently effective. A transient suppression of CFU-S proliferation occurred during recovery of the haemopoietic tissue from damage caused by cyclophosphamide. The results support the view that changes in CFU-S numbers and in the proportion of them in DNA synthesis may be positively correlated when CFU-S numbers fluctuate physiologically about their normal values. The failure to manipulate the CFU-S proliferation rate easily suggests that proliferation of these cells may not be under a strong 'switch on - switch off' control.     

The production of factors regulating the proliferation of haemopoietic spleen colony-forming cells by bone marrow macrophages

Abstract. Media conditioned by normal murine bone marrow cells contain an inhibitor of haemopoietic spleen colony-forming cell proliferation that is concentrated in a nominal 50-100K fraction. Media conditioned by regenerating marrow cells contain a proliferation-stimulatory activity that is concentrated in a nominal 30-50K fraction. Cell separation experiments demonstrated that the activities are produced by adherent, phagocytic, radioresistant, Thy 1.2^- Fc⁺, F4/80⁺ cells. Cultured macrophages, obtained from long-term marrow cultures or derived from progenitor cells in methyl cellulose cultures are also capable of producing inhibitory and stimulatory activities. The results are consistent with macrophages being an important source of stem cell proliferation regulators in the bone marrow.     

Role of splenic stroma in the action of bacterial lipopolysaccharides on radiation mortality: a study in mice carrying the Slj allele

Slj/+ mice display a slight macrocytic anaemia due to a defect in their haemopoietic organ stroma. They have a deficient endogenous spleen colony (CFU-end) formation following sublethal doses of gamma-radiation compared with their normal +/+ littermates, which is likely to be due to the low pre-irradiation CFU-S content of the Slj/+ spleen. CFU-S in these congenic mice do not differ in their sensitivity to gamma-irradiation or stem cell-activating factor. While injection of +/+ mice with 10 micrograms of lipopolysaccharide-W (LPS) one day prior to irradiation led to a substantial increase in their survival, the survival of Slj/+ mice was only slightly increased. Irradiation induced a similar dose-related reduction in the numbers of CFU-S in the spleen and femora of LPS-injected Slj/+ mice compared to similarly treated +/+ mice when measured directly after irradiation. At Day 9 after irradiation, injection of LPS led to a significantly higher CFU-end formation and higher numbers of CFU-S and nucleated cells in the Slj/+ spleens compared to LPS-injected +/+ mice. No such differences in the radioprotective effect of LPS were observed in the +/+ and Slj/+ mice with respect to the splenic and femoral 59Fe-incorporation and the femoral CFU-S numbers at Day 9. These data strongly suggest a contribution by immigrating CFU-S to the CFU-S numbers and endogenous colony formation in at least the Slj/+ spleen after LPS injection and subsequent sublethal irradiation. The observations also imply that the splenic organ stroma may play a mediatory role in the radioprotective action of LPS. In addition, the data represent an extreme example of a lack of correlation between animal survival and haemopoietic parameters. Caution should be taken when applying endogenous colony counts as a means of screening potential anti-radiation drugs.     

Sl/Sld mice have an increased number of gap junctions in their bone marrow stromal cells

To study the defect of the hematopoietic inductive microenvironment (HIM) in Sl/Sld mice, femoral bone marrow tissue of 10 of each mutant, (Sl/Sld and W/Wv) their normal littermates (Sl+/Sl+ and W+/W+), and 20 normal C57BL mice were examined by electron microscopy using morphometric and statistical methods. Gap junctions were observed in all strains of mice, in the following stromal cell types: 1) reticular cells, 2) between reticular cells and periarterial adventitial cells, and 3) between periarterial adventitial cells. The frequency of gap junctions in bone marrow stromal cells of Sl/Sld mice (mean = 2.2/9.4 X 10(-3) mm2) was significantly higher than in control mice. It is suggested that there is a relationship between the increased numbers of gap junctions in bone marrow stromal cells of Sl/Sld mice and the defect in HIM function in these genetically anemic animals.     

Studies of Sl/Sld in equilibrium with +/+ mouse aggregation chimaeras. II. Effect of the steel locus on spermatogenesis

Mutant mice of Sl/Sld genotype are deficient in melanocytes, erythrocytes, mast cells and germ cells. Deficiency of melanocytes, erythrocytes and mast cells is not attributable to an intrinsic defect in their precursor cells but to a defect in the tissue environment that is necessary for migration, proliferation and/or differentiation. We investigated the mechanism of germ cell deficiency in male Sl/Sld mice by producing aggregation chimaeras from Sl/Sld and +/+ embryos. Chimaeric mice with apparent white stripes were obtained. Two of four such chimaeras were fertile and the phenotypes of resulting progenies showed that some Sl/Sld germ cells had differentiated into functioning sperms in the testis of the chimaeras. In cross sections of the testes of chimaeras, both differentiated and nondifferentiated tubules were observed. However, the proportions of type A spermatogonia to Sertoli cells in both types of tubules were comparable to the values observed in differentiated tubules of normal +/+ mice. We reconstructed the whole length of four tubules from serial sections. Differentiated and nondifferentiated segments alternated in a single tubule. The shortest differentiated segment contained about 180 Sertoli cells and the shortest nondifferentiated segment about 150 Sertoli cells. These results suggest that Sertoli cells of either Sl/Sld or +/+ genotype make discrete patches and that differentiation of type A spermatogonia does not occur in patches of Sl/Sld Sertoli cells.     

Stimulator of proliferation of spleen colony-forming cells in T-cell deprived mice treated with cyclophosphamide or irradiation

A role for T-cells in the regulation of CFU-S proliferation was investigated by determining the presence and activity of CFU-S proliferation stimulator (CFU-S stimulator) in adult mouse bone marrow after irradiation or cyclophosphamide (Cy) treatment. CBA mice previously deprived of T-cells by thymectomy, irradiation and bone marrow reconstitution (TIR) were thereafter treated with 4.5 Gy irradiation or 200 mg/kg Cy. Regenerating bone marrow cells of TIR and corresponding control mice after irradiation or Cy treatment produced CFU-S stimulator. The dose dependent increase in cytosine arabinoside cell death of normal bone marrow day 8 CFU-S was found when both CFU-S stimulators obtained after irradiation of TIR or corresponding control animals were tested. CFU-S stimulator activity in the bone marrow of TIR-Cy treated mice was also detected, but the effect was not dose-dependent. This was not related to the presence of an inhibitor of CFU-S proliferation. It appears that the CFU-S stimulator activity is not related to IL-6, IL-1 or IL-2, or to an inhibitor of IL-6 or IL-1 activity. The results demonstrate the existence of CFU-S proliferation stimulator unrelated to the two major monokines in the bone marrow of immunosuppressed mice.     

Studies of Sl/Sld in equilibrium with +/+ mouse aggregation chimaeras. I. Different distribution patterns between melanocytes and mast cells in the skin

In spite of their different origin, both melanocytes and mast cells are deficient in the skin of mutant mice of the Sl/Sld genotype. Since the neural crest and the liver of Sl/Sld embryos contain normal precursors of melanocytes and mast cells, respectively, the deficiency is attributed to a defect in tissue environment necessary for migration and/or differentiation of precursor cells. We investigated whether the tissue environment used for differentiation of melanocytes and mast cells was identical by producing aggregation chimaeras from Sl/Sld and +/+ embryos. Chimaeric mice with apparent pigmented and nonpigmented stripes were obtained. In the nonpigmented stripes of these Sl/Sld in equilibrium with +/+ chimaeras, melanocytes were not detectable in hair follicles but were detectable in the dermis. In contrast, melanocytes were detectable neither in hair follicles nor in the dermis of nonchimaeric Sl/Sld mice. Concentrations of mast cells were comparable in the pigmented and nonpigmented stripes of Sl/Sld in equilibrium with +/+ chimaeras, but the average concentration of mast cells significantly varied in the chimaeras (from 8% to 74% of the value observed in control +/+ mice). The present result suggests that mesodermal cells that support the migration and differentiation of both melanocyte precursors and mast-cell precursors mix homogeneously in the dermis and that ectodermal cells that influence the invasion of differentiating melanocytes into hair follicles make discrete patches.     

Cyclic AMP response to various haemopoietic regulators

Diffusible inhibitors and stimulators are involved in the regulation of bone marrow pluripotent stem cell (CFU-S) proliferation. We have previously shown the existence of CFU-S inhibitors in foetal calf marrow and liver and have started their purification. The lack of a simple and time-saving test to determine the kinetic state of CFU-S and the activity of the inhibitors led us to explore the possibility of a biochemical proliferation marker that could be used for screening purpose. Since it was shown that cyclic AMP was implicated in the regulation of CFU-S proliferation, it was of interest to study the variations in cAMP levels after stimulation and inhibition of CFU-S entry into cycle. The results of in vitro experiments showed that the increase in cAMP levels observed in bone marrow cells after incubation with different haemopoietic stimulators was specific neither for bone marrow cells nor for the various haematopoietic regulators. In the in vivo experiments, an increased cAMP level was observed 8 hr after one injection of Ara-C at the time when CFU-S are recruited into S phase. However, no modification of cAMP levels has been observed after injection of CFU-S inhibitors in the Ara-C-treated mice. Although cAMP does not seem to be a suitable marker for testing the activity of inhibitory fractions during the purification process, this work has contributed to the study of CFU-S stimulators.     

Cyclic Amp Response to Various Haemopoietic Regulators

Diffusible inhibitors and stimulators are involved in the regulation of bone marrow pluripotent stem cell (CFU-S) proliferation. We have previously shown the existence of CFU-S inhibitors in foetal calf marrow and liver and have started their purification. the lack of a simple and time-saving test to determine the kinetic state of CFU-S and the activity of the inhibitors led us to explore the possibility of a biochemical proliferation marker that could be used for screening purpose. Since it was shown that cyclic AMP was implicated in the regulation of CFU-S proliferation, it was of interest to study the variations in cAMP levels after stimulation and inhibition of CFU-S entry into cycle. the results of in vitro experiments showed that the increase in cAMP levels observed in bone marrow cells after incubation with different haemopoietic stimulators was specific neither for bone marrow cells nor for the various haematopoietic regulators. In the in vivo experiments, an increased cAMP level was observed 8 hr after one injection of Ara-C at the time when CFU-S are recruited into S phase. However, no modification of cAMP levels has been observed after injection of CFU-S inhibitors in the Ara C-treated mice. Although cAMP does not seem to be a suitable marker for testing the activity of inhibitory fractions during the purification process, this work has contributed to the study of CFU-S stimulators.     

Functionally abnormal stromal cells and megakaryocyte size, ploidy, and ultrastructure in Sl/Sld mice

The first goal of the present studies was to determine if Sl/Sld megakaryocytes have features in common with the macrocytic megakaryocytes that genetically normal mice produce in response to acute platelet depletion. The second was to test the hypothesis that megakaryocyte abnormalities in Sl/Sld mice are due to genetically determined hemopoietic stromal cell abnormalities. Sizes and ploidies of mature Sl/Sld megakaryocytes were measured. Macrocytosis and a shift to higher ploidy values were found compared with normal. Within ploidy groups 16N-64N, Sl/Sld megakaryocytes were larger than normal megakaryocytes of the same ploidy. Transmission electron microscopy revealed that Sl/Sld megakaryocyte nuclei contain more and larger nucleoli, and the chromatin was more dispersed than in normal megakaryocyte nuclei of comparable maturity. Asynchronous megakaryocyte cytoplasmic maturation was found. Sl/Sld macrophages were also ultrastructurally abnormal. Megakaryocytic macrocytosis was reproduced in long-term bone marrow cultures in which the adherent layer was formed by Sl/Sld cells. It was the same if cultures were recharged with Sl/Sld or +/+ hemopoietic cells. Previously reported ambiguities in mixed cell cultures were avoided by recharging the adherent layers with only a million cells. These results were correlated with previously published observations. Sl/Sld megakaryocytes have features in common with megakaryocytes from acutely thrombocytopenic animals. One feature, macrocytosis, appears to be due to abnormal Sl/Sld stromal cells that are reproduced as adherent layer cells in long-term cultures. The responsible stromal cells in Sl/Sld mice may be counterparts of megakaryocytopoietic regulatory cells in the marrow stroma of normal animals.     

Pluripotent (Cfu-S) and Granulocyte-Committed (Cfu-C) Stem Cells In Intact and 89Sr Marrow-Ablated S1/S1D Mice

Peripheral blood values, femur cell counts, spleen weights, pluripotent (CFU-S) and granulocyte progenitor cell (CFU-C) concentrations and total content of spleens and femurs have been evaluated in intact (non-marrow-ablated) and ⁸⁹Sr marrow-ablated S1/S1^d and +/+ mice. ⁸⁹Sr-irradiated mice were studied 6 and 11 days after the administration of ⁸⁹Sr. In intact S1/S1^d mice the femur CFU-S concentration, total femur CFU-S, femur CFU-C concentration and total femur CFU-C were 84, 54, 105 and 68% that of +/+ mice femurs respectively; the respective values for the spleens of S1/S1^d mice were 40,46,61 and 69%. These are the first simultaneous determinations of CFU-S and CFU-C concentrations, and content of spleens and marrows, of S1/S1^d and +/+ mice. In ⁸⁹Sr marrow-ablated mice, 11 days after injection of the radionuclide: (a) the total content of marrow CFU-C and CFU-S was about 1% of that found in the marrows of intact mice for both +/+ and S1/S1^d groups; (b) the spleens of +/+ mice increased in weight to 162% of the control, but the spleens of S1/S1^d mice did not increase in weight; and (c) the spleens of +/+ mice had a total content of CFU-C and CFU-S of 800% and 260% of the control, respectively, whereas the respective values for the S1/S1^d mice were 120% and 76% of the control. Thus the S1/S1^d spleen fails to compensate for marrow ablation by housing additional CFU-S and has an impaired ability to compensate by housing additional CFU-C.     

Characteristics of the Cfu-S Population In Mice Carrying the SlJ Allele

Abstract Abstract. A tentative characterization of haemopoietic stem cells with respect to their organ distribution, seeding fraction and colony formation in the spleen, radiosen-sitivity and humoral regulation was attempted in mice heterozygous for the mutant allele Sl^J and in their normal littermates. Sl^J/+ mice were characterized by a deficient CFU-s content of the blood and spleen and had slightly lower femoral CFU-s numbers. This CFU-s distribution could not be explained by differences in seeding efficiency ‘f’ between CFU-s of Sl^J/+ and +/+ origin in lethally irradiated recipients used in the CFU-s assay. the seeding fraction of CFU-s of +/+ origin did not differ in +/+ and Sl^J/+ recipients. However, in irradiated SI^J/+ recipient mice a 30% decrease was observed in the number of the colonies derived from splenic and femoral CFU-s of both +/+ and Sl^J/+ origin. the serum level of SHSF (splenic haemopoiesis stimulating factor) was decreased in Sl^J/+ mice, but significantly increased in Sl/Sl^d mice, as compared to their respective normal +/+ littermates. Endogenous colony formation in Sl^J/+ spleens was deficient in comparison to that observed in +/+ spleens, and distinct sex differences were observed. However, mutant and normal CFU-s from spleen and bone marrow had a similar survival following in-vitro y irradiation. Femurs and spleens of both Sl^J/+ and +/+ origin were implanted into both Sl^J/+ and +/+ hosts. Six weeks later the Sl^J/+ grafts contained less CFU-s than the +/+ grafts. These data show that the splenic stroma of Sl^J/+ mice is not defective in its capacity to lodge injected CFU-s but is deficient in its ability to maintain CFU-s under ‘steady-state’ conditions and stimulate their colony formation in a ‘perturbed state’. Some of the characteristics of Sl^J/+ mice segregate them from Sl/Sl^d mice, i.e. a deficient splenic CFU-s content, normal seeding fractions ‘f’ of CFU-s from spleen and bone marrow in the presence of an almost compensated anemia, and decreased serum levels of SHSF. the study of the Sl^J trait may be a useful extension of the current Sl/Sl^d model for exploration of hereditary defects in haematopoietic stroma.