Anorexia, a recessive mutation causing starvation in preweanling mice

A new autosomal recessive lethal mutation in mice, anorexia (anx), located close to pallid (pa) on chromosome (chr) 2, is described. Mutant mice are characterized by growth failure, an emaciated appearance, and abnormal behavior including headweaving, body tremors, uncoordinated gait, and hyperactivity during the late preweanling period. Data suggest that the mutant mice are not ingesting the levels of nutrients necessary to sustain life. This mutation may provide an important tool for studying the neurobiology of suckling behavior in the preweanling animal.

Adrenal changes in genetically hypothyroid mice

The adrenocortical X-zone was very poorly developed in young female mice homozygous for the hypothyroid, hyt, mutation, Feeding the mice thyroid powder resulted in the development of an X-zone. This subsequently degenerated in the same way as the X-zone found in the normal litter-mates of the mutants. We suggest that the adrenocortical effects may be due to changes in prolactin stimulation consequent upon the lack of response to thyrotrophin of the mutants.

"Viable motheaten," a new allele at the motheaten locus. I. Pathology

A new spontaneous autosomal recessive mutation has recently occurred at the motheaten (me) locus on Chromosome 6 in strain C57BL/6J mice. Homozygotes for the new allele, designated "viable motheaten" (mev), have a mean life span of 61 +/- 2.4 days, compared with only 22 +/- 1.3 days for C57BL/6J-me/me mice. Like the original motheaten mutation, the immediate cause of death in mev/mev mice appears to be severe pneumonitis associated with accumulations of macrophages, granulocytes, and lymphocytes in the lungs. However, because of its longer life span, progression of the disease in mev/mev mice is more amenable to investigation. Eosinophilic crystalline material in alveolar macrophages from mev/mev mice is associated with extravasation of erythrocytes into alveoli. These crystals are morphologically indistinguishable from hematoidin, which results from hemoglobin breakdown following uptake of erythrocytes by macrophages. Severe macrocytic hypochromic anemia with abnormalities in size and shape of erythrocytes develops by 7 weeks. A two-fold increase in peripheral leukocyte count and a five-fold increase in the percentage of neutrophils is seen by 10 weeks. Viable motheaten mice develop focal granulocytic skin lesions by 4 days of age, show depletion of cells from the thymus cortex by 4 weeks, and lack lymphoid follicles in the lymph nodes, spleen, and Peyer's patches. Excessive erythropoiesis and myelopoiesis in the spleen result in marked splenomegaly. Lymph nodes and spleens from mev/mev mice contain increased numbers of plasma cells by 3 weeks; and by 6 weeks, large numbers of atypical plasma cells with Russell bodies are evident. Development of glomerulonephritis by 10 weeks is characterized by granular depositis of immunoglobulin and complement within glomeruli. A twofold increase of blood urea nitrogen levels is present by 15 weeks. Sterility of male mev/mev mice is associated with Leydig cell depletion in the testes, lowered testosterone levels, and impaired spermatogenesis.

Etiology of growth hormone deficiency in little, Ames, and Snell dwarf mice

There are three recessive genes (little, Snell, and Ames) which cause dwarfism and GH deficiency in mice. These genes are nonallelic, and in the case of little mice, GH deficiency is isolated, while Snell and Ames dwarfs have deficiencies of GH as well as other anterior pituitary hormones. Previous reports in which restriction endonuclease analyses were used suggested that the GH genes are grossly intact in each of these types of dwarfs. In this report, ultrastructural studies of the anterior pituitary glands of little mice showed a deficiency or absence of secretory granules within somatotropes, while Snell and Ames dwarf pituitaries lacked identifiable somatotropes. Furthermore, there were deficiencies of GH precursor RNA and mRNA in total RNA from little pituitaries, while GH transcripts appeared to be absent in total RNA from Snell or Ames dwarf pituitaries. Thus, the primary defect in little mice may be in the production of GH transcripts, while GH deficiency in Snell and Ames dwarfs is probably due to defects other than alterations of the GH genes.

The effect of immunosuppression on streptozotocin-induced diabetes in C57BL/KsJ mice

The objective of this study was to determine whether mature thymic-derived T-lymphocytes were required for streptozotocin (SZ)-induced insulitis. C57BL/KsJ male mice were immunocrippled by thymectomy at 3 wk of age followed 1 wk later by lethal irradiation (1000 R) and hematopoietic reconstitution with syngeneic bone marrow (pretreated with anti-Thy 1.2 antiserum and complement to eliminate mature T-lymphocytes). As a control for the systemic effects of lethal irradiation itself, thymus-intact males were also irradiated and reconstituted with anti-Thy-1.2-treated marrow cells. This latter treatment resulted in a reconstitution of functional T-lymphocytes. Independent of the presence or absence of functional T-lymphocytes, irradiation extensively damaged the testes and produced at least a 50% reduction in plasma testosterone levels. In such effeminized males, the hyperglycemic response following 6 daily injections of SZ (35 mg/kg) was reduced in comparison to unirradiated males. Pancreatic insulin content was reduced 50% in both thymus-intact and thymectomized groups receiving lethal irradiation and SZ treatment; this correlated with histologic findings of small, beta-cell-depleted islets. Focal leukocytic infiltrates of the exocrine pancreas were induced by the irradiation. Streptozotocin-induced insulitis was also observed regardless of the presence (in thymus-intact mice) or absence (in thymectomized mice) of phytohemagglutinin-responsive T-lymphocytes. Both groups exhibited intact B-lymphocyte function as measured by proliferative responsiveness to lipopolysaccharide. Severe immunosuppression of both T- and B-lymphocyte function was produced by subcutaneous injection of hydrocortisone into thymectomized mice 48 h prior to initiation of SZ treatments. This treatment prevented SZ-induced beta-cell necrosis and eliminated lymphocytic infiltrates in the endocrine and exocrine pancreas. We conclude that functional (mature) T-lymphocytes are not required to mediate the beta cytotoxicity of multiple low doses of SZ in inbred strains in which insulitis accompanies islet destruction. The ability of hydrocortisone to protect beta-cells from the direct cytotoxic action of SZ as well as to eliminate leukocytic infiltration in the pancreas would support the hypothesis that insulitis is a consequence of beta-cell destruction, in this model, rather than its cause. DIABETES 32:148-155, February 1983.

Defective thyroid ontogenesis in fetal hypothyroid (hyt/hyt) mice

Thyroid glands of fetal hypothyroid (hyt/hyt) mice were studied to determine the effects of the mutant gene during embryogenesis. Comparisons of mutant and normal thyroids were made with respect to morphology, iodine-concentrating ability, and glandular thyroxine (T4) content at day 18 of gestation. Fetal hyt/hyt thyroid tissue was properly located, but incompletely differentiated. The mutant thyroid was characterized microscopically by small, poorly developed follicles with colloid diminished in PAS-staining properties. The mutant glands' ability to concentrate iodine was found to be only 5--16% of that exhibited by normal glands. When litters contained both mutant and normal off-spring, the differential iodine-concentrating ability allowed fetuses to be separated into two distinct, nonoverlapping populations. The distribution of fetal mice into high or low iodine-concentrating groups agreed closely with predicted frequencies for normal and mutant phenotypes. Thyroid content of T4 in mutant mice was found to be approximately equal to that found in age-matched normal controls. The poorly developed morphology and deficient iodine-concentrating ability of fetal thyroids from day 18 hyt/hyt mice indicated that the mutant gene acts during the ontogeny of this gland. Although such data are not available on human fetuses affected by thyroid dysgenesis, postnatal hyt/hyt mice display characteristics similar to those of infants born with this form of congenital primary hypothyroidism. Thus, elucidation of the site of mutant gene action in the mouse should contribute to our knowledge of disturbed fetal thyroid development and its implications in the adult mammal.

Analysis of growth hormone genes in mice with genetic defects of growth hormone expression

Restriction endonuclease analysis of genomic DNA was carried out for three types of dwarf mice (Little, Ames dwarf and Snell dwarf) that have genetic defects in GH expression. We found the GH genes to be present in homozygotes for each mutant allele as well as in their control litter-mates. These three type of dwarf mice may be useful in studying the molecular basis of inherited GH deficiency and as models for analogous genetic disorders of human GH expression.

Successful treatment of genetically hypophosphatemic mice by 1 alpha-hydroxyvitamin D3 but not 1,25-dihydroxyvitamin D3

The X-linked hypophosphatemia (Hyp) mutation in the mouse, a model for X-linked familial hypophosphatemic rickets in man, is characterized by defective phosphate transport. The role of vitamin D3 in the defective phosphate transport was investigated in three experiments by treatment of mutant mice with the natural hormonal form of vitamin D3, 1,25-dihydroxyvitamin D3, or its potent synthetic analog, 1 alpha-hydroxyvitamin D3. The results showed that both compounds were able to increase urinary phosphate conservation and improve rachitic bone morphology. Only 1 alpha-hydroxyvitamin D3, however, repaired the critically important hypophosphatemia and significantly increased intestinal transport of phosphate. These results indicate that defective phosphate transport in genetic hypophosphatemia is amenable to effective treatment. We hypothesize that the intestinal phosphate transport system is not genetically deleted but, instead, is unable to respond to 1,25-dihydroxyvitamin D3. Elucidation of the mechanism whereby 1 alpha-hydroxyvitamin D3 is able to stimulate the defective phosphate transport may provide fresh insight into the metabolic basis of the disease.

New mouse dw allele: genetic location and effects on lifespan and growth hormone levels

We have reported the finding of a new mutation at the dwarf locus, named dwarf-J, gene symbol dwJ, in the C3H/HeJ inbred mouse strain. The C3H/HeJ-dwJ/dwJ mice are like DW/J-dw/dw mice in that both homozygotes are virtually devoid of GH in either pituitary glands or serum. Lifespan of dwJ/dwJ mice was not reduced. Linkage experiments designed to assign the dw gene, together with another gene weaver (wv), were successful in that both were found to be on chromosome 16. The dw locus is probably more proximally located on chromosome 16 than the wv locus.

A cytogenetic investigation of inherited true hermaphroditism in BALB/cWt mice

A predictably high incidence of true hermaphroditism (3%) among fetal BALB/cWt mice provided the opportunity for studying the cause of inherited hermaphroditism. G-banded liver metaphase chromosomes were analyzed from 20 fetal hermaphrodites and from 15 normal female and male littermate controls. All hermaphrodites and seven males were chromosomal mosaics, i.e. XO/XY or XO/XY/XYY. In each mosaic fetus there were more XO than XYY cells. From these findings we hypothesize that BALB/cWt hermaphrodites arise from non-disjunction and probable loss of the Y-chromosome during mitosis. Results from breeding experiments indicated that a defect in the BALB/cWt Y-chromosome per se accounts for its nondisjunction and loss. A significant relationship was found between the amount of ovarian tissue and the percentage of XO cells in mosaic fetuses. If all chromosomally mosaic (XO/XY and XO/XY/XYY) individuals are considered, ovarian tissue was formed if there was 24% or more XO cells in an individual. If only hermaphroditic individuals are considered, ovarian tissue was formed if there were 44% or more XO cells. Finally, we found that the distribution of ovarian and testicular tissue within an ovotestis of BALB/cWt hermaphrodites was not random: ovarian tissue was situated at both ends or only at the cranial end; in only one case was ovarian tissue situated in the center flanked by testicular tissue. We suggest that such nonrandom distribution of ovarian and testicular tissue argues against the hypothesis that the organization of testicular tissue is dependent only on the presence of H-Y antigen.

The morphology of fetal gonads of spontaneous mouse hermaphrodites

The gonads of 107 spontaneous, chromosomal mosaic, day-15 fetal hermaphrodites derived from BALB/cWt strain male mice are described and photographs of seven gonads representative of the major types are presented. There were 16 ovaries, 15 testes, and 183 ovotestes. The ovotestes contained on the average more testicular tissue than ovarian, and the ovarian tissue was more frequently located at the gonad poles, particularly the craniad pole. There was no difference between left and right sides with regard to gonad type, but more pure gonads were found on the left than on the right side (21/10), Meioses were observed throughout the ovarian tissue and also in some testicular cords, particularly in the caudad pole of the gonad. Some meiotic figures contained sex vesicles. The significance of these findings is discussed in relation to several aspects of sex determination.

Inherited ateliotic dwarfism in mice. Characteristics of the mutation, little, on chromosome 6

A new autosomal recessive mutation in the mouse, little (lit), has been shown to be located on Chromosome 6. The mutation in the homozygous state causes ateliotic dwarfism that is first detected at 15 days of age by decreased body weight. Long bone lengths are significantly reduced. Skull width, however, is not affected. Female little mice are fully fertile; they may lose their first litters. Although most of the little males sire one or two litters, they rarely sire a third litter. Analysis of pituitary extracts electrophoresed on acrylamide gels reveal a significant reduction of the two anterior pituitary hormones, GH and PRL, in both male and female little mice. Because the little mouse shares a number of similarities with the human ateliotic dwarfism, isolated growth hormones deficiency type I, it may be a useful animal model for this inherited human growth disorder.