Hemopoietic precursor cell defects in nonanemic but stem cell-deficient W44/W44 mice

Hematopoietic stem cell deficiencies cause a severe macrocytic anemia in W/Wv mice. W44/W44 mice, on the other hand, are not anemic, but, since they accept marrow implants without prior total body irradiation, they have inherited a stem cell lesion. In an attempt to identify the aberrant stem cell(s), we have determined the concentration in W44/W44 marrow of hematopoietic precursors known to be deficient in W/Wv marrow. The in vitro erythroid burst-forming units (BFU-E), the in vivo spleen colony-forming units (CFU-S), and the cells that repopulate the erythroid compartment of stem cell-deficient mice were examined. The progenitors of 7-day bursts are dramatically reduced in W/Wv marrow but are present in normal concentrations in W44/W44 marrow. W44/W44 marrow CFU-S, unlike W/Wv, generate visible spleen colonies 10 days after injection into lethally irradiated recipients. The colonies are, however, smaller and at least 2 times less numerous than those produced from equivalent numbers of +/+ marrow. An additional defect was the inability of W44/W44 stem cells to compete with genetically marked +/+ cells during erythroid repopulation. An estimate of the number of W44/W44 stem cells needed to compete with +/+ cells was provided by enriching W44/W44 progenitors fivefold. Twice as many enriched W44/W44 marrow cells as unfractionated +/+ cells were required to replace competitor cells. This suggests that there are up to 10 times fewer stem cells somewhere in the W44/W44 erythrogenerative pathway. The data support the conclusion that an erythroid progenitor less mature than the BFU-E is one of the cells most severely affected by expression of the mutant gene.     

The shadow

Blepharospasm, the most frequent feature of cranial dystonia, and hemifacial spasm are two involuntary movement disorders that affect facial muscles. The cause of blepharospasm and other forms of cranial dystonia is not known. Hemifacial spasm is usually due to compression of the seventh cranial nerve at its exit from the brain stem. Cranial dystonia may result in severe disability. Hemifacial spasm tends to be much less disabling but may cause considerable distress and embarrassment. Patients affected with these disorders are often mistakenly considered to have psychiatric problems. Although the two disorders are quite distinct pathophysiologically, therapy with botulinum toxin has proven very effective in both. We review the clinical features, proposed pathophysiologic features, differential diagnosis and treatment, including the use of botulinum toxin, of cranial dystonia and hemifacial spasm.     

Contribution of midbody channels to embryogenesis in the mouse

Summary We have examined the persistence of midbody channels during the second, third, and fourth cleavage cycles of the mouse using immunofluorescence to map the distribution of midbody microtubule bundles in intact embryos. Electron microscopy showed these bundles to be a characteristic feature of midbodies throughout the interphase period. In recently-divided embryos at each cleavage stage the number of midbodies was half the number of blastomeres, and declined towards zero as the next cleavage approached. This indicated to us that the only midbodies present in each stage were those which had arisen in the immediately-preceding division. Of those blastomeres which were in mitosis at the time of fixation, less than 4% were connected via a midbody to another blastomere, demonstrating that persistence of midbodies beyond a single cleavage cycle is a rare event. We conclude that midbody channels in our embryos are likely to connect only pairs of sister blastomeres because midbodies do not persist through multiple cleavage cycles. Midbody channels cannot, therefore, be regarded as providing extensive cell coupling in advance of the onset of gap junctional communication.     

Airway responsiveness and prostaglandin generation in scorbutic guinea pigs

Airway responsiveness to histamine aerosol and lung prostaglandin generation were investigated in normal, partially vitamin C deficient and scorbutic guinea pigs. The ascorbic acid content of the lung expressed as microgram/100 mg wet weight lung parenchyma decreased from 22.1 +/- 1.8 (mean +/- SE) in the control group to 9.0 +/- 1.4 and 1.8 +/- 0.4 in tissues from partially ascorbic acid deficient and scorbutic animals, respectively. Guinea pigs on low and ascorbic acid deficient diets developed significant airway hyperresponsiveness to histamine aerosol after 3 and 4 weeks. Indomethacin (30 mg/Kg, i.p.) further increased the airway hyperresponsiveness in scorbutic animals but was without effect in control animals. Prostaglandin generation from different parts of the lung was significantly changed by the diets. However, airway hyperresponsiveness was not directly attributable to altered prostanoid generation. Scorbutic conditions did not alter the electrophysiological characteristics of airway smooth muscle namely, resting membrane potential and electrogenic sodium pump activity. In summary, ascorbic acid deficiency causes airway hyperresponsiveness to histamine in guinea pigs. This alteration seems not to be related to an altered prostaglandin generation by the lung or to the electrophysiological properties of airway smooth muscle.     

Microtiter micromass cultures of limb-bud mesenchymal cells

Summary A method is described for growing high-density micromass cultures of chick and mouse limb mesenchyme cells in 96-well microtiter plates (μTμM cultures). Rapid quantitative estimates of chondrogenic expression were obtained by automated spectrophotometric analysis of Alcian-blue-stained cartilage matrix extracts performed in the wells in which the cells had been grown. Quantitative estimates of myogenic expression were obtained similarly using anti-sarcomere myosin monoclonal antibody and modified ELISA techniques. This μTμM-ELISA method may be adapted for use with other antigens for which specific antibodies are available. These methods were used to compare cartilage and muscle differentiation in 1 to 4 d μTμM cultures grown in serum-containing (SCM) and defined (DM) media. The DM contains minimal additives (insulin, hydrocortisone, and in some cases, ascorbate or transferrin) and supports both chondrogenesis and myogenesis. The colorimetric analyses agree well with the morphologic appraisal of chondrogenesis and myogenesis. Similar numbers of cartilage nodules formed in all cultures, but in DM the nodules failed to enlarge; explaining the reduced matrix synthesis in DM as compared with SCM, and suggesting that nodule enlargement is a discrete, serum-dependent step. Studies of selected additives to DM show that transferrin enhances myogenesis, ascorbic acid enhances chondrogenesis, and retinoic acid inhibits chondrogenesis. Together, the μTμM system, in situ colorimetric assays of chondrogenesis and myogenesis, and DM will allow rapid prescreening of teratogens and screening of various bioactive compounds (e.g., hormones, growth factors, vitamins, adhesion factors) for effects on limb mesenchymal cell differentiation. This work was supported by grants RR08006-13 (DFP) and HD05505 and HD18577 (MS) from the National Institutes of Health, Bethesda, MD. MF-20 hybridoma supernatant was obtained from the Developmental Studies Hybridoma Bank, Department of Biology, University of Iowa, Iowa City, Iowa 52242 (maintained by NIH grant NO1-HD62915).     

Is the epithelium-derived inhibitory factor in guinea-pig trachea a prostanoid?

To examine further the possible prostanoid involvement in the influence of the epithelium on guinea-pig tracheal smooth muscle responsiveness, we have analyzed the effects of LTD₄, methacholine and histamine on the level of airway smooth muscle tone and on the amounts of PGE_2α and PGI₂ (determined by radioimmunoassay) in the presence and absence of the epithelium. Removal of the epithelium increased the sensitivity of guinea-pig trachea to the contractile effects of LTD₄, methacholine and histamine. LTD₄ (3–100 nM), methacoline (0.1–10 μM) or histamine (0.3–30 μM) did not increase prostanoid release above control values in either the presence or absence of the epithelium. The unstimulated release of PGE₂ and PGF_2α but not PGI₂, was decreased in tissues lacking epithelium. Indomethacin (1 μM) reduced the baseline tone to a smaller extent in the absence of epithelium. In the presence but not the absence of the epithelium, indomethacin increased the sensitivity of preparations to the contractile effect of methacholine. The results support the postulate of an epithelium-derived inhibitory factor modulating guinea-pig tracheal smooth muscle responsiveness. The identity of this factor is not known but is not PGI₂ and is unlikely to be PGF_2α or PGE₂. However, the possibility remains that the basal release of PGE₂ and/or PGF_2α derived from the epithelium may markedly affect the responsiveness of guinea-pig tracheal smooth muscle. Furthermore, the epithelium is a significant source of PGE₂ and PGF_2α which may be involved in the maintenance of baseline tone.     

Scales and costs of habitat selection in heterogeneous landscapes

Summary Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes. At one scale, habitat selection is determined by the differential use of foraging locations within a home range. At a larger scale, habitat selection is determined by dispersal and the ability to relocate the home range. The limits of both scales must be known for accurate assessments of habitat selection and its role in effecting spatial patterns in abundance. Isodars, which specify the relationships between population density in two habitats such that the expected reproductive success of an individual is the same in both, allow us to distinguish the two scales of habitat selection because each scale has different costs. In a two-habitat environment, the cost of rejecting one of the habitats within a home range can be expressed as a devaluation of the other, because, for example, fine-grained foragers must travel through both. At the dispersal scale, the cost of accepting a new home range in a different habitat has the opposite effect of inflating the value of the original habitat to compensate for lost evolutionary potential associated with relocating the home range. These costs produce isodars at the foraging scale with a lower intercept and slope than those at the dispersal scale.Empirical data on deer mice occupying prairie and badland habitats in southern Alberta confirm the ability of isodar analysis to differentiate between foraging and dispersal scales. The data suggest a foraging range of approximately 60 m, and an effective dispersal distance near 140 m. The relatively short dispersal distance implies that recent theories may have over-emphasized the role of habitat selection on local population dynamics. But the exchange of individuals between habitats sharing irregular borders may be substantial. Dispersal distance may thus give a false impression of the inability of habitat selection to help regulate population density.