Factors contributing to ice nucleation and sequential freezing of leaves in wheat.

MAIN CONCLUSION: Anatomical, metabolic and microbial factors were identified that contribute to sequential freezing in wheat leaves and likely contribute to supercooling in the youngest leaves and potentially meristematic regions. Infrared thermography (IR) has been used to observe wheat leaves freezing independently and in an age-related sequence with older leaves freezing first. To determine mechanisms that might explain this sequence of freezing several analytical approaches were used: (1) The size of xylem vessels, in proximity to where freezing initiated, was measured to see if capillary freezing point depression explained sequential freezing. The sequence of freezing in the four youngest leaves was correlated, with the largest vessels freezing first. (2) Carbohydrate and amino acids were analyzed to determine if solute concentrations as well as interactions with membranes explained the freezing sequence. Sucrose was highly correlated to the freezing sequence for all leaves suggesting a prominent role for this sugar as compared to other simple sugars and fructans. Among individual free amino acids proline and serine were correlated to the freezing sequence, with younger leaves having the highest concentrations. (3) Microflora within and on leaf surfaces were determined to measure potential freezing initiation. Levels of bacteria and fungi were correlated to the freezing sequence for all leaves, and species or genera associated with high ice nucleation activity were absent in younger leaves. Moisture content and transcript expression of ice binding proteins were also measured. As expected, our results show that no single mechanism explains the freezing sequence observed via infrared analyses. While these multiple mechanisms are operative at different levels according to the leaf age, they seem to converge when it comes to the protection of vital meristematic tissues. This provides potential phenotypic characters that could be used by breeders to develop more winter-hardy genotypes.

Spinocerebellar ataxia type 5 in a family descended from the grandparents of President Lincoln maps to chromosome 11.

Autosomal dominant ataxias are a genetically heterogeneous group of disorders for which spinocerebellar ataxia (SCA) loci on chromosomes 6p, 12q, 14q and 16q have been reported. We have examined 170 individuals (56 of whom were affected) from a previously unreported ten-generation kindred with a dominant ataxia that is clinically and genetically distinct from those previously mapped. The family has two major branches which both descend from the paternal grandparents of President Abraham Lincoln. Among those examined, 56 individuals have a generally non-life threatening cerebellar ataxia. Disease onset varies from 10-68 years and anticipation is evident. We have mapped this gene, spinocerebellar ataxia type 5 (SCA5), to the centromeric region of chromosome 11.

Localization of human BRCA1 and its loss in high-grade, non-inherited breast carcinomas.

Although the link between the BRCA1 tumour-suppressor gene and hereditary breast and ovarian cancer is established, the role, if any, of BRCA1 in non-familial cancers is unclear. BRCA1 mutations are rare in sporadic cancers, but loss of BRCA1 resulting from reduced expression or incorrect subcellular localization is postulated to be important in non-familial breast and ovarian cancers. Epigenetic loss, however, has not received general acceptance due to controversy regarding the subcellular localization of BRCA1 proteins, reports of which have ranged from exclusively nuclear, to conditionally nuclear, to the ER/golgi, to cytoplasmic invaginations into the nucleus. In an attempt to resolve this issue, we have comprehensively characterized 19 anti-BRCA1 antibodies. These reagents detect a 220-kD protein localized in discrete nuclear foci in all epithelial cell lines, including those derived from breast malignancies. Immunohistochemical staining of human breast specimens also revealed BRCA1 nuclear foci in benign breast, invasive lobular cancers and low-grade ductal carcinomas. Conversely, BRCA1 expression was reduced or undetectable in the majority of high-grade, ductal carcinomas, suggesting that absence of BRCA1 may contribute to the pathogenesis of a significant percentage of sporadic breast cancers.

Suppression of tumor growth through disruption of hypoxia-inducible transcription.

Chronic hypoxia, a hallmark of many tumors, is associated with angiogenesis and tumor progression. Strategies to treat tumors have been developed in which tumor cells are targeted with drugs or gene-therapy vectors specifically activated under hypoxic conditions. Here we report a different approach, in which the normal transcriptional response to hypoxia is selectively disrupted. Our data indicate that specific blockade of the interaction of hypoxia-inducible factor with the CH1 domain of its p300 and CREB binding protein transcriptional coactivators leads to attenuation of hypoxia-inducible gene expression and diminution of tumor growth. Thus, disrupting the normal co-activational response to hypoxia may be a new and useful therapeutic strategy.

Radioimmunoassay of mammalian type C viral proteins. 3. Detection of viral antigen in normal murine cells and tissues.

A radioimmunoassay specific for a murine leukemia virus structural protein, the gs antigen, detects an antigenic reactivity in normal murine cells in culture and natural tissues. The assay was shown to measure an antigen that is highly related to the virion protein as shown by absorption tests, immunoadsorbent chromatography, and by analysis of linearized dose-response curves. These findings combined with the finding of viral-specific RNA indicate that portions of the viral genome are being expressed with a much greater frequency than previously appreciated.

3D volumes constructed from pixel-based images by digitally clearing plant and animal tissue.

Construction of three-dimensional volumes from a series of two-dimensional images has been restricted by the limited capacity to decrease the opacity of tissue. The use of commercial software that allows colour-keying and manipulation of two-dimensional images in true three-dimensional space allowed us to construct three-dimensional volumes from pixel-based images of stained plant and animal tissue without generating vector information. We present three-dimensional volumes of (1) the crown of an oat plant showing internal responses to a freezing treatment, (2) a sample of a hepatocellular carcinoma from a woodchuck liver that had been heat-treated with computer-guided radiofrequency ablation to induce necrosis in the central portion of the tumour, and (3) several features of a sample of mouse lung. The technique is well suited to images from large sections (greater than 1 mm) generated from paraffin-embedded tissues. It is widely applicable, having potential to recover three-dimensional information at virtually any resolution inherent in images generated by light microscopy, computer tomography, magnetic resonance imaging or electron microscopy.

Characterization of primary rabbit kidney cultures that express proximal tubule functions in a hormonally defined medium.

Primary cultures of rabbit-kidney epithelial cells derived from purified proximal tubules were maintained without fibroblast overgrowth in a hormone-supplemented serum-free medium (Medium RK-1). A hormone-deletion study indicated that the primary cultures derived from purified rabbit proximal tubules required all of the three supplements in Medium RK-1 (insulin, transferrin, and hydrocortisone) for optimal growth but did not grow in response to EGF and T3. In contrast, the epithelial cells in primary cultures derived from an unpurified preparation of rabbit kidney tubules and glomeruli grew in response to EGF and T3, as well as insulin, transferrin, and hydrocortisone. These observations suggest that kidney epithelial cells derived from different segments of the nephron grow differently in response to hormones and growth factors. Differentiated functions of the primary cultures derived from proximal tubules were examined. Multicellular domes were observed, indicative of transepithelial solute transport by the monolayers. The proximal tubule cultures also accumulated alpha-methylglucoside (alpha-MG) against a concentration gradient. However, little or no alpha-MG accumulation was observed in the absence of Na+. Metabolic inhibitor studies also indicated that alpha-MG uptake by the primaries is an energy-dependent process, and depends upon the activity of the Na+/K+ ATPase. Phlorizin at 0.1 mM significantly inhibited 1 mM alpha-MG uptake whereas 0.1 mM phloretin did not have a significant inhibitory effect. Similar observations have been made concerning the Na+-dependent sugar-transport system located on the lumenal side of the proximal tubule, whereas the Na+-independent sugar transporter on the peritubular side is more sensitive to inhibition by phloretin than phlorizin. The cultures also exhibited PTH-sensitive cyclic AMP synthesis and brush-border enzymes typical of proximal cells. However, the activities of the enzymes leucine aminopeptidase, alkaline phosphatase, and gamma-glutamyl-transpeptidase were lower in the cultures than in purified proximal-tubule preparations from which they are derived.

Binding to DNA and the retinoblastoma gene product promoted by complex formation of different E2F family members.

The E2F family of transcription factors functions in the control of the mammalian cell cycle. Here it is shown that two family members, E2F-1 and DP-1, form specific heterodimers in vivo, a process that enhances DNA binding, transactivation, and the binding of the retinoblastoma gene product. These results suggest that heterodimerization regulates E2F function and contributes to cell cycle control.

Superinduction of endogenous type C virus by 5-bromodeoxyuridine from transformed mouse clones.

Certain transformed subclones of the mouse cell line BALB/3T3 release 5 to 15 times more type C virus per cell than the parent cell line after treatment with 5-bromodeoxyuridine. Virus release begins within 8 hours and exponentially increases for the first 24 to 48 hours. Superinducibility is associated with the transformed phenotype.

Myoglobin diffusion in bovine heart muscle.

The rotational mobility of myoglobin in situ was determined by proton nuclear magnetic resonance line width measurements of a characteristic myoglobin resonance observed in bovine heart muscle spectra. The protein diffuses intracellularly at nearly half the rate observed in dilute solution. This high mobility allows the oxygenated form of myoglobin to contribute significantly to the overall diffusive flux of oxygen in respiring heart muscle.

Interaction of p107 with cyclin A independent of complex formation with viral oncoproteins.

The p107 protein and the retinoblastoma protein (RB) both bind specifically to two viral oncoproteins, the SV40 T antigen (T) and adenoviral protein E1A (E1A). Like RB, p107 contains a segment (the pocket) that, alone, can bind specifically to T, E1A, and multiple cellular proteins. Cyclin A bound to the p107 pocket, but not the RB pocket. Although both pockets contain two, related collinear subsegments (A and B), the unique sequence in the p107 pocket that occupies the space between A and B is required for the interaction with cyclin A.

Mammalian cells in culture frequently release type C viruses.

Cell cultures commonly used in animal cell research, both cell strains and continuous cell lines from various mammalian species, spontaneously produce type C RNA viruses.

Interaction between human cyclin A and adenovirus E1A-associated p107 protein.

The products of the adenovirus early region 1A (E1A) gene are potent oncoproteins when tested in standard transformation and immortalization assays. Many of the changes induced by E1A may be due to its interaction with cellular proteins. Four of these cellular proteins are the retinoblastoma protein (pRB), p107, cyclin A, and p33cdk2. The pRB and p107 proteins are structurally related and have several characteristics in common, including that they both bind to the SV40 large T oncoprotein as well as to E1A. Cyclin A and p33cdk2 are thought to function in the control of the cell cycle. They bind to one another, forming a kinase that closely resembles the cell cycle-regulating complexes containing p34cdc2. Cyclin A is now shown to bind to p107 in the absence of E1A. The association of p107 with cyclin A suggests a direct link between cell cycle control and the function of p107.

Altered cytokine export and apoptosis in mice deficient in interleukin-1 beta converting enzyme.

The interleukin-1 beta (IL-1 beta) converting enzyme (ICE) processes the inactive IL-1 beta precursor to the proinflammatory cytokine. Adherent monocytes from mice harboring a disrupted ICE gene (ICE-/-) did not export IL-1 beta or interleukin-1 alpha (IL-1 alpha) after stimulation with lipopolysaccharide. Export of tumor necrosis factor-alpha and interleukin-6 (IL-6) from these cells was also diminished. Thymocytes from ICE-/- mice were sensitive to apoptosis induced by dexamethasone or ionizing radiation, but were resistant to apoptosis induced by Fas antibody. Despite this defect in apoptosis, ICE-/- mice proceed normally through development.

Role of T-bet in commitment of TH1 cells before IL-12-dependent selection.

How cytokines control differentiation of helper T (TH) cells is controversial. We show that T-bet, without apparent assistance from interleukin 12 (IL-12)/STAT4, specifies TH1 effector fate by targeting chromatin remodeling to individual interferon-gamma (IFN-gamma) alleles and by inducing IL-12 receptor beta2 expression. Subsequently, it appears that IL-12/STAT4 serves two essential functions in the development of TH1 cells: as growth signal, inducing survival and cell division; and as trans-activator, prolonging IFN-gamma synthesis through a genetic interaction with the coactivator, CREB-binding protein. These results suggest that a cytokine does not simply induce TH fate choice but instead may act as an essential secondary stimulus that mediates selective survival of a lineage.

Activation of interferon-gamma inducing factor mediated by interleukin-1beta converting enzyme.

The interleukin-1beta (IL-1beta) converting enzyme (ICE) processes the inactive IL-1beta precursor to the proinflammatory cytokine. ICE was also shown to cleave the precursor of interferon-gamma inducing factor (IGIF) at the authentic processing site with high efficiency, thereby activating IGIF and facilitating its export. Lipopolysaccharide-activated ICE-deficient (ICE-/-) Kupffer cells synthesized the IGIF precursor but failed to process it into the active form. Interferon-gamma and IGIF were diminished in the sera of ICE-/- mice exposed to Propionibacterium acnes and lipopolysaccharide. The lack of multiple proinflammatory cytokines in ICE-/- mice may account for their protection from septic shock.

Rescue of a telomere length defect of Nijmegen breakage syndrome cells requires NBS and telomerase catalytic subunit.

Nijmegen breakage syndrome (NBS) is a rare human disease displaying chromosome instability, radiosensitivity, cancer predisposition, immunodeficiency, and other defects [1, 2]. NBS is complexed with MRE11 and RAD50 in a DNA repair complex [3-5] and is localized to telomere ends in association with TRF proteins [6, 7]. We show that blood cells from NBS patients have shortened telomere DNA ends. Likewise, cultured NBS fibroblasts that exhibit a premature growth cessation were observed with correspondingly shortened telomeres. Introduction of the catalytic subunit of telomerase, TERT, was alone sufficient to increase the proliferative capacity of NBS fibroblasts. However, NBS, but not TERT, restores the capacity of NBS cells to survive gamma irradiation damage. Strikingly, NBS promotes telomere elongation in conjunction with TERT in NBS fibroblasts. These results suggest that NBS is a required accessory protein for telomere extension. Since NBS patients have shortened telomeres, these defects may contribute to the chromosome instability and disease associated with NBS patients.

Effects of controlled RAD52 expression on repair and recombination in Saccharomyces cerevisiae.

We have examined the effects of RAD52 overexpression on methyl methanesulfonate (MMS) sensitivity and spontaneous mitotic recombination rates. Cells expressing a 10-fold excess of RAD52 mRNA from the ENO1 promoter are no more resistant to MMS than are wild-type cells. Similarly, under the same conditions, the rate of mitotic recombination within a reporter plasmid does not exceed that measured in wild-type cells. This high level of expression is capable of correcting the defects of rad52 mutant cells in carrying out repair and recombination. From these observations, we conclude that wild-type amounts of Rad52 are not rate limiting for repair of MMS-induced lesions or plasmid recombination. By placing RAD52 under the control of the inducible GAL1 promoter, we find that induction results in a 12-fold increase in the fraction of recombinants within 4 h. After this time, the fraction increases less rapidly. When RAD52 expression is quickly repressed during induction, the amount of RAD52 mRNA decreases rapidly and no nascent recombinants are formed. This result suggests a short active half-life for the protein product. Induction of RAD52 in G1-arrested mutant cells also causes a rapid increase in recombinants, suggesting that replication is not necessary for plasmid recombination.

Mitotic gene conversion lengths, coconversion patterns, and the incidence of reciprocal recombination in a Saccharomyces cerevisiae plasmid system.

Plasmids capable of undergoing genetic exchange in mitotically dividing Saccharomyces cerevisiae cells were used to measure the length of gene conversion events, to determine patterns of coconversion when multiple markers were present, and to correlate the incidence of reciprocal recombination with the length of conversion tracts. To construct such plasmids, restriction site linkers were inserted both within the HIS3 gene and in the flanking sequences, and two different his3- alleles were placed in a vector. Characterization of the genetic exchanges in these plasmids showed that most occur with the conversion of one his3- allele. Many of these events included coconversions in which more than one marker along the allelic sequence was replaced. The frequency of coconversion decreased with the distance between two markers such that markers further than 1 kilobase apart were infrequently coconverted. From these results the average length of conversion was determined to be approximately 0.5 kilobase. Examination of coconversions involving three or more markers revealed an almost obligatory, simultaneous coconversion pattern of all markers. Thus, when two markers which flank an intervening marker are converted, the intervening marker is 20 times more likely to be converted than to remain unchanged. The results of these studies also showed that the incidence of reciprocal recombination, which accompanies more than 20% of the conversion events, is more frequent when the conversion tract is longer than average.

Cell cycle analysis of E2F in primary human T cells reveals novel E2F complexes and biochemically distinct forms of free E2F.

The transcription factor E2F activates the expression of multiple genes involved in cell proliferation, such as c-myc and the dihydrofolate reductase gene. Regulation of E2F involves its interactions with other cellular proteins, including the retinoblastoma protein (Rb), the Rb-related protein p107, cyclin A, and cdk2. We undertook a detailed analysis of E2F DNA-binding activities and their cell cycle behavior in primary human T cells. Three E2F DNA-binding activities were identified in resting (G0) T cells with mobilities in gel shift assays distinct from those of previously defined E2F complexes. One of these activities was found to be a novel, less abundant, Rb-E2F complex. The most prominent E2F activity in resting T cells (termed complex X) was abundant in both G0 and G1 but disappeared as cells entered S phase, suggesting a possible role in negatively regulating E2F function. Complex X could be dissociated by adenovirus E1A with a requirement for an intact E1A conserved region 2. However, X failed to react with a variety of antibodies against Rb or p107, implicating the involvement of an E1A-binding protein other than Rb or p107. In addition to these novel E2F complexes, three distinct forms of unbound (free) E2F were resolved in gel shift experiments. These species showed different cell cycle kinetics. UV cross-linking experiments suggested that a distinct E2F DNA-binding protein is uniquely associated with the S-phase p107 complex and is not associated with Rb. Together, these results suggest that E2F consists of multiple, biochemically distinct DNA-binding proteins which function at different points in the cell cycle.