The postmodernity of football hooliganism

By using a 'cultural' definition of 'postmodernism' (derived from Jameson and Martin) in which postmodernism is regarded as the transgression of modern boundaries, this article traces the emergence of postmodern aspects to violent male fandom at football games since the 1960s. It is argued that at games, male fans have created imaginary masculine and national boundaries by which they have affirmed their identities but that in fighting they have sought to breach these boundaries in postmodern fashion.

Dissecting the roles of VP0 cleavage and RNA packaging in picornavirus capsid stabilization: the structure of empty capsids of foot-and-mouth disease virus

Empty capsids of foot-and-mouth disease virus (FMDV) type A22 Iraq 24/64, whose structure has been solved by X-ray crystallography, are unusual for picornaviruses since they contain VP2 and VP4, the cleavage products of the protein precursor VP0. Both the N terminus of VP1 and the C terminus of VP4, which pack together close to the icosahedral threefold symmetry axis where three pentamers associate, are more disordered in the empty capsid than they are in the RNA-containing virus. The ordering of these termini in the presence of RNA strengthens interactions within a single protomer and between protomers belonging to different pentamers. The disorder in the FMDV empty capsid forms a subset of that seen in the poliovirus empty capsid, which has VP0 intact. Thus, VP0 cleavage confers stability on the picornavirus capsid over and above that attributable to RNA encapsidation. In both FMDV and poliovirus empty capsids, the internal disordering uncovers a conserved histidine which has been proposed to be involved in the cleavage of VP0. A comparison of the putative active sites in FMDV and poliovirus suggests a structural explanation for the sequence specificity of the cleavage reaction.

Lymphocytes of human term decidua decrease cell adhesion to a plastic substrate

Although human decidual lymphocytes have been widely studied, their function and possible interaction with trophoblast are still unclear. Here we show that whereas human early (EDL) and term (TDL) decidual lymphocytes were unable to kill human trophoblast by necrosis (assessed by the 51Cr-release assay) or apoptosis (DNA fragment assay), TDL but not EDL decreased trophoblast adhesion to a plastic substrate as determined by a [3H]thymidine assay. This effect, however, was not selective for trophoblast, as TDL also decreased the adhesion to plastic of human decidual stromal cells and HeLa cells. Our results suggest that TDL may play a role in placental detachment during parturition by decreasing trophoblast or decidual stromal cell adhesion.

Fluconazole disc diffusion testing for the routine laboratory

The increasing incidence of resistance to the antifungal agent, fluconazole, prompted the need for a rapid, reliable and easy-to-use susceptibility test. We have developed a disc diffusion test for fluconazole against Candida spp. suitable for a clinical laboratory. Disc diffusion tests on six different media were compared with MIC values. On the basis of correlation coefficient with MICs (r = -0.95), quality of growth and zone edge definition, Yeast Nitrogen Base agar with glucose (YNBG) produced the best results. Further studies on YNBG showed that the method is reliable for Candida albicans and for resistant isolates with no zone of inhibition, but results for the slower growing and uncommon species must be interpreted with some caution. Implementation of this test in the clinical laboratory has provided a much needed therapeutic service for clinicians within the hospital. It has also reduced the reliance on the reference laboratory for susceptibility results and the consequent costs involved.

Regions of human chromosome 2 (2q32-q35) and mouse chromosome 1 show synteny with the pufferfish genome (Fugu rubripes)

We have isolated and sequenced a cosmid clone from the compact genome of the Japanese pufferfish (Fugu rubripes) containing portions of three genes that have the same order as in human. The gene order is microtubule-associated protein (MAP-2), myosin light chain (MYL-1), and carbamoyl phosphate synthetase (CPS III). The intron-exon organization of Fugu CPS III is identical with that of rat CPS I, although the equivalent genomic fragments of rat and Fugu CPS span 87.9 and 21 kb, respectively. This is the first report of a piscine CPS III genomic structure and predicts a close evolutionary link between CPS III and CPS I. The 8-kb intergenic region between MYL-1 and CPS gave no clear areas of transcription factor-binding sites by pairwise comparison with shark or rat CPS promoter regions. However, there was a match with the rat myosin light chain 2 (MLC-2) gene promoter and a MyoD transcription factor-binding site 874 bp upstream of the MYL-1 gene.

The incorporation of mannoproteins in the cell wall of S. cerevisiae and filamentous Ascomycetes

In yeast, glucanase extractable cell wall proteins are anchored to the plasma membrane at an intermediate stage in their biogenesis via a glycosylphosphatidylinositol (GPI) moiety before they become anchored to the wall glucan via a beta 1,6-glucan linkage. The mechanism of the membrane processing step of cell wall proteins is not known. Here, we report that Ascomycete filamentous fungi involved in food spoilage such as Aspergillus, Paecilomyces and Penicillium, also contain GPI membrane-anchored proteins some of which are processed by an endogenous phospholipase C activity. Furthermore, similar to the situation in yeast, their cell walls contain mannoproteins which are linked to the glucan backbone through a beta 1,6-glucan linkage. Interestingly, one mould which contains a significant amount of non covalently linked beta 1,6-glucosylated cell wall proteins, is much more sensitive towards beta 1,3-glucanases and membrane perturbing peptides than the others.

Evolution of European bat lyssaviruses

Forty-seven European bat lyssaviruses (EBL) and two African insectivorous bat lyssaviruses (Duvenhage viruses) were selected for a comparison to be made of their evolutionary relationships. Studies were based on direct sequencing of the PCR-amplified products of the 400 nucleotides coding for the amino terminus of the nucleoprotein. Phylogenetic relationships were analysed after bootstrap resampling using the maximum parsimony and the neighbour-joining methods. Analyses of both the nucleotide and amino acid sequences placed these viruses in three separate clusters, namely genotype 4 (Duvenhage), genotype 5 (EBL1) and genotype 6 (EBL2). Evolutionary analysis of the nucleoprotein gene of EBL1 and EBL2 indicated low intrinsic heterogeneity mainly due to synonymous substitutions. In addition, both EBL1 and EBL2 evolved into at least two genetically distinguishable lineages (a and b) following geographical drifting. We can speculate that subsequently the lineages EBL1a and EBL1b were introduced into parts of northern Europe from two different geographical directions; EBL1b was probably introduced most recently and was from North Africa. Eptesicus serotinus appears to be the principal reservoir for EBL1 and Myotis dasycneme and M. daubentonii the reservoirs for EBL2.

Measurement of synovial lining volume by magnetic resonance imaging of the knee in chronic synovitis

OBJECTIVES

Current methods of monitoring chronic synovitis in a single joint rely on clinical examination derived indices, such as the detection of synovial thickening. This study aimed to develop a reproducible method for quantifying the volume of synovial lining in chronic synovitis using contrast enhanced magnetic resonance (MR) imaging.

METHODS

The knees of 18 patients with chronic synovitis were examined (34 studies). A 2D T1 weighted FLASH sequence was used to evaluate the temporal enhancement of synovial structures after intravenous contrast. Synovial lining volume was calculated from subtraction of pre and post-enhancement 3D T1 weighted MP RAGE images with thresholding and pixel counting. Eleven patients were examined before and after intra-articular glucocorticoid (mean interval 14 weeks) and MR data compared with changes in clinical examination derived indices of disease activity.

RESULTS

Synovial lining volume varied from 52-267 ml. The coefficient of variation in volume calculation was 3.5% for a single observer and was 3.8% for two observers. Synovial lining volume was quantified in all patients where synovial lining thickening could not be detected clinically. A decrease in synovial lining volume of > 40% was associated with an improvement in synovial lining thickening, detected clinically. Decreases in synovial lining volume were quantified by MR in two of three patients where changes in clinical examination derived indices were inconsistent.

CONCLUSIONS

A reproducible method of estimating the volume of synovial lining in patients with chronic synovitis has been developed. MR measurement of synovial lining volume may quantify changes in chronic synovitis that remain unidentified by clinical measures.

Phosphorylation of Raf-1 serine 338-serine 339 is an essential regulatory event for Ras-dependent activation and biological signaling

Activation of the Raf serine/threonine protein kinases is tightly regulated by multiple phosphorylation events. Phosphorylation of either tyrosine 340 or 341 in the catalytic domain of Raf-1 has been previously shown to induce the ability of the protein kinase to phosphorylate MEK. By using a combination of mitogenic and enzymatic assays, we found that phosphorylation of the adjacent residue, serine 338, and, to a lesser extent, serine 339 is essential for the biological and enzymatic activities of Raf-1. Replacement of S338 with alanine blocked the ability of prenylated Raf-CX to transform Rat-1 fibroblasts. Similarly, the loss of S338-S339 in Raf-1 prevented protein kinase activation in COS-7 cells by either oncogenic Ras[V12] or v-Src. Consistent with phosphorylation of S338-S339, acidic amino acid substitutions of these residues partially restored transforming activity to Raf-CX, as well as kinase activation of Raf-1 by Ras[V12] or v-Src. Two-dimensional phosphopeptide mapping of wild-type Raf-CX and Raf-CX[A338A339] confirmed the presence of a phosphoserine-containing peptide with the predicted mobility in the wild-type protein which was absent from the mutant. This peptide could be quantitatively precipitated by an antipeptide antibody specific for the 18-residue tryptic peptide containing S338-S339 and was demonstrated to contain only phosphoserine. Phosphorylation of this peptide in Raf-1 was significantly increased by coexpression with Ras[V12]. These data demonstrate that Raf-1 residues 338 to 341 constitute a unique phosphoregulatory site in which the phosphorylation of serine and tyrosine residues contributes to the regulation of Raf by Ras, Src, and Ras-independent membrane localization.

Evaluation of trophoblast HLA-G antigen with a specific monoclonal antibody

A monoclonal antibody to HLA-G has been generated by immunizing HLA-A2.1/human beta 2-microglobulin (beta 2 m) double transgenic mice with murine L cells transfected with both human beta 2 m and HLA-G. This monoclonal antibody, designated as G233, has been found not to cross-react with other HLA class I antigens when tested on numerous cell lines by flow cytometry. With immunohistology, all populations of extravillous trophoblast (cell columns, interstitial trophoblast, endovascular trophoblast, placental bed giant cells) were stained. An extensive range of adult and fetal tissues was also tested but none reacted with monoclonal antibody G233, including those previously reported to express HLA-G mRNA, indicating that the protein has a highly restricted distribution. Failure to detect HLA-G in the fetal thymus raises the question as to how T-cell tolerance to this antigen is induced. Immunoprecipitation of trophoblast surface proteins with monoclonal antibody G233 revealed a heavy chain of 39 kDa and a light chain of 12 kDa, indicating that HLA-G expressed on the surface of trophoblast is complexed with beta 2 m. However, sequential immunoprecipitation with monoclonal antibody W6/32 followed by monoclonal antibody G233 continued to detect a residual band of 39 kDa, suggesting that trophoblast surface HLA-G may also occur as free heavy chains not associated with beta 2 m. Immunoprecipitation followed by two dimensional gel electrophoresis showed that monoclonal antibody G233 recognizes several isoforms of HLA-G from trophoblast similar to the characteristic spot array previously described for HLA-G. This monoclonal antibody G233 will be highly useful in future experiments to elucidate the function of HLA-G.

Silane-coated silica particle colloid processing of human sperm

PURPOSE

The purpose of this study was to determine differences in the quality of human sperm processed through different lots of silane-coated silica particle colloid solutions. The objectives were to compare (a) sperm kinematic parameters, (b) the sperm acrosome status, (c) the membrane integrity of the head and tail regions, (d) the DNA normality, and (e) the heat-inducible hyperactivation motility after processing sperm through either a Silane-coated silica particle colloid solution, a Percoll solution, or a simple centrifuge sperm wash (control).

METHODS

Sperm cells were derived from pooled cryopreserved-thawed specimens of several donors (n = 10). The pooled sperm were divided and processed through either the centrifuge wash, the 90:47% two-layer Percoll, or one of three lots of silane-coated silica particle colloidal solutions from three vendors. Aliquots of sperm cells were analyzed using the Hamilton-Thorn HTM-C motility analyzer for differences in kinematics and hyperactivation. Sperm were also analyzed for membrane integrity at both head and tail regions, normal morphology, acrosome status, and viability. Sperm undergoing apoptosis were determined using the acridine orange stain. Processed sperm were also incubated at 40 degrees C for 4 hr and the quality of the sperm was assessed using the heat-induced hyperactivation and motility parameter.

RESULTS

The data showed that after sperm processing, the number of sperm recovered was higher for the three lots of colloids (silane-coated silica particle colloid solutions) compared with Percoll processing. Total sperm motility was higher in the colloidal washes compared with the control. There were no differences in motility between Percoll- and colloid-processed sperm. In contrast, the percentages of sperm exhibiting progressive motility or hyperactivation varied among the different lots of colloid solutions. The Percoll wash solution yielded the highest percentage of sperm with intact tail membranes, whereas some lots of colloid solutions disrupted sperm head membranes. The percentages of sperm undergoing apoptosis varied for the different lots of colloid solutions. There was a marked increase in hyperactivation associated with one colloid solution after heat induction.

CONCLUSIONS

The results demonstrated variability in the different lots of silane-coated silica particle colloid solutions for processing sperm. Each lot of colloid solution excelled at improving different sperm parameters. The silane-coated silica particle colloid solutions were shown to be effective in recovering motile sperm compared with Percoll but the types of motility and sperm quality varied for the different lots of colloid solutions. Due to the variability in lots of silane-coated silica colloid solutions, reported studies based on only one lot or one source of colloid solution may be difficult to interpret. Furthermore, it may be advantageous to select the best lot of silane-coated silica particle colloid solution to produce the highest number of sperm exhibiting the ideal parameters for use in assisted reproduction technologies.

Chromosomal localization of three human dual specificity phosphatase genes (DUSP4, DUSP6, and DUSP7)

Mitogen-activated protein (MAP) kinase phosphatases constitute a growing family of dual specificity phosphatases thought to play a role in the dephosphorylation and inactivation of MAP kinases and are therefore likely to be important in the regulation of diverse cellular processes such as proliferation, differentiation, and apoptosis. For this reason it has been suggested that MAP kinase phosphatases may be tumor suppressors. We have determined the chromosomal locations of three human dual specificity phosphatase genes by fluorescence in situ hybridization and radiation hybrid mapping. The genes were localized to three different chromosomes, MKP2 (DUSP4) to 8p11-p12, MKP3 (DUSP6) to 12q22-q23, and MKPX (DUSP7) to 3p21. This will allow the potential roles of these genes in disease processes to be evaluated.

Lethal graft-versus-host disease after simultaneous kidney-pancreas transplantation

BACKGROUND

This case report is the first documentation of the occurrence and potential source of lethal graft-versus-host disease (GVHD) after simultaneous kidney-pancreas transplantation. The patient was a 27-year-old African-American male who received an ABO-compatible, five HLA antigen-mismatched kidney-pancreas transplant from a 17-year-old African-American female donor, who died after childbirth.

METHODS

Preoperative crossmatches using lymphocytotoxicity and flow cytometry were negative. The patient received four blood transfusions within 10 days of transplantation. Immunosuppression consisted of OKT3 induction, and then cyclosporine, azathioprine, and corticosteroids.

RESULTS

On postoperative day (POD) 9, the patient became febrile, and leukocytopenia and pancytopenia developed. Immunosuppression was reduced and granulocyte colony-stimulating factor was begun. Cultures were negative, interleukin 6 and interleukin 8 levels were elevated, and a cutaneous rash appeared on POD 18. A skin biopsy demonstrated dermatitis with focal epidermal necrosis consistent with GVHD. In an attempt to identify the source of GVHD, variable-number tandem repeat analysis fingerprinting was performed with DNA from donor splenocytes, from the skin biopsy, as well as from the patient's buccal mucosa. The skin biopsy showed a mixed variable-number tandem repeat analysis type containing DNA fragments matching the recipient and donor. Blood donors were excluded as a source because they were serologically different from the organ donor. The patient developed liver abnormalities and died from multiorgan failure on POD 22.

CONCLUSIONS

We speculate that carryover of passenger donor lymphocytes within the transplanted organ were responsible for GVHD. Furthermore, donor traits such as sexual mismatching, African-American race, and alloimmune status may be important potential risk factors for GVHD.

Antibiotics: effect on cryopreserved-thawed human sperm motility in vitro

OBJECTIVE

To analyze the motility and fertilizing capacity of sperm treated with different antibiotics.

DESIGN

Prospective comparative study.

SETTING

Clinical and academic research environment.

PATIENT(S)

Pooled cryopreserved donor sperm (n = 14).

INTERVENTION(S)

Sperm were washed with Percoll and resuspended in HEPES-buffered human tubal fluid medium containing either amoxicillin, ofloxacin, ciprofloxacin hydrochloride, nitrofurantoin monohydrate, doxycycline hyclate, cefuroxime axetil, or control medium.

MAIN OUTCOME MEASURE(S)

Sperm kinematic and fertilizing parameters.

RESULT(S)

Sperm hyperactivation was decreased in physiologic concentrations of ciprofloxacin hydrochloride and doxycycline hyclate over the course of 48 hours. At pharmacologic concentrations, ciprofloxacin hydrochloride, cefuroxime axetil, and nitrofurantoin monohydrate adversely affected motility with decreased rapid progression. Cessation of motility occurred in cefuroxime axetil and nitrofurantoin monohydrate. Sperm hyperactivation was also absent. Cefuroxime axetil decreased the percentage of intact acrosomes. In contrast, physiologic doses of ciprofloxacin hydrochloride or ofloxacin enhanced sperm fertilizing capacity.

CONCLUSION(S)

Ciprofloxacin affected hyperactivation by altering membrane properties, whereas doxycycline inhibited the capacitation process. Cessation of motility in cefuroxime axetil was linked to disrupted sperm head membranes. Sperm motility and fertilizing capacity were decreased in nitrofurantoin because of decreased metabolism. The positive effect of ofloxacin on fertilizing capacity did not involve changes in acrosome.

Uterine NK cells and trophoblast HLA class I molecules

PROBLEM

To investigate the proposal that NK cells in decidua may control trophoblast migration during implantation of the human placenta.

METHOD

Use Mab specific for HLA-G and for HLA-C in association with flow cytometry and immunoprecipitation to determine the expression of these HLA molecules by trophoblast. Expression of Killer inhibitory/activatory receptors (KIR/KAR) and the CD94 receptor by decidual NK cells was also studied.

RESULTS

Extravillous trophoblast expressed HLA-G and HLA-C in both beta2m-associated form and as free heavy chains. KIR and KAR are expressed by decidual NK cells. The repertoire of receptors varied between different women and also between blood and decidual NK cells from the same women. The expression of CD94 was also different between blood and decidual NK cells.

CONCLUSION

The recognition of HLA-G/HLA-C by KIR/KAR and CD94 could provide a mechanism by which decidual NK cells control trophoblast migration.

Standardization of susceptibility testing methods

Standardization of antibiotic susceptibility tests is desirable but faces several problems. Despite considerable effort, it has been impossible to devise an ideal medium, and discussion continues as to the best inoculum, disk content, atmosphere of incubation, method of reading results, and interpretation of those results in both microbiological and clinical contexts. A range of methods, from manual to almost completely automated, is in current use. Some microbiologists, especially those who use NCCLS methods, advocate the universal adoption of one method for each type of manual test--agar dilution, broth dilution or agar diffusion. Others accept diversity, believing that strict adherence to protocols will make it possible for the results obtained by one method--though not necessarily their interpretation--to be super-imposed on those obtained by other methods.

Human uterine NK cells have a similar repertoire of killer inhibitory and activatory receptors to those found in blood, as demonstrated by RT-PCR and sequencing

The expression of natural killer (NK) cell receptors specific for HLA class I molecules has been studied in CD56bright, CD3- NK cells isolated from the pregnant uterine mucosa, the decidua. RT-PCR was performed on cDNA from uterine NK cells with primers designed to amplify members of the killer inhibitory receptor (KIR)/killer activatory receptor (KAR) gene family. Sequencing of the PCR products revealed that uterine NK cells express KIR/KAR which have two or three extracellular immunoglobulin superfamily (Ig-SF) domains. NK receptors for both groups of HLA-C alleles were found. KIR, characterised by a long cytoplasmic tail containing the immune receptor tyrosine-based inhibitory motif (ITIM), and KAR, characterised by a short cytoplasmic domain with a transmembrane region containing a charged lysine, were both identified. Different individuals appear to have a distinct but overlapping repertoire of KIR/KAR. No new members of this NK receptor gene family were identified in the uterine CD56bright NK cells. Similar findings were obtained from non-pregnant endometrial tissues representative of different stages of the menstrual cycle. Immunohistology confirmed that the KIR protein products were expressed by decidual NK cells. These results reveal that NK receptors for trophoblast HLA class I molecules are present in maternal uterine NK cells. Fetal trophoblast cells infiltrating the decidua express HLA-G and HLA-C gene products. This suggests that maternal recognition of the fetus may be mediated by an NK allorecognition system.

Structure of the complex of an Fab fragment of a neutralizing antibody with foot-and-mouth disease virus: positioning of a highly mobile antigenic loop

Data from cryo-electron microscopy and X-ray crystallography have been combined to study the interactions of foot-and-mouth disease virus serotype C (FMDV-C) with a strongly neutralizing monoclonal antibody (mAb) SD6. The mAb SD6 binds to the long flexible GH-loop of viral protein 1 (VP1) which also binds to an integrin receptor. The structure of the virus-Fab complex was determined to 30 A resolution using cryo-electron microscopy and image analysis. The known structure of FMDV-C, and of the SD6 Fab co-crystallized with a synthetic peptide corresponding to the GH-loop of VP1, were fitted to the cryo-electron microscope density map. The SD6 Fab is seen to project almost radially from the viral surface in an orientation which is only compatible with monovalent binding of the mAb. Even taking into account the mAb hinge and elbow flexibility, it is not possible to model bivalent binding without severely distorting the Fabs. The bound GH-loop is essentially in what has previously been termed the 'up' position in the best fit Fab orientation. The SD6 Fab interacts almost exclusively with the GH-loop of VP1, making very few other contacts with the viral capsid. The position and orientation of the SD6 Fab bound to FMDV-C is in accord with previous immunogenic data.

Expression of killer cell inhibitory receptors on human uterine natural killer cells

The establishment of the human placenta in early pregnancy is characterized by the presence of large numbers of natural killer (NK) cells within the maternal decidua in close proximity to the fetally-derived invading extravillous trophoblast which expresses at least two HLA class I molecules, HLA-G and HLA-C. These NK cells have an unusual phenotype, CD56(bright) CD16, distinguishing them from adult peripheral blood NK cells. They may control key events in trophoblast migration and therefore placentation. Human NK cells in peripheral blood express receptors for polymorphic HLA class I molecules. This family of receptors, known as killer cell inhibitory receptors (KIR), are expressed on overlapping subsets of NK cells to give an NK cell repertoire which differs between individuals. Using a panel of monoclonal antibodies to several members of the KIR family and analysis by flow cytometry, we have found that KIR are expressed by decidual NK cells. There is variation in both the percentage of cells expressing a particular receptor and the density of receptor expression between decidual NK cells from different individuals. Comparison of NK cells from decidua and peripheral blood of the same individual showed that NK cells from these two different locations express different repertoires of KIR. Receptors are present in individuals who do not possess the relevant class I ligand, raising the possibility that these NK receptors may be involved in recognition of the allogeneic fetus by the mother at the implantation site.

Immunology of human placental implantation: clinical implications of our current understanding

In the early 1950s, Medawar proposed the concept of "the fetus as an allograft". Since then, the immunological relationship between the mammalian fetus and its mother during pregnancy has been considered to be similar to that between a transplanted allograft and its recipient. Because of this analogy, it has been assumed that implantation of the fetal placenta in the uterus would similarly be controlled by a maternal immune response mediated by T cells recognizing paternally derived alloantigens expressed by the placenta. Surprisingly, recent evidence suggests that implantation might predominantly involve a novel allogeneic recognition system based on natural killer cells rather than T cells. The cellular and molecular basis of this local immune interaction between the fetal placenta and maternal uterus is now the focus of intense research interest. Because aberrant implantation can cause a variety of clinical problems including miscarriage, intrauterine growth retardation and pre-eclampsia, an understanding of the immunological mechanism by which this process is controlled could lead to the development of regimes to treat these important obstetric conditions.

Transgenic mouse model for studying the transcriptional activity of the p53 protein: age- and tissue-dependent changes in radiation-induced activation during embryogenesis

The p53 tumor suppressor protein is a sequence-specific transcriptional activator of target genes. Exposure of cells to DNA damage results in accumulation of biochemically active p53, with consequent activation of p53-responsive promoters. In order to study how the transcriptional activity of the p53 protein is regulated in vivo, a transgenic mouse strain was generated. These mice harbor the p53-dependent promoter of the mdm2 gene, fused to a lacZ reporter gene. Induction of lacZ activity by DNA damage (ionizing radiation) was monitored in embryos of different p53 genotypes. The transgenic promoter was substantially activated in vivo following irradiation; activation required functional p53. The activation pattern became more restricted with increasing embryo age, as well as with the state of differentiation of a given tissue. Generally, maximal p53 activation occurred in rapidly proliferating, relatively less differentiated cells. A striking extent of haploinsufficiency was revealed-induction of promoter activity was far less efficient in mice carrying only one wild-type p53 allele. This suggests that normal levels of cellular p53 are limiting, and any further reduction already compromises the p53 response significantly. Thus, the activation potential of p53 is tightly controlled in vivo, both spatially and temporally, and an important element in this control is the presence of limiting basal levels of activatable p53.