Expression of human basic fibroblast growth factor cDNA in baby hamster kidney-derived cells results in autonomous cell growth

Growth factor over-production by responsive cells might contribute to their autonomous proliferation as well as their acquisition of a transformed phenotype in culture. Basic fibroblast growth factor (bFGF) has been shown to induce transient changes in cell behavior that resemble those encountered in transformed cells. In addition, several types of human tumor cells have been shown to produce bFGF. To determine directly the role that bFGF might play in the induction of the transformed phenotype, we have introduced a human bFGF cDNA expression vector into baby hamster kidney-derived (BHK-21) fibroblasts. One of the BHK transfectants, termed clone 19, expresses the bFGF mRNA and produces biologically active bFGF that accumulates to a high concentration inside the cells. These properties correlate with the ability of the cells to grow in serum-free medium without the addition of exogenous bFGF. Clone 19 cells also proliferated in soft agar, indicating that constitutive expression of the bFGF gene results in a loss of anchorage-dependent growth.     

Catecholamine innervation of enkephalinergic neurons in guinea pig hypothalamus: demonstration by an in vitro autoradiographic technique combined with a post-embedding immunogold method

To study the relationship between the catecholamine (CA) nerve endings and the enkephalinergic cell bodies in the magnocellular dorsal nucleus (MDN) of guinea pig hypothalamus, double-labeling experiments were performed on the same tissue section at the electron microscopic level. An in vitro autoradiographic (ARG) method for [3H]-norepinephrine (NE) or [3H]-dopamine (DA) was combined with a post-embedding immunogold cytochemical technique for Met-enkephalin (Met-enk) in colchicine-treated animals. Hypothalamic slices (450 micrograms) were perfused with [3H]-NE or [3H]-DA at the fluid-gas interface, then fixed by immersion with glutaraldehyde and osmic acid. Semi-thin sections processed from the thickness of the slices showed adequate penetration of the tracers to all parts of the tissue. Frontal sections permitted visualization of some CA-uptake structures distributed around the cells. At the ultrastructural level, preservation appeared good on about 60% of the thickness of slices, and [3H]-CA structures were easily distinguished. Ultra-thin sections were successively incubated with Met-enk and colloidal gold-labeled antisera, followed by ARG processing. At the electron microscopic level, the good integrity of the tissue made possible visualization of [3H]-CA nerve terminals making synaptic contacts with enkephalinergic perikarya. These results provide morphological evidence for direct catecholaminergic control of enkephalinergic neurons of the MDN.     

Generation of different nucleosome spacing periodicities in vitro. Possible origin of cell type specificity

We have been able to generate ordered nucleosome arrays that span the physiological range of spacing periodicities, using an in vitro system. Our system (a refinement of the procedure previously developed) uses the synthetic polynucleotide poly[d(A-T)], poly[d(A-T)], core histones, purified H1, and polyglutamic acid, a factor that increases nucleohistone solubility and greatly promotes the formation of ordered nucleosome arrays. This system has three useful features, not found in other chromatin assembly systems. First, it allowed us to examine histones from three different cell types/species (sea urchin sperm, chicken erythrocyte, and HeLa) as homologous or heterologous combinations of core and H1 histones. Second, it allowed us to control the average packing density (core histone to polynucleotide weight ratio) of nucleosomes on the polynucleotide; histone H1 is added in a second distinct step in the procedure to induce nucleosome alignment. Third, it permitted us to study nucleosome array formation in the absence of DNA base sequence effects. We show that the value of the spacing periodicity is controlled by the value of the initial average nucleosome packing density. The full range of physiological periodicities appears to be accessible to arrays generated using chicken erythrocyte (or HeLa) core histones in combination with chicken H5. However, chromatin-like structures cannot be assembled for some nucleosome packing densities in reactions involving some histone types, thus limiting the range of periodicities that can be achieved. For example, H1 histone types differ significantly in their ability to recruit disordered nucleosomes into ordered arrays at low packing densities. Sea urchin sperm H1 is more efficient than chicken H5, which is more efficient than H1 from HeLa or chicken erythrocyte. Sea urchin sperm core histones are more efficient in this respect than the other core histone types used. These findings suggest how different repeat lengths arise in different cell types and species, and provide new insights into the problems of nucleosome linker heterogeneity and how different types of chromatin structures could be generated in the same cell.     

Resistance ofSpodoptera frugiperda [Lep.: Noctuidae] to a nuclear polyhedrosis virus in the field and laboratory

Median lethal doses (LD₅₀s) of nuclear polyhedrosis virus (NPV) were determined in neonatal offspring ofSpodoptera frugiperda (J. E. Smith) (Sf) larvae captured in southeastern Louisiana in 1981, 1982, and 1984. These LD₅₀s ranged from 1.8 to 16.3 polyhedral inclusion bodies (PIB)/insect. The LD₅₀s significantly (P<0.05) increased during the season of 1982 but had no pattern in 1981 or 1984. However, the Sf populations increased in heterogeneity of response to the NPV during all 3 years. The LD₅₀ increased from 4.1 to 18.7 PIB/insect in a Sf laboratory colony exposed to the NPV LD₈₀ for 7 generations, whereas in a control colony not exposed to NPV the LD₅₀ was 5.9 PIB/insect after 7 generations.     

Cellular differences in the regeneration of murine skeletal muscle: a quantitative histological study in SJL/J and BALB/c mice

Summary Skeletal muscle regeneration in SJL/J and BALB/c mice subjected to identical crush injuries is markedly different: in SJL/J mice myotubes almost completely replace damaged myofibres, whereas BALB/c mice develop fibrotic scar tissue and few myotubes. To determine the cellular changes which contribute to these differential responses to injury, samples of crushed tibialis anterior muscles taken from SJL/J and BALB/c mice between 1 and 10 days after injury were analysed by light and electron microscopy, and by autoradiography. Longitudinal muscle sections revealed about a 2-fold greater total mononuclear cell density in SJL/J than BALB/c mice at 2 to 3 days after injury. Electron micrographs identified a similar proportion of cell types at 3 days after injury. Autoradiographic studies showed that the proportions of replicating mononuclear cells in both strains were similar: therefore greater absolute numbers of cells (including muscle precursors and macrophages) were proliferating in SJL/J muscle. Removal of necrotic muscle debris in SJL/J mice was rapid and extensive, and by 6 to 8 days multinucleated myotubes occupied a large part of the lesion. By contrast, phagocytosis was less effective in BALB/c mice, myotube formation was minimal, and fibrotic tissue conspicuous. These data indicate that the increased mononuclear cell density, more efficient removal of necrotic muscle, together with a greater capacity for myotube formation in SJL/J mice, contribute to the more successful muscle regeneration seen after injury.     

Isolation and mapping of polymorphic cosmid clones used for sublocalization of the multiple endocrine neoplasia type 1 (MEN1) locus

Summary Multiple endocrine neoplasia type 1 (MEN1) is characterized by neoplasia of the parathyroids, the pancreas, and the pituitary. Tumorigenesis involves unmasking of a recessive mutation at the MEN1 locus, which has been mapped to the centromeric part of chromosomal region 11q. In order to localize the MEN1 gene further and to make its isolation possible, a number of new markers were isolated. Two radiation-reduced somatic cell hybrids were identified that only contained markers close to and flanking the MEN1 region. DNA from these hybrids was used for the construction of a cosmid library, and clones containing human inserts were isolated. In addition, cosmid clones were isolated for locus expansion of 7 other markers that were mapped to the 11q12–13.2 region. The 33 newly isolated clones together with 25 previously published markers from this region were analyzed in a panel of radiation-reduced somatic cell hybrids. From the hybridization pattern, the region was divided into 11 parts. New restriction fragment length polymorphisms were identified in 7 of the newly isolated cosmid clones and in one plasmid. These were then used to sublocalize meiotic cross-overs more precisely in two MEN1 families, thus refining the mapping of the disease gene.     

Nitroxide-mediated protection against X-ray- and neocarzinostatin-induced DNA damage.

The stable free radical Tempol (4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy) has been shown to protect against X-ray-induced cytotoxicity and hydrogen peroxide- or xanthine oxidase-induced cytotoxicity and mutagenicity. The ability of Tempol to protect against X-ray- or neocarzinostatin (NCS)-induced mutagenicity or DNA double-strand breaks (dsb) was studied in Chinese hamster cells. Tempol (50 mM) provided a protection factor of 2.7 against X-ray-induced mutagenicity in Chinese hamster ovary (CHO) AS52 cells, with a protection factor against cytotoxicity of 3.5. Using the field inversion gel electrophoresis technique of measuring DNA dsb, 50 mM Tempol provides a threefold reduction in DNA damage at an X-ray dose of 40 Gy. For NCS-induced damage, Tempol increased survival from 9% to 80% at 60 ng/mL NCS and reduced mutation induction by a factor of approximately 3. DNA dsb were reduced by a factor of approximately 7 at 500 ng/mL NCS. Tempol is representative of a class of stable nitroxide free radical compounds that have superoxide dismutase-mimetic activity, can oxidize metal ions such as ferrous iron that are complexed to DNA, and may also detoxify radiation-induced organoperoxide radicals by competitive scvenging. The NCS chromophore is reduced by sulfhydryls to an active form. Electron spin resonance (ESR) spectroscopy shows that 2-mercaptoethanol-activated NCS reacts with Tempol 3.5 times faster than does unactivated NCS. Thus, Tempol appears to inactivate the NCS chromophore before a substantial amount of DNA damage occurs.     

Hydrotropism and Its Interaction with Gravitropism in Maize Roots

We have partially characterized root hydrotropism and its interaction with gravitropism in maize (Zea mays L.). Roots of Golden Cross Bantam 70, which require light for orthogravitropism, showed positive hydrotropism; bending upward when placed horizontally below a hydrostimulant (moist cheesecloth) in 85% relative humidity (RH) and in total darkness. However, the light-exposed roots of Golden Cross Bantam 70 or roots of a normal maize cultivar, Burpee Snow Cross, showed positive gravitropism under the same conditions; bending downward when placed horizontally below the hydrostimulant in 85% RH. Light-exposed roots of Golden Cross Bantam 70 placed at 70° below the horizontal plane responded positively hydrotropically, but gravitropism overcame the hydrotropism when the roots were placed at 45° below the horizontal. Roots placed vertically with the tip down in 85% RH bent to the side toward the hydrostimulant in both cultivars, and light conditions did not affect the response. Such vertical roots did not respond when the humidity was maintained near saturation. These results suggest that hydrotropic and gravitropic responses interact with one another depending on the intensity of one or both factors. Removal of the approximately 1.5 millimeter root tip blocked both hydrotropic and gravitropic responses in the two cultivars. However, removal of visible root tip mucilage did not affect hydrotropism or gravitropism in either cultivar.