Transient Appearance Research Articles

Mosaic tetraploidy and transient GFI1 mutation in a patient with severe chronic neutropenia

This report presents the case of a 15-year-old male with severe chronic neutropenia, leukopenia, and persistent tetraploid mosaicism in the bone marrow and peripheral blood. His father had mild neutropenia and bone marrow tetraploidy. Flow cytometric analysis of DNA content peripheral blood showed tetraploidy in 20% of granulocytes and 15% of monocytes. Sequence analysis of the ELA2 gene was normal, but the GFI1 gene exhibited transient appearance of single base changes the coding region and promoter. We speculate that an underlying genetic defect, inherited in an autosomal dominant pattern, leads to both disordered mitosis and neutropenia in this kindred.

Notch pathway gene expression and wool follicle cell fates

The Notch family of genes has been implicated in specifying cell fates during hair follicle morphogenesis. We examined Notch gene expression during wool follicle formation, as an understanding of genes that influence cell distributions in the developing follicle is a prerequisite for devising molecular strategies to manipulate fibre characters and follicle density. We identified transcripts for the Notch1 receptor and one of its ligands, Jagged1, in fetal sheep skin by reverse transcriptase polymerase chain reaction. The sheep-specific cDNA sequences were used as templates to produce probes to investigate the expression patterns of Notch1 and Jagged1 in developing ovine fetal skin by in situ hybridisation. Notch1 and Jagged1 were detected in the epidermis and in a subpopulation of mesenchymal cells before follicle initiation. At day 70 during follicle initiation, transcripts were also detected in cells at the tip of the epidermal plug and in dermal condensates. By day 86, Notch1 and Jagged1 were detected in the distal cells of the epidermal downgrowths and epidermis and Notch1 was no longer detected in the mesenchyme and dermal condensates. After day 96, transcripts were absent from the epidermis, but localised to differentiating outer root sheath (ORS) cells. The distributions of transcripts implicate a Notch1–Jagged1 signal pathway in the fates of prospective ORS cells. The transient appearance of Notch1 in cells at the epidermal–mesenchymal junction during early follicle morphogenesis suggests that the receptor may be responsible for the specification of a cell subpopulation committed to a prepapilla fate at initiation.

Effects of Exogenous Thyroid Hormone on the Postnatal Morphogenesis of the Rat Parotid Gland

Administration of thyroid hormone has been shown to accelerate the early postnatal development of the rat parotid gland, but these studies have dwelt almost entirely on biochemical changes. The objective of this study was to describe the effects of exogenous thyroid hormone on morphologic aspects of the developing parotid gland, in particular the transient appearance of scattered mucous cells in this otherwise serous gland. Pups were given a daily subcutaneous injection of thyroxine (T(4)) of 0.1, 0.5, or 5.0 microg/g body weight, vehicle only (injection control), or no injection (normal control) beginning at 4 days, and killed for the collection of blood and parotid glands at intervals through 15 days. The serum was analyzed for T(4) and the glands were examined by light and electron microscopy. The results indicated that both serum T(4) and the pace of gland development were proportional to the dose of T(4). In particular, T(4) accelerated decreases in acinar size and gland area occupied by stroma and translocation of a subset of cells with small secretory granules, deeply stained with periodic acid-Schiff, from acini to intercalated ducts. However, the chronology of mucous cell disappearance was indifferent to treatment. In addition, signs of toxicity, including slower gain in body weight and greatly increased apoptosis and vacuoles in the glands, occurred with the higher doses of T(4).

Atrial tachycardias following circumferential pulmonary vein ablation: observations during catheter ablation

Circumferential pulmonary vein ablation performing linear lesions around the ostia of the pulmonary veins has been shown to be effective for the treatment of atrial fibrillation. During the follow-up period, persistent atrial tachycardia may occur as a proarrhythmic complication. Only little information is available about the underlying mechanism. In our study, atrial tachycardia following circumferential pulmonary vein ablation was identified in 13 out of 84 consecutive patients (15.5%), as a transient appearance in four and with recurrences for more than 3 months in nine patients (10.7%). Electrophysiological study and ablation was performed in eight cases, revealing common atrial flutter in two, a focal origin secondary to conduction recovery from the pulmonary vein to the left atrium in two and macro reentrant left atrial flutter in four patients. The electrophysiological characteristics demonstrated by electroanatomic activation mapping CARTO and consecutive ablation therapy with a 100% success rate are described and discussed with regard to the literature.

Clothing and modern human behaviour: prehistoric Tasmania as a case study

AbstractA general model is outlined showing how the prehistoric development of clothing for thermal reasons may be relevant to the emergence of modern human behaviour. A distinction is drawn between simple and complex clothing, with the latter leading to repercussions that can ultimately became decoupled from thermal contingencies. Archaeological correlates of complex clothing can be linked to attributes of modern human behaviour, some but not all of which made a transient appearance in late Pleistocene Tasmania. Cave sites in the southwest of the island have yielded bone tools and distinctive stone scraper tools, along with evidence for the targeting of prey species and parietal artworks in some caves. Thermal conditions in late Pleistocene Tasmania approached the known limits of human cold tolerance, necessitating the use of clothing. The archaeological record is reviewed in relation to likely technological and other correlates of the manufacture of clothing. It is argued that thermal parameters were a significant aspect of the human response to climate change in Tasmania. These developments invite comparison with those witnessed outside the region during the Upper and late Middle Pleistocene, particularly in northern middle latitudes and also in Africa, where they are interpreted as indicating the emergence of modern human behaviour.

Appearance of prolactin-releasing peptide-producing cells in the area postrema of postnatal rats

Prolactin-releasing peptide (PrRP) was recently isolated from bovine hypothalamus. PrRP is the natural ligand for an orphan G-protein-coupled receptor, hGR3, and directly stimulates prolactin secretion from the anterior pituitary in vitro and in vivo. It has also been reported that PrRP plays an important role as a neurotransmitter and/or neuromodulator in the brain. Although much knowledge has been gained concerning PrRP in the adult rat brain, little attention has been paid to the fetal and postnatal stages. We therefore examined the development of PrRP neurons in the rat brain. In immunocytochemical and in situ hybridization experiments, we observed the transient appearance of PrRP-producing cells in the area postrema (AP), in which PrRP-producing cells do not exist in the normal adult rat. PrRP-producing cells in the AP were detected at P14, and many PrRP-producing cells were observed at P17, though none were detected at P19. This is the first report of the appearance of PrRP-producing cells in the postnatal AP. Our findings suggest that PrRP may play a previously unknown role in the AP of postnatal rats.

Identification of a Denitrase Activity against Calmodulin in Activated Macrophages Using High-Field Liquid Chromatography−FTICR Mass Spectrometry

We have identified a denitrase activity in macrophages that is upregulated following macrophage activation, which is shown by mass spectrometry to recognize nitrotyrosines in the calcium signaling protein calmodulin (CaM). The denitrase activity converts nitrotyrosines to their native tyrosine structure without the formation of any aminotyrosine. Comparable extents of methionine sulfoxide reduction are also observed that are catalyzed by endogenous methionine sulfoxide reductases. Competing with repair processes, oxidized CaM is a substrate for a peptidase activity that results in the selective cleavage of the C-terminal lysine (i.e., Lys148) that is expected to diminish CaM function. Thus, competing repair and peptidase activities define the abundances and functionality of CaM in modulating cellular metabolism in response to oxidative stress, where the presence of the truncated CaM species provides a useful biomarker for the transient appearance of oxidized CaM.

195Pt NMR Chemical Shift Trend Analysis as a Method to Assign New Pt(IV)−Halohydroxo Complexes

A 195Pt NMR spectroscopy study of the speciation of [PtCl6]2-, [PtBr6]2-, and the mixed [PtCl6-mBrm]2- (m=0-6) anions in aqueous medium after hydroxide ion substitution of coordinated halide ions has been carried out under dynamic conditions. Of the 56 possible [PtCl6-m-nBrm(OH)n]2- (m, n=0-6) complex anions in solution under dynamic conditions, the relative chemical shifts delta(195Pt) of 52 observable species have been assigned, 33 of which had not been reported previously. The assignment of all these species including the possible stereoisomers is facilitated by systematic linear relationships between the delta(195Pt) increments resulting from substitutions of the halide ions by OH- ions. Under dynamic conditions, the relative concentration (as indicated by resonance intensities) of the [PtCl6-m-nBrm(OH)n]2- (m, n=0-6) species was found to be largely determined by the trans effects on ligand substitution reactions, leading to the transient appearance of previously unobserved complexes. Only the 2c2c2t and 2t2t2t isomers of the ternary [PtCl2Br2(OH)2]2- complex, the 3m12t [PtCl3Br(OH)2]2- and the 13m2t [PtClBr3(OH)2]2- anions could not be observed under our conditions, although their delta(195Pt) are confidently predictable from the linear trend analysis. This chemical shift trend analysis constitutes a powerful method for the virtually unambiguous assignment of 195Pt chemical shifts for such complex anions undergoing slow ligand exchange on the NMR time scale, as facilitated by the strikingly good correlations of delta(195Pt) for the species as a function of the number of hydroxide ions in the coordination sphere.

Shuttling of G Protein Subunits between the Plasma Membrane and Intracellular Membranes

Heterotrimeric G proteins (alphabetagamma) mediate the majority of signaling pathways in mammalian cells. It is long held that G protein function is localized to the plasma membrane. Here we examined the spatiotemporal dynamics of G protein localization using fluorescence recovery after photobleaching, fluorescence loss in photobleaching, and a photoswitchable fluorescent protein, Dronpa. Unexpectedly, G protein subunits shuttle rapidly (t1/2 < 1 min) between the plasma membrane and intracellular membranes. We show that consistent with such shuttling, G proteins constitutively reside in endomembranes. Furthermore, we show that shuttling is inhibited by 2-bromopalmitate. Thus, contrary to present thought, G proteins do not reside permanently on the plasma membrane but are constantly testing the cytoplasmic surfaces of the plasma membrane and endomembranes to maintain G protein pools in intracellular membranes to establish direct communication between receptors and endomembranes.

Spatial‐Temporal characteristics of ion beamlets in the plasma sheet boundary layer of magnetotail

The processes of nonadiabatic ion acceleration occurring in the vicinity of magnetic neutral lines produce highly accelerated (up to 2500 km/s) field‐aligned ion beams (beamlets) with transient appearance streaming earthward in the plasma sheet boundary layer (PSBL) of the Earth’s magnetotail. Previous studies of these phenomena based on single spacecraft (s/c) missions supported the view that beamlets are temporal transients, since the typical time of a beamlet observation at a given s/c very rarely exceeds ∼1–2 min. Now multipoint Cluster observations have led to a new understanding of these phenomena with a spatial rather than a temporal structure. On the basis of 3‐year Cluster measurements made in the PSBL, we present statistical evaluation of the beamlet duration (at least 5–15 min) and confirm well‐manifested localization of the beamlet along Z and in some cases along Y directions, i.e., approximately across the lobe magnetic field. Earlier results reporting shorter beamlet observations could be understood by invoking not only PSBL flapping motions but also of an additional effect revealed by Cluster: earthward propagation of kink‐like perturbations along the beamlet filaments. Phase velocity of these perturbations is of the order of the local Alfven velocity (V ∼ 600–1400 km/s) and related fast flappings of localized beamlet structures in the Y‐Z direction significantly decreasing the time of their observation at a given spacecraft. Multipoint observations of beamlets revealed that they represent long‐living (∼5–15 min) plasma filaments elongated along the lobe magnetic field (∼60–100RE) and strongly localized in direction perpendicular to the PSBL‐lobe boundary (∼0.2–0.7RE). In some cases, it was also possible to estimate the width of beamlet in dawn‐dusk direction which was of the order of fractions of RE.

Attenuation of DNA damage checkpoint by PBK, a novel mitotic kinase, involves protein–protein interaction with tumor suppressor p53

Pathways adopted by developing cancer cells for evasion of cellular surveillance mechanism deserve attention for therapeutic exploitation as well as for better prognosis. A novel mitotic kinase, PDZ-binding kinase or PBK, which is upregulated in a variety of neoplasms including hematological malignancies, has been the focus of our attention with a goal to understand its role in malignant conversion and to examine as a possible new therapeutic target in disparate types of cancer. Earlier, we reported that PBK expression was downregulated during macrophage differentiation of HL60 promyelocytic leukemia cells, during doxorubicin-induced growth arrest in G2/M phase and that PBK was regulated by cell cycle-specific transcription factors E2F and CREB/ATF. Here, we demonstrate that HT1080 fibrosarcoma cells become adapted to doxorubicin-induced DNA damage checkpoint upon ectopic expression of a phosphomimetic mutant of PBK as indicated by the accumulation of polyploid cells. Aberrant entry into the mitotic phase by these cells is suggested by the appearance of a mitotic phase-specific marker, MPM-2. We propose that the effect is due to downregulation of p53 caused by direct physical interaction with PBK as detected by both a biochemical means as well as by yeast two-hybrid analysis. Together, our studies provide a plausible explanation for the role of PBK augmenting tumor cell growth following transient appearance in different types of progenitor cells in vivo as reported.

The continuum and line spectra of SGR 1806-20 bursts

The defining property of Soft Gamma Repeaters is the emission of short, bright bursts of X-rays and soft γ-rays. Here we present the continuum and line spectral properties of a large sample of bursts from SGR 1806-20, observed with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Using 10 trail spectral models (5 single and 5 two component models), we find that the burst continua are best fitted by the single component models: cutoff power-law, optically thin bremsstrahlung, and simple power-law. Time resolved spectroscopy show that there are two absorption lines at ∼5 keV and 20 keV in some bursts. The lines are relatively narrow with 90% upper limit on the line widths of 0.5–1.5 keV for the 5 keV feature and 1–3 keV for the 20 keV feature. Both lines have considerable equivalent width of 330–850 eV for the 5 keV feature and 780–2590 eV for the 20 keV feature. We examined whether theses spectral lines are dependent upon the choice of a particular continuum model and find no such dependence. Besides, we find that the 5 keV feature is pronounced with high confidence in the cumulative joint spectrum of the entire burst sample, both in the individual detectors of the PCA and in the co-added detectors spectrum. We confront the features against possible instrumental effects and find that none can account for the observed line properties. The two features do not seem to be connected to the same physical mechanism because (1) they do not always occur simultaneously, (2) while the 5 keV feature occurs at about the same energy, the 20 keV line centroid varies significantly from burst to burst over the range 18–22 keV, and (3) the centroid of the lines shows anti-correlated red/blue shifts. The transient appearance of the features in the individual bursts and in portions of the same burst, together with the spectral evolution seen in some bursts point to a complex emission mechanism that requires further investigation.

Magnetic flux emergence in granular convection: radiative MHD simulations and observational signatures

Aims. We study the emergence of magnetic flux from the near-surface layers of the solar convection zone into the photosphere. Methods. To model magnetic flux emergence, we carried out a set of numerical radiative magnetohydrodynamics simulations. Our simulations take into account the effects of compressibility, energy exchange via radiative transfer, and partial ionization in the equation of state. All these physical ingredients are essential for a proper treatment of the problem. Furthermore, the inclusion of radiative transfer allows us to directly compare the simulation results with actual observations of emerging flux. Results. We find that the interaction between the magnetic flux tube and the external flow field has an important influence on the emergent morphology of the magnetic field. Depending on the initial properties of the flux tube (e.g. field strength, twist, entropy etc.), the emergence process can also modify the local granulation pattern. The emergence of magnetic flux tubes with a flux of 10 19 Mx disturbs the granulation and leads to the transient appearance of a dark lane, which is coincident with upflowing material. These results are consistent with observed properties of emerging magnetic flux.

Induced sensitization of tumor stroma leads to eradication of established cancer by T cells

Targeting cancer cells, as well as the nonmalignant stromal cells cross-presenting the tumor antigen (Ag), can lead to the complete destruction of well-established solid tumors by adoptively transferred Ag-specific cytotoxic T lymphocytes (CTLs). If, however, cancer cells express only low levels of the Ag, then stromal cells are not destroyed, and the tumor escapes as Ag loss variants. We show that treating well-established tumors expressing low levels of Ag with local irradiation or a chemotherapeutic drug causes sufficient release of Ag to sensitize stromal cells for destruction by CTLs. This was shown directly using high affinity T cell receptor tetramers for visualizing the transient appearance of tumor-specific peptide–MHC complexes on stromal cells. Maximum loading of tumor stroma with cancer Ag occurred 2 d after treatment and coincided with the optimal time for T cell transfer. Under these conditions, tumor rejection was complete. These findings may set the stage for developing rational clinical protocols for combining irradiation or chemotherapy with CTL therapy.

Imaging Tumors with an Albumin-Binding Fab, a Novel Tumor-Targeting Agent

Association with albumin as a means to improve biodistribution and tumor deposition of a Fab was investigated using AB.Fab4D5, a bifunctional molecule derived from trastuzumab (HERCEPTIN) capable of binding albumin and tumor antigen HER2 (erbB2) simultaneously. AB.Fab4D5 was compared with trastuzumab and a trastuzumab-derived Fab (Fab4D5) for the ability to target tumors overexpressing HER2 in mouse mammary tumor virus/HER2 allograft models. Biodistribution was monitored using intravital microscopy, histology, and integrated single-photon emission computed tomography/computed tomography analysis. Fab4D5 tumor deposition was characterized by rapid but transient appearance in tumor at 2 h with little retention, followed by rapid accumulation in kidney by 6 h. Trastuzumab was slow to accumulate in tumors and slow to clear from normal tissues, although significant tumor deposition was achieved by 24 h. In contrast, AB.Fab4D5 was observed at 2 h in tumor and its presence was sustained beyond 24 h similar to trastuzumab. Intravital microscopy revealed that at peak tumor accumulation, tumor cell staining by AB.Fab4D5 was more uniform than for Fab4D5 or trastuzumab. Similar tumor deposition was achieved for both AB.Fab4D5 and trastuzumab at 48 h (35.9 +/- 1.8% and 38.2 +/- 3.1% injected dose/g); however, AB.Fab4D5 targeted tumors more rapidly and quickly cleared from blood, leading to a lower overall normal tissue exposure. Importantly, unlike Fab4D5, AB.Fab4D5 did not accumulate in kidney, suggesting that association with albumin leads to an altered route of clearance and metabolism. Rapid targeting, excellent tumor deposition and retention, coupled with high tumor to blood ratios may make AB.Fab an exceptional molecule for imaging and cancer therapy.

Dynamics of generating transients of delayed fluorescence induction signal and photosynthetic antennas: A possible relationship: Mathematical modeling approach

A mathematical model was developed for resolved temporal transients of experimentally recorded delayed fluorescence (DF) induction signal. During an intermittent light regime, antennas of the photosynthetic apparatus were treated as targets, repeatedly hit by potentially absorbable photons within a series of consecutive light flashes. Formulas were derived for the number of antennas, cumulatively hit by a specific number of photons, as function of the flash serial number (time). Model parameters included: number of absorbable photons in one flash, antenna sizes and numbers. A series of induction curves were analyzed, obtained from a ZeamaysL. leaf segment and differing in the previous dark period (td). Each curve, consisting of the two most prominent DF transients (C and D), was fitted with several model types, differing in the number of absorbed photons. For both transients, the best fitting result was achieved when DF induction was linked to the second absorbed photon. As expected, model parameters related to antenna sizes showed weaker dependence on td than those referring to antenna numbers. With restrictions applied in this model, the two DF induction transients may be related to two classes of photosynthetic antennas. Their different sizes may have a predominant influence on the efficiency of photon absorption, and possibly time-dependent appearance of DF transients.

Cell-wall lectins during winter wheat cold hardening

The polypeptide composition and functional activity of cell-wall lectins from roots of winter wheat (Triticum aestivum L., cv. Mironovskaya 808) seedlings during cold hardening were studied. Several phases of lectin activity changes were observed, which indicates their involvement in the development of general adaptation syndrome of the cell. After 0.5-h low-temperature treatment, marked alterations occurred in the profile of protein elution: lectins with mol wts of 78 and 42.5 kD disappeared and new ones with mol wts of 72, 69, 37, and 34.5 kD appeared. It was established that 17.5-and 69-kD lectins and most lectins eluted with glucose were arabinogalactan proteins (AGP), which permitted a supposition that these lectins were involved in the interaction between the cell wall and cytoskeleton. After 7-day-long hardening, total protein content reduced and lectins with mol wts of 69 and 37 kD disappeared, which corresponded to reduced lectin activity by the end of hardening. A transient appearance of 37-and 69-kD lectins, which are AGP, might indicate their involvement in the triggering the development of plant-cell defense responses.

Incidence of simultaneous epidural and vascular injection during lumbosacral transforaminal epidural injections

The incidence of vascular penetration during contrast confirmed fluoroscopically guided transforaminal lumbosacral epidural injections has been reported as 8.9% to 21.3% depending on the level of injection. Recently, intermittent fluoroscopy was shown to miss more than half of the vascular injections observed under live fluoroscopy. The number of misses increased when epidural and vascular contrast flow appeared simultaneously, even if the fluoroscopic image was taken during contrast injection. To date, no studies have documented the incidence of simultaneous epidural and vascular contrast injections. Also, most previous studies of vascular injections did not document use of live fluoroscopy during contrast injection, so the incidence of vascular injections may be higher than reported. To determine the incidence of simultaneous epidural and vascular contrast injection during lumbosacral transforaminal epidural injections. A prospective, observational, in vivo, study. Patients receiving lumbar transforaminal epidural injections at a university-based outpatient spine center. Incidence of epidural, vascular, and simultaneous epidural and vascular contrast patterns. One interventional spine physician and three fellows under his direct supervision recorded contrast patterns observed during 191 fluoroscopically guided lumbosacral transforaminal epidural steroid injections with injection of contrast observed under live fluoroscopy. The incidence of simultaneous epidural and vascular injection during lumbosacral transforaminal epidural injections was 8.9%. The incidence of a vascular injection alone was 4.2%, for a total vascular injection incidence of 13.1%. Subjects with a simultaneous epidural and vascular injection who returned for repeat injection had a statistically significant chance of a repeat simultaneous epidural and vascular injection when the injection was done at the same location. Fluoroscopy time was significantly increased, an average of 8.8 seconds, when a vascular injection was identified. There was no statistically significant correlation between the incidence of simultaneous epidural and vascular injection with subjects' age, sex, level of injection, side of injection, needle gauge, or diagnosis. Simultaneous epidural and vascular injection is twice as likely to occur as vascular injection alone. Use of intermittent fluoroscopy can miss the transient appearance of the vascular component of these injections, giving the false impression of successful contrast placement. In light of these results, live fluoroscopy is recommended during contrast injection for confirmation of lumbosacral transforaminal epidural injections.

Mosaic Tetraploidy and Transient Mutations in the GFI1 Gene in a Patient with Severe Chronic Neutropenia.

Severe congenital neutropenia (SCN), also known as Kostmann disease, is a rare disorder characterized by peripheral blood agranulocytosis and maturation arrest of neutrophils within the bone marrow at the promyelocytic stage. Patients usually present with an absolute neutrophil count below 0.2 x 109/L and severe infections, with the typical onset of symptoms during infancy. Most patients respond to treatment with granulocyte colony-stimulating factor, but retain an increased risk for death from sepsis and for development of myelodysplastic syndrome and acute myeloid leukemia (MDS/AML). Several reports have described karyotype abnormalities associated with this syndrome, most typically clonal loss of chromosome 7 or abnormalities of chromosome 21 associated with transformation to MDS/AML. The etiology of these abnormalities and their role in progression to MDS/AML remains unclear. Here we present a case of a 15 year-old boy with SCN, lymphopenia, and persistent tetraploid mosaicism in the bone marrow and in subpopulations of peripheral blood leukocytes. His phenotype, including growth and development, was otherwise normal. The patient's father, who had mild neutropenia and a history of monoclonal gammopathy, also showed a tetraploid subpopulation in his bone marrow. Flow cytometric analysis of the DNA content of CD45+ nucleated cells in the patient's peripheral blood showed that 20% of CD13+ granulocytes, and 15% of CD14+ monocytes were tetraploid. The lifelong persistence of the mosaicism and the similar finding in the patient's father suggest that it represents a congenital propensity towards acquiring tetraploidy. However, cytogenetic evaluation of the patient's skin fibroblasts detected no tetraploidy, indicating failure of the putative tetraploid embryonic cells to contribute to that lineage. The fact that the patient's father also had a population of tetraploid cells in his bone marrow and a history of neutropenia suggests a common underlying genetic cause for both conditions in this kindred.Mutational analysis revealed that the ELA2 gene sequence was normal, but the GFI1 gene exhibited transient, simultaneous appearance of two novel mutations: a missense substitution in exon 1 and a single base change in the promoter region, at a putative binding site for the myeloid-specific transcription factor MZF1. The GFI1 mutations were repeatedly identified in a DNA sample obtained in 2003, but not in 2001, 2002, or 2006 samples. Sequencing of DNA obtained from buccal swabs of the patient and his parents also revealed no GFI1 mutation. The transient appearance may represent the emergence and subsequent loss of a clone of hematopoietic stem or progenitor cells with GFI1 mutations. This hypothesis is supported by a recent report demonstrating that GFI1 mutation results in premature apoptosis of myeloid cells, similar to apoptosis-inducing mutations in the neutrophil elastase gene ELA2. The fact that GFI1 mutations were identified in a DNA sample from one year, but not from others, raises the possibility that GFI1 mutations reported in other neutropenic patients may also be transient. We speculate that an underlying genetic defect, inherited in an autosomal dominant pattern, leads to both disordered mitosis and leukopenia in this kindred.

Assembling microtubules disintegrate the postsynaptic density in vitro

The postsynaptic density (PSD), a disk-shaped protein aggregation of several hundred nm in diameter, plays important roles in the signal transduction and molecular organization of the excitatory synapses in mammalian CNS. The PSD resides in the microfilament-enriched cytoplasm of dendritic spines where the transient appearance of microtubules has been reported. When PSD isolated from porcine brain was incubated with polymerizing alpha,beta-tubulins, its turbidity became greater than that of the original PSD, suggesting that the PSD's structure was altered upon incubating with assembling microtubules. By transmission electron microscopy, smaller PSD fragments and several novel structures, including holes and finger-like extensions, were found in the PSD after incubation with assembling microtubules, but not in the original PSD or in the PSD incubated with alpha,beta-tubulins pretreated with vincristine. The results suggest that the interactions with assembling microtubules may result in the formation of holes in the PSD, and the rupture of these holes subsequently leads to the formation of smaller PSD fragments.