Incidence of stroke and myocardial infarction in women of reproductive age

BACKGROUND AND PURPOSE

Information on the incidence of vascular disease in women of reproductive age has been limited. These disease are rare in this age group, and a large population base is required for reliable estimation of incidence.

METHODS

For a case-control study of vascular disease and low-dose oral contraceptive use, we used emergency department logs and hospital admission and discharge records to ascertain fatal and nonfatal cases of first-ever stroke and myocardial infarction (MI) in women 15 to 44 years of age who were-members of a large California HMO. Incidence rates of stroke and MI were calculated on the basis of these data.

RESULTS

The incidence of MI not associated with pregnancy was 5.0 per 100,000 women-years. The incidence of stroke not associated with pregnancy was 10.7 per 100,000 women-years. MI was very rare until age 35 years. At every age, about half of hemorrhagic strokes were due to subarachnoid hemorrhage.

CONCLUSIONS

The incidence rates of stroke and MI are low in women of reproductive age in the United States.

Stress-signalling kinase Sek1 protects thymocytes from apoptosis mediated by CD95 and CD3

Distinct and evolutionarily conserved signal transduction cascades mediate survival or death in response to developmental and environmental cues. The stress-activated protein kinases, or Jun N-terminal kinases (SAPKs/JNKs), are activated in response to a variety of cellular stresses such as changes in osmolarity and metabolism, DNA damage, heat shock, ischaemia, or inflammatory cytokines. Sek1 (JNKK/MKK4) is a direct activator of SAPKs/JNKs in response to environmental stresses or mitogenic factors. Here we investigate the role of Sek1 in development and apoptosis by deleting sek1 in embryonic stem (ES) cells by homologous recombination. We provide genetic evidence that different stresses utilize distinct signalling pathways for SAPK/JNK activation. sek1(-/-) rag2(-/-) chimaeric mice have normal numbers of mature T cells but fewer immature CD4+CD8+ thymocytes. The sek1 mutation did not affect the induction of apoptosis in response to environmental stresses in ES and T cells: instead, sek1 protected thymocytes from CD95 (Fas)- and CD3-mediated apoptosis. These data indicate that SEK1 mediates survival signals in T-cell development.

Long-range genomic rearrangements upstream of Kit dysregulate the developmental pattern of Kit expression in W57 and Wbanded mice and interfere with distinct steps in melanocyte development

Mutations in the murine dominant white spotting (W) locus cause pleiotropic developmental defects that affect hematopoietic cells, melanocytes, germ cells and the interstitial cells of Cajal in the gut. W mutations either alter the coding sequence of the Kit receptor tyrosine kinase, resulting in a receptor with impaired kinase activity, or affect Kit expression. Here we describe the molecular and cell-type-specific developmental defects of two of the latter class of regulatory W alleles, W57 and Wbanded(bd). In both mutants, the temporal and spatial patterns of Kit expression are dysregulated during embryogenesis and in adult animals. In Wbd mice, ectopic expression of Kit in the dermatome of the somites at days 10.8 and 11.8 of development seemed to interfere with melanoblast development. In contrast, the W57 allele leads to an intrinsic pigmentation defect by downregulating developmental Kit expression in trunk melanoblasts, but not melanoblasts around the otic vesicle. Both mutations affect transcriptional initiation of the Kit gene. The W57 allele is associated with a 80 kb deletion 5′ of the Kit-coding region while Wbd is associated with a 2.8 Mb genomic inversion of chromosome 5 with the distal breakpoint between Kit and the platelet-derived growth factor receptor alpha (Pdgfra) gene, and the proximal breakpoint between the genes for the GABA receptor beta 1 (Gabrb1) and the Tec tyrosine kinase, juxtaposing the Kit and Tec tyrosine kinase genes. Neither W57 nor Wbd affect genomic sequences previously suggested in in vitro experiments to control cell-type-specific expression of Kit. These results link specific mechanisms of cellular and developmental defects to long-range genomic rearrangements that positively and negatively affect Kit transcription in different cell lineages as well as in different subpopulations of the same lineage.

Oncogenic mutation in the Kit receptor tyrosine kinase alters substrate specificity and induces degradation of the protein tyrosine phosphatase SHP-1

Activating mutations in the Kit receptor tyrosine kinase have been identified in both rodent and human mast cell leukemia. One activating Kit mutation substitutes a valine for aspartic acid at codon 816 (D816V) and is frequently observed in human mastocytosis. Mutation at the equivalent position in the murine c-kit gene, involving a substitution of tyrosine for aspartic acid (D814Y), has been described in the mouse mastocytoma cell line P815. We have investigated the mechanism of oncogenic activation by this mutation. Expression of this mutant Kit receptor tyrosine kinase in a mast cell line led to the selective tyrosine phosphorylation of a 130-kDa protein and the degradation, through the ubiquitin-dependent proteolytic pathway, of a 65-kDa phosphoprotein. The 65-kDa protein was identified as the src homology domain 2 (SH2)-containing protein tyrosine phosphatase SHP-1, a negative regulator of signaling by Kit and other hematopoietic receptors, and the protein product of the murine motheaten locus. This mutation also altered the sites of receptor autophosphorylation and peptide substrate selectivity. Thus, this mutation activates the oncogenic potential of Kit by a novel mechanism involving an alteration in Kit substrate recognition and the degradation of SHP-1, an attenuator of the Kit signaling pathway.

Update on adolescent health care in pediatric practice

PURPOSE

To determine current adolescent health care practices of pediatricians and evaluate whether changes have taken place during the past decade.

METHODS

A questionnaire completed by 101 pediatricians in 1985 was abbreviated and adapted by Committee on Youth of Chapter 2, District II of the American Academy of Pediatrics and sent to 1,633 members of the Chapter in June 1993.

RESULTS

Forty-three percent of the 436 respondents in 1993 were female, 43% < or = 40 years of age and 53% were in private practice. Most accept new patients > or = 16 years of age (76%), continue to see patients > or = 19 years of age (63%), and interview adolescents without their parents (86%). Although between one-third and two-thirds of respondents report having equipment for gynecologic examinations, most indicate they are "not entirely comfortable" treating adolescent issues and therefore refer to others for management. Between one-quarter and one-half indicate they are "very interested" in learning more about adolescent issues and an additional 40-50% are "somewhat interested." Obstacles to providing adolescent care include: "image as a baby doctor" (65%), fear that parents would object (61%), no separate hours (57%), difficulty in providing confidential care (56%), and difficulty in charging appropriate fees (47%). Females and younger pediatricians are more comfortable with some aspects of gynecologic care and more likely to be satisfied with the adolescent care they are providing. There were few differences between responses in 1993 and 1995.

CONCLUSIONS

Few of the pediatricians surveyed provide comprehensive care to adolescent patients. Future policy decisions and medical education must respond to these realities in pediatric practice.

A long-term study of symptoms, spirometry and survival amongst home nebulizer users

Although home nebulizers are widely used to deliver bronchodilator medication to patients with asthma and chronic obstructive pulmonary disease (COPD), the long-term benefits and hazards are unknown. The present authors have previously reported a prospective 12-month study of home nebulizer use involving 49 patients (15 asthma, mean forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) 1.3/2.1 1; 34 COPD, mean FEV1/FVC 0.7/1.8 1). Thirty-two of these patients were treated with long-term domiciliary nebulized bronchodilator treatment, the other 17 patients chose metered dose inhaler (MDI) therapy. The present paper reports the progress of these patients over 5 yr. Five-year survival was similar in both groups (nebulizer users 56%, MDI users 53%). Most deaths were due to respiratory failure (14 deaths) or lung cancer (four deaths). Survival was determined mainly by FEV1 (R = 0.54, P = 0.0001) and age (R = -0.47, P = 0.0007). Laboratory lung function tests (16 nebulizer users) showed that FEV1 and FVC were still higher than pre-nebulizer baseline measurements after 36 months of nebulizer use, but PEFR had fallen by 7%. Twenty-one of 23 surviving nebulizer users completed a questionnaire after 36 months of treatment. All used their nebulizer at least once per day and 20 of 21 patients reported that they still obtained full benefit from each nebulized treatment. The morning peak flow response to nebulized treatment was the same at baseline and at 36 months (48 1 min-1). All patients remained breathless (mean subjective score 4.8 on seven-point scale) but the subjective response to nebulized treatment was unchanged at 36 months. Tachyphylaxis did not develop among 13 patients who underwent repeated reversibility studies using 200 micrograms of salbutamol at 6, 12 and 36 months. It is concluded that home nebulizer therapy is safe and effective for a small number of carefully selected patients with severe asthma or COPD, who have been evaluated by a rigorous home nebulizer assessment protocol prior to commencing home nebulizer therapy.

A novel family of repeat sequences in the mouse genome responsive to retinoic acid

Repetitive DNA sequences form a substantial portion of eukaryotic genomes and exist as members of families that differ in copy number, length, and sequence. Various functions, including chromosomal integrity, gene regulation, and gene rearrangement have been ascribed to repetitive DNA. Although there is evidence that some repetitive sequences may participate in gene regulation, little is known about how their own expression may be regulated. During the course of gene trapping experiments with embryonic stem (ES) cells, we identified a novel class of expressed repetitive sequences in the mouse, using 5' rapid amplification of cDNA ends-polymerase chain reaction (5' RACE-PCR) to clone fusion transcripts from these lines. The expression of these repeats was induced by retinoic acid (RA) in cultured ES cells examined by Northern blot analyses. In vivo, their expression was spatially restricted in embryos and in the adult brain as determined by RNA in situ hybridization. We designated this family of sequences as Dr (developmentally regulated) repeats. The members of the Dr family, identified by cDNA cloning and through database search, are highly similar in sequence and show peculiar structural features. Our results suggest the expression of Dr-containing transcripts may be part of an ES cell differentiation program triggered by RA.

Cell autonomous functions of the receptor tyrosine kinase TIE in a late phase of angiogenic capillary growth and endothelial cell survival during murine development

TIE is a receptor tyrosine kinase expressed in both mature endothelial cells and their precursors, as well as in some hematopoietic cells. Mouse embryos homozygous for a disrupted Tie allele die at midgestation due to impaired endothelial cell integrity and resulting hemorrhage. Here we have performed chimeric analysis to study further the function of the murine TIE in the development of embryonic vasculature and in the hematopoietic system. Cells lacking a functional Tie gene (tie(lcz)/tie(lczn-) cells) contributed to the embryonic vasculature at E10.5 as efficiently as cells heterozygous for a targeted Tie allele (tie(lcz)/+ cells). Thus, TIE does not play a significant role in vasculogenesis or in early angiogenic processes, such as formation of the intersomitic arteries and limb bud vascularization. At E15.5 tie(lcz)/tie(lczn-) cells still readily contributed to major blood vessels and to endothelial cells of organs such as lung and heart, which have been suggested to be vascularized by angioblast differentiation. In contrast, the tie(lcz)/tie(lczn-) cells were selected against in the capillary plexuses of several angiogenically vascularized tissues, such as brain and kidney. Our results thus support a role for TIE in late phases of angiogenesis but not vasculogenesis. Furthermore, the results suggest that different mechanisms regulate early and late angiogenesis and provide support for a model of differential organ vascularization by vasculogenic or angiogenic processes. Analysis of adult chimeras suggested that TIE is required to support the survival or proliferation of certain types of endothelial cells demonstrating heterogeneity in the growth/survival factor requirements in various endothelial cell populations. Chimeric analysis of adult hematopoietic cell populations, including peripheral platelets and bone marrow progenitor cells, revealed that tie(lcz)/tie(lczn-) cells were able to contribute to these cell types in a way indistinguishable from tie(lcz)/+ or wild-type cells. Thus, the primary function of TIE appears to be restricted to the endothelial cell lineage.

Stroke in users of low-dose oral contraceptives

BACKGROUND

Previous studies have linked the use of oral contraceptive agents to an increased risk of stroke, but those studies have been limited to oral contraceptives containing more estrogen than is now generally used.

METHODS

In a population-based, case-control study, we identified fatal and nonfatal strokes in female members of the California Kaiser Permanente Medical Care Program and who were 15 through 44 years of age. Matched controls were randomly selected from female members who had not had strokes. Information about the use of oral contraceptives (essentially limited to low-estrogen preparations) was obtained in interviews.

RESULTS

A total of 408 confirmed strokes occurred in a total of 1.1 million women during 3.6 million woman-years of observation. The incidence of stroke was thus 11.3 per 100,000 woman-years. On the basis of data from 295 women with stroke who were interviewed and their controls, the odds ratio for ischemic stroke among current users of oral contraceptives, as compared with former users and women who had never used such drugs, was 1.18 (95 percent confidence interval, 0.54 to 2.59) after adjustment for other risk factors for stroke. The adjusted odds ratio for hemorrhagic stroke was 1.14 (95 percent confidence interval, 0.60 to 2.16). With respect to the risk of hemorrhagic stroke, there was a positive interaction between the current use of oral contraceptives and smoking (odds ratio for women with both these factors, 3.64; 95 percent confidence interval, 0.95 to 13.87).

CONCLUSIONS

Stroke is rare among women of childbearing age. Low-estrogen oral-contraceptive preparations do not appear to increase the risk of stroke.

Signalling by the W/Kit receptor tyrosine kinase is negatively regulated in vivo by the protein tyrosine phosphatase Shp1

Protein tyrosine phosphorylation plays a key role in regulating eukaryotic cell proliferation and differentiation. Genetic analysis in invertebrates has been invaluable for dissecting the signalling events downstream of receptor tyrosine kinases (RTKs). We have used this approach in mammals to analyse the interactions between the Kit RTK encoded by the murine Dominant white spotting (W) locus and the Shp1 protein tyrosine phosphatase, the product of the murine motheaten (me) gene. Homozygosity for mutations in both W and me ameliorates aspects of both the me and W phenotypes, including the lethal lung disease associated with me and the embryonic lethality and mast cell deficiency associated with W, demonstrating that the Kit receptor plays a role in the pathology of the me phenotype and conversely that Shp1 negatively regulates Kit signalling in vivo.

Generation of a novel Fli-1 protein by gene targeting leads to a defect in thymus development and a delay in Friend virus-induced erythroleukemia

The proto-oncogene Fli-1 is a member of the ets family of transcription factor genes. Its activation by either chromosomal translocation or proviral insertion leads to Ewing's sarcoma in humans or erythroleukemia in mice, respectively, Fli-1 is preferentially expressed in hematopoietic and endothelial cells. This expression pattern resembled that of c-ets-1, another ets gene closely related and physically linked to Fli-1. We also generated a germ line mutation in Fli-1 by homologous recombination in embryonic stem cells. Homozygous mutant mice exhibit thymic hypocellularity which is not related to a defect in a specific subpopulation of thymocytes or to increased apoptosis, suggesting that Fli-1 is an important regulator of a prethymic T-cell progenitor. This phenotype was corrected by crossing the Fli-1 deficient mice expressing Fli-1 cDNA. Homozygous mutant mice remained susceptible to erythroleukemia induction by Friend murine leukemia virus, although the latency period was significantly increased. Surprisingly, the mutant Fli-1 allele was still a target for Friend murine leukemia virus integration, and leukemic spleens with a rearranged Fli-1 gene expressed a truncated Fli-1 protein that appears to arise from an internal translation initiation site and alternative splicing around the neo cassette used in the gene targeting. The fortuitous discovery of the mutant Fli-1 protein, revealed only as the result of the clonal expansion of leukemic cells harboring a rearranged Fli-1 gene, suggests caution in the interpretation of gene-targeting experiments that result in either no or only a subtle phenotypic alteration.

A point mutation in the catalytic domain of c-kit induces growth factor independence, tumorigenicity, and differentiation of mast cells

The murine W and Steel loci encode the Kit receptor tyrosine kinase and its ligand, Steel factor, respectively. Loss of function mutations at either the W or Sl loci lead to a variety of pleiotropic developmental defects, including mast cell deficiency and severe macrocytic anemia. In addition to these loss-of-function mutations, gain-of-function mutations in c-kit, leading to constitutive activation of the Kit receptor, have also been identified in both rodent and human mastocytomas. In this study, we have examined the transforming potential and biologic effects of a point mutation that results in substitution of the aspartic acid at codon 814 in the cytoplasmic kinase domain to tyrosine (D814Y) by introducing either wild-type (Kit) or mutant KitD814Y (KDY) cDNA into an interleukin-3-dependent mast cell line IC2. Stimulation of cells expressing the wild-type Kit receptor (IC2/Kit) with Steel factor in vitro resulted in a short-term growth response, whereas IC2/KDY cells were capable of sustained proliferation in a ligand-independent manner. In addition, expression of KDY resulted in the oncogenic transformation of IC2 cells, as determined by colony formation in vitro in the absence of exogenous growth factors and the formation of mastocytomas in vivo in syngeneic DBA/2 mice. Surprisingly, KDY expression in IC2 cells triggered dramatic changes in cell size and the extent of granulation. In addition, KDY induced the expression of mouse mast cell protease-4 (MMCP-4) and MMCP-6. In contrast, neither of these molecular or cellular changes was observed in IC2/Kit cells treated with Steel factor. These results show that the D814Y mutation in the cytoplasmic kinase domain of the Kit receptor induces ligand-independent mast cell growth in vitro, tumorigenicity in vivo, and mast cell differentiation.

Steel mutant mice are deficient in hippocampal learning but not long-term potentiation

Mice carrying mutations in either the dominant white-spotting (W) or Steel (Sl) loci exhibit deficits in melanogenesis, gametogenesis, and hematopoiesis. W encodes the Kit receptor tyrosine kinase, while Sl encodes the Kit ligand, Steel factor, and the receptor-ligand pair are contiguously expressed at anatomical sites expected from the phenotypes of W and Sl mice. The c-kit and Steel genes are also both highly expressed in the adult murine hippocampus: Steel is expressed in dentate gyrus neurons whose mossy fiber axons synapse with the c-kit expressing CA3 pyramidal neurons. We report here that Sl/Sld mutant mice have a specific deficit in spatial learning. These mutant mice are also deficient in baseline synaptic transmission between the dentate gyrus and CA3 but show normal long-term potentiation in this pathway. These observations demonstrate a role for Steel factor/Kit signaling in the adult nervous system and suggest that a severe deficit in hippocampal-dependent learning need not be associated with reduced hippocampal long-term potentiation.

An induction gene trap screen in embryonic stem cells: Identification of genes that respond to retinoic acid in vitro

We have developed a novel induction gene trap approach that preselects in vitro for integrations into genes that lie downstream of receptor/ligand-mediated signaling pathways. Using this approach, we have identified 20 gene trap integrations in embryonic stem cells, 9 of which were induced and 11 of which were repressed after exposure to exogenous retinoic acid (RA). All but one of these integrations showed unique spatially restricted or tissue-specific patterns of expression between 8.5 and 11.5 days of embryogenesis. Interestingly, expression was observed in tissues that are affected by alterations in RA levels during embryogenesis. Sequence analysis of fusion transcripts from six integrations revealed five novel gene sequences and the previously identified protooncogene c-fyn. To date, germ-line transmission and breeding has uncovered one homozygous embryonic lethal and three homozygous viable insertions. These studies demonstrate the potential of this induction gene trap approach for identifying and mutating genes downstream of signal transduction pathways.

Each domain of the N-ethylmaleimide-sensitive fusion protein contributes to its transport activity

N-Ethylmaleimide-sensitive fusion protein (NSF) has been shown to be involved in numerous intracellular transport events. In an effort to understand the basic mechanism of NSF in vesicle-target membrane fusion events, we have examined the role that each of its three domains play in how NSF interacts with the SNAP.SNARE complex. Mutagenesis of the first ATP-binding domain (D1, amino acids 206-477) demonstrates that nucleotide binding by this domain is required for 20 S particle assembly. A second mutation, which permits ATP binding but not hydrolysis, yields a protein that can form 20 S particle but fails to mediate its disassembly. Similar mutations of the second ATP-binding domain (D2, amino acids 478-744) result in trimeric molecules that behave like wild type NSF. Domain rearrangement mutants were used to further probe the functional role of each domain. The amino-terminal domain (N, amino acids 1-205) is absolutely required for binding of NSF to the SNAP.SNARE complex, because the truncated mutant, D1D2, is unable to form 20 S particle. When tested as an isolated recombinant protein, the N domain is not sufficient for binding to the SNAP.SNARE complex, but when adjacent to the D1 domain or in a trimeric molecule, the N domain does mediate binding to the SNAP.SNARE complex. Monomeric N-D1 and trimeric N-D2 could both participate in particle formation. Only the N-D1 mutant was able to facilitate MgATP-dependent release from the SNAP.SNARE complex. These data demonstrate that NSF binding to the SNAP.SNARE complex is mediated by the N domain and that both ATP binding and hydrolysis by the D1 domain are essential for 20 S particle dynamics. The intramolecular interactions outlined suggest a mechanism by which NSF may use ATP hydrolysis to facilitate the vesicle fusion process.

An immunological renal disease in transgenic mice that overexpress Fli-1, a member of the ets family of transcription factor genes

The proto-oncogene Fli-1 is a member of the ets family of transcription factor genes. Its high expression in the thymus and spleen and the presence of DNA binding sites for Fli-1 in a number of lymphoid cell-specific gene suggest that Fli-1 is involved in the regulation of lymphopoiesis. Activation of the Fli-1 gene by either chromosomal translocation or viral insertion leads to Ewing's sarcoma in humans and erythroleukemia in mice, respectively. Thus, Fli-1 is normally involved in pathways involved in the regulation of cell growth and differentiation. We have generated H-2Kk-Fli-1 transgenic mice that overexpress Fli-1 in various mouse tissues, with the highest levels of Fli-1 protein in the thymus and spleen. These Fli-1 transgenic mice developed a high incidence of a progressive immunological renal disease and ultimately died of renal failure caused by tubulointerstitial nephritis and immune-complex glomerulonephritis. The incidences of renal disease correlated with the levels of Fli-1 protein in lymphoid tissues of transgenic lines. The hypergammaglobulinemia, splenomegaly, B-cell hyperplasia, accumulation of abnormal CD3+ B220+ T lymphoid cells and CD5+ B220+ B cells in peripheral lymphoid tissues, and detection of various autoantibodies in the sera of diseased Fli-1 transgenic mice suggested the involvement of an immune dysfunction in the pathogenesis of the renal disease. In addition, splenic B cells from transgenic mice exhibited increased proliferation and prolonged survival in vitro in response to mitogens. Taken together, these data suggest that overexpression or ectopic expression of Fli-1 perturbs normal lymphoid cell function and programmed cell death. Thus, H-2Kk-Fli-1 transgenic mice may serve as a murine model for autoimmune disease in humans, such as systemic lupus erythematosus.

Regulation of p53-mediated apoptosis and cell cycle arrest by Steel factor

Activation of the p53 protein can lead to apoptosis and cell cycle arrest. In contrast, activation of the signalling pathway controlled by the Kit receptor tyrosine kinase prevents apoptosis and promotes cell division of a number of different cell types in vivo. We have investigated the consequences of activating the Kit signalling pathway by its ligand Steel factor on these opposing functions of the p53 protein in Friend erythroleukemia cells. A temperature-sensitive p53 allele (Val-135) was introduced into the Friend erythroleukemia cell line (DP-16) which lacks endogenous p53 expression. At 38.5 degrees C, the Val-135 protein maintains a mutant conformation and has no effect on cell growth. At 32 degrees C, the mutant protein assumes wild-type properties and induces these cells to arrest in G1, terminally differentiate, and die by apoptosis. We demonstrate that Steel factor inhibits p53-mediated apoptosis and differentiation but has no effect on p53-mediated G1/S cell cycle arrest. These results demonstrate that Steel factor functions as a cell survival factor in part through the suppression of differentiation and apoptosis induced by p53 and suggest that cell cycle arrest and apoptosis may be separable functions of p53.

The receptor tyrosine kinase TIE is required for integrity and survival of vascular endothelial cells

Vascular endothelial cells are critical for the development and function of the mammalian circulatory system. We have analyzed the role of the endothelial cell-specific receptor tyrosine kinase TIE in the mouse vasculature. Mouse embryos homozygous for a disrupted Tie allele developed severe edema, their microvasculature was ruptured and they died between days 13.5 and 14.5 of gestation. The major blood vessels of the homozygous embryos appeared normal. Cells lacking a functional Tie gene were unable to contribute to the adult kidney endothelium in chimeric animals, further demonstrating the intrinsic requirement for TIE in endothelial cells. We conclude that TIE is required during embryonic development for the integrity and survival of vascular endothelial cells, particularly in the regions undergoing angiogenic growth of capillaries. TIE is not essential, however, for vasculogenesis, the early differentiation of endothelial cells.

Receptor tyrosine kinases and the regulation of hematopoiesis

The ongoing production of mature blood cells during the lifetime of an animal is vital for survival. Hematopoiesis is the complex process whereby a small population of pluripotential stem cells give rise to mature cell types with specialized functions. The development of mature blood cells proceeds in a hierarchical fashion originating from a self-renewable stem cell population that gradually becomes committed to lineage-restricted differentiation. Two major themes concerning the regulation of hematopoiesis have emerged. First, the proliferation, survival and differentiation of immature progenitor cells depends on extracellular signals produced by cells within the hematopoietic microenvironment. Second, protein tyrosine phosphorylation is the major biochemical mechanism by which the extracellular signals are transmitted and interpreted. In this review we will concentrate on the role of receptors with intrinsic tyrosine kinase activity (RTKs) in hematopoietic regulation. RTKs form part of a highly conserved signaling mechanism that plays an important role in the development of evolutionary diverse organisms. During hematopoiesis, RTKs are a central component of the mechanism by which hematopoietic stem cells receive extracellular signals and interpret these signals to direct the lineage restricted differentiation of multipotential progenitors. In addition, RTKs may also play an important regulatory role in the ontogeny of the hematopoietic system during embryonic and fetal development. Taken together, RTKs are an important component of the mechanisms that regulate the development and behavior of hematopoietic stem cells.

Dysphagia due to secondary achalasia as an early manifestation of squamous cell carcinoma

A 59-year-old man, a smoker, presented with features of airflow obstruction due to squamous cell carcinoma of central airways mimicking chronic obstructive airways disease. He also had pronounced dysphagia. Computed tomographic and magnetic resonance imaging scans showed mediastinal tumour invasion but no direct oesophageal involvement. Oesophageal manometry studies revealed that dysphagia was due to the oesophageal motility disorder, secondary achalasia.

A comparative study of the application of scanning acoustic microscopy and confocal laser scanning microscopy to the structural assessment of human bones

The Scanning Acoustic Microscope (SAM) is used to image mechanical structure and to measure the sound velocity in micrometers of in vitro samples from human bone. A similar principle is used in confocal laser scanning microscopy. The same sample is imaged by both methods and the results compared. We concentrated on the SAM, the function of which is described in greater detail. We demonstrate that the confocal scanning principle is applied in both microscopes, although information about structure differs, depending on the method used.

Apoptosis, cancer and the p53 tumour suppressor gene

One of the most commonly detected abnormalities in human cancer is mutation of the p53 tumour suppressor gene. Intrinsic to the function of p53 is its ability to induce apoptotic cell death and to cause cell cycle arrest. Moreover, p53 plays an important role in controlling the cellular response to DNA damaging agents such as ionizing radiation and cancer chemotherapeutic drugs. Loss of p53 function causes increased resistance to radiation and chemotherapeutic agents, and there is increasing evidence that p53 mutational status is an important determinant of clinical outcome in cancer. This review will focus on recent data describing the biochemistry of p53 function, its role in mediating apoptosis and cell cycle arrest and in the control of tumour growth and death.