Chromosomal instability in aneuploid acute lymphoblastic leukemia associates with disease progression

Chromosomal instability (CIN) lies at the core of cancer development leading to aneuploidy, chromosomal copy-number heterogeneity (chr-CNH) and ultimately, unfavorable clinical outcomes. Despite its ubiquity in cancer, the presence of CIN in childhood B-cell acute lymphoblastic leukemia (cB-ALL), the most frequent pediatric cancer showing high frequencies of aneuploidy, remains unknown. Here, we elucidate the presence of CIN in aneuploid cB-ALL subtypes using single-cell whole-genome sequencing of primary cB-ALL samples and by generating and functionally characterizing patient-derived xenograft models (cB-ALL-PDX). We report higher rates of CIN across aneuploid than in euploid cB-ALL that strongly correlate with intraclonal chr-CNH and overall survival in mice. This association was further supported by in silico mathematical modeling. Moreover, mass-spectrometry analyses of cB-ALL-PDX revealed a "CIN signature" enriched in mitotic-spindle regulatory pathways, which was confirmed by RNA-sequencing of a large cohort of cB-ALL samples. The link between the presence of CIN in aneuploid cB-ALL and disease progression opens new possibilities for patient stratification and offers a promising new avenue as a therapeutic target in cB-ALL treatment.

ESHRE PGT Consortium good practice recommendations for the detection of monogenic disorders

The field of preimplantation genetic testing (PGT) is evolving fast and best practice advice is essential for regulation and standardisation of diagnostic testing. The previous ESHRE guidelines on best practice for PGD, published in 2005 and 2011, are considered outdated, and the development of new papers outlining recommendations for good practice in PGT was necessary. The current paper provides recommendations on the technical aspects of PGT for monogenic/single-gene defects (PGT-M) and covers recommendations on basic methods for PGT-M and testing strategies. Furthermore, some specific recommendations are formulated for special cases, including de novo pathogenic variants, consanguineous couples, HLA typing, exclusion testing and disorders caused by pathogenic variants in the mitochondrial DNA. This paper is one of a series of four papers on good practice recommendations on PGT. The other papers cover the organisation of a PGT centre, embryo biopsy and tubing and the technical aspects of PGT for chromosomal structural rearrangements/aneuploidies. Together, these papers should assist scientists interested in PGT in developing the best laboratory and clinical practice possible.

The clinical utility of PGD with HLA matching: a collaborative multi-centre ESHRE study

STUDY QUESTION

Has PGD-HLA been successful relative to diagnostic and clinical efficacy?

SUMMARY ANSWER

The diagnostic efficacy of PGD-HLA protocols was found lower in this study in comparison to published PGD-HLA protocols and to that reported for general PGD by ESHRE (78.5 vs 94.1% and vs 92.6%, respectively), while the clinical efficacy has proven very difficult to assess due to inadequate follow-up of both the ART/PGD and HSCT procedure outcomes.

WHAT IS KNOWN ALREADY

The first clinical cases for PGD-HLA were reported in 2001. It is now a well-established procedure, with an increasing number of cycles performed every year. However, PGD-HLA is still offered by relatively few PGD centres, the currently available data is fragmented and most reports on PGD-HLA applications are limited in number and scope. Published systematic details on methodology, diagnostic results, overall ART success and haematopoietic stem cell transplantation (HSCT) outcomes are limited, precluding an evaluation of the true clinical utility of PGD-HLA cycles.

STUDY DESIGN, SIZE, DURATION

This retrospective multi-centre cohort study aimed to investigate the diagnostic and clinical efficacy of the PGD-HLA procedure and the aspects of PGD-HLA cycles influencing positive outcomes: birth of genetically suitable donor-baby (or babies) and HSCT. In April 2014, 32 PGD centres (Consortium members and non-members) with published/known PGD-HLA activity were invited to participate. Between February and September 2015, 14 centres submitted their data, through a custom-designed secure database, with unique login access for each centre. Data parameters covered all aspects of PGD-HLA cycles (ART, embryology and genetic diagnosis), donor-babies born and HSCT.

PARTICIPANTS/MATERIALS, SETTING, METHODS

From 716 cycles submitted by 14 centres (performed between August 2001 and September 2015), the quality evaluation excluded 12 cycles, leaving 704, from 364 couples. The online database, based on REDCap, a free, secure, web-based data-capture application, was customized by Centre for Clinical Epidemiology and Outcomes Research (CLEO), Athens. Continuous variables are presented using mean, standard deviation, median and interquartile range, and categorical variables are presented as absolute and relative frequencies.

MAIN RESULTS AND THE ROLE OF CHANCE

The data included 704 HLA-PGD cycles. Mean maternal age was 33.5 years. Most couples (81.3%) requested HLA-typing with concurrent exclusion of a single monogenic disease (58.6% for beta-thalassaemia). In 92.5% couples, both partners were fertile, with an average 1.93 HLA-PGD cycles/couple. Overall, 9751 oocytes were retrieved (13.9/cycle) and 5532 embryos were analysed (7.9/cycle). Most cycles involved fresh oocytes (94.9%) and Day 3 embryo biopsy (85.3%). In 97.5% of cycles, the genotyping method involved PCR only. Of 4343 embryos diagnosed (78.5% of analysed embryos), 677 were genetically suitable (15.4% of those analysed for HLA alone, 11.6% of those analysed for HLA with exclusion of monogenic disease). Of the 364 couples, 56.6% achieved an embryo transfer (ET) and 598 embryos were transferred in 382 cycles, leading to 164 HCG-positive pregnancies (pregnancy rate/ET 41.3%, pregnancy rate/initiated cycle 23.3%) and 136 babies born (live birth rate/ET 34.3%, live birth rate/initiated cycle 19.3%) to 113 couples. Data analysis identified the following limitations to the overall success of the HLA-PGD procedure: the age of the mother undergoing the treatment cycle, the number of oocytes collected per cycle and genetic chance. HSCT was reported for 57 cases, of which 64.9% involved combined umbilical cord-blood and bone marrow transplantation from the HLA-identical sibling donor; 77.3% of transplants reported no complications.

LIMITATIONS REASONS FOR CAUTION

The findings of the study may be limited as not all PGD centres with PGD-HLA experience participated. Reporting bias on completion of the online database may be another potential limitation. Furthermore, the study is based on retrospective data collection from centres with variable practices and strategies for ART, embryology and genetic diagnosis.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first multi-centre study evaluating the clinical utility of PGD-HLA, indicating variations in practice and outcomes throughout 15 years and between centres. The study highlights parameters important for positive outcomes and provides important information for both scientists and couples interested in initiating a cycle. Above all, the study underlines the need for better collaboration between all specialists involved in the ART-PGD/HLA procedure, as well as the need for comprehensive and prospective long-term data collection, and encourages all specialists to aim to properly evaluate and follow-up all procedures, with the ultimate aim to promote best practice and encourage patient informed decision making.

STUDY FUNDING/COMPETING INTEREST(S)

The study wishes to acknowledge ESHRE for funding the customization of the REDCap database. There are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

[Molecular bases of hereditary hyperekplexia]

INTRODUCTION

Hereditary hyperekplexia is a rare clinical syndrome typically characterized by sudden and generalized startle in response to trivial but unexpected tactile or acoustic stimulations. Typically it is accompanied by a temporally but complete muscular rigidly, and usually it manifests shortly after birth. Some affected infants die suddenly from lapses in cardiorespiratory function. Mental development usually is normal.

AIM

To summarize and update the molecular bases underlying the hereditary hyperekplexia syndrome.

DEVELOPMENT

Approximately 30% of the individuals suffering hereditary hyperekplexia show mutations on a gene located on chromosome 5q32 with a dominant or recessive trait. This gene encodes the alpha subunit of the strychnine-sensitive glycine receptor, which plays a crucial role in inhibitory glycinergic neurotransmission that process sensory and motor information. About 70% of the patients with hyperekplexia do not show genetic defects in the glycine receptor gene; this suggested that additional genes might be affected in this disease. Recent studies have reveals that mutations in the neuronal glycine transporter GLYT2 are a second major cause of hyperekplexia.

CONCLUSIONS

Hereditary hyperekplexia is a complex genetic disease in which several genes can be implicated, all of them directly or indirectly involved in inhibitory glycinergic neurotransmission. Two major proteins involved in hyperekplexia are the strychnine-sensitive glycine receptor (GlyR) and the neuronal glycine transporter GLYT2. Implication of secondary additional accompanying or interacting proteins in glycinergic terminals are not ruled out.

Pregnancy outcome after preimplantation genetic diagnosis in an affected couple with X-linked adrenoleukodystrophy

OBJECTIVE

To achieve a pregnancy free of X-linked adrenoleukodystrophy (X-ALD) by intracytoplasmic sperm injection (ICSI) and preimplantation genetic diagnosis (PGD).

DESIGN

Case report.

SETTING

Clínica FIV Recoletos, a private IVF center.

PATIENT(S)

A couple in which the man had X-ALD.

INTERVENTION(S)

The ICSI protocol and PGD of the obtained embryos.

MAIN OUTCOME MEASURE(S)

Blastomeres were analyzed by fluorescence in situ hybridization using sex selection techniques. Embryos were transferred and pregnancy was diagnosed by hCG analysis and ultrasonographic examination.

RESULT(S)

Ten embryos were obtained by ICSI. A biopsy was taken from eight embryos to perform PGD and two male embryos were transferred resulting in a twin pregnancy.

CONCLUSION(S)

This is the first registered gestation in which PGD has been used to prevent X-ALD transmission.

Immunohistochemical localization of the amino acid transporter SNAT2 in the rat brain

SNAT2 is a neutral amino acid carrier that belongs to the system A family. Since its function in the nervous system remains unclear, we have analyzed its distribution in the rat CNS using specific antisera. Although SNAT2 is expressed widely in the CNS, it is enriched in the spinal cord and the brainstem nuclei, especially those of the auditory system. At the cellular level, SNAT2 was preferentially located in neuronal cell bodies and processes, although it was also strongly expressed in the meninges and ependyma. In astrocytes, the localization of SNAT2 was more restricted since it was intensely expressed in the perivascular end-feet, glia limitans, cerebellar astrocytes and Bergmann glia, but it was less intense in astrocytes of the cerebral parenchyma. Among neurons, the primary sensory neurons of the mesencephalic trigeminal nucleus appeared to be those that most strongly express SNAT2, but many other neurons, including cortical pyramidal cells and their dendrites were also intensely stained. In several regions the transporter was detected in axons, especially in the brainstem, and its presence in both dendrites and axons was confirmed by confocal microscopy and ultrastructural studies. However, while SNAT2 was observed in the large principal dendrites and the small distal dendrites, it was only found in axonal shafts and was excluded from terminals. Some glutamatergic neurons were among the more intensely labeled cells whereas SNAT2 was not detected on GABAergic neurons. The expression of SNAT2 partially coincides with that reported for SNAT1, especially in glutamatergic neurons. Hence, both proteins could fulfill complementary roles in replenishing glutamate pools and be differentially regulated under different physiological conditions. They also seem to co-localize in non-neuronal cells probably contributing to amino acid fluxes through the blood-brain barrier.

Preimplantation genetic screening and human implantation

In recent years, preimplantation genetic screening (PGS) has been used and recommended to increase the implantation rate in older women or in couples with previous assisted reproduction (ART) failures, to try to increase pregnancy rates in couples with recurrent abortions, to prevent the transmission of chromosome anomalies to the offspring of carriers of balanced chromosomal rearrangements, or even to try to decrease the incidence of trisomic births in older women. So far, PGS has contributed to increase the implantation rate in older women; however, the rate of clinical pregnancies has not increased, either in older women or in couples with previous ART failures. In couples with recurrent abortions, the pregnancy rate seems to increase, but only when the woman is young (< or =35). In carriers of balanced reorganizations, the prognosis is poor. Attempts to decrease the birth of trisomic children to older women are difficult to evaluate. This absence of relevant results is not related to the technique itself, which is quite safe, but to other still largely unknown factors.

Molecular determinants involved in the asymmetrical distribution of glycine transporters in polarized cells

The asymmetrical distribution of neurotransmitter transporters on the cell surface of neurons seems to be a generalized feature of these proteins, and is thought to be important for an appropriate removal of neurotransmitters from the extracellular milieu. To study the subcellular distribution of the glycine transporter isoforms (GLYT1a, GLYT1b, GLYT2a and GLYT2b), these proteins were expressed in epithelial cells [Madin-Darby canine kidney (MDCK) cells] and in cultured hippocampal neurons, as models of polarized cells. The localization of the transporters was assessed by immunofluorescence assays. Our results indicated that the subcellular distribution of glycine transporters is dependent on both the protein isoform and the cell type. By using site-directed mutagenesis we have been able to identify signals for basolateral/somatodendritic localization in the alternative amino terminal region of GLYT1 and in two di-leucine motifs that are located in the carboxyl tail of this protein. Moreover, the N-glycosylation sites located in the large extracellular loop of GLYT2 are involved in apical localization of this protein in polarized MDCK cells. These results contribute to define the mechanisms of asymmetrical distribution of transporters on the cell surface of polarized cells.

Transcription factors Zic1 and Zic2 bind and transactivate the apolipoprotein E gene promoter

We have used the yeast one-hybrid system to identify transcription factors that bind to specific sequences in proximal regions of the apolipoprotein E gene promoter. The sequence between -163 and -124, that has been previously defined as a functional promoter element, was used as a bait to screen a human brain cDNA library. Ten cDNA clones that encoded portions of the human Zic1 (five clones) and Zic2 (five clones) transcription factors were isolated. Electrophoretic mobility shift assays confirmed the presence of a binding site for Zic1 and Zic2 in the -136/-125 region. Displacement of binding with oligonucleotides derived from adjacent sequences within the APOE promoter revealed the existence of two additional Zic-binding sequences in this promoter. These sequences were identified by electrophoretic mobility shift assays and mutational analysis in regions -65/-54 and -185/-174. Cotransfection of Zic1 and Zic2 expression vector and different APOE promoter-luciferase reporter constructs in U87 glioblastoma cell line showed that the three binding sites partially contributed to the trans-stimulation of the luciferase reporter. Ectopic expression of Zic1 and Zic2 in U87 cells also trans-stimulated the expression of the endogenous gene, increasing the amount of apolipoprotein E produced by glial cells. These data indicate that Zic proteins might contribute to the transcriptional activity of the apolipoprotein E gene and suggest that apolipoprotein E could mediate some of the developmental processes in which Zic proteins are involved.

The role of N-glycosylation in transport to the plasma membrane and sorting of the neuronal glycine transporter GLYT2

Glycine transporter GLYT2 is an axonal glycoprotein involved in the removal of glycine from the synaptic cleft. To elucidate the role of the carbohydrate moiety on GLYT2 function, we analyzed the effect of the disruption of the putative N-glycosylation sites on the transport activity, intracellular traffic in COS cells, and asymmetrical distribution of this protein in polarized Madin-Darby canine kidney (MDCK) cells. Transport activity was reduced by 35-40% after enzymatic deglycosylation of the transporter reconstituted into liposomes. Site-directed mutagenesis of the four glycosylation sites (Asn-345, Asn-355, Asn-360, and Asn-366), located in the large extracellular loop of GLYT2, produced an inactive protein that was retained in intracellular compartments when transiently transfected in COS cells or in nonpolarized MDCK cells. When expressed in polarized MDCK cells, wild type GLYT2 localizes in the apical surface as assessed by transport and biotinylation assays. However, a partially unglycosylated mutant (triple mutant) was distributed in a nonpolarized manner in MDCK cells. The apical localization of GLYT2 occurred by a glycolipid rafts independent pathway.

Preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) includes a variety of techniques that have been developed to detect the transmission to the offspring of genetic diseases or of chromosome abnormalities by couples at risk before a pregnancy is established, to avoid these couples the risk of recurrent abortions and/or of repeated terminations of pregnancy. Candidate couples are carriers of gene mutations or of structural chromosome rearrangements, or with recurrent spontaneous abortions of unknown origin. Diagnostic procedures include different modalities of gene amplification using the polymerase chain reaction (PCR) or of fluorescent in situ hybridization (FISH). Embryo biopsies are carried out at the 6-8 cell stage. Healthy embryos are transferred on day 4 or at the blastocyst stage. By now, several hundred healthy children have been born using PGD, and only one diagnostic error has been reported.

Is there a place for preimplantation genetic diagnosis screening in recurrent miscarriage patients?

Chromosomal abnormalities are one of the factors known to interfere with normal embryo development; thus preimplantation genetic diagnosis (PGD) for chromosome anomalies may be a new tool for improving the pregnancy rate in selected groups of patients. Embryos from three groups of patients (control, aged and recurrent miscarriage patients) were screened by PGD using specific DNA probes for chromosomes 13, 16, 18, 21, 22, X and Y. The control and aged groups were included in the PGD study because the women carried sex-linked genetic disease. The frequencies of chromosome anomalies observed in older women (46.3%) and in recurrent miscarriage patients (53%) were significantly higher (P < 0.05) than the frequency in the control group (19.3%). After PGD screening and transfer of normal embryos, pregnancies were obtained in women who had undergone repeated abortions (approximate 25% pregnancy rate per transfer) but not in older women. On the basis of these data, it seems that PGD screening of embryos can help some women undergoing repeated abortions, as these techniques allow successful pregnancies to be obtained or, if no pregnancy can be obtained, the results may help the couple to decide whether to enter an embryo or gamete donation programme.

The decision to cancel a preimplantation genetic diagnosis cycle

It has been suggested that a minimum number (six) of cumulus-oocyte complexes (COCs) should be retrieved for fertilization to offer enough chances to ensure a pregnancy after a preimplantation genetic diagnosis (PGD) procedure. Therefore a decision to cancel a PGD cycle should be adequately weighted to offer the patients the highest chances to obtain a pregnancy. We describe a case where, after retrieving only three COCs suitable for fertilization, a triplet pregnancy was obtained. This case suggests that, although low numbers of COCs can reduce the effectiveness of the PGD procedure, other factors are involved in its final result. Thus, the opportunity of routinely cancelling such cycles should be reconsidered. In addition, this is, to our knowledge, the first case where sex selection was carried out to prevent the birth of carriers of the abnormal gene, and not of affected offspring.

Polarized distribution of glycine transporter isoforms in epithelial and neuronal cells

Asymmetrical distribution of Na(+)- and Cl(-)-dependent neurotransmitter transporters on the cell surface of polarized cells seems to be a generalized feature in this gene family. In the present study we analyzed the subcellular distribution of the various isoforms of the glycine transporters GLYT1 and GLYT2 after heterologous expression in polarized MDCK cells and in hippocampal neurons. Our results indicate that glycine transporters are asymmetrically distributed in an isoform- and cell-type-specific manner. GLYT1b is localized in the basolateral and somatodendritic domains of MDCK cells and neurons, respectively. However, GLYT1a is somatodendritic in neurons but is predominantly expressed in the apical surface of MDCK cells. The two isoforms of GLYT2 (GLYT2a and GLYT2b) are found at the apical surface in epithelial cells but are uniformly distributed in neurons. By using site-directed mutagenesis we have been able to identify signals for basolateral/somatodendritic localization in the amino-terminal region of GLYT1 and in two dileucine motifs located in the carboxyl tail of this protein. These results contribute to defining the mechanisms of asymmetrical distribution of transporters on the cell surface of polarized cells.

In vitro fertilization plus preimplantation genetic diagnosis in patients with recurrent miscarriage: an analysis of chromosome abnormalities in human preimplantation embryos

OBJECTIVE

To analyze the incidence of numeric chromosomal abnormalities in preimplantation embryos from women with unexplained recurrent miscarriage (RM) so as to seek an etiology and to determine whether the use of IVF may be indicated to treat these cases.

DESIGN

Prospective controlled study.

SETTING

University laboratory of reproductive genetics and a tertiary referral center for infertility.

PATIENT(S)

Nine women with a mean (+/-SD) of 3.9 +/- 0.6 RMs who were undergoing IVF and preimplantation genetic diagnosis, and a control group of young (n = 10) and older (n = 6) patients who were undergoing preimplantation genetic diagnosis because of sex-linked diseases.

INTERVENTION(S)

In vitro fertilization, embryo culture for 72 hours, blastomere biopsy, and analysis of chromosomes 13, 16, 18, 21, 22, X, and Y with the use of fluorescent in situ hybridization. Transfer of chromosomally normal embryos into the uterus.

MAIN OUTCOME MEASURE(S)

Numeric chromosomal abnormalities in human embryos.

RESULT(S)

Sixty-six embryos from patients with RM were compared with 62 embryos from young patients and 41 embryos from older patients. There was a significant increase in the rate of abnormal embryos in the patients with RM and the older patients compared with the controls. Abnormalities in most of the chromosomes studied were higher in the RM group than in the control group, especially those affecting chromosome 13.

CONCLUSION(S)

There was an increase in numeric chromosomal abnormalities in preimplantation embryos from women with RM that could be the cause of infertility in many couples with unexplained RM. The use of IVF in such circumstances may be indicated if successful preimplantation genetic diagnosis is added to the procedure.

FISH preimplantation diagnosis of chromosome aneuploidy in recurrent pregnancy wastage

PURPOSE

Our purpose was to detect aneuploidy for chromosomes 13, 16, 18, 21, 22, X, and Y in preimplantation embryos from patients with a history of unexplained recurrent miscarriage.

METHODS

Three patients with a history of unexplained recurrent spontaneous abortion were included in this study. Embryos were biopsied at the eight-cell stage, individually fixed on slides, and processed for fluorescent in situ hybridization (FISH). A multiple FISH protocol for seven chromosomes pairs (13, 16, 18, 21, 22, X, and Y) has been developed.

RESULTS

A total of 39 embryos was studied with the multiple FISH protocol developed. Successful analysis of the biopsied embryos was achieved within the time limits usually allowed in a preimplantation diagnosis program. Analysis of the blastomeres showed that 17 embryos were chromosomally normal for the probes used, 16 embryos were aneuploid, and in 6 embryos no informative results were obtained.

CONCLUSIONS

In the patients studied, a large proportion of embryos (41%) exhibited chromosomal abnormalities for the probes used. Preimplantation diagnosis to screen for chromosome abnormalities could be a feasible approach to improve the possibility of successful pregnancy in these couples.

Characterization of the 5' region of the rat brain glycine transporter GLYT2 gene: identification of a novel isoform

We have identified two alternative 5' ends for the GLYT2 glycine transporter in rat brain DNA by using rapid amplification of cDNA ends (RACE) analysis. Study of the genomic DNA revealed that the isoform diversity is generated by alternative use of exons 1a or 1b, respectively. Upon translation, the mRNA corresponding to the novel isoform GLYT2b would yield a protein five amino acids longer than the previously characterized isoform GLYT2a. Both forms display similar regional distribution and kinetics characteristics. However, whereas GLYT2a is able to actively accumulate glycine into transfected COS cells, GLYT2b seems only to exchange (or release) glycine.

[Composition and structure of the neuronal membrane: molecular basis of its physiology and pathology]

INTRODUCTION AND OBJECTIVE

Neurons besides its ability to selectively detect signals from their surrounding, are able to integrate then in time and space when transmitting their message to other cells. This exceptional ability of the neuron is mainly due to the composition and characteristics of its plasma membrane. In this review, starting with a description of the general principles of cell membrane organization, on which the nerve cell membrane structure is based, we describe the structures and functions which are unique and peculiar to the neuronal membrane and its implications in pathological processes.

DEVELOPMENT

This review article starts with a description of the lipids forming the neuronal membrane, and the forces which maintain their cohesion to form the basic structure of the membrane. We describe some of the intrinsic biophysical properties of biological bilayers, and also to make special mention of the neuronal membrane proteins, both peripheral and integral proteins which are, finally, responsible for specificity and functional differentiation of the neurons.

CONCLUSIONS

Now a days, it is becoming clear that the knowledge of the neuronal membrane at the molecular level, specially the proteins involved in neuronal activity, is basic to understand neuronal physiology and pathology. Many disorders of the nervous system have their origins in defective synthesis or incorrect functioning of a particular protein in the neuronal membrane.

The glycine transporter GLYT2 is a reliable marker for glycine-immunoreactive neurons

The glycine transporter GLYT2 is present in neurons of the spinal cord, the brain stem and the cerebellum. This localization is similar to that of glycine immunoreactivity, suggesting a causal relationship between GLYT2 expression and glycine distribution. In this report, we analyzed if such a relationship does exist by using neuronal cultures derived from embryonic spinal cord. GLYT2 was synthesized in a small subpopulation of neurons where it was targeted both to dendrites and to axons, being the axonal content higher than the dendritic one. At early stages in the development of cultured spinal neurons, the highest GLYT2 levels were found in the axonal growth cones. As the culture matured, immunoreactivity extended to the axonal shaft. Double-immunofluorescence experiments indicated a perfect co-localization of GLYT2 and glycine immunoreactivity in cultured neurons. Moreover, the concentration of glycine into neurons expressing GLYT2 was proportional to the concentration of the transporter. This observation was reproduced in GLYT2-transfected COS cells. These evidences indicate that the high content of glycine observed in some neurons in culture is indeed achieved by the concentrative task performed by GLYT2, and that GLYT2 can be used as a reliable marker for identification of glycine-enriched neurons.

Molecular biology of glycinergic neurotransmission

Glycine is a major inhibitory neurotransmitter in the spinal cord and brainstem of vertebrates. Glycine is accumulated into synaptic vesicles by a proton-coupled transport system and released to the synaptic cleft after depolarization of the presynaptic terminal. The inhibitory action of glycine is mediated by pentameric glycine receptors (GlyR) that belong to the ligand-gated ion channel superfamily. The synaptic action of glycine is terminated by two sodium- and chloride-coupled transporters, GLYT1 and GLYT2, located in the glial plasma membrane and in the presynaptic terminals, respectively. Dysfunction of inhibitory glycinergic neurotransmission is associated with several forms of inherited mammalian myoclonus. In addition, glycine could participate in excitatory neurotransmission by modulating the activity of the NMDA subtype of glutamate receptor. In this article, we discuss recent progress in our understanding of the molecular mechanisms that underlie the physiology and pathology of glycinergic neurotransmission.

Analysis of the transmembrane topology of the glycine transporter GLYT1

A theoretical 12-transmembrane segment model based on the hydrophobic moment has been proposed for the transmembrane topology of the glycine transporter GLYT1 and all other members of the sodium- and chloride-dependent transporter family. We tested this model by introducing N-glycosylation sites along the GLYT1 sequence as reporter for an extracellular localization and by an in vitro transcription/translation assay that allows the analysis of the topogenic properties of different segments of the protein. The data reported herein are compatible with the existence of 12 transmembrane segments, but support a rearrangement of the first third of the protein. Contrary to prediction, hydrophobic domain 1 seems not to span the membrane, and the loop connecting hydrophobic domains 2 and 3, formerly believed to be intracellular, appears to be extracellularly located. In agreement with the theoretical model, we provide evidence for the extracellular localization of loops between hydrophobic segments 5 and 6, 7 and 8, 9 and 10, and 11 and 12.

Transcription factor AP-2 regulates human apolipoprotein E gene expression in astrocytoma cells

Apolipoprotein E (apoE), one of the major plasma lipoproteins, also is expressed in a variety of cell types, including the glial cells of the nervous system. apoE is involved in processes of degeneration and regeneration after nerve lesions as well as in the pathogenesis of Alzheimer's disease (AD). Glial synthesis of apoE is activated in response to injury both in the peripheral and central nervous system. We now report that the activity of the proximal apoE promoter in astrocytes is upregulated by cAMP and retinoic acid, which act synergistically. Sequence analysis of the apoE promoter indicated the presence of several AP-2 consensus sequences that could mediate the stimulatory effect of cAMP and retinoic acid. The possible functional role of AP-2 was examined by cotransfection of AP-2-deficient HepG2 cells with an apoE promoter construct and a human AP-2 expression construct. Cotransfection with AP-2 significantly elevated apoE promoter activity. DNase I footprinting technique revealed the existence of two binding sites for recombinant AP-2 in regions from -48 to -74 and from -107 to -135 of the apoE promoter. Mutations in these regions markedly impaired the trans-stimulatory effect of AP-2. These results indicate the existence of functional AP-2 sites in the promoter region of apoE that could contribute to the complex regulation of this gene in developmental, degenerative, and regenerative processess of the nervous system.

[Cervical epidural anesthesia for carotid mycotic aneurysms]

Extracranial mycotic aneurysms of the carotid are unusual. We present such an aneurysm of the right primary carotid caused by enteritis due to Salmonella in a 75-year-old patient at high risk for surgery (myocardial ischemia evolving over 3 months) and with coexisting stenosis of 75% of the left internal carotid. Endarterectomy of the left internal carotid, with shunting, was performed, after which the right primary carotid was tied during the same operation. Epidural anesthesia to C6-C7 was provided through a catheter supplemented with an intravenous propofol infusion. Neurological and hemodynamic variables monitored during surgery were stable. No neurological deficits or myocardial ischemic changes were recorded. Three months after discharge the patient was asymptomatic.

Regional distribution and developmental variation of the glycine transporters GLYT1 and GLYT2 in the rat CNS

The high-affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. Previous molecular cloning studies have indicated heterogeneity of glycine transporters in the CNS. Here the distribution of glycine transporter GLYT1 and GLYT2 transcripts and proteins in different regions and developmental stages of the rat brain were analysed by Northern, Western and in situ hybridization techniques. Sequence-specific riboprobes and two specific antibodies raised against fusion proteins were used, containing either 76 or 193 amino acids of the C or N terminus of the GLYT1 and GLYT2 transporters respectively. High levels of GLYT1 transcripts were found in the spinal cord, brainstem and cerebellum, and moderate levels in forebrain regions such as the cortex or hippocampus. GLYT2 transcripts are restricted to the spinal cord, brainstem and cerebellum. The onset of both GLYT1 and GLYT2 expression in the brainstem occurred in late fetal life, and full expression of these proteins was observed before weaning. There was a stepwise increase in the levels of mRNA and protein for these two transporters, reaching a maximum by the second postnatal week, followed by a slight decrease until adult values were reached by the fourth postnatal week. These data reveal interesting parallelism between the distribution of different glycine transporters and glycine receptor subunits, and suggest discrete roles for distinct glycine transporters.

Glycine transporters are differentially expressed among CNS cells

Glycine is the major inhibitory neurotransmitter in the spinal cord and brainstem and is also required for the activation of NMDA receptors. The extracellular concentration of this neuroactive amino acid is regulated by at least two glycine transporters (GLYT1 and GLYT2). To study the localization and properties of these proteins, sequence-specific antibodies against the cloned glycine transporters have been raised. Immunoblots show that the 50-70 kDa band corresponding to GLYT1 is expressed at the highest concentrations in the spinal cord, brainstem, diencephalon, and retina, and, in a lesser degree, to the olfactory bulb and brain hemispheres, whereas it is not detected in peripheral tissues. Pre-embedding light and electron microscopic immunocytochemistry show that GLYT1 is expressed in glial cells around both glycinergic and nonglycinergic neurons except in the retina, where it is expressed by amacrine neurons, but not by glia. The expression of a 90-110 kDa band corresponding to GLYT2 is restricted to the spinal cord, brain-stem, and cerebellum; in addition, very low levels occur in the diencephalon. GLYT2 is found in presynaptic elements of neurons thought to be glycinergic. However, in the cerebellum, GLYT2 is expressed both in terminal boutons and in glial elements. The physiological consequences of the regional and cellular distributions of these two proteins as well as the possibility of the existence of an unidentified neuronal form of GLYT1 are discussed.

The role of N-glycosylation in the targeting and activity of the GLYT1 glycine transporter

To elucidate the role of N-glycosylation in the function of the high affinity glycine transporter GLYT1, we have investigated the effect of the glycosylation inhibitor tunicamycin as well as the effect of the disruption of the putative glycosylation sites by site-directed mutagenesis. SDS-polyacrylamide gel electrophoresis of proteins from GLYT1-transfected COS cells reveals a major band of 80-100 kDa and a minor one of 57 kDa. Treatment with tunicamycin produces a 40% inhibition in transport activity and a decrease in the intensity of the 80-100-kDa band, whereas the 57-kDa band decreases in size to yield a 47-kDa protein corresponding to the unglycosylated form of the transporter. Simultaneous mutation of Asn-169, Asn-172, Asn-182, and Asn-188 to Gln also produces the 47-kDa form of the protein, indicating that there are no additional sites for N-glycosylation. Progressive mutation of the potential glycosylation sites produces a progressive decrease in transport activity and in size of the protein, indicating that the four putative glycosylation sites are actually glycosylated. N-Glycosylation of the GLYT1 is not indispensable for the transport activity itself, as demonstrated by enzymatic deglycosylation of the transporter. Analysis of surface proteins by biotinylation and by immunofluorescence demonstrates that a significant portion of the unglycosylated GLYT1 mutant remains in the intracellular compartment. This suggests that the carbohydrate moiety of glycine transporter GLYT1 is necessary for the proper trafficking of the protein to the plasma membrane.

Regulation by phorbol esters of the glycine transporter (GLYT1) in glioblastoma cells

The high-affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. The effects of 12-O-tetradecanoylphorbol ester (TPA), a potent activator of protein kinase C (PKC), on the high-affinity Na(+)-dependent glycine transport were investigated in C6 cells, a cell line of glial origin. Incubation of C6 cells with TPA led to concentration- and time-dependent decrease in the glycine transport that could be completely suppressed by the addition of the PKC inhibitor staurosporine. The TPA effect could be mimicked by oleoylacetylglycerol and exogenous phospholipase C. Northern and Western blot analysis indicate that C6 cells express the GLYT1 glycine transporter. Incubation of COS cells transiently transfected with a full-length clone of the GLYT1 transporter in the presence of TPA, produces a decrease in glycine uptake.

Carboxyl terminus of the glycine transporter GLYT1 is necessary for correct processing of the protein

The high affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. To understand the structure-function relationships, especially the role of the intracellular carboxyl- and amino-terminal domains, we have modified the glycine transporter GLYT1 by using a polymerase chain reaction-based mutagenesis approach. Deletion of the first 30 amino acids of the amino terminus does not alter transport of glycine. Truncation of the last 34 amino acids of the carboxyl terminus did not impair glycine transport, but progressively more extensive deletions produced a progressive decrease in transport activity. All the fully active or partially active forms of the transporter retain the characteristic sodium and chloride dependence of the wild type. When the nonfunctional mutants of the carboxyl terminus were examined by an immunofluorescence technique, the carrier was no longer found in the membrane. This suggests that the carboxyl terminus of GLYT1 may be involved in the membrane insertion process. Moreover, the transporter that is not fully processed is not functional, because transport activity cannot be rescued in a solubilization-reconstitution experiment.

Sexing sibling mouse blastomeres by polymerase chain reaction and fluorescent in-situ hybridization

The diagnosis of human genetic diseases at preimplantation stages allows the transmission of genetic anomalies in high risk couples to be prevented. Embryo sexing can be carried out using the polymerase chain reaction (PCR) or by fluorescent in-situ hybridization (FISH). However, it is still questionable whether the results obtained from a single analysed cell are fully predictive of the genetic characteristics of the whole embryo. We have isolated all the blastomeres from 4-cell stage mouse embryos and analysed them by PCR and FISH to assess the consistency of the results obtained. One half of each embryo (2/4-embryo) was spread and fixed to be processed by FISH, while the blastomeres of the other half embryo were isolated (1/4 + 1/4-embryo) and individually processed for PCR. We have determined the efficiency of both techniques when applied to different cells of the same embryo. We were able to amplify 92.5% of the embryos. Of these, 91.8% were classified as male or female, while the remaining 8.2% gave contradictory results (one male and its sibling blastomere female). Of the 40 embryos analysed by FISH, 97.5% could be classified as male or female with a sex distribution close to the expected 1:1. When comparing both techniques, 24 out of 36 embryos gave the same result. In nine cases the results did not coincide, and in three embryos comparison was not possible because of PCR contradictory results.

Twin pregnancy after preimplantation diagnosis for sex selection

A twin female pregnancy was obtained in a haemophilia carrier after two preimplantation diagnosis cycles. The embryonic sex of biopsied blastomeres was determined with the use of dual fluorescence in-situ hybridization with directly labelled DNA probes specific for the X and Y chromosome. A twin female pregnancy was confirmed by means of ultrasonography and amniocentesis at the 14th week of amenorrhoea. The patient delivered two healthy females by Caesarian section at the 37th week of pregnancy.

Characteristics and regulation of proline transport in cultured glioblastoma cells

L-Proline transport in C6 glioblastoma cells takes place mainly via a saturable Na(+)-dependent mechanism. The uptake process can be discriminated into two components, system A and system ASC. A minor proportion of L-proline transport is carried out by the ASC system, which appears to be constitutively expressed by the cell, but most is by system A which shows adaptive responses to amino acid deprivation and sensitivity to N-methyl-alpha-aminoisobutyric acid. The transport system is inhibited by proline derivatives, such as methyl and benzyl esters, and also hydroxyproline, and is stereospecific. Incubation of glioblastoma cells with phorbol 12-myristate 13-acetate led to concentration- and time-dependent decreases in L-proline transport. This effect could be mimicked by exogenous phospholipase C. Proline transport is significantly stimulated in the presence of Ca(2+)-mobilization agents and strongly inhibited in the absence of Ca2+. The present data suggest a complex regulation of L-proline transport by different kinases in glioblastoma cells.

The role of pyruvate in neuronal calcium homeostasis. Effects on intracellular calcium pools

It has long been known that pyruvate is essential for survival of prenatal neurons in culture. To understand the role of exogenous pyruvate in neuronal calcium homeostasis, we have investigated the effects of pyruvate (plus malate) addition to dissociated adult rat hippocampal and cerebral cortex cells and cultured CNS neurons having an unrestricted glucose supply. We found that pyruvate (plus malate) increased the respiration rate while ATP levels were unchanged. At the same time, cytosolic free calcium concentrations, [Ca2+]i, decreased while total 45Ca2+ and 40Ca2+ accumulation increased. The extra Ca2+ accumulated by the cells is attributable to an increase in the size of the intracellular calcium pools. Two such pools were identified on the basis of their sensitivity to specific drugs. The first pool was mobilized by thapsigargin plus tert-butyl hydroquinone and caffeine while the second pool was discharged by the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxphenylhydrazone (FCCP) (plus oligomycin). The two pools represented about 15-20% and 15-30%, respectively, of the rapidly exchangeable 45Ca2+ pools in cerebral cortex cells. In cultured hippocampal neurons, the collapse of the mitochondrial membrane potential (as induced by uncouplers (FCCP) or respiratory chain inhibitors (antimycin) caused a large increase in [Ca2+]i which varied in size and shape among cells and was reduced by external Ca2+ chelation. The latter condition also resulted in a partial discharge of FCCP-releasable 45Ca2+. The effects of FCCP did not result simply from ATP depletion since incubation in glucose-free medium and sequential additions of 2 mM deoxyglucose and 10 microM oligomycin, conditions that led to a dramatic reduction in cellular ATP levels, did not abolish the FCCP-induced [Ca2+]i rise. Taken together, the results indicate that mitochondria harbor a significant proportion of cellular Ca2+. The sensitivity of the mitochondrial pool size to pyruvate (plus malate) questions previous hypotheses concerning a kinetic limitation for Ca2+ accumulation in mitochondria in resting neurons.

Cellular distribution and regulation by cAMP of the GABA transporter (GAT-1) mRNA

The high-affinity GABA transporter in neurons and glial cells is the primary means of inactivating synaptic GABA. In the present study, a rat GABA transporter (GAT-1)-specific probe was used to quantitate GAT-1 mRNA in cultured neurons and glial cells from rat brain. GAT-1 mRNA is expressed in neurons but not in pure cultures of astrocytes. Incubation of neurons with forskolin led to concentration- and time-dependent decreases in GAT-1 mRNA. This effect could be also achieved by chronic exposure of neurons to 8-Br-cAMP and dib-cAMP but not with 1,9-dideoxyforskolin. This effect on the levels of GAT-1 mRNA correlates with a decrease in the Na(+)-dependent GABA transport activity in neurons. Treatment with agents that increase cellular levels of cAMP did not affect GABA transport or GAT-1 mRNA expression in glial cells.

Phosphorylation and modulation of brain glutamate transporters by protein kinase C

High affinity sodium- and potassium-coupled L-glutamate transport into presynaptic nerve terminals and fine glial processes removes the neurotransmitter from the synaptic cleft, thereby terminating glutamergic transmission. This report describes that the purified L-glutamate transporter from pig brain is phosphorylated by protein kinase C, predominantly at serine residues. Upon exposure of C6 cells, a cell line of glial origin, to 12-O-tetradecanoylphorbol-13-acetate, about a 2-fold stimulation of L-glutamate transport is observed within 30 min. Concomitantly, the level of phosphorylation increases with similar kinetics. The phorbol ester also stimulates L-glutamate transport in HeLa cells infected with a recombinant vaccinia virus expressing T7 RNA polymerase and transfected with pT7-GLT-1. The latter is a recently cloned rat brain glutamate transporter of glial origin. Mutation of serine 113 to asparagine does not affect the levels of expressed transport but abolishes its stimulation by the phorbol ester. To our knowledge, this is the first direct demonstration of the regulation of a neurotransmitter transporter by phosphorylation.

Cytogenetic sexing of mouse embryos

Cytogenetic sexing by means of chromosome C-banding was carried out in 1/2 and 2/4 biopsied mouse embryos. Chromosome spreads were obtained in 85.0% of 1/2-embryos and in 77.5% of 2/4-embryos. Sexing was accomplished in 30.0% of 1/2-embryos and 52.5% of 2/4-embryos, with a loss due to poor technique of 12.5 and 15.0% respectively. Transfer of sexed embryos resulted in a low implantation rate. The two live fetuses obtained were of the predicted sex.

L-glutamate transporter derived from mRNAs of primary glial cultures: expression in Xenopus laevis oocytes

A high-affinity sodium-dependent L-glutamate transporter was expressed in Xenopus oocytes after microinjection of poly(A)+ RNA from primary astrocyte cultures from rat brain cortex. mRNA-induced L-glutamate transport was saturable by substrate and shows kinetic features similar to those found in intact glial cell preparations. L-Glutamate accumulation was prevented by rising the external K+ concentration or by coincubation with L-, D-aspartate or D-glutamate. After fractionation by sucrose density gradient, the mRNA encoding for the expressed L-glutamate transporter from glial cells was found in fractions containing messages of 2.05-2.9 kilobases (kb) in length.

High-affinity transport of choline and amino acid neurotransmitters in synaptosomes from brain regions after lesioning the nucleus basalis magnocellularis of young and aged rats

Bilateral lesion of the nucleus basalis with ibotenic acid infusions in young and aged rats results in the degeneration of cholinergic neurons which innervate the cortex. As expected, high-affinity uptake of choline was decreased in the frontal cortex subsequent to the lesion. Twenty one days after surgery there was a significantly decrease of the transport rate of GABA, glutamate and glycine in the frontal cortex of young rats, but those activities showed a recovery six months after lesion. On the contrary, 12-month old rats lesioned with the same experimental protocol showed no recovery of the transport rates in the frontal cortex. Uptake of choline, GABA, glutamate and glycine has also been studied in other areas of the brain, namely, hippocampus, olfactory bulb and cerebellum. The present results suggest that lesioning the nucleus basalis of rats led to a more effective and permanent impairment of some biochemical functions of the brain, when compared to young lesioned animals, and also suggest a functional relationship between the nucleus basalis and other areas of the brain.

Activation of high-affinity uptake of glutamate by phorbol esters in primary glial cell cultures

The effects of 12-O-tetradecanoylphorbol 13-acetate (TPA), a potent activator of protein kinase C, on high-affinity Na(+)-dependent glutamate transport were investigated in primary cultures of neurons and glial cells from rat brain cortex. Incubation of glial cells with TPA led to concentration- and time-dependent increases in the glutamate transport that could be completely suppressed by the addition of the protein kinase C (PKC) inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine. The TPA effects could be mimicked by oleoylacetylglycerol and by the diacylglycerol kinase inhibitor R59022. The effects of TPA were potentiated by the Ca2+ ionophore A23187. Under the chosen experimental conditions TPA had no effect on glutamate transport in neurons. We conclude that PKC activates the sodium-dependent high-affinity glutamate transport in glial cells and that it has dissimilar effects on neurons and glial cells.

Determination of monoamines in rat brain regions after chronic administration of lithium

The effect of chronic administration of lithium on the concentration of biogenic amines and some of their metabolites in striatum, hippocampus, hypothalamus, pons-medulla and parietal cortex of rat were studied. Longterm lithium treatment modifies significantly the content of indoleamines in striatum and hypothalamus with minor changes in other structures. Catecholamine levels change after the treatment in striatum, hypothalamus, pons-medulla and parietal cortex. These results indicate that lithium treatment at therapeutic doses selectively modifies the catecholamine and indoleamine contents in discrete areas of the brain.