Epigenetic Dysregulation of Mammalian Male Meiosis Caused by Interference of Recombination and Synapsis.

Meiosis involves a series of specific chromosome events, namely homologous synapsis, recombination, and segregation. Disruption of either recombination or synapsis in mammals results in the interruption of meiosis progression during the first meiotic prophase. This is usually accompanied by a defective transcriptional inactivation of the X and Y chromosomes, which triggers a meiosis breakdown in many mutant models. However, epigenetic changes and transcriptional regulation are also expected to affect autosomes. In this work, we studied the dynamics of epigenetic markers related to chromatin silencing, transcriptional regulation, and meiotic sex chromosome inactivation throughout meiosis in knockout mice for genes encoding for recombination proteins SPO11, DMC1, HOP2 and MLH1, and the synaptonemal complex proteins SYCP1 and SYCP3. These models are defective in recombination and/or synapsis and promote apoptosis at different stages of progression. Our results indicate that impairment of recombination and synapsis alter the dynamics and localization pattern of epigenetic marks, as well as the transcriptional regulation of both autosomes and sex chromosomes throughout prophase-I progression. We also observed that the morphological progression of spermatocytes throughout meiosis and the dynamics of epigenetic marks are processes that can be desynchronized upon synapsis or recombination alteration. Moreover, we detected an overlap of early and late epigenetic signatures in most mutants, indicating that the normal epigenetic transitions are disrupted. This can alter the transcriptional shift that occurs in spermatocytes in mid prophase-I and suggest that the epigenetic regulation of sex chromosomes, but also of autosomes, is an important factor in the impairment of meiosis progression in mammals.

BMP-7 protects male and female rodents against neuropathic pain induced by nerve injury through a mechanism mediated by endogenous opioids.

Neuropathic pain is highly prevalent in pathological conditions such as diabetes, herpes zoster, trauma, etc. The severity and refractoriness to treatments make neuropathic pain a significant health concern. The transforming growth factor (TGF-ß) family of cytokines is involved in pain modulation. Bone morphogenetic proteins (BMPs) constitute the largest subgroup within the TGF-ß family. BMP-7 induces the transcription of genes coding endogenous opioid precursors in vitro. However, a nociception modulatory function for this cytokine remains unexplored in vivo. Herein, we show that BMP-7 and its type I receptors were detected in regions of the nervous system involved in pain transmission, processing, and modulation. BMP-7 haploinsufficiency confers to male and female mice a tactile hyperalgesia phenotype to mechanical stimuli, both at baseline and after sciatic nerve injury (SNI). The administration of recombinant BMP-7 (rBMP-7) reduced the severity of the allodynia after SNI in rodents without sexual dimorphism. Central administration of rBMP-7 delayed allodynia development after SNI and reduced the severity of allodynia. The opioid antagonist naloxone antagonized the antinociceptive effect of rBMP-7 in rats. The analgesic effect of morphine was significantly attenuated in BMP-7+/- mice. The antiallodynic effect of voluntary exercise after SNI, whose mechanism involves the endogenous opioid system, was hampered by BMP-7 deficiency while potentiated by rBMP-7. Our results suggest that BMP-7 may constitute a novel therapeutic target for the treatment of neuropathic pain, which improves the function of the endogenous pain-resolution mechanisms to alleviate chronic pain.

Chromatin organization and remodeling of interstitial telomeric sites during meiosis in the Mongolian gerbil (Meriones unguiculatus).

Telomeric DNA repeats are key features of chromosomes that allow the maintenance of integrity and stability in the telomeres. However, interstitial telomere sites (ITSs) can also be found along the chromosomes, especially near the centromere, where they may appear following chromosomal rearrangements like Robertsonian translocations. There is no defined role for ITSs, but they are linked to DNA damage-prone sites. We were interested in studying the structural organization of ITSs during meiosis, a kind of cell division in which programmed DNA damage events and noticeable chromatin reorganizations occur. Here we describe the presence of highly amplified ITSs in the pericentromeric region of Mongolian gerbil (Meriones unguiculatus) chromosomes. During meiosis, ITSs show a different chromatin conformation than DNA repeats at telomeres, appearing more extended and accumulating heterochromatin markers. Interestingly, ITSs also recruit the telomeric proteins RAP1 and TRF1, but in a stage-dependent manner, appearing mainly at late prophase I stages. We did not find a specific accumulation of DNA repair factors to the ITSs, such as γH2AX or RAD51 at these stages, but we could detect the presence of MLH1, a marker for reciprocal recombination. However, contrary to previous reports, we did not find a specific accumulation of crossovers at ITSs. Intriguingly, some centromeric regions of metacentric chromosomes may bind the nuclear envelope through the association to SUN1 protein, a feature usually performed by telomeres. Therefore, ITSs present a particular and dynamic chromatin configuration in meiosis, which could be involved in maintaining their genetic stability, but they additionally retain some features of distal telomeres, provided by their capability to associate to telomere-binding proteins.

Inactivation or non-reactivation: what accounts better for the silence of sex chromosomes during mammalian male meiosis?

During the first meiotic prophase in male mammals, sex chromosomes undergo a program of transcriptional silencing called meiotic sex chromosome inactivation (MSCI). MSCI is triggered by accumulation of proteins like BRCA1, ATR, and γH2AX on unsynapsed chromosomes, followed by local changes on the sex chromatin, including histone modifications, incorporation of specific histone variants, non-histone proteins, and RNAs. It is generally thought that MSCI represents the transition of unsynapsed chromatin from a transcriptionally active state to a repressed state. However, transcription is generally low in the whole nucleus during the early stages of the first meiotic prophase, when markers of MSCI first appear, and is then reactivated globally during pachytene. Thus, an alternative possibility is that MSCI represents the targeted maintenance and/or reinforcement of a prior repressed state, i.e., a failure to reactivate. Here, we present an analysis of the temporal and spatial appearance of transcriptional and MSCI markers, as well as chromatin modifications related to transcriptional regulation. We show that levels of RNA pol II and histone H3 acetylated at lysine 9 (H3K9ac) are low during leptotene, zygotene, and early pachytene, but increase strongly in mid-pachytene, indicating that reactivation occurs with some delay after synapsis. However, while transcription markers appear abundantly on the autosomes at mid-pachytene, they are not directed to the sex chromosomes. Interestingly, we found that chromatin modifications related to transcriptional silencing and/or MSCI, namely, histone H3 trimethylated at lysine 9 (H3K9me3), histone H3 monomethylated at lysine 4 (H3K4me1), γH2AX, SUMO1, and XMR, appear on the sex chromosomes before autosomes become reactivated. These results suggest that the onset of MSCI during late zygotene and early pachytene may prevent sex chromosome reactivation during mid-pachytene instead of promoting inactivation de novo. Additionally, we found temporal differences between the X and Y chromosomes in the recruitment of DNA repair and MSCI markers, indicating a differential regulation of these processes. We propose that many of the meiotic defects attributed to failure to silence sex chromosomes could be interpreted as a more general process of transcriptional misregulation that occurs under certain pathological circumstances in zygotene and early pachytene.

[Postoperative fibrosis after lumbar surgery]. / Fibrosis postquirúrgica de la columna lumbar.

INTRODUCTION: Postoperative fibrosis is the excessive scarring resulting from any surgery; that is, the formation of more fibrous tissue than is normal. In some lumbar surgeries this fibrous tissue compresses or distends the dura mater and/or nerve roots, causing low back pain or radiculopathy. MATERIAL AND METHODS: This report considers the results of 680 simple lumbar discectomies and 80 repeated surgeries resulting from failed lumbar operations. Among both groups an important reduction of the postoperative fibrosis incidence was observed. All patients were operated by the same surgeons, using the same surgical technique (open technique) and the same implanted materials. A Gore's antifibrotic spinal membrane was applied in all patients. RESULTS: Among the 680 patients who underwent a simple lumbar discectomy, 98% experienced clinical improvement, while in the group of patients who were reoperated after a failed lumbar surgery the recovery index was 92%. The incidence of postoperative fibrosis in both groups was 0.58% and 2.5%, respectively. DISCUSSION: As compared to the postoperative fibrosis reported worldwide (2-18%) we believe this material has a great influence in the healing process.

Meiotic pairing and segregation of achiasmate sex chromosomes in eutherian mammals: the role of SYCP3 protein.

In most eutherian mammals, sex chromosomes synapse and recombine during male meiosis in a small region called pseudoautosomal region. However in some species sex chromosomes do not synapse, and how these chromosomes manage to ensure their proper segregation is under discussion. Here we present a study of the meiotic structure and behavior of sex chromosomes in one of these species, the Mongolian gerbil (Meriones unguiculatus). We have analyzed the location of synaptonemal complex (SC) proteins SYCP1 and SYCP3, as well as three proteins involved in the process of meiotic recombination (RAD51, MLH1, and gamma-H2AX). Our results show that although X and Y chromosomes are associated at pachytene and form a sex body, their axial elements (AEs) do not contact, and they never assemble a SC central element. Furthermore, MLH1 is not detected on the AEs of the sex chromosomes, indicating the absence of reciprocal recombination. At diplotene the organization of sex chromosomes changes strikingly, their AEs associate end to end, and SYCP3 forms an intricate network that occupies the Y chromosome and the distal region of the X chromosome long arm. Both the association of sex chromosomes and the SYCP3 structure are maintained until metaphase I. In anaphase I sex chromosomes migrate to opposite poles, but SYCP3 filaments connecting both chromosomes are observed. Hence, one can assume that SYCP3 modifications detected from diplotene onwards are correlated with the maintenance of sex chromosome association. These results demonstrate that some components of the SC may participate in the segregation of achiasmate sex chromosomes in eutherian mammals.

Sex chromosomes, synapsis, and cohesins: a complex affair.

During first meiotic prophase, homologous chromosomes are held together by the synaptonemal complex, a tripartite proteinaceous structure that extends along the entire length of meiotic bivalents. While this feature is applicable for autosomes, sex chromosomes often escape from this rule. Many species present sex chromosomes that differ between them in their morphology, length, and gene content. Moreover, in some species, sex chromosomes appear in a single dose in one of the sexes. In all of these cases, the behavior of sex chromosomes during meiosis is conspicuously affected, and this includes the assembly and dynamics of the synaptonemal complex. We review in this study the structure of the synaptonemal complex in the sex chromosomes of three groups of organisms, namely: mammals, orthopterans, and hemipterans, which present different patterns of sex chromosome structure and behavior. Of special interest is the analysis of the organization of the axial/lateral elements of the synaptonemal complex in relation to other axial structures organized along meiotic chromosomes, mainly the cohesin axis. The differences found in the behavior of both axial structures reveal that while the organization of a cohesin axis along sex chromosomes is a conserved feature in most organisms and it shows very little morphological variations, the axial/lateral elements of the synaptonemal complex present a wide range of structural modifications on these chromosomes.

La placa cervical Spineblock / The spineblock cervical plate

Se han aplicado 100 placas cervicales Spineblock de septiembre de 1998 a junio de 2001. La placa es de diseño original y está fabricada en titanio (Ti6A14B), cuya resistencia es óptima y se caracteriza por ser semitransparente a los rayos X. Tiene una doble curvatura para su acoplamiento longitudinal y transversal a los cuerpos vertebrales. Cuenta con cuatro picos en forma de arpón en los ángulos para su fijación primaria, lo que evita el desplazamiento al momento de atornillarla. Los orificios son centrales, alternando ovales y redondos. Se requiere de un solo tornillo para cada cuerpo vertebral. Los pacientes fueron adultos con una o varias hernias discales a quienes se les resecaron los discos afectados, dejando los segmentos operados con la placa descrita. Los resultados hasta la fecha han sido uniformemente satisfactorios.

Uso de colágeno-gentamicina (Garacoll) como profiláctico de infecciones en cirugía de disquectomía lumbar / The employment of gentamicin-collagen (Garacoll) as prophylaxis in surgery for lumbar discectomy

Del 10 de enero de 1997 al 30 de septiembre de 1999 se intervinieron 200 pacientes con el diagnóstico de hernia lumbar única L-4 o L-5, realizándoles disquectomía abierta. Fueron 138 pacientes masculinos y 62 femeninos. La edad promedio fue de 42 años, el tiempo quirúrgico promedio fue de 35 minutos con un sangrado promedio transoperatorio de 130 cc. A todos los pacientes se les colocó una esponja de colágeno con gentamicina (Garacoll) antes del cierre de la herida como única medida preventiva de infección. A ningún paciente se le administró antibiótico sistémico. No se desarrolló ninguna infección en los 200 pacientes estudiados.

Uso de una nueva placa en pacientes con discartrosis cervical / The use of a new plate for treatment of cervical discarthrosis

En el Hospital CIMA de la ciudad de Chihuahua, Chih., del 14 de septiembre de 1998 al 10 de septiembre de 1999 se intervinieron 40 pacientes con el diagnóstico de hernia(s) cervical, realizándoles discectomía(s), con aplicación de homoinjerto de cresta iliaca y una nueva placa cervical con ventajas muy superiores a las placas convencionales ya existentes en el mercado. Fueron 17 pacientes masculinos y 23 femeninos, con una edad promedio de 45.4 años. La principal causa de este tipo de lesiones son los accidentes automovilísticos y las caídas de sentón de las escaleras o de su propia altura. En todos los casos se logró remisión de los síntomas y las complicaciones fueron mínimas. La placa es diseño del segundo autor.