Postirradiation dynamics of T-lymphocyte precursors and thymus regeneration in mice

Irradiation of CBA mice elicits a pronounced response of intrathymus and bone marrow precursors of T-lymphocytes (PTL) which is manifested by an increase in a relative content of PTL in the thymus and their transfer from bone marrow to thymus. The estimate of the regenerative potency of the thymus most adequately reflects the cellular events leading to regeneration thereof. The differences in the thymus regeneration dynamics between CBA and AKR mice are associated with different radiation response of the intrathymic SC-1-PTL in mice of these strains.     

Postirradiation recovery dependent on the uvr-1 locus in Bacillus subtilis.

A mutant (uvr-1) of Bacillus subtilis that is deficient in excision of ultraviolet (UV)-induced pyrimidine dimers from deoxyribonucleic acid (DNA) shows a marked increase in ability to survive UV irradiation when plated on amino acid-supplemented agar medium compared with its survival ability when plated on nutrient plating medium, the effect is considered to be one of growth-dependent lethality. Irradiated stationary phase uvr-1 cells, incubated in liquid medium lacking amino acids required for growth, recover from this sensitivity to rich medium within 3 to 4 h after irradiation. Recovery is greatly reduced in the absence of glucose oiminated. Exponentially growing cells have a limited ability to recover from sensitivity to rich medium. Growth-dependent lethality can also occur in liquid medium. In nutrient broth the ability of irradiated stationary-phase uvr-1 cells to form colonies on defined agar medium decreases during postirradiation incubation, but treatmeth with chloramphenicol inhibits the loss of colony-forming ability. Recovery from sensitivity to rich media is inhibited by caffeine but not by 6-(p-hydroxyphenylazo)-uracil, and inhibitor of DNA replication. Alkaline sucrose gradient profiles show that conditions allowing recovery also favor maintaining intact DNA strands, whereas DNA strand breakage or degradation is associated with loss of viability. Recovery from sensitivity to rich medium has not been observed in the Ur+ parent or in strains carrying the mutations uvs-42 (another deficiency in dimer excision), recA1, or polA59. A uvr-1 recA1 mutants shows a higher level of recovery than does the recA1 single mutant, but a much lower level than the uvr-1 single mutant. Apparently, both the uvr-1 defect and Rec+ and PoII+ functions are essential for recovery from sensitivity to rich medium. For optimal recovery, growth immediately after irradiation must be delayed. The process requires energy, apparently involves recombination, and probably results in rejoining of DNA strands in which incision but not excision has occurred.     

Influence of thymic humoral factor(s) on haemopoiesis in mice

Postirradiation administration of Leukotrophin to whole-body irradiated mice was associated with increased LD50/30 and DRF. As indicated by 59Fe uptake and ESC number, haemopoiesis was significantly stimulated in spleen and bone marrow after Leukotrophin application to irradiated mice. DNA content and the uptake of 3H-thymidine in DNA was significantly enhanced in the thymus and bone marrow of irradiated and Leukotrophin-treated mice. The micronucleus test confirmed that Leukotrophin is a therapeutic agents, while administered before irradiation it does not influence the initial radio-lesions.     

Steel (Sl) mutation in mice: Identification of mutant embryos early in development

A method is described for the reliable identification of Steel mutant mouse embryos in segregating litters as early as Day 11 of gestation based on the color of hair developed in embryonic skin explants.     

Effect of T-lymphocytes on normal haemopoiesis: studies in congenitally athymic nude mice.

The germ-free nude mouse represents a most useful animal for investigating the effects of a congenital deficiency of T-lymphocytes on various physiological processes, including haemopoiesis. Nude mice (nu/nu) of the CBA strain, nonmutant inbred CBA mice, and inbred C3H mice were reared in germ-free isolators and used to compare (1) the haematological parameters of nu/nu mice and CBA mice at different ages and (2) the labelling pattern of circulating leucocytes at various times after a single intraperitoneal injection of 3H-thymidine into 3-month-old nu/nu and C3H mice. The data suggest that the deficiency of T-lymphocytes in nu/nu mice may lead to a disturbance of haemopoiesis in 2 to 6-month animals which is characterised by a mild macrocytosis and a very marked reduction in the proportion of labelled leucocytes which can be seen in the blood after an injection of 3H-thymidine. Despite these perturbations, unstressed nu/nu mice were able to maintain adequate numbers of blood cells (other than lymphocytes) in their circulation. Nine-month-old nu/nu mice did not show a macrocytosis and the disappearance of the marcrocytosis at this age was associated with an increase both in the blood lymphocyte count and in the mass of lymphoid tissue in the spleen and mesenteric lymph nodes.     

Extracellular matrix from normal but not Steel mutant mice enhances melanogenesis in cultured mouse neural crest cells

The Steel mutation is a non-cell-autonomous defect in mice that affects the development of several stem cell populations, including germ cells, hematopoietic cells, and neural crest-derived pigment cells. To characterize the environmental lesion caused by the Steel mutation, we have compared the ability of normal and mutant extracellular matrix material to support the differentiation of normal mouse neural crest cells in vitro. Extracellular matrix deposited by cultured skin cells isolated from normal fetuses enhanced melanogenesis by crest cells over that observed on plastic substrata. In contrast, matrix material produced by Steel-Dickie (Sld) fetal skin cells failed to enhance melanogenesis. Adrenergic differentiation by neural crest-derived cells was promoted equally by both normal and mutant extracellular matrix compared to control substrata. We conclude that the environmental defect in mutant embryos selectively affects a melanogenic subpopulation of neural crest cells and resides, at least in part, in the extracellular matrix.     

Dynamics of haemopoiesis across mammals

Haemopoiesis is a fundamental physiologic process found in many animals. Among mammals, the diversity in size and function required suitable adaptations of this process. In this work, we use allometric principles to determine whether this required a change in the basic architecture of haemopoiesis. We show that it is possible to express both the number and rate with which haemopoietic stem cells replicate as well as total marrow output across all mammals as a function of adult mass. This unified view, which is compatible with the existing data, suggests that there was no need for major adaptations in the architecture of haemopoiesis across mammals.     

The role of growth factors in haemopoiesis

Many of the haemopoietic cell growth factors have now been purified to homogeneity and their structural genes cloned. Methods are also now available for obtaining pure populations of haemopoietic cells. The use of such cells, in combination with pure growth factors, has provided intriguing information about the biological activities and mode of action of the factors in faciliating survival, proliferation and differentiation of the haemopoietic cells.     

Altered cell-surface targeting of stem cell factor causes loss of melanocyte precursors in Steel17H mutant mice.

The normal products of the murine Steel (Sl) and Dominant white spotting (W) genes are essential for the development of melanocyte precursors, germ cells, and hematopoietic cells. The Sl locus encodes stem cell factor (SCF), which is the ligand of c-kit, a receptor tyrosine kinase encoded by the W locus. One allele of the Sl mutation, Sl17H, exhibits minor hematopoietic defects, sterility only in males, and a complete absence of coat pigmentation. The Sl17H gene encodes SCF protein which exhibits an altered cytoplasmic domain due to a splicing defect. In this paper we analyzed the mechanism by which the pigmentation phenotype in Sl17H mutant mice occurs. We show that in embryos homozygous for Sl17H the number of melanocyte precursors is severely reduced on the lateral neural crest migration pathway by e11.5 and can no longer be detected by e13.5 when they would enter the epidermis in wildtype embryos. The reduced number of dispersing melanocyte precursors correlates with a reduction of SCF immunoreactivity in mutant embryos in all tissues examined. Regardless of the reduced amount, functional SCF is present at the cell surface of fibroblasts transfected with Sl17H mutant SCF cDNA. Since SCF immunoreactivity normally accumulates in basolateral compartments of SCF-expressing embryonic epithelial tissues, we analyzed the localization of wildtype and Sl17H mutant SCF protein in transfected epithelial (MDCK) cells in vitro. As expected, wildtype forms of SCF localize to and are secreted from the basolateral compartment. In contrast, mutant forms of SCF, which either lack a membrane anchor or exhibit the Sl17H altered cytoplasmic tail, localize to and are secreted from the apical compartment of the cultured epithelium. We suggest, therefore, that the loss of melanocyte precursors prior to epidermal invasion, and the loss of germ cells from mature testis, can be explained by the inability of Sl17H mutant SCF to be targeted to the basolateral compartment of polarized epithelial keratinocytes and Sertoli cells, respectively.     

d-Aminoaciduria in mutant mice lackingd-amino-acid oxidase activity

Summary Urine of mutant ddY/DAO^– mice lackingd-amino-acid oxidase activity contained more serine and proline than that of normal ddY/DAO⁺ mice.d-Amino-acid oxidase treatment of urinary amino acids decreased the serine and proline, suggesting that they containedd-isomers. An HPLC analysis confirmed the presence ofd-serine. Urinary serine and proline contents were not decreased when the ddY/DAO^– mice were fed a diet which did not contain supplementaryd-methionine or when they were given water containing antibiotics. These results suggest that thed-serine andd-proline do not derive from thed-methionine supplemented in the diet or from intestinal bacteria. In urine of the ddY/DAO^– mice, a substance which seemed to bed-methionine sulfoxide and/ord-methionine sulfone was present. It is probably a metabolite of thed-methionine supplemented in the diet. Thed-aminoaciduria in the mutant mice lackingd-amino-acid oxidase activity indicates that this enzyme is involved in the metabolism of thed-amino acids in normal mice.     

Responses to novelty in staggerer mutant mice

Responses to novelty in normal C57BL/6 and staggerer mutant mice were recorded. The normal mice confronted a novel object in their familiar environment showed avoidance and burying responses while the staggerer mutant mice contacted it. When given the opportunity to move around freely in simultaneously presented novel and familiar environments, the mutant mice more quickly entered the novel areas than normal animals. these data reveal a significant decrease in the neophobic components of the neotic behaviour in the staggerer mice. However, since the mutant mice did not show a locomotor deficit, the impairment of neophobia seems not to be due to the gait abnormalities of these animals. The results support the view that the cerebellum may contribute to the organization of complex behaviours.     

Aberrant T cells in beige mutant mice

Cytotoxic T lymphocyte (CTL) morphology and function was examined in beige (bg/bg) mutant mice during infection with lymphocytic choriomeningitis virus (LCMV). Virus-specific, class I-restricted CTL activity mediated by total spleen leukocytes isolated from bg/+ or +/+ mice on days 7 or 9 postinfection with LCMV was moderately higher than that mediated by spleen cells isolated from bg/bg mice. The CTL generated in bg/bg mice had aberrant morphology. Lyt-2+ cells isolated from bg/+ or +/+ mice had typical large granular lymphocyte (LGL) morphology and contained numerous small azurophilic granules, whereas Lyt-2+ cells isolated from bg/bg mice contained only one or two large atypical granules in their cytoplasm. Aberrant LGL morphology correlated with reduced lytic capacity. The bg/bg CTL were inefficient killer cells mediating, on a per cell basis, only one fourth of the lysis mediated by bg/+ CTL. The bg/bg mice appeared to mount a compensatory response to regulate virus replication, because frequencies of Lyt-2+ cells and cells that specifically bound to virus-infected target cells were elevated as compared with their frequencies in bg/+ mice. The higher proportion of the CTL phenotype cells appeared to be a consequence of expanded proliferation of Lyt-2+ cells. These results demonstrate that, in comparison with bg/+ and +/+ mice, bg/bg mice have CTL with reduced lytic capacities, but may compensate during virus infection by expanding the number of these cells. Furthermore, these data suggest that the depressed lytic activity may be a consequence of aberrant granule formation.