Treatments and rehabilitation in the acute and chronic state of traumatic brain injury.

Traumatic brain injury (TBI) is a major cause of acquired disability globally, and effective treatment methods are scarce. Lately, there has been increasing recognition of the devastating impact of TBI resulting from sports and other recreational activities, ranging from primarily sport-related concussions (SRC) but also more severe brain injuries requiring hospitalization. There are currently no established treatments for the underlying pathophysiology in TBI and while neuro-rehabilitation efforts are promising, there are currently is a lack of consensus regarding rehabilitation following TBI of any severity. In this narrative review, we highlight short- and long-term consequences of SRCs, and how the sideline management of these patients should be performed. We also cover the basic concepts of neuro-critical care management for more severely brain-injured patients with a focus on brain oedema and the necessity of improving intracranial conditions in terms of substrate delivery in order to facilitate recovery and improve outcome. Further, following the acute phase, promising new approaches to rehabilitation are covered for both patients with severe TBI and athletes suffering from SRC. These highlight the need for co-ordinated interdisciplinary rehabilitation, with a special focus on cognition, in order to promote recovery after TBI.

Prolonged latency of preterm prelabour rupture of membranes and neurodevelopmental outcomes: a secondary analysis.

OBJECTIVE: To determine whether prolonged latency after preterm prelabour rupture of membranes (PPROM) is associated with an increased risk for adverse neurodevelopmental outcomes. DESIGN: This is a secondary analysis of the randomised controlled trial of magnesium sulphate for the prevention of cerebral palsy. SETTING: Multicentre trial. POPULATION: A total of 1305 women with PPROM were analysed, 1056 of whom had an interval of <3 weeks between diagnosis and delivery and 249 of whom had an interval of ≥3 weeks between diagnosis and delivery. METHODS: We evaluated whether the time interval between diagnosis of PPROM and delivery was associated with an increased risk for adverse neurodevelopmental outcomes. Latency was analysed as a continuous variable and categorised by weeks of latency. MAIN OUTCOME MEASURES: The primary outcome was motor and mental Bayley scores of <70 at 2 years of age. Secondary outcomes included motor and mental Bayley scores <85 and mean Bayley scores. Logistic regression was used to control for confounding factors. RESULTS: In the univariate analysis, motor and mental Bayley scores of <70 were similar in the <3 weeks (16.8 and 14.4%) and ≥3 weeks (15.3 and 14.1%) groups. In the regression analysis adjusting for confounding factors, PPROM for ≥3 weeks was an independent risk factor for motor (adjusted odds ratio (aOR) 2.12; 95% confidence interval, 95% CI 1.29-3.49) and mental (aOR 1.83, 95% CI 1.13-3.00) Bayley scores of <70. Neonatal sepsis, gestational age at delivery, maternal education, and race were significantly associated with neurodevelopmental outcomes. CONCLUSIONS: Whereas delivery at later gestational age is associated with improved prognosis for many outcomes, prolonged exposure to an intrauterine environment of PPROM is an independent risk factor for adverse neurodevelopmental outcomes. TWEETABLE ABSTRACT: Prolonged PPROM was associated with motor and mental Bayley scores of <70.

Clinical indication and timing of antenatal corticosteroid administration at a single centre.

OBJECTIVE: To determine how well antenatal corticosteroids (ACS) were timed, based on the indication for administration for women delivering preterm. DESIGN: Retrospective cohort study. SETTING: Tertiary medical centre. POPULATION: Six hundred and thirty women who had singleton preterm births between 24 and 34 weeks' gestational age. METHODS: Charts from 2006 to 2011 were reviewed for indications for ACS administration, which included premature rupture of membranes, threatened preterm labour, risk factors for spontaneous preterm birth such as short ultrasound cervical length, positive fetal fibronectin, and hypertensive disorders of pregnancy. Charts were reviewed for timing of ACS administration in relation to delivery. MAIN OUTCOME MEASURES: The primary outcome was optimal timing, defined as administration of ACS ≥ 24 hours to ≤ 7 days prior to delivery. RESULTS: Of 630 women who delivered preterm, 589 (93%) received ACS prior to delivery. ACS timing was optimal in 40% (238 of 589) of cases. Women with hypertensive disorders were most likely to have steroids optimally timed (62%). Asymptomatic women at increased risk for preterm delivery were less likely to receive optimally timed ACS (12%). The majority of women who received steroids >2 weeks prior to delivery (57%) received a second course. CONCLUSION: A majority of women who delivered preterm did not receive optimally timed ACS. Diagnostic tools that identified women at risk for preterm birth were not able to identify patients for appropriate steroid timing. Given the range of clinical scenarios in which patients are at increased risk for preterm delivery, further research is needed to assist clinicians in optimising steroid administration. TWEETABLE ABSTRACT: Optimal timing of antenatal steroids prior to delivery does not occur in most cases.

The effect of maternal haematocrit on offspring IQ at 4 and 7 years of age: a secondary analysis.

OBJECTIVE: To determine whether maternal haematocrit during pregnancy is associated with offspring IQ. DESIGN/SETTING/POPULATION: A secondary analysis of the Collaborative Perinatal Project, which enrolled women between 1959 and 1966 at 12 university hospitals in the United States. METHODS: We evaluated the relation between maternal haematocrit and IQ at 4 and 7 years of age. Linear and log-linear regression models were used to adjust for possible confounders. Marginal structural models with stabilised weights were used to account for selection bias due to children lost to follow up. MAIN OUTCOME MEASURES: Offspring IQ at 4 and 7 years of age. RESULTS: Of 35 959 patients, 1521 (4.2%) had moderate anaemia, 13 769 (38.3%) had mild anaemia, 18 227 (50.7%) had a normal haematocrit, and 2442 (6.8%) had a high haematocrit. The mean IQ at 4 and 7 years was significantly lower in the moderate and mild anaemia groups than in the normal haematocrit group (92.3 and 94.7 versus 100.6, respectively, P < 0.01, at 4 years; and 90.2 and 93.4 versus 99.1 at 7 years, P < 0.01). The high haematocrit group had a significantly higher mean IQ (104.5 at 4 years; 103.2 at 7 years) when compared with the normal haematocrit group (P < 0.01). Women with moderate anaemia were more likely to have children with IQ of 70-84 at 4 years (RR 1.22, 95% CI 1.08-1.38) and <70 at 7 years (RR 1.59, 95% CI 1.14-2.23). Women with a high haematocrit were more likely to have children with an IQ ≥120 at 7 years (RR 1.22, 95% CI 1.08-1.39). CONCLUSIONS: Maternal haematocrit is associated with offspring IQ at 4 and 7 years of age. TWEETABLE ABSTRACT: There is a nonlinear relation between maternal haematocrit and offspring IQ at 4 and 7 years of age.

Ten-year outcome of early childhood traumatic brain injury: Diffusion tensor imaging of the ventral striatum in relation to executive functioning.

PRIMARY OBJECTIVE: The long-term effects of TBI on verbal fluency and related structures, as well as the relation between cognition and structural integrity, were evaluated. It was hypothesized that the group with TBI would evidence poorer performance on cognitive measures and a decrease in structural integrity. RESEARCH DESIGN: Between a paediatric group with TBI and a group of typically-developing children, the long-term effects of traumatic brain injury were investigated in relation to both structural integrity and cognition. Common metrics for diffusion tensor imaging (DTI) were used as indicators of white matter integrity. METHODS AND PROCEDURES: Using DTI, this study examined ventral striatum (VS) integrity in 21 patients aged 10-18 years sustaining moderate-to-severe traumatic brain injury (TBI) 5-15 years earlier and 16 demographically comparable subjects. All participants completed Delis-Kaplan Executive Functioning System (D-KEFS) sub-tests. MAIN OUTCOMES AND RESULTS: The group with TBI exhibited lower fractional anisotropy (FA) and executive functioning performance and higher apparent diffusion coefficient (ADC). DTI metrics correlated with D-KEFS performance (right VS FA with Inhibition errors, right VS ADC with Letter Fluency, left VS FA and ADC with Category Switching). CONCLUSIONS: TBI affects VS integrity, even in a chronic phase, and may contribute to executive functioning deficits.

Ventilation rates and health: multidisciplinary review of the scientific literature.

UNLABELLED: The scientific literature through 2005 on the effects of ventilation rates on health in indoor environments has been reviewed by a multidisciplinary group. The group judged 27 papers published in peer-reviewed scientific journals as providing sufficient information on both ventilation rates and health effects to inform the relationship. Consistency was found across multiple investigations and different epidemiologic designs for different populations. Multiple health endpoints show similar relationships with ventilation rate. There is biological plausibility for an association of health outcomes with ventilation rates, although the literature does not provide clear evidence on particular agent(s) for the effects. Higher ventilation rates in offices, up to about 25 l/s per person, are associated with reduced prevalence of sick building syndrome (SBS) symptoms. The limited available data suggest that inflammation, respiratory infections, asthma symptoms and short-term sick leave increase with lower ventilation rates. Home ventilation rates above 0.5 air changes per hour (h(-1)) have been associated with a reduced risk of allergic manifestations among children in a Nordic climate. The need remains for more studies of the relationship between ventilation rates and health, especially in diverse climates, in locations with polluted outdoor air and in buildings other than offices. PRACTICAL IMPLICATIONS: Ventilation with outdoor air plays an important role influencing human exposures to indoor pollutants. This review and assessment indicates that increasing ventilation rates above currently adopted standards and guidelines should result in reduced prevalence of negative health outcomes. Building operators and designers should avoid low ventilation rates unless alternative effective measures, such as source control or air cleaning, are employed to limit indoor pollutant levels.

Antigen recognition and antibody specificity. Carrier specificity and genetic control of anti-dinitrophenyl-oligolysine antibody.

The exact specifiicity of anti-DNP antibody produced by Hartley guinea pigs immunized with a series of defined alpha,DNP and epsilon,DNP-oligolysines was studied by fluorescence quenching. All responder animals made anti-DNP antibody which recognized the precise chain length, +/- 1 lysyl residue, of the DNP-oligolysines used to induce the immune response as measured by an increase in binding energy (-DeltaF degrees ) for that antigen. The ability of the immune system to detect the smallest possible change in oligolysine chain length suggests that the anti-hapten antibody-forming cell possesses a highly specific recognition system for carrier conformation. When DNP-oligolysines are incorporated in an adjuvant containing M. tuberculosis H37Rv, both responder and nonresponder produce anti-DNP antibody, but only the responder develops delayed skin sensitivity. In addition to their failure to develop delayed hypersensitivity, nonresponders produced anti-DNP oligolysine antibody which did not show the increase in -DeltaF degrees for the immunizing antigen characteristic of responder antibody. These observations support a local environment hypothesis for antigen recognition at the level of the anti-hapten antibody-forming cell and suggest that the polylysine gene exerts its control at the same cell.

The compartmentalization of antigen-reactive lymphocytes in desensitized guinea pigs.

A single injection of epsilon,DNP-Lys(7-10) can render previously sensitized guinea pigs specifically unreactive to subsequent intradermal challenge with that antigen. Antigen-reactive lymphocytes, as assayed by macrophage-migration in-inhibition or thymidine incorporation, were depleted from the peritoneal exudates of those animals. In contrast, it was intriguing to find that lymph node lymphocytes from such animals responded normally in the antigen-induced thymidine incorporation assay. These studies demonstrate a compartmentalization of antigen-reactive lymphocytes in desensitized animals which may account for the short-lived nature of this phenomenon.

The evolution of white matter microstructural changes after mild traumatic brain injury: A longitudinal DTI and NODDI study.

Neuroimaging biomarkers that can detect white matter (WM) pathology after mild traumatic brain injury (mTBI) and predict long-term outcome are needed to improve care and develop therapies. We used diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) to investigate WM microstructure cross-sectionally and longitudinally after mTBI and correlate these with neuropsychological performance. Cross-sectionally, early decreases of fractional anisotropy and increases of mean diffusivity corresponded to WM regions with elevated free water fraction on NODDI. This elevated free water was more extensive in the patient subgroup reporting more early postconcussive symptoms. The longer-term longitudinal WM changes consisted of declining neurite density on NODDI, suggesting axonal degeneration from diffuse axonal injury for which NODDI is more sensitive than DTI. Therefore, NODDI is a more sensitive and specific biomarker than DTI for WM microstructural changes due to mTBI that merits further study for mTBI diagnosis, prognosis, and treatment monitoring.

Cognitive declines following bilateral subthalamic nucleus deep brain stimulation for the treatment of Parkinson's disease.

BACKGROUND: We investigated the cognitive and psychiatric outcome 6 months after bilateral subthalamic nucleus deep brain stimulation (DBS) for the treatment of Parkinson's disease (PD) using a disease control group. METHODS: 23 patients who underwent DBS were compared with 28 medically treated patients with PD at baseline and at 6 months for neuropsychological measures. In addition to the group outcomes, we report reliable change indices (RCI) and a dementia caseness analysis. RESULTS: Patients who underwent DBS demonstrated a significant decline in verbal memory compared with the control group (p<0.003), and trends for decline on oral information processing, including verbal fluency, timed transcription and word naming. Patients who underwent DBS demonstrated declines in attention, set shifting and semantic fluency but these changes were similar to the rate of decline in the PD group. RCI indicated that patients who underwent DBS demonstrated clinically significant declines in verbal fluency (p<0.01) and inhibition of a dominant response (p<0.003), with trends for declines in set shifting (p<0.02) and verbal long term recall (p<0.08), indicative of frontostriatal dysfunction. Patients who underwent DBS did not demonstrate significant changes in depression, anxiety or psychological distress scores. The caseness analysis revealed that one of the patients who underwent DBS (4%) converted to dementia over 6 months compared with none of the PD controls. CONCLUSIONS: Our findings demonstrated that patients who underwent DBS experienced declines in verbal recall and trends for declines in oral information processing 6 months following surgery, even when good motor outcome was achieved. Potential candidates should be counselled about the risk of mild frontostriatal cognitive declines following DBS to weigh the risks and benefits of surgery.

cerebellar atrophy after moderate-to-severe pediatric traumatic brain injury.

BACKGROUND AND PURPOSE: Although the cerebellum has not attracted the same degree of attention as cortical areas and the hippocampus in traumatic brain injury (TBI) literature, there is limited structural and functional imaging evidence that the cerebellum is also vulnerable to insult. The cerebellum is emerging as part of a frontocerebellar system that, when disrupted, results in significant cognitive and behavioral consequences. We hypothesized that cerebellar volume would be reduced in children following TBI and wished to examine the relation between the cerebellum and known sites of projection, including the prefrontal cortex, thalamus, and pons. MATERIALS AND METHODS: Quantitative MR imaging was used to measure cerebellar white and gray matter and lesion volumes 1-10 years following TBI in 16 children 9-16 years of age and 16 demographically matched typically developing children 9-16 years of age. Cerebellar volumes were also compared with volumetric data from other brain regions to which the cerebellum projects. RESULTS: A significant group difference was found in cerebellar white and gray matter volume, with children in the TBI group consistently exhibiting smaller volumes. Repeating the analysis after excluding children with focal cerebellar lesions revealed that significant group differences still remained for cerebellar white matter (WM). We also found a relation between the cerebellum and projection areas, including the dorsolateral prefrontal cortex, thalamus, and pons in 1 or both groups. CONCLUSION: Our finding of reduced cerebellar WM volume in children with TBI is consistent with evidence from experimental studies suggesting that the cerebellum and its related projection areas are highly vulnerable to fiber degeneration following traumatic insult.

An unusual mechanism of self-primed reverse transcription requires the RNase H domain of reverse transcriptase to cleave an RNA duplex.

The reverse transcription of retroviruses and long terminal repeat-containing retrotransposons requires that tRNA species serve as primers. We recently reported that the long terminal repeat-containing retrotransposon Tf1 is a unique exception in that reverse transcription is independent of tRNA and is instead initiated by a self-priming mechanism. The first 11 bases of the Tf1 transcript fold back and anneal to the primer binding site in a process that results in the priming of minus-strand strong-stop DNA. Data presented here demonstrate that a cleavage occurs between the 11th and 12th bases of the transcript, resulting in the generation of the primer. Mutagenesis experiments presented here indicate that the RNase H domain of the Tf1 reverse transcriptase is required for the cleavage reaction, suggesting that this RNase H may have the novel ability to cleave double-stranded RNA at the end of a duplexed region.

A novel mechanism of self-primed reverse transcription defines a new family of retroelements.

Retroviruses and long terminal repeat (LTR)-containing retrotransposons initiate reverse transcription by using a specific tRNA primer than anneals to the primer-binding site of the retroelement transcript. Sequences from a large number of retroviruses and LTR-containing retrotransposons had indicated that the role of tRNAs in priming reverse transcription is universal among these LTR-containing retroelements. Data presented here strongly support the surprising conclusion that Tf1, a highly active LTR-containing retrotransposon isolated from Schizosaccharomyces pombe, undergoes a novel self-priming process that requires hybridization between the primer-binding site and the first 11 bases of the Tf1 transcript. Single-base mutations in these regions block transposition and reverse transcription, while compensatory mutations that reestablish complementarily rescue both defects. In addition, the sequence of the minus-strand RNA primer of reverse transcription was consistent with its being derived from the 5' end of the Tf1 transcript. Evidence that this mechanism defines a new family of retroelements is presented.

Nuclear import of the retrotransposon Tf1 is governed by a nuclear localization signal that possesses a unique requirement for the FXFG nuclear pore factor Nup124p.

Retroviruses, such as human immunodeficiency virus, that infect nondividing cells generate integration precursors that must cross the nuclear envelope to reach the host genome. As a model for retroviruses, we investigated the nuclear entry of Tf1, a long-terminal-repeat-containing retrotransposon of the fission yeast Schizosaccharomyces pombe. Because the nuclear envelope of yeasts remains intact throughout the cell cycle, components of Tf1 must be transported through the envelope before integration can occur. The nuclear localization of the Gag protein of Tf1 is different from that of other proteins tested in that it has a specific requirement for the FXFG nuclear pore factor, Nup124p. Using extensive mutagenesis, we found that Gag contained three nuclear localization signals (NLSs) which, when included individually in a heterologous protein, were sufficient to direct nuclear import. In the context of the intact transposon, mutations in the NLS that mapped to the first 10 amino acid residues of Gag significantly impaired Tf1 retrotransposition and abolished nuclear localization of Gag. Interestingly, this NLS activity in the heterologous protein was specifically dependent upon the presence of Nup124p. Deletion analysis of heterologous proteins revealed the surprising result that the residues in Gag with the NLS activity were independent from the residues that conveyed the requirement for Nup124p. In fact, a fragment of Gag that lacked NLS activity, residues 10 to 30, when fused to a heterologous protein, was sufficient to cause the classical NLS of simian virus 40 to require Nup124p for nuclear import. Within the context of the current understanding of nuclear import, these results represent the novel case of a short amino acid sequence that specifies the need for a particular nuclear pore complex protein.

Reverse transcription of a self-primed retrotransposon requires an RNA structure similar to the U5-IR stem-loop of retroviruses.

An inverted repeat (IR) within the U5 region of the Rous sarcoma virus (RSV) mRNA forms a structure composed of a 7-bp stem and a 5-nucleotide (nt) loop. This U5-IR structure has been shown to be required for the initiation of reverse transcription. The mRNA of Tf1, long terminal repeat-containing retrotransposon from fission yeast (Schizosaccharomyces pombe) contains nucleotides with the potential to form a U5-IR stem-loop that is strikingly similar to that of RSV. The putative U5-IR stem-loop of Tf1 consists of a 7-bp stem and a 25-nt loop. Results from mutagenesis studies indicate that the U5-IR stem-loop in the mRNA of Tf1 does form and that it is required for Tf1 transposition. Although the loop is required for transposition, we were surprised that the specific sequence of the nucleotides within the loop was unimportant for function. Additional investigation indicates that the loss of transposition activity due to a reduction in the loop size to 6 nt could be rescued by increasing the GC content of the stem. This result indicates that the large loop in the Tf1 mRNA relative to that of the RSV allows the formation of the relatively weak U5-IR stem. The levels of Tf1 proteins expressed and the amounts of Tf1 RNA packaged into the virus-like particles were not affected by mutations in the U5-IR structure. However, all of the mutations in the U5-IR structure that caused defects in transposition produced low amounts of reverse transcripts. A unique feature in the initiation of Tf1 reverse transcription is that, instead of a tRNA, the first 11 nt of the Tf1 mRNA serve as the minus-strand primer. Analysis of the 5' end of Tf1 mRNA revealed that the mutations in the U5-IR stem-loop that resulted in defects in reverse transcription caused a reduction in the cleavage activity required to generate the Tf1 primer. Our results indicate that the U5-IR stems of Tf1 and RSV are conserved in size, position, and function.

Two related families of retrotransposons from Schizosaccharomyces pombe.

Two related families of transposons were isolated from schizosaccharomyces pombe, an organism which has been the object of extensive genetic studies which had previously produced no evidence for the existence of such elements. These two classes of repeated DNAs, dubbed Tf1 (transposon of fission yeast 1) and Tf2 have many properties of retrotransposons. Tf1 and Tf2 both possess long terminal repeats and predicted protein sequences that resemble the protease, reverse transcriptase, and integrase domains of retroviruses. The chromosomal locations and total numbers of Tf1 and Tf2 differ greatly in various isolates of S. pombe. The Tf elements are expressed in the form of 4.5-kb mRNAs. The complete sequence of Tf1 was determined and suggests that a novel mechanism for regulating its gene expression may be used.

Schizosaccharomyces pombe retrotransposon Tf2 mobilizes primarily through homologous cDNA recombination.

The Tf2 retrotransposon, found in the fission yeast Schizosaccharomyces pombe, is nearly identical to its sister element, Tf1, in its reverse transcriptase-RNase H and integrase domains but is very divergent in the gag domain, the protease, the 5' untranslated region, and the U3 domain of the long terminal repeats. It has now been demonstrated that a neo-marked copy of Tf2 overexpressed from a heterologous promoter can mobilize into the S. pombe genome and produce true transposition events. However, the Tf2-neo mobilization frequency is 10- to 20-fold lower than that of Tf1-neo, and 70% of the Tf2-neo events are homologous recombination events generated independently of a functional Tf2 integrase. Thus, the Tf2 element is primarily dependent on homologous recombination with preexisting copies of Tf2 for its propagation. Finally, production of Tf2-neo proteins and cDNA was also analyzed; surprisingly, Tf2 was found to produce its reverse transcriptase as a single species in which it is fused to protease, unlike all other retroviruses and retrotransposons.

The retrotransposon Tf1 assembles virus-like particles that contain excess Gag relative to integrase because of a regulated degradation process.

The retrotransposon Tf1, isolated from Schizosaccharomyces pombe, contains a single open reading frame with sequences encoding Gag, protease, reverse transcriptase, and integrase (IN). Tf1 has previously been shown to possess significant transposition activity. Although Tf1 proteins do assemble into virus-like particles, the assembly does not require readthrough of a translational reading frame shift or stop codon, common mechanisms used by retroelements to express Gag in molar excess of the polymerase proteins. This study was designed to determine if Tf1 particles contain equal amounts of Gag and polymerase proteins or whether they contain the typical molar excess of Gag. After using two separate methods to calibrate the strength of our antibodies, we found that both S. pombe extracts and partially purified Tf1 particles contained a 26-fold molar excess of Gag relative to IN. Knowing that Gag and IN are derived from the same Tf1 primary translation product, we concluded that the excess Gag most likely resulted from specific degradation of IN. We obtained evidence of regulated IN degradation in comparisons of Tf1 protein extracted from log-phase cells and that extracted from stationary-phase cells. The log-phase cells contained equal molar amounts of Gag and IN, whereas cells approaching stationary phase rapidly degraded IN, leaving an excess of Gag. Analysis of the reverse transcripts indicated that the bulk of reverse transcription occurred within the particles that possess a molar excess of Gag.

Nup124p is a nuclear pore factor of Schizosaccharomyces pombe that is important for nuclear import and activity of retrotransposon Tf1.

The long terminal repeat (LTR)-containing retrotransposon Tf1 propagates within the fission yeast Schizosaccharomyces pombe as the result of several mechanisms that are typical of both retrotransposons and retroviruses. To identify host factors that contribute to the transposition process, we mutagenized cultures of S. pombe and screened them for strains that were unable to support Tf1 transposition. One such strain contained a mutation in a gene we named nup124. The product of this gene contains 11 FXFG repeats and is a component of the nuclear pore complex. In addition to the reduced levels of Tf1 transposition, the nup124-1 allele caused a significant reduction in the nuclear localization of Tf1 Gag. Surprisingly, the mutation in nup124-1 did not cause any reduction in the growth rate, the nuclear localization of specific nuclear localization signal-containing proteins, or the cytoplasmic localization of poly(A) mRNA. A two-hybrid analysis and an in vitro precipitation assay both identified an interaction between Tf1 Gag and the N terminus of Nup124p. These results provide evidence for an unusual mechanism of nuclear import that relies on a direct interaction between a nuclear pore factor and Tf1 Gag.

A new member of the Sin3 family of corepressors is essential for cell viability and required for retroelement propagation in fission yeast.

Tf1 is a long terminal repeat (LTR)-containing retrotransposon that propagates within the fission yeast Schizosaccharomyces pombe. LTR-retrotransposons possess significant similarity to retroviruses and therefore serve as retrovirus models. To determine what features of the host cell are important for the proliferation of this class of retroelements, we screened for mutations in host genes that reduced the transposition activity of Tf1. We report here the isolation and characterization of pst1(+), a gene required for Tf1 transposition. The predicted amino acid sequence of Pst1p possessed high sequence homology with the Sin3 family of proteins, known for their interaction with histone deacetylases. However, unlike the SIN3 gene of Saccharomyces cerevisiae, pst1(+) is essential for cell viability. Immunofluorescence microscopy indicated that Pst1p was localized in the nucleus. Consistent with the critical role previously reported for Sin3 proteins in the histone acetylation process, we found that the growth of the strain with the pst1-1 allele was supersensitive to the specific histone deacetylase inhibitor trichostatin A. However, our analysis of strains with the pst1-1 mutation was unable to detect any changes in the acetylation of specific lysines of histones H3 and H4 as measured in bulk chromatin. Interestingly, the pst1-1 mutant strain produced wild-type levels of Tf1-encoded proteins and cDNA, indicating that the defect in transposition occurred after reverse transcription. The results of immunofluorescence microscopy showed that the nuclear localization of the Tf1 capsid protein was disrupted in the strain with the pst1-1 mutation, indicating an important role of pst1(+) in modulating the nuclear import of Tf1 virus-like particles.