Peptide signaling for drought-induced tomato flower drop.

The premature abscission of flowers and fruits limits crop yield under environmental stress. Drought-induced flower drop in tomato plants was found to be regulated by phytosulfokine (PSK), a peptide hormone previously known for its growth-promoting and immune-modulating activities. PSK formation in response to drought stress depends on phytaspase 2, a subtilisin-like protease of the phytaspase subtype that generates the peptide hormone by aspartate-specific processing of the PSK precursor in the tomato flower pedicel. The mature peptide acts in the abscission zone where it induces expression of cell wall hydrolases that execute the abscission process. Our results provide insight into the molecular control of abscission as regulated by proteolytic processing to generate a small plant peptide hormone.

Cross talk between stimulated NF-kappaB and the tumor suppressor p53.

Nuclear factor-kappaB (NF-kappaB) and p53 critically determine cancer development and progression. Defining the cross talk between these transcription factors can expand our knowledge on molecular mechanisms of tumorigenesis. Here, we show that induction of replicational stress activates NF-kappaB p65 and triggers its interaction with p53 in the nucleus. Experiments with knockout cells show that p65 and p53 are both required for enhanced NF-kappaB activity during S-phase checkpoint activation involving ataxia-telangiectasia mutated and checkpoint kinase-1. Accordingly, the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) also triggers formation of a transcriptionally active complex containing nuclear p65 and p53 on kappaB response elements. Gene expression analyses revealed that, independent of NF-kappaB activation in the cytosol, TNF-induced NF-kappaB-directed gene expression relies on p53. Hence, p53 is unexpectedly necessary for NF-kappaB-mediated gene expression induced by atypical and classical stimuli. Remarkably, data from gain- and loss-of function approaches argue that anti-apoptotic NF-kappaB p65 activity is constitutively evoked by a p53 hot-spot mutant frequently found in tumors. Our observations suggest explanations for the outstanding question why p53 mutations rather than p53 deletions arise in tumors of various origins.

Determination by interphase-FISH of the clonality of aberrant karyotypes in human hematopoietic neoplasias.

Interphase-FISH (fluorescence in situ hybridization) studies have been devoted to the determination of clonality of aberrant karyotypes in human leukemia. Various levels of its extent have been examined, including the meaning of a single aberrant karyotype as representing a microclone, the use of FISH to confirm clonality in bi- or multiclonal leukemia, the estimation of the residual (aberrant) clone after contrasexual bone marrow transplantation, and the redetectability in interphase of the abl/bcr rearrangement. The quantitative findings of all these lines of interphase FISH analyses were based on the comparison with data from a large-scale "control" study on normal cells using the same DNA probes which have been chosen for the determination of clonality, i.e. centromeric DNA probes for chromosomes #1, #3, from #6 to #12, from #15 to #18, #20, X and Y, and a specific probe for the abl/bcr rearrangement. In addition, the validity of interphase-FISH analysis on classical bone marrow smears was examined. As a common outcome it was concluded that interphase-FISH technique is a valuable tool for defining clonality of karyotypic changes and, as a consequence, yields additional prognostic information in many human leukemias. It is recommended to perform interphase FISH in routine cytogenetics of leukemia, whenever reasonable.

Chromosomal heterogeneity of aneuploid leukemic cell populations detected by conventional karyotyping and by fluorescence in situ hybridization (FISH).

Beside the frequent aneusomies of chromosomes # 7 and # 8 gains or losses of several other chromosomes are found in bone marrow cells of leukemia patients. Chromosomal heterogeneity of interphase cell populations was studied by fluorescence in situ hybridization (FISH) with centromeric DNA probes for chromosomes #2, #3, #4, #6, #9, #11, #12, #15, #16, #17, #18, #20, as well as X and Y which were found to be aberrant by routine karyotyping of 28 cases of various malignant hematopoietic diseases. Particularly, the data obtained by both routes of analysis were compared quantitatively. As the most prominent result, all aberrations found by classical karyotyping were redetected by interphase cytogenetics, but additional aberrant clones could be observed among the interphase cell populations. The frequencies of the cell clones with hypersomies were in general higher in metaphase than in interphase, and, vice versa, monosomic cells were found more frequently in interphase than in metaphase. Single aberrant karyotypes in all cases were redetected as microclones of interphase cells. Interphase cytogenetics using FISH, therefore, was shown not only to be a reliable measure of the genomic heterogeneity of leukemic cell populations but, in addition, to be a valuable and informative supplement to routine leukemia cytogenetics with regard to the detection of microclones which, later on, could dominate the progression of the malignant disease.

Use of fluorescence in-situ hybridization (fish) for the estimation of the aberrant cell clone in leukemias with trisomy-8 or monosomy-7 detected by karyotyping.

The sizes of leukemic cell clones with hypersomies of the chromosome #8 or monosomy #7, which primarily were detected by classical karyotyping, were estimated by fluorescence in situ hybridization (FISH) with centromeric DNA probes in interphase cell populations of the bone marrow of 31 leukemia patients. Particularly, the data obtained by both routes of analysis were compared quantitatively. As most prominent result, all aberrations found by classical karyotyping were redetected by interphase cytogenetics, but additional aberrant clones could be observed among the interphase cell populations. The frequencies of the cell clones with hypersomies #8, in general, were higher in metaphase than' in interphase, and, vice versa, cells monosomic for #7, in the majority of cases, were found to be more frequent in interphase than in metaphase. These data support the idea that metaphase data per se may not sufficiently reflect the actual portions of aneuploid cell clones in the whole leukemic cell population. This may be of practical importance in diagnostic and prognostic respects but also for the choice of specific therapies.