Morphologic characterisation of the posterior inferior cerebellar artery. A direct anatomic study.

BACKGROUND: The number of studies on the cerebellar arteries has increased. The purpose of this study was to determine the morphological expression of posterior inferior cerebellar artery in a sample of Colombian population. MATERIALS AND METHODS: One hundred eighty-six posterior inferior cerebellar arteries of fresh cadavers were studied. In each specimen, vertebral arteries were injected with 100 mL of semi-synthetic resin, dyed with mineral red. RESULTS: In the 93 blocks of brainstem and cerebellum evaluated, 174 (93.5%) posterior inferior cerebellar arteries were found. Also, there were 12 (6.5%) ageneses. There was single posterior inferior cerebellar artery in 159 (91.4%) samples and duplicate in 10 (5.7%), while 5 (2.9%) specimens showed hypoplasia. The posterior inferior cerebellar artery originated from the vertebral artery in 121 (69.5%) samples and from the basilar artery in 42 (24.1%) samples; while in 11 (6.4%) it originated in a common trunk with the anterior inferior cerebellar artery. In 101 (83.5%) cases, the posterior inferior cerebellar artery originated from the intracranial segment of the vertebral artery, while 20 (16.5%) samples originated from the extracranial segment. The calibres of posterior inferior cerebellar artery in its proximal and distal segments were 1.45 ± 0.37 mm and 1.33 ± 0.31 mm, respectively. CONCLUSIONS: This study, carried out in cadaveric material, provides relevant qualitative and morphometric information of the posterior inferior cerebellar artery, useful for the diagnosis and clinical management, as well as for the surgical approaches that may compromise this structure.

Diaphragm pacing in a pediatric patient with Acquired Central Hypoventilation syndrome. / Marcapasos diafragmático en paciente pediátrico con síndrome de Hipoventilación Central Adquirido.

INTRODUCTION: Diaphragmatic pacemaker is a device that reduces or eliminates the need of mechanical ventilation in patients with chronic respiratory failure who keep the phrenic nerve-diaphragm axis intact, as long as they do not present intrinsic lung disease. Although its implantation has been practiced for deca des, its use is not widespread and to date, there is little published literature about it, mostly related to high spinal cord injury and congenital central hypoventilation syndrome. OBJECTIVE: To describe an experience of diaphragmatic pacemaker implantation in a pediatric patient with acquired cen tral hypoventilation syndrome. CLINICAL CASE: Female patient with central hypoventilation syndrome secondary to ischemic brainstem lesion as a result of ventriculoperitoneal shunt malfunction. For this reason, for 5 years she was supported by inpatient mechanical ventilation. At 7 years of age, a diaphragmatic pacemaker was implanted by thoracoscopic surgery, which allowed, after a period of rehabilitation and respiratory conditioning, mechanical ventilation withdrawal, and hospital dischar ge. CONCLUSIONS: Diaphragmatic pacemaker is a feasible, potentially safe, and cost-effective option for decreasing or eliminating mechanical ventilation dependence and improve life quality in patients with acquired central hypoventilation syndrome.

Features and applications of Ent35-MccV hybrid bacteriocin: current state and perspectives.

Bacteriocins are peptides of ribosomal synthesis that are active against bacteria related to the producing strain. They have been widely used in the food industry as biopreservatives. The generation of hybrid peptides by combining the genes that encode two different bacteriocins has made it possible to study the mechanisms of action of the bacteriocins that compose them and also develop new peptides with improved biotechnological applications. Hybrid bacteriocins may be obtained in several ways. In our laboratory, by combining enterocin CRL35 and microcin V (Ent35-MccV), we obtained a broad-spectrum peptide that is active against both Gram-positive and Gram-negative bacteria. Ent35-MccV is sensitive to the action of intestinal proteases and is heat resistant, which makes it a good candidate for use as a biopreservative. For this reason, the peptide was tested in skim milk and beef burgers as food models. We also obtained more potent variants of the hybrid by modifying the central amino acid of the hinge region that connects the two bacteriocins. This review also discusses future applications and perspectives regarding the Ent35-MccV and other hybrid peptides.Key Points• Ent35-MccV is a new broad-spectrum bacteriocin.• The mechanism of action of bacteriocins can be studied using hybrid peptides.• Genetic engineering allows obtaining improved bacteriocin derivatives.• Hybrid peptides can be used in the food, pharmaceutical, and veterinary applications.

Marcapasos diafragmático en paciente pediátrico con síndrome de Hipoventilación Central Adquirido / Diaphragm pacing in a pediatric patient with Acquired Central Hypoventilation syndrome

Resumen: Introducción: El marcapasos diafragmático permite reducir o eliminar la necesidad de ventilación mecánica en pacientes con insuficiencia respiratoria crónica que conservan el eje nervio frénico-diafragma in tacto, siempre que no presenten enfermedad pulmonar intrínseca. Aunque su implantación ha sido practicada por décadas, su uso no está ampliamente difundido, y existe poca literatura pu blicada al respecto, la mayoría relacionada con lesión medular alta y síndrome de hipoventilación central congénito. Objetivo: Describir una experiencia de implantación de marcapasos diafragmático en paciente pediátrico con síndrome de hipoventilación central adquirido. Caso Clínico: Pa ciente femenino con síndrome de hipoventilación central secundario a lesión isquémica de tronco cerebral como resultado de disfunción de válvula de derivación ventrículo peritoneal, motivo por el cual durante 5 años se mantuvo con asistencia de ventilación mecánica intrahospitalaria. A los 7 años de edad se implantó marcapasos diafragmático mediante cirugía toracoscópica, lo que per mitió posterior a un periodo de rehabilitación y acondicionamiento respiratorio el destete de la ventilación mecánica y el egreso hospitalario. Conclusiones: El marcapasos diafragmático es una opción factible, potencialmente segura y costo efectiva para disminuir o eliminar la dependencia de ventilación mecánica y mejorar la calidad de vida en pacientes con síndrome de hipoventilación central adquirido.

Abstract: Introduction: Diaphragmatic pacemaker is a device that reduces or eliminates the need of mechanical ventilation in patients with chronic respiratory failure who keep the phrenic nerve-diaphragm axis intact, as long as they do not present intrinsic lung disease. Although its implantation has been practiced for deca des, its use is not widespread and to date, there is little published literature about it, mostly related to high spinal cord injury and congenital central hypoventilation syndrome. Objective: To describe an experience of diaphragmatic pacemaker implantation in a pediatric patient with acquired cen tral hypoventilation syndrome. Clinical Case: Female patient with central hypoventilation syndrome secondary to ischemic brainstem lesion as a result of ventriculoperitoneal shunt malfunction. For this reason, for 5 years she was supported by inpatient mechanical ventilation. At 7 years of age, a diaphragmatic pacemaker was implanted by thoracoscopic surgery, which allowed, after a period of rehabilitation and respiratory conditioning, mechanical ventilation withdrawal, and hospital dischar ge. Conclusions: Diaphragmatic pacemaker is a feasible, potentially safe, and cost-effective option for decreasing or eliminating mechanical ventilation dependence and improve life quality in patients with acquired central hypoventilation syndrome.

Obtaining an Ent35-MccV derivative with mutated hinge region that exhibits increased activity against Listeria monocytogenes and Escherichia coli.

The present paper describes the generation of derivatives from the hybrid peptide called Ent35-MccV, active against Gram-positive and Gram-negative bacteria. This peptide has a triple glycine hinge region between enterocin CRL35 and microcin V. In order to obtain variants of Ent35-MccV with greater biotechnological potential, a saturation mutagenesis was carried out in the hinge region. As a result, we obtained a bank of E. coli strains expressing different mutated hybrid bacteriocins in the central position of the hinge region. From all these variants, we found that the one bearing a tyrosine in the central region of the hinge (Ent35-GYG-MccV) is 2-fold more active against E. coli and 4-fold more active against Listeria than the original peptide Ent35-MccV. This derivative was purified and characterized. The development and evaluation of alternative hinges for Ent35-MccV represents a step forward in the bioengineering of antimicrobial peptides. This approach fosters the rational design of peptides with enhanced antimicrobial activity.

Histological and morphometric study of the components of the sinus and atrioventricular nodes in horses and dogs.

The cardiac nodes are the source of the electrical impulse that is transmitted to the heart, the aim of this work is study the histological and morphometric characteristics of the different components of the sinus and atrioventricular nodes in horses and dogs that help to know the physiopathology of these nodes. A group of ten horse hearts and five dog hearts were used. The region of the sinus and atrioventricular nodes was sectioned serially, and the block of tissue removed for study. The samples were assessed using a morphometric analysis with the Image-Pro Plus 7.1 software and the acquisition of the images using a Leica DMD108 optic microscope. The shape of the horse's sinus node is oblong and its P cells are large. The shape of the dog's sinus is rounded or oblong. The P cells are large and pale. The area of P cells in horses was 976 (SD 223.7) µm2 and in dogs the area for P cells was 106 (SD 30.4) µm2, which indicates that the value for P cells in horses are significantly higher than in dogs (p = .001). The horse atrioventricular node presented an oblong shape and in dogs, presents a spindle shape. The lower cell density in any of the cardiac nodes, especially in P cells of sinus node, can decrease electrical conduction within the nodes and in the internodal tracts, which would reflect the presence of cardiac arrhythmias derived from poor conduction, even in morphologically normal hearts.

Redox properties of nanostructured lanthanide-doped ceria spheres prepared by microwave assisted hydrothermal homogeneous co-precipitation.

In this work, nanostructured LnxCe(1-x)O2-δ (Ln: Gd and Pr; x = 0.1 and 0.2) spheres were synthesized by microwave assisted hydrothermal homogeneous co-precipitation and their properties were characterized by synchrotron radiation XRD, X-ray absorption near-edge spectroscopy (XANES) and scanning and high-resolution electron microscopy (SEM and HRTEM). In situ XRD and XANES experiments were carried out under reducing and oxidizing conditions in order to investigate the redox behaviour of these materials. The nanostructured mixed oxide spheres were found to have a cubic crystal structure (Fm3m space group). The spheres were composed of nanoparticles with an average crystallite size of about 10 nm. The Ln(0.1)Ce(0.9)O2-δ compositions exhibited the highest specific surface area (∼ 60 m(2) g(-1)). In situ XRD experiments showed an increase in lattice parameters upon reduction, which was attributed to the reduction of Ce(4+) and Pr(4+) cations to Ce(3+) and Pr(3+), which have larger radii, and to the associated increase in VO concentration. This increase in lattice parameters was considerably more pronounced for PrDC than GDC, and was explained by the considerably larger change in ionic radius for Pr upon reduction. XANES absorption experiments at the Ce and Pr L3-edge showed that the changes observed upon reduction of the Pr-containing samples resulted mostly from the formation of Pr(3+) rather than Ce(3+), and supported the previously reported proposal that Pr(3+) has a stabilizing effect on Ce(4+).

Prevalencia de patología cardíaca en la enfermedad de Chagas: años 2004-2012. Programa y Red de Chagas de CABA / Prevalence of cardiac pathology in Chagas disease: 2004 -2012. Program and Chagas CABA network

El Instituto Universitario de Ciencias de las Salud ha mostrado un particular compromiso con la formación de sus estudiantes en la estrategia de Atención Primaria de la Salud, con las prácticas asistenciales dedicadas al 1er nivel de atención ambulatoria y a las patologías prevalentes en ese ámbito. Del mismo modo se han desenvuelto las actividades de formación en investigación. Como exponente de esa orientación, la revista Ciencias de la Salud publicó en el Vol. 2, N°1, 2011:4-9, el artículo “Prevalencia de la Enfermedad de Chagas” de Érica G. Morais, que había obtenido el premio “Futuros Líderes”, otorgado por el Curso Anual Internacional de Investigación en Ciencias de la Salud (IUCS-AMA, Prof. Carlos Álvarez Bermúdez). Aquella investigación formaba parte de un proyecto más amplio realizado en el Hospital Teodoro Álvarez entre 2004 y 2012, en el que participaron un conjunto de investigadores, que compartieron la autoría de la actual publicación. El Dr. Jorge Mitelman, Prosecretario de Ciencia y Técnica del IUCS e integrante de ese equipo, preparó además una reseña sobre la jornada del INCOSUR, realizada en abril del presente año, describiendo asimismo el proceso de desarrollo de la Ciudad de Buenos Aires, como área no endémica, para encarar las consecuencias de la enfermedad de Chagas

Interlaboratory comparison of dicentric chromosome assay using electronically transmitted images.

The bottleneck in data acquisition during biological dosimetry based on a dicentric assay is the need to score dicentrics in a large number of lymphocytes. One way to increase the capacity of a given laboratory is to use the ability of skilled operators from other laboratories. This can be done using image analysis systems and distributing images all around the world. Two exercises were conducted to test the efficiency of such an approach involving 10 laboratories. During the first exercise (E1), the participant laboratories analysed the same images derived from cells exposed to 0.5 and 3 Gy; 100 images were sent to all participants for both doses. Whatever the dose, only about half of the cells were complete with well-spread metaphases suitable for analysis. A coefficient of variation (CV) on the standard deviation of ∼15 % was obtained for both doses. The trueness was better for 3 Gy (0.6 %) than for 0.5 Gy (37.8 %). The number of estimated doses classified as satisfactory according to the z-score was 3 at 0.5 Gy and 8 at 3 Gy for 10 dose estimations. In the second exercise, an emergency situation was tested, each laboratory was required to score a different set of 50 images in 2 d extracted from 500 downloaded images derived from cells exposed to 0.5 Gy. Then the remaining 450 images had to be scored within a week. Using 50 different images, the CV on the estimated doses (79.2 %) was not as good as in E1, probably associated to a lower number of cells analysed (50 vs. 100) or from the fact that laboratories analysed a different set of images. The trueness for the dose was better after scoring 500 cells (22.5 %) than after 50 cells (26.8 %). For the 10 dose estimations, the number of doses classified as satisfactory according to the z-score was 9, for both 50 and 500 cells. Overall, the results obtained support the feasibility of networking using electronically transmitted images. However, before its implementation some issues should be elucidated, such as the number and resolution of the images to be sent, and the harmonisation of the scoring criteria. Additionally, a global website able to be used for the different regional networks, like Share Points, will be desirable to facilitate worldwide communication.

Prevalencia de factores de riesgo cardiovascular en una población de la ciudad de Buenos Aires, Argentina / Prevalence of cardiovascular risk factors in a population of the city of Buenos Aires, Argentina

Las enfermedades cardiovasculares en la Argentina, como en la mayoría de los países son la primera causa demuerte y están entre las de mayor prevalencia. Por ello la investigación a fin de caracterizar y cuantificar los principalesfactores de riesgo cardiovasculares y las conductas preventivas de la población, resultan fundamentales para la prevencióny el control de estas afecciones. Se investigaron las características de los principales factores de riesgo relacionados con las enfermedades delaparato circulatorio, en una población de 917 personas, de ambos sexos, estratificada por grupos etáreos, encontrándose las siguientes cifras globales: Hipertensión arterial: 23,82%, Tabaquismo: 25,35%, Obesidad: 28,82%, Hipercolesterolemia,:17,70% y Diabetes: 6,12%. Su prevalencia aumenta en forma exponencial con la edad, salvo en el Tabaquismo y la Obesidad, donde luego de los 50 años decrece. Si bien se ha constatado la importancia del factor heredo familiar en la Hipertensión y la Diabetes, ambas se inician en la década de los 40 años de edad. La asociación de 2 factores de riesgo cardiovascular: Hipertensión arterial y Obesidad aumenta exponencialmente con la edad, llegando al 16,33% En el estudio demostró que el tabaquismo se inicia a un promedio de edad de 18,55 años, en ambos sexos, que es más prevalente en los jóvenes que en los adultos mayores, aunque éstos consumen más cigarrillos por día. Se constató además, que un importante número de personas dejan de fumar: 18,75%. Los datos sobre individuos hipertensos som compatibles con estudios anteriores, aunque con respecto a la población de obesos, se observa un incremento de laprevalencia en ambos sexos, con respecto a investigaciones anteriores un alto porcentaje de obesidad y sobrepeso en ambos sexos. Preocupa el porcentaje alto de personas que reconocieron su sedentarismo: 69,90%...

Meningomielitis asociadas a infección por herpes virus humano 7: Comunicación de dos casos / Meningomyelitis associated with infection by human herpes virus 7: Report of two cases

Human herpesvirus 7 (HHV-7) may cause encephalomyelitis in immune competent adults. We report two patients infected by the virus. A 34-year-old male presenting with paraparesis and a sensitive deficiency located in D6 dermatome. Cerebrospinal fluid had 35 white blood cells per mm³ and 75 mg protein per dl. A PCR-microarray examination was positive for HHV-7. The patient was treated with prednisolone and ganciclovir with full recovery. A 27-year-old male presenting with headache, fever and diarrhea. Cerebrospinal fluid analysis showed 160 cells per mm³ and 75 mg protein per dl. Viral RNA detection was positive for HHV-7. The patient was managed with analgesia and rest and was discharged with the diagnosis of viral meningitis. Our communication supports the notion that HHV-7 may be considered as pathogen factor in humans, even in immune competent ones.

Etiología de la neumonía en pacientes chilenos infectados por el virus de la inmunodeficiencia humana / Etiology of pneumonia in Chilean HIV-infected adult patients

Objectives: To establish the etiology of pneumonia and to compare the yield of diagnostic techniques for diagnosis of Pneumocystis jiroveci and Mycobacterium tuberculosis infections in HIV-1-infected patients. Patients and Methods: Subjects underwent sputum induction and bronchoalveolar lavage (BAL). Gram, Ziehl-Neelsen, silver stain (SS) and immunofluorescense staining (IF) for P. jiroveci, fluorescent stain for mycobacteria, PCR for P. jiroveci andM. tuberculosis, aerobic, fungal and mycobacterial cultures, respiratory viruses and CMV cultures were performed on the sputum and BAL. IgM for Mycoplasma pneumoniae and Chlamydophyla pneumoniae, and Legionella pneumophila urinary antigen were also obtained. Results: Sixty patients were included. An etiologic diagnosis was made in 97 percent. Pneumocystisjiroveci was the most frequent etiology (58 percent) followed by Streptococcus pneumoniae (12 percent), and Mycobacterium avium complex (12 percent). Mycobacterium tuberculosis was found in 5 percent. Conclusions: The comparison of diagnostic methods for P. jiroveci showed a higher sensitivity of IF and SS in BAL than in sputum, however PCR was equally sensitive in both samples. With this approach a precise etiologic diagnosis was reached in the great majority of patients. The most common etiology was P. jiroveci. IF in BAL remains the gold standard for diagnosis of P. jiroveci pneumonia.

Objetivos: Establecer la etiología de la neumonía y comparar el rendimiento de diferentes técnicas para el diagnóstico de las infecciones por Pneumocystis jiroveci y Mycobacterium tuberculosis en pacientes con infección por virus de inmunodeficiencia humana (VIH). Material y Métodos: De cada paciente se obtuvo esputo inducido y se efectuó LBA. A las muestras obtenidas se les realizó tinciones de Gram, Ziehl-Neelsen, plata e inmunofluores-cencia (IF) para P. jiroveci y M. tuberculosis; reacción de polimerasa en cadena (RPC) para ambos microorganismos; cultivos aeróbicos, fúngicos, para micobacterias, virus respiratorios y citomegalovirus. También se realizó determinación de IgM de Mycoplasma pneumoniae y Chlamydophyla pneumoniae y antígeno urinario de Legionella pneumophila. Resultados: Se incluyeron 60 pacientes, lográndose diagnóstico etiológico en 97 por ciento de los casos. Pneumocystis jiroveci fue la etiología más frecuente (58 por ciento), seguida por Streptococcus pneumoniae (12 por ciento) y Mycobacterium avium complex (MAC) (12 por ciento). Mycobacterium tuberculosis fue encontrado en 5 por ciento. Conclusiones: La comparación de los métodos diagnósticos para P. jiroveci mostró una mayor sensibilidad de la IF y tinción de plata en LBA que en esputo; sin embargo, la RPC fue igualmente sensible en ambos tipos de muestras. Con esta estrategia se logró establecer etiología en la gran mayoría de los pacientes. La etiología más común fue P. jiroveci. IF en LBA sigue siendo el estándar para el diagnóstico de la neumonía por P. jiroveci.

Biological dosimetry intercomparison exercise: an evaluation of triage and routine mode results by robust methods.

Well-defined protocols and quality management standards are indispensable for biological dosimetry laboratories. Participation in periodic proficiency testing by interlaboratory comparisons is also required. This harmonization is essential if a cooperative network is used to respond to a mass casualty event. Here we present an international intercomparison based on dicentric chromosome analysis for dose assessment performed in the framework of the IAEA Regional Latin American RLA/9/054 Project. The exercise involved 14 laboratories, 8 from Latin America and 6 from Europe. The performance of each laboratory and the reproducibility of the exercise were evaluated using robust methods described in ISO standards. The study was based on the analysis of slides from samples irradiated with 0.75 (DI) and 2.5 Gy (DII). Laboratories were required to score the frequency of dicentrics and convert them to estimated doses, using their own dose-effect curves, after the analysis of 50 or 100 cells (triage mode) and after conventional scoring of 500 cells or 100 dicentrics. In the conntional scoring, at both doses, all reported frequencies were considered as satisfactory, and two reported doses were considered as questionable. The analysis of the data dispersion among the dicentric frequencies and among doses indicated a better reproducibility for estimated doses (15.6% for DI and 8.8% for DII) than for frequencies (24.4% for DI and 11.4% for DII), expressed by the coefficient of variation. In the two triage modes, although robust analysis classified some reported frequencies or doses as unsatisfactory or questionable, all estimated doses were in agreement with the accepted error of ±0.5 Gy. However, at the DI dose and for 50 scored cells, 5 out of the 14 reported confidence intervals that included zero dose and could be interpreted as false negatives. This improved with 100 cells, where only one confidence interval included zero dose. At the DII dose, all estimations fell within ±0.5 Gy of the reference dose interval. The results obtained in this triage exercise indicated that it is better to report doses than frequencies. Overall, in both triage and conventional scoring modes, the laboratory performances were satisfactory for mutual cooperation purposes. These data reinforce the view that collaborative networking in the case of a mass casualty event can be successful.

[Meningomyelitis associated with infection by human herpes virus 7: report of two cases]. / Meningomielitis asociadas a infección por herpes virus humano 7: Comunicación de dos casos.

Human herpesvirus 7 (HHV-7) may cause encephalomyelitis in immune competent adults. We report two patients infected by the virus. A 34-year-old male presenting with paraparesis and a sensitive deficiency located in D6 dermatome. Cerebrospinal fluid had 35 white blood cells per mm³ and 75 mg protein per dl. A PCR-microarray examination was positive for HHV-7. The patient was treated with prednisolone and ganciclovir with full recovery. A 27-year-old male presenting with headache, fever and diarrhea. Cerebrospinal fluid analysis showed 160 cells per mm³ and 75 mg protein per dl. Viral RNA detection was positive for HHV-7. The patient was managed with analgesia and rest and was discharged with the diagnosis of viral meningitis. Our communication supports the notion that HHV-7 may be considered as pathogen factor in humans, even in immune competent ones.

Histone post-translational modifications in DNA damage response.

The fact that eukaryotic DNA is packed into chromatin constitutes a physical barrier to enzymes and regulatory factors to reach the DNA molecule for replication, transcription, recombination and repair. Although most studies in this field have concentrated on how chromatin regulates transcription, there is a recent emphasis on studying the role of chromatin in the response to DNA damage. Two main chromatin-remodeling mechanisms have been identified, namely, ATP-dependent chromatin-remodeling complexes and histone post-translational modifications (PTMs). PTMs constitute reversible covalent modifications in aminoacidic residues, such as serine and threonine phosphorylation, lysine acetylation, lysine and arginine methylation and lysine ubiquitylation, among others. Moreover, nucleosome composition can be modified by the incorporation of histone variants, which are assembled into nucleosomes independently of DNA replication. The phosphorylation of the histone variant H2AX (gammaH2AX) is one of the best examples of histone PTMs in response to DNA damage induction, but many others have recently been revealed. In this review, we focus on and summarize the best-known histone PTMs observed in excision repair (base excision and nucleotide excision) and double-strand break (non-homologous end-joining and homologous recombination) repair pathways. In brief, the interplay between chromatin remodelers and DNA repair factors is discussed in relation to DNA damage response mechanisms.

Distribution of UVC-induced chromosome aberrations along the X chromosome of TCR deficient and proficient Chinese hamster cell lines.

Cells with a transcription coupled repair (TCR) deficiency are characterized by a higher sensitivity to UVC irradiation and by an increase in apoptosis and chromosomal aberration frequencies. It has been claimed that the higher frequency of chromosomal aberrations results from the transcription blockage caused by UVC-lesions located in the transcribed strands of the genome. The distribution of chromosome breakpoints in euchromatic and heterochromatic regions of the X chromosome from TCR deficient and proficient Chinese hamster cell lines was studied. Most UVC-induced breakpoints occurred in euchromatic regions of the X chromosome in both cell lines. No increase of UVC-induced breakpoints in the euchromatic region of the UV61 X chromosome was observed, indicating that TCR failure alone cannot be responsible for the increased frequency of chromosomal aberrations. Differential chromatin remodeling in the TCR defective cell line is proposed as a possible mechanism involved in the distribution of UVC-induced breakpoints along the Chinese hamster X chromosome. A similar explanation for the increase of UVC-induced chromosomal aberrations in TCR defective cells is given.