Enhanced fidelity of 3TC-selected mutant HIV-1 reverse transcriptase

Monotherapy with (-)2',3'-dideoxy-3'-thiacytidine (3TC) leads to the appearance of a drug-resistant variant of human immunodeficiency virus-type 1 (HIV-1) with the methionine-184 --> valine (M184V) substitution in the reverse transcriptase (RT). Despite resulting drug resistance, treatment for more than 48 weeks is associated with a lower plasma viral burden than that at baseline. Studies to investigate this apparent contradiction revealed the following. (i) Titers of HIV-neutralizing antibodies remained stable in 3TC-treated individuals in contrast to rapid declines in those treated with azidothymidine (AZT). (ii) Unlike wild-type HIV, growth of M184V HIV in cell culture in the presence of d4T, AZT, Nevirapine, Delavirdine, or Saquinavir did not select for variants displaying drug resistance. (iii) There was an increase in fidelity of nucleotide insertion by the M184V mutant compared with wild-type enzyme.

Human fatty acid synthase: properties and molecular cloning

Fatty acid synthase (FAS; EC 2.3.1.85) was purified to near homogeneity from a human hepatoma cell line, HepG2. The HepG2 FAS has a specific activity of 600 nmol of NADPH oxidized per min per mg, which is about half that of chicken liver FAS. All the partial activities of human FAS are comparable to those of other animal FASs, except for the beta-ketoacyl synthase, whose significantly lower activity is attributable to the low 4'-phosphopantetheine content of HepG2 FAS. We cloned the human brain FAS cDNA. The cDNA sequence has an open reading frame of 7512 bp that encodes 2504 amino acids (M(r), 272,516). The amino acid sequence of the human FAS has 79% and 63% identity, respectively, with the sequences of the rat and chicken enzymes. Northern analysis revealed that human FAS mRNA was about 9.3 kb in size and that its level varied among human tissues, with brain, lung, and liver tissues showing prominent expression. The nucleotide sequence of a segment of the HepG2 FAS cDNA (bases 2327-3964) was identical to that of the cDNA from normal human liver and brain tissues, except for a 53-bp sequence (bases 3892-3944) that does not alter the reading frame. This altered sequence is also present in HepG2 genomic DNA. The origin and significance of this sequence variance in the HepG2 FAS gene are unclear, but the variance apparently does not contribute to the lower activity of HepG2 FAS.

Differential expression of transforming growth factor-beta receptors I and II and activation of Smad 3 in keloid fibroblasts

Keloids represent a dysregulated response to cutaneous wounding that results in an excessive deposition of extracellular matrix, especially collagen. However, the molecular mechanisms regulating this pathologic collagen deposition still remain to be elucidated. A previous study by this group demonstrated that transforming growth factor (TGF)-beta1 and -beta2 ligands were expressed at greater levels in keloid fibroblasts when compared with normal human dermal fibroblasts (NHDFs), suggesting that TGF-beta may play a fibrosis-promoting role in keloid pathogenesis.To explore the biomolecular mechanisms of TGF-beta in keloid formation, the authors first compared the expression levels of the type I and type II TGF-beta receptors in keloid fibroblasts and NHDFs. Next, they investigated the phosphorylation of Smad 3, an intracellular TGF-beta signaling molecule, in keloid fibroblasts and NHDFs. Finally, they examined the regulation of TGF-beta receptor II by TGF-beta1, TGF-beta2, and TGF-beta3 ligands. Our findings demonstrated an increased expression of TGF-beta receptors (types I and II) and increased phosphorylation of Smad 3 in keloid fibroblasts relative to NHDFs. These data support a possible role of TGF-beta and its receptors as fibrosis-inducing growth factors in keloids. In addition, all three isoforms of recombinant human TGF-beta proteins could further stimulate the expression of TGF-beta receptor II in both keloids and NHDFs. Taken together, these results substantiate the hypothesis that the elevated levels of TGF-beta ligands and receptors present in keloids may support increased signaling and a potential role for TGF-beta in keloid pathogenesis.

AMPA receptors in the rat and primate hippocampus: a possible absence of GluR2/3 subunits in most interneurons

Amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors are assembled from the four subunits GluR1, 2, 3, 4 (or GluRA, B, C, D). AMPA channels that do not contain the GluR2 subunit are permeable to calcium. Recent studies indicate that excitotoxic as well as epileptic and ischemic cell damage may be mediated not only by N-methyl-Daspartate receptors, but also by AMPA receptors. The majority of interneurons in the hippocampus are resistant, but subsets of interneurons are consistently damaged in different disease states. Single immunolabeling using antibodies against AMPA receptor subunits, together with double immunolabeling for calcium-binding proteins (parvalbumin, calbindin and calretinin) and the neuropeptide somatostatin, were performed to study GluR1-4 immunoreactivity in interneuronal populations and principal cells. The ultrastructure of GluR1-4 labeled neurons was also examined using electron microscopy. With the exception of calbindin-positive interneurons, GluR2/3 was absent from hippocampal interneurons in both rat and monkey. In the rat, interneurons were more strongly immunoreactive against GluR1 than principal cells. In the monkey, immunoreactivity for GluR4 in interneurons was stronger than for GluR1. All GluR subunits were confined to spines, dendritic membrane and cytoplasm surrounding the nucleus but absent from axons and presynaptic terminals. Our findings suggest that hippocampal principal cells and interneurons express different complements of AMPA receptor subunits. Furthermore, the absence of GluR2 and/or GluR3 in both vulnerable and resistant interneurons subtypes indicates that knowledge of receptor subunit composition is not sufficient to predict neuronal vulnerability.

Cadherin repertoire determines partner-specific gap junctional communication during melanoma progression

Reduced gap junction activity has long been implicated in tumorigenesis. To elucidate the potential role of intercellular communication in melanoma development, we examined gap junctional capability of melanocytic cells from various stages of tumor progression in coculture models using dye transfer assays. Normal melanocytes coupled with keratinocytes by gap junctional formation, whereas melanoma cells did not. Instead, melanoma cells communicated among themselves and with fibroblasts. This switch in communication partners coincided with a shift from E-cadherin to N-cadherin expression during melanoma development. Forced expression of E-cadherin by adenoviral gene transfer in N-cadherin-expressing melanoma cells restored gap junctional compatibility with keratinocytes. Our data suggest that (1) melanocyte transformation is associated with loss of the pre-existing gap junctional activity with keratinocytes but a concomitant gain of communication with a newly juxtaposed cell type, the fibroblasts, (2) the specificity of gap junctional formation during melanoma development is determined by the cadherin profile on the melanocytic cells and (3) the overall gap junctional activity of melanocytic cells is not reduced with transformation.

Altering the specificity of restriction endonuclease: effect of replacing Mg2+ with Mn2+

In the presence of 100 mM Tris buffer (pH 7.5) and 1-10 mM Mg2+ EcoRI endonuclease cleaves DNA at a specific nucleotide sequence and in a characteristic way: -GAATTC-. But if Mg2+ is replaced by Mn2+, the specificity of the cleavage is relaxed and cleavages occur at many other sites; moreover, there appears to be a hierarchy of cleavage rates at the pseudo-EcoRI restriction sites. For example, SV40 DNA is cleaved only once in the usual digestion conditions, but with Mn2+ more than ten cleavages are made; the five most rapidly cleaved SV40 DNA map locations are 0/1.0 larger than 0.93 larger than 0.33 approximately equal to 0.42 larger than 0.29 approximately equal to 0.40 larger than 0.25. Mn2+ also alters the restriction specificity of HindIII but not HpaII endonuclease.

A comparison of the composition of silk proteins produced by spiders and insects

Proteins that are highly expressed and composed of amino acids that are costly to synthesize are likely to place a greater drain on an organism's energy resources than proteins that are composed of ingested amino acids or ones that are metabolically simple to produce. Silks are highly expressed proteins produced by all spiders and many insects. We compared the metabolic costs of silks spun by arthropods by calculating the amount of ATP required to produce their component amino acids. Although a definitive conclusion requires detailed information on the dietary pools of amino acids available to arthropods, on the basis of the central metabolic pathways, silks spun by herbivorous, Lepidoptera larvae require significantly less ATP to synthesize than the dragline silks spun by predatory spiders. While not enough data are available to draw a statistically based conclusion, comparison of homologous silks across ancestral and derived taxa of the Araneoidea seems to suggest an evolutionary trend towards reduced silk costs. However, comparison of the synthetic costs of dragline silks across all araneomorph spiders suggests a complicated evolutionary pattern that cannot be attributed to phylogenetic position alone. We propose that the diverse silk-producing systems of the araneoid spiders (including three types of protein glues and three types of silk fibroin), evolved through intra-organ competition and that taxon-specific differences in the composition of silks drawn from homologous glands may reflect limited or fluctuating amino acid availability. The different functional properties of spider silks may be a secondary result of selection acting on different polypeptide templates.

Ontogeny of expression of transforming growth factor-beta 1 (TGF-beta 1), TGF-beta 3, and TGF-beta receptors I and II in fetal rat fibroblasts and skin

Fetal cutaneous wounds that occur in early gestation heal without scar formation. Although much work has been done to characterize the role of transforming growth factor-beta (TGF-beta) isoforms in the adult wound repair process, their function in fetal scarless wound repair is not well understood. The authors hypothesized that the pattern of expression for TGF-beta isoforms and their receptors may influence the phenotypic transition from scarless to scar-forming repair observed during fetal gestation. Using time-dated fetal Sprague-Dawley rat fibroblasts and unwounded skin at gestational ages 14, 16, 18, and 21 days postcoitum of the scarless (< or =16 days) and scar-forming (>16 days) periods of gestation (term = 21.5 days), the authors analyzed the endogenous messenger RNA (mRNA) levels of TGF-beta 1 and TGF-beta 3 and their signaling receptors TGF-beta-RI and TGF-beta-RII. Northern blot analyses in both fibroblasts and unwounded skin revealed that levels of TGF-beta 1 were not differentially expressed, whereas more TGF-beta 3 mRNA transcript was found in early than in late gestation. Fibroblast expression of TGF-beta-RI showed no substantial differences, whereas expression of TGF-beta-RII increased during gestation. In contrast, expression of both TGF-beta-RI and TGF-beta-RII in unwounded skin showed decreasing levels as a function of gestational age. The differential levels of TGF-beta 1 and TGF-beta 3 suggest that the ratio of these cytokines may provide a predominantly antiscarring or profibrotic signal upon wounding during the scar-free or scar-forming periods of gestation, respectively. Furthermore, lower amounts of the ligand-binding TGF-beta-RII seen in early gestation fibroblasts suggest a decreased ability to perceive ligand during the period of scarless repair.

Pre-treatment with R-lipoic acid alleviates the effects of GSH depletion in PC12 cells: implications for Parkinson's disease therapy

Oxidative stress is believed to play a key role in the degeneration of dopaminergic neurons in the substantia nigra (SN) of Parkinson's disease (PD) patients. An important biochemical feature of PD is a significant early depletion in levels of the thiol antioxidant compound glutathione (GSH) which may lead to the generation of reactive oxygen species (ROS), mitochondrial dysfunction, and ultimately to subsequent neuronal cell death. In earlier work from our laboratory, we demonstrated that depletion of GSH in dopaminergic PC12 cells affects mitochondrial integrity and specifically impairs the activity of mitochondrial complex I. Here we report that pre-treatment of PC12 cells with R-lipoic acid acts to prevent depletion of GSH content and preserves the mitochondrial complex I activity which normally is impaired as a consequence of GSH loss.

Four modified silver methods for thick sections of formaldehyde-fixed mammalian central nervous tissue: 'dark' neurons, perikarya of all neurons, microglial cells and capillaries

Four reliable silver methods for the visualization of acute or advanced phases of neuronal damage have been modified so that they can be performed with good results on materials freshly fixed with transcardial perfusion of buffered formaldehyde for other silver methods and immunocytochemical techniques. The four modified methods respectively stain: (1) the somata and dendrites of 'dark' (impaired) neurons, (2) the perikarya of all neurons, (3) microglial cells, and (4) capillaries. Without the present modifications the 'dark' neuron method is only effective with glutaraldehyde fixation while the other three methods predominantly stain myelin in freshly fixed mammalian nervous tissue.

Higher fidelity of RNA-dependent DNA mispair extension by M184V drug-resistant than wild-type reverse transcriptase of human immunodeficiency virus type 1

Reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1) has low fidelity compared with RTs of other retroviruses and cellular DNA polymerases. We and others have previously found that the fidelity of DNA-dependent DNA polymerization (DDDP) of M184V-mutated HIV-1 RT is significantly higher than that of wild-type RT. Viruses containing the M184V substitution are highly resistant to (-)-2'-dideoxy-3'-thiacytidine (3TC) in vitro and in patients treated with 3TC monotherapy. It was of interest to determine the fidelity of RNA-dependent DNA polymerization (RDDP) of M184V RT compared with wild-type because this step occurs first in reverse transcription; errors made during this step may be copied in subsequent polymerization steps. Using an in vitro mispaired primer extension assay, M184V-mutated RT exhibited 3-49-fold decreased frequency of mispair extension compared with wild-type RT. Fidelity differences between M184V and wild-type RT were most marked in extension of A:G (49-fold) and A:C (16-fold) mispairs, with only a marginal (3-fold) decrease in the extension of A:A mispairs. RT containing a methionine to isoleucine (M184I) mutation showed only slight increases in RDDP fidelity compared with wild-type, ranging from 1.5- to 6-fold increases. Of the three RTs tested, wild-type RT was the most error-prone, with mispair extension frequencies ranging from 6.674 x 10(-1) to 7.454 x10(-2).

Long-term outcome of 487 patients with early-stage extra-nodal marginal zone lymphoma

Background

Localized early-stage extra-nodal marginal zone lymphoma (MZL) presents with heterogeneous organ involvement and is treated with various modalities, including resection, radiotherapy, and systemic therapy. We report the long-term outcome of a large cohort of extra-nodal MZL and assess the impact of patient and disease characteristics, organ site, and treatment strategy on disease control and survival.

Patients and methods

We identified 487 consecutive patients with stage IE or IIE MZL referred between 1992 and 2012 to Memorial Sloan Kettering Cancer Center. Pathology was reviewed by hematopathologists at our institution. Patient and disease factors as well as treatment types were analyzed for association with relapse-free survival, overall survival, and cumulative incidence of relapse.

Results

Median follow-up after treatment was 4.7 years. Five-year relapse-free survival and overall survival were 60% and 89%, respectively. Cumulative incidence of disease-specific death at 5 years was 1.3%. Radiotherapy alone was the initial treatment in 50% of patients, followed by surgical resection (30%), observation (8%), immunotherapy (4%), and chemotherapy (2%). Initial treatment type, primary disease site, and number of involved sites were significant factors in multivariable analysis of relapse (all P < 0.05). When compared with stomach, MZL originating in other disease sites (HR > 2.0, P ≤ 0.001), except for thyroid, had higher risk of relapse. Strategies such as antibiotics or topical therapies were associated with higher risk of relapse when compared with radiation therapy (P < 0.001). Crude rate of transformation to pathologically confirmed large-cell lymphoma was 2% (11 patients).

Conclusion

Overall and cause-specific survival are high in early-stage extra-nodal MZL. Curative-intent treatment led to fewer relapses and reduced the need for salvage. Stomach cases had lower risk of relapse than other anatomic primary sites. This study supports the use of local therapies to treat stage IE and IIE MZL.

Arabidopsis mutants define an in vivo role for isoenzymes of aspartate aminotransferase in plant nitrogen assimilation

Arabidopsis contains five isoenzymes of aspartate aminotransferase (AspAT) localized to the cytosol, chloroplast, mitochondria, or peroxisomes. To define the in vivo function of individual isoenzymes, we screened for Arabidopsis mutants deficient in either of the two major isoenzymes, cytosolic AAT2 or chloroplastic AAT3, using a native gel activity assay. In a screen of 8,000 M2 seedlings, three independent mutants deficient in cytosolic AAT2 (aat2) and two independent mutants deficient in chloroplastic AAT3 (aat3) were isolated. Mapping of aat2 and aat3 mutations and the five AspAT genes (ASP1-ASP5) established associations as follows: the mutation affecting aat2 maps with and cosegregates with ASP2, one of two expressed genes for cytosolic AspAT; the mutation affecting aat3 maps to the same location as the ASP5 gene encoding chloroplastic AspAT. Phenotypic analysis of the aat2 and aat3 mutants revealed a dramatic aspartate-related phenotype in one of the mutants deficient in cytosolic AAT2. The aat2-2 mutant displays an 80% reduction in levels of aspartate transported in the phloem of light-grown plants, and a 50% reduction in levels of asparagine transported in dark-adapted plants. These results indicate that cytosolic AAT2 is the major isoenzyme controlling aspartate synthesized for nitrogen transport in the light, and that this aspartate pool is converted to asparagine when plants are dark adapted.

Delayed degeneration of the optic tract and neurons in the superior colliculus after forebrain ischemia

Neuronal damage induced by 15-min forebrain ischemia was investigated in adult rats 1-5 days (short-term group) and 1-5 months (long-term group) after the initial ischemic attack. In addition to the vulnerable areas reported previously, we observed that the optic tract was also very susceptible. Degeneration of the optic tract and subsequent transsynaptic cell death in the superior colliculus developed slowly and was observed only in the long-term group. The delayed, progressive neuronal damage in this sensory system may serve as a suitable model to investigate the mechanisms of long-term changes in the injured brain.

Emergence and propagation of interictal spikes in the subcortically denervated hippocampus

Spontaneous and evoked field potentials and cellular discharges of the subcortically denervated dorsal hippocampus were studied by multisite recordings in the freely behaving rat. Characteristic short-duration (< 100 ms), large-amplitude (up to 10 mV) transients, termed interictal spikes (IIS), were seen after fimbria-fornix (FF) lesion. Both pyramidal cells and putative interneurons fired maximally during IIS, with some interneurons sustaining long bursts (up to 400 ms) of high-frequency discharges (400-600 Hz) after the IIS. The speed of propagation of IIS along the longitudinal axis of the hippocampus varied from 0.2 m/s to > 3 m/s. The majority of IIS (type 1) could be accounted for by an enhanced activity of the intrahippocampal associational systems; a second class of IIS (type 2) had positive polarities in the stratum radiatum of CA1 and CA3 and propagated very rapidly (> 1.5 m/s). The authors propose that type 2 IIS reflect somatic depolarization and discharge of pyramidal neurons due to nonsynaptic (probably ephaptic) effects. Ephaptic interactions may also explain the longitudinal propagation of IIS at speeds higher than the conduction velocities (0.5 m/s) of hippocampal fiber systems. IIS emerged during the first 3 weeks after fimbria-fornix lesion, their incidence reaching a plateau of 2/min thereafter. During the same time period, paired-pulse suppression increased in the dentate gyrus. The amplitude of test responses to angular bundle stimulation was potentiated by small-amplitude IIS but suppressed by large-amplitude IIS. The incidence of IIS was significantly suppressed during walking relative to standing still. Tetanic stimulation of the angular bundle or handling-induced stress resulted in a 10- to 20-fold increase in the incidence of IIS that lasted for about 30 minutes. There was a negative correlation between evoked field PSP slope and population spike amplitude in the dentate gyrus of FF-lesioned rats; this correlation was positive in intact rats. The authors attribute the above pathophysiological changes to sprouting of both excitatory and inhibitory GABAergic pathways as a result of denervation of the intrahippocampal circuitry. They hypothesize that the majority of the observed physiological alterations can be traced to a weakening of feedforward inhibition coupled with an enhancement of feedback inhibition and excitation.

Roles of the human immunodeficiency virus type 1 nucleocapsid protein in annealing and initiation versus elongation in reverse transcription of viral negative-strand strong-stop DNA

To study the initiation of human immunodeficiency virus type 1 reverse transcription, we have used the viral nucleocapsid protein (NC7) to anneal tRNA3Lys primer onto viral genomic RNA and have then eliminated NC7 from this primer-template complex by digestion with proteinase K and phenol-chloroform extraction of residual protein. Our data show that saturating concentrations of NC7 resulted in the formation of an active tRNA-template complex that yielded enhanced production of full-length negative-strand strong-stop DNA [(-)ssDNA] and that this complex remained active even after the elimination of NC7. While both of the two Zn finger motifs found within NC7 were essential for efficient elongation, NC protein that contained a point mutation in the first Zn finger or that was devoid of both Zn fingers yielded primer-template complexes that could still be initiated in 1-base-extension assays. In contrast, the use of heat annealing to produce primer-template complexes resulted in proportions of full-length (-)ssDNA lower than those seen with NC protein, and the addition of NC protein to such preformed primer-template complexes was able to reverse this defect only to a marginal extent.

A prospective study of total plasma cell-free DNA as a predictive biomarker for response to systemic therapy in patients with advanced non-small-cell lung cancers

BACKGROUND

While previous studies have reported on the prognostic value of total plasma cell-free deoxyribonucleic acid (cfDNA) in lung cancers, few have prospectively evaluated its predictive value for systemic therapy response.

PATIENTS AND METHODS

We conducted a prospective study to evaluate the association between changes in total cfDNA and radiologic response to systemic therapy in patients with stage IIIB/IV non-small-cell lung cancers (NSCLCs). Paired blood collections for cfDNA and computed tomography (CT) assessments by RECIST v1.0 were performed at baseline and 6-12 weeks after therapy initiation. Total cfDNA levels were measured in plasma using quantitative real-time polymerase chain reaction. Associations between changes in cfDNA and radiologic response, progression-free survival (PFS), and overall survival (OS) were measured using Kruskal-Wallis and Kaplan-Meier estimates.

RESULTS

A total of 103 patients completed paired cfDNA and CT response assessments. Systemic therapy administered included cytotoxic chemotherapy in 57% (59/103), molecularly targeted therapy in 17% (17/103), and combination therapy in 26% (27/103). Median change in cfDNA from baseline to response assessment did not significantly differ by radiologic response categories of progression of disease, stable disease and partial response (P = 0.10). However, using radiologic response as continuous variable, there was a weak positive correlation between change in radiologic response and change in cfDNA (Spearman's correlation coefficient 0.21, P = 0.03). Baseline cfDNA levels were not associated with PFS [hazard ratio (HR) = 1.06, 95% confidence interval (CI) 0.93-1.20, P = 0.41] or OS (HR = 1.04, 95% CI 0.93-1.17, P = 0.51), neither were changes in cfDNA.

CONCLUSIONS

In this large prospective study, changes in total cfDNA over time did not significantly predict radiologic response from systemic therapy in patients with advanced NSCLC. Pretreatment levels of total cfDNA were not prognostic of survival. Total cfDNA level is not a highly specific predictive biomarker and future investigations in cfDNA should focus on tumor-specific genomic alterations using expanded capabilities of next-generation sequencing.

Integrated temporal regulation of the photorespiratory pathway. Circadian regulation of two Arabidopsis genes encoding serine hydroxymethyltransferase

The photorespiratory pathway is comprised of enzymes localized within three distinct cellular compartments: chloroplasts, peroxisomes, and mitochondria. Photorespiratory enzymes are encoded by nuclear genes, translated in the cytosol, and targeted into these distinct subcellular compartments. One likely means by which to regulate the expression of the genes encoding photorespiratory enzymes is coordinated temporal control. We have previously shown in Arabidopsis that a circadian clock regulates the expression of the nuclear genes encoding both chloroplastic (Rubisco small subunit and Rubisco activase) and peroxisomal (catalase) components of the photorespiratory pathway. To determine whether a circadian clock also regulates the expression of genes encoding mitochondrial components of the photorespiratory pathway, we characterized a family of Arabidopsis serine hydroxymethyltransferase (SHM) genes. We examined mRNA accumulation for two of these family members, including one probable photorespiratory gene (SHM1) and a second gene expressed maximally in roots (SHM4), and show that both exhibit circadian oscillations in mRNA abundance that are in phase with those described for other photorespiratory genes. In addition, we show that SHM1 mRNA accumulates in light-grown seedlings, although this response is probably an indirect consequence of the induction of photosynthesis and photorespiration by illumination.

The effect of strength training on the force of twitches evoked by corticospinal stimulation in humans

AIM

Although there is considerable evidence that strength training causes adaptations in the central nervous system, many details remain unclear. Here we studied neuromuscular responses to strength training of the wrist by recording electromyographic and twitch responses to transcranial magnetic stimulation (TMS) and cervicomedullary stimulation of the corticospinal tract.

METHODS

Seventeen participants performed 4 weeks (12 sessions) of strength training for the radial deviator (RD) muscles of the wrist (n = 8) or control training without external load (n = 9). TMS recruitment curves were constructed from stimuli at five to eight intensities ranging between 15% below resting motor threshold and maximal stimulator output, both at rest and during isometric wrist extension (EXT) and RD at 10% and 50% of maximal voluntary contraction (MVC). Responses to weak TMS and cervicomedullary stimulation (set to produce a response of 10% maximal M wave amplitude during 10% MVC EXT contraction) were also compared at contraction strengths ranging from 10% to 75% MVC.

RESULTS

Isometric strength increased following strength training (10.7% for the RD MVC, 8.8% for the EXT MVC), but not control training. Strength training also significantly increased the amplitude of TMS- and cervicomedullary-evoked twitches during low-force contractions. Increases in the force-generating capacity of the wrist extensor muscles are unlikely to account for this finding because training did not affect the amplitude of twitches elicited by supra-maximal nerve stimulation.

CONCLUSION

The data suggest that strength training induces adaptations that increase the net gain of corticospinal-motor neuronal projections to the trained muscles.

Absence of magnetic resonance imaging evidence of pontine abnormality in infantile autism

In vivo studies involving magnetic resonance imaging and studies of neuropathologic specimens have shown that autism is most consistently associated with developmental hypoplasia of the neocerebellum. We investigated whether the cerebellar hypoplasia was accompanied by gross structural abnormalities in the major input (cerebrocerebellar) and output (cerebrorubral) pathways to the cerebellum by measuring the area of the ventral pons (including the pontine nuclei and the transverse fibers) and the midbrain on midsagittal magnetic resonance images in 34 autistic and 44 subjects. The area of the entire pons and several regions of interest within the midbrain (including the superior and inferior colliculi) were also determined with midsagittal magnetic resonance images. We found no significant difference between measurements of the pons and midbrain in autistic and control subjects. Our data show no evidence of gross anatomic abnormalities in the input and output pathways to the cerebellum in autism, a finding that is consistent with previous studies of neuropathologic specimens; rather, the reduced size of the neocerebellum in autism appears to be the result of maldevelopment within the cerebellum itself.

Discoidin domain receptors and their ligand, collagen, are temporally regulated in fetal rat fibroblasts in vitro

The biochemical regulation of collagen deposition during adult cutaneous wound repair is poorly understood. Likewise, how collagen is perceived and modulated in fetal scarless healing remains unknown. Recently, discoidin domain receptors-1 and 2 (DDR1 and DDR2) with tyrosine kinase activity have been identified as novel receptors for collagen. In light of these findings, it was speculated that the production of collagen receptors DDR1 and DDR2 by fetal fibroblasts may be temporally regulated to correlate with the ontogeny of embryonic scar formation. More specifically, because DDRs directly bind collagen and transmit the signals intracellularly, it was hypothesized that they may play an important role in fetal scarless healing by ultimately regulating and modulating collagen production and organization. As part of a fundamental assessment to elucidate the role of DDRs in scarless fetal wound repair, the endogenous expression of DDR1, DDR2, collagen I, and total collagen, as a function of fetal Sprague-Dawley rat skin fibroblasts of different gestational ages, representing scar-free (<E16.5 days) and scar-forming (>E16.5) periods was determined. Using explanted dermal fibroblasts of gestational days E13.5, E16.5, E18.5, and E21.5 (term gestation = 21.5 days) fetuses (n = 92), [3H]proline incorporation assay and Northern and Western blotting analysis were performed to compare the expressions of these molecules with scar-free and scar-forming stages of embryonic development. These results revealed a pattern of increasing collagen production with increasing gestational ages, whereas DDR1 expression decreased with increasing gestational age. This observation suggests that elevated levels of DDR1 may play an important role in scarless tissue regeneration by early gestation fetal fibroblasts. In contrast, DDR2 was expressed by fetal rat fibroblasts at a similar level throughout gestation. These data demonstrate for the first time the temporal expression of collagen and DDR tyrosine kinases in fetal rat fibroblasts as a function of gestational ages. Overall, these data suggest that differential temporal expression of the above-mentioned molecules during fetal skin development may play an important role in the ontogeny of scar formation. Future studies will involve the characterization of the biomolecular functions of these receptor kinases during fetal wound repair.

Fetal fraction-based risk algorithm for non-invasive prenatal testing: screening for trisomies 13 and 18 and triploidy in women with low cell-free fetal DNA

OBJECTIVE

To identify pregnancies at increased risk for trisomy 13, trisomy 18 or triploidy attributable to low fetal fraction (FF).

METHODS

A FF-based risk (FFBR) model was built using data from more than 165 000 singleton pregnancies referred for single-nucleotide polymorphism (SNP)-based non-invasive prenatal testing (NIPT). Based on maternal weight and gestational age (GA), FF distributions for normal, trisomy 13, trisomy 18 and triploid pregnancies were constructed and used to adjust prior risks for these abnormalities. A risk cut-off of ≥ 1% was chosen to define pregnancies at high risk for trisomy 13, trisomy 18 or triploidy (high FFBR score). The model was evaluated on an independent blinded set of pregnancies for which SNP-based NIPT did not return a result, and for which pregnancy outcome information was gathered retrospectively.

RESULTS

The evaluation cohort comprised 1148 cases, of which approximately half received a high FFBR score. Compared with rates expected based on maternal age (MA) and GA, cases with a high FFBR score had a significantly increased rate of trisomy 13, trisomy 18 or triploidy combined (5.7% vs 0.7%; P < 0.001) and also of unexplained pregnancy loss (14.7% vs 10.4%; P < 0.001). For cases that did not receive a high FFBR score, the incidence of a chromosomal abnormality or pregnancy loss was not significantly different from that expected based on MA and GA. In this study cohort, the sensitivity of the FFBR model for detection of trisomy 13, trisomy 18 or triploidy was 91.4% (95% CI, 76.9-98.2%) with a positive predictive value of 5.7% (32/564; 95% CI, 3.9-7.9%).

CONCLUSIONS

For pregnancies with a FF too low to receive a result on standard NIPT, the FFBR algorithm identified a subset of cases at increased risk for trisomy 13, trisomy 18 or triploidy. For the remainder of cases, the risk of a fetal chromosomal abnormality was unchanged from that expected based on MA and GA. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Maximizing comfort and minimizing ischemia: a comparison of four methods of spinal immobilization

OBJECTIVE

To determine which of four methods of spinal immobilization causes the least ischemic pain.

METHODS

A prospective, nonblinded comparative trial was conducted at a statewide emergency medical services training facility using a convenience sample of emergency medical technician students. After lying motionless for 10 minutes, students evaluated each device using a 10-centimeter visual analog scale. Subjective comfort was used as a measure of ischemia.

RESULTS

Comfort scores were significantly different for all methods (F = 101, p < 0.001). A backboard padded with a gurney mattress and eggcrate foam (the equivalent of a spinal rehabilitation bed) caused the least ischemic pain (9.6 cm, 95% CI, 8.9 to 9.8 cm). A backboard padded with a gurney mattress was the second most comfortable device (7.0 cm, 95%/CI, 6.4 to 7.4 cm). A backboard padded with a folded blanket was the third most comfortable (3.3 cm, 95% CI, 2.6 to 4.9 cm). The backboard alone caused the most pain (0.8 cm, 95% CI, 0.7 to 2.1 cm).

CONCLUSION

Increasing the amount of padding on a backboard decreased the amount of ischemic pain caused by immobilization.

Effectiveness of 3TC in HIV clinical trials may be due in part to the M184V substitution in 3TC-resistant HIV-1 reverse transcriptase

OBJECTIVE

To measure the extent of HIV resistance to (-)-2',3'-dideoxy-3'-thiacytidine (3TC, lamivudine) within the context of monotherapy and to assess the presence of the M184V substitution in the case of 3TC-resistant viruses. Whether the success of 3TC in clinical trials could be due, in part, to an increase in the fidelity of HIV reverse transcriptase conferred by the M184V substitution was also considered.

METHODS

Two separate monotherapy studies were evaluated, one involving adults with CD4 counts > or = 300 x 10(6)/l, and the second involving children, some of whom had received antiretroviral treatment previously, while others were drug naive. Peripheral blood and plasma samples were collected regularly, and HIV isolation and determinations of drug median inhibitory concentration values were performed using umbilical cord mononuclear cells as targets. Amplification of the 184 mutation was performed by the polymerase chain reaction, using specific primer pairs. Fidelity determinations using purified, recombinant HIV reverse transcriptase derived from either wild-type virus or viruses that contained the 184V substitution were performed.

RESULTS

Phenotypic resistance was detected in almost all subjects at times ranging from 8-20 weeks after initiation of therapy. The 184V substitution was usually detected prior to the occurrence of phenotypic resistance to 3TC. Fidelity determinations revealed that the 184V substitution conferred an approximately 5- to 10-fold increase in HIV reverse transcriptase fidelity. In addition, titres of patient sera tested for their ability to neutralize autologous sequential viral isolates were stabilized in patients receiving 3TC therapy as opposed to other drugs.

CONCLUSIONS

Resistance to 3TC developed in virtually all subjects treated with this drug, and was associated with the appearance of an M184V mutation in HIV reverse transcriptase. The clinical benefit of 3TC therapy may be attributable in part to selection of viruses that are less able to replicate and mutate than the wild types.