The organization, regulation, and biological functions of the synaptonemal complex / 亚洲男科学杂志(英文版)

The synaptonemal complex (SC) is a meiosis-specific proteinaceous macromolecular structure that assembles between paired homologous chromosomes during meiosis in various eukaryotes. The SC has a highly conserved ultrastructure and plays critical roles in controlling multiple steps in meiotic recombination and crossover formation, ensuring accurate meiotic chromosome segregation. Recent studies in different organisms, facilitated by advances in super-resolution microscopy, have provided insights into the macromolecular structure of the SC, including the internal organization of the meiotic chromosome axis and SC central region, the regulatory pathways that control SC assembly and dynamics, and the biological functions exerted by the SC and its substructures. This review summarizes recent discoveries about how the SC is organized and regulated that help to explain the biological functions associated with this meiosis-specific structure.

Synaptic configuration of quadrivalents and their association with the XY bivalent in spermatocytes of Robertsonian heterozygotes of Mus domesticus

BACKGROUND: The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains and consequently is prone to modification by chromosomal rearrangements. We have shown that nuclear architecture is modified in spermatocytes of Robertsonian (Rb) homozygotes of Mus domesticus. In this study we analyse the synaptic configuration of the quadrivalents formed in the meiotic pro- phase of spermatocytes of mice double heterozygotes for the dependent Rb chromosomes: Rbs 11.16 and 16.17. RESULTS: Electron microscope spreads of 60 pachytene spermatocytes from four animals of Mus domesticus 2n = 38 were studied and their respective quadrivalents analysed in detail. Normal synaptonemal complex was found between arms 16 of the Rb metacentric chromosomes, telocentrics 11 and 17 and homologous arms of the Rb metacentric chromosomes. About 43% of the quadrivalents formed a synaptonemal complex between the heterologous short arms of chromosomes 11 and 17. This synaptonemal complex is bound to the nuclear envelope through a fourth synapsed telomere, thus dragging the entire quadrivalent to the nuclear envelope. About 57% of quadrivalents showed unsynapsed single axes in the short arms of the telocentric chromosomes. About 90% of these unsynapsed quadrivalents also showed a telomere-to-telomere association between one of the single axes of the telocentric chromosome 11 or 17 and the X chromosome single axis, which was otherwise normally paired with the Y chromosome. Nucleolar material was associated with two bivalents and with the quadrivalent. CONCLUSIONS: The spermatocytes of heterozygotes for dependent Rb chromosomes formed a quadrivalent where four chromosomes are synapsed together and bound to the nuclear envelope through four telomeres. The nuclear configuration is determined by the fourth shortest telomere, which drags the centromere regions and heterochromatin of all the chromosomes towards the nuclear envelope, favouring the reiterated encounter and eventual rearrangement between the heterologous chromosomes. The unsynapsed regions of quadrivalents are frequently bound to the single axis of the X chromosome, possibly perturbing chromatin condensation and gene expression.

Dose-dependent effects of busulfan on dog testes in preparation for spermatogonial stem cell transplantation / 한국실험동물학회지

Successful male germ cell transplantation requires depletion of the host germ cells to allow efficient colonization of the donor spermatogonial stem cells. Although a sterilizing drug, busulfan, is commonly used for the preparation of recipient models before transplantation, the optimal dose of this drug has not yet been defined in dogs. In this study, 1-year-old mongrel dogs were intravenously injected with three different concentrations of busulfan (10, 15, or 17.5 mg/kg). Four weeks after busulfan treatment, no fully matured spermatozoa were detected in any of the busulfan-treated groups. However, small numbers of PGP9.5-positive spermatogonia were detected in all treatment groups, although no synaptonemal complex protein-3-positive spermatocytes were detected. Of note, acrosin-positive spermatids were not detected in the dogs treated with 15 or 17.5 mg/kg busulfan, but were detected in the other group. Eight weeks after busulfan treatment, the dogs treated with 10 mg/kg busulfan fully recovered, but those in the other groups did not. PGP9.5-positive spermatogonia were detected in the 10 mg/kg group, and at a similar level as in the control group, but these cells were rarely detected in the 15 and 17.5 mg/kg groups. These results suggest that a dose of 15-17.5 mg/kg is optimal for ablative treatment with busulfan to prepare the recipient dogs for male germ cell transplantation. At least eight weeks should be allowed for recovery. The results of this study might facilitate the production of recipient dogs for male germ cell transplantation and can also contribute to studies on chemotherapy.

Abnormalities of meiotic recombination in Han Chinese azoospermic patients / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To analyze defective homologous chromosomal recombination in Han Chinese azoospermic patients.</p><p><b>METHODS</b>Testicular biopsy samples from 7 healthy controls and 7 Han Chinese azoospermic patients including 2 obstructive azoospermia (OA group) and 5 non-obstructive azoospermia (NOA group) were analyzed. Immunofluorescence staining was performed to categorize early stage cells at meiosis prophase and to analyze chromosome pairing and recombination of pachytene spermatocyte. Newly developed meiotic proteins antibodies (anti-SCP3, anti-synaptonemal complex proteins 3, anti-MLH1, anti-Mut-L Homolog 1, anti-CREST, chromosome centromere antibody) were used to identify synaptonemal complex (anti-SCP3), recombination sites (anti-MLH1) and centromere (anti-CREST), respectively. Staging of spermatocyte was determined according to SCP3 formation progression. Qualitative data were compared by a Chi-square test, and ANOVA was used to analyze quantitative data.</p><p><b>RESULTS</b>Respectively, 2346 and 2932 spermatocytes were categorized in the controls and azoospermic patients. The proportions of zygotene cells in both OA group and NOA group were significantly higher than that of the control group. Investigation of 1967 pachytene cells from the controls and 354 pachytene cells from azoospermic patients indicated that the mean MLH1 foci per pachytene cell of NOA group was statistically lower than that of the controls. Compared with the controls, incomplete synaptonemal complexes cells (containing gap and/or split) were significantly increased in the NOA group.</p><p><b>CONCLUSION</b>Delayed meiosis prophase is relatively common in azoospermic patients, and changes in quantity and distribution of recombination foci may be the cause for spermatogenesis arrest in Han Chinese population.</p>

Chronology of meiosis & synaptonemal complex abnormalities in normal & abnormal spermatogenesis.

Background & objectives: The study was taken up to define criteria of normality for meiosis by assessing the frequency of meiotic prophase cell types, the frequency of pachytene substage in normal and abnormal spermatogenesis and to determine what synaptonemal complex. Methods: A quantitative and qualitative analysis of the first meiotic prophase was performed in 10 patients presenting with non-obstructive infertility and 10 controls, using dual colour immunocytochemistry with SCP3 and BRCA1 which visualise axial elements and synaptonemal complexes (SC). The respective frequencies of the leptotene, zygotene and pachytene stages as well as the frequencies of the four substages of pachytene were evaluated. The frequencies of the main types of meiotic abnormalities at pachytene were also assessed. Results: The frequencies of leptotene and zygotene stages were significantly higher in patients (7.95 and 9.75%) than in controls (2.30 and 1.45%), whereas the frequency of pachytene was significantly higher in controls than in patients (96.25 vs. 75.30%). Detailed analysis of the sex chromosomes revealed that the controls showed a presence of late pachytene substages (P3 + P4 = 64.40%), whereas the patients showed a early pachytene substages (P1 + P2 = 63.40%). From these results, a new index was defined to evaluate spermatogenesis: the Pachytene Index, or PI (PI = P1 + P2 / P1 + P2 + P3 + P4). The same abnormalities (asynapsis, fragmented SC, dotted SC, thin SC) were observed in controls and in patients, but with different frequencies. The most frequent abnormality was fragmented SC, with a significant difference between patients and controls (15.28 vs. 9.74%). There was a significant difference between patients and controls for the frequency of asynapsed nuclei (7.97 vs. 2.95%) while the difference in other abnormalities were not significant. Interpretation & conclusion: The accumulation of early primary spermatocytes is an indication that progression of meiosis is defective in spermatogenesis failures. The value of the PI less than 0.50 indicates that the kinetic of meiosis is normal at pachytene. There is no normal spermatogenesis when the frequency of one or several SC abnormalities is significantly higher than in controls and/ or when the PI is more than 0.50.

Synaptonemal complexes and XY behavior in two species of argentinian armadillos: Chaetophractus villosus and Dasypus hybridus (Xenarthra, Dasypodidae)

Spermatocytes from the two armadillo species, C. villosus and D. hybridus were studied in microspreads for synaptonemal complexes (SCs) and in thin sections for electron microscopy (EM). The complete se karyotype generally agrees with previous reports on mitotic chromosomes, except for the sex chromosomes. The X chromosome is submetacentric in both species and the Y is the shortest one in C. villosus and the second shortest in D. hybridus, and an extremely acrocentric one. A SC is formed along the total length of the Y chromosome, and this SC persists along all the pachytene substages. A single recombi-nation nodule (RN) is located in the region of the se nearest to the attachment to the nuclear envelope. The lateral element (LE) of the X axis in the SC shows a wavy aspect in most of the se length distant from the nuclear envelope. Nucleoli are attached to acrocentric or submetacentric bivalents, are visibly double in some cells , and in thin sections show an elaborate nucleolonema. Some differences in the XY are species-specific, as the higher degree of tangling and stronger heteropycnosis in D. hybridus. The effective, single crossover of the XY pair is highly localized, despite the permanence of a long tract of SC

Expression of synaptonemal complex protein 3 [SYCP3] m RNAin the testis: a molecular marker for spermatogenesis in azoospermic men

Men with unexplained infertility and azoospermia are often observed in the context of genetic defects. The expression of a wide variety of genes is developmentally regulated during human meiosis. Synaptonemal Protein 3 [SYCP3] gene, located on chromosome 12, encodes a DNA-binding protein as the structural component of the synaptonemal complex,which mediates the synopsis or homologous pairing of chromosomes during meiosis. Absence of SYCP3 in mice may lead to male infertility as well as female sub-fertility. SYCP3 expression analysis could be a tool for the prediction of human spermatogenesis progression, especially in infertile men. SYCP3 mRNA expression in testicular samples of 110 patients with non-obstructive azoospermia were studied in Avesina Infertility Clinic in Tehran, Iran during 2005 and early 2006. Semi-quantitative nested reverse transcriptase-PCR was employed in order to find the strength of gene expression. Using histopathological scoring for all samples, the expression level of SYCP3 during spermatogenesis was also evaluated. Testicular SYCP3 mRNA expression was observed in 67 patients [60.9%]. The expression level correlated with the degree of spermatogenic failure [p<0.0001]. While this gene had been expressed in patients with hypo-spermatogenesis and maturation arrest, a lack of expression was seen in those with spermatogonial arrest, Sertoli cell-only syndrome and testicular atrophy. These data indicate that SYCP3 is expressed in the human testis and it is restricted to germ cells. Our findings, in association with those obtained in experimental animals, show that lack of SYCP3 expression may have negative effects on spermatogenesis and male fertility. SYCP3 gene expression may help detect specific spermatogenesis stages in conjunction with histopathological findings

First demonstration of the substructure of recombination nodules

Recombination nodules are submicroscopic structures that are found in all the sexually reproducing, eukaryotic organisms during the pachytene stage of meiotic prophase I. Despite many reports on their number and location, no definite substructure was previously reported in these nodules. The present observations on spread oocytes and spermatocytes of the pigeon, using an improved technique for protein preservation, shown the presence of particulate subunits or "recombinomeres" in late recombination nodules, besides an interparticle matrix. The number of subunits per each nodule ranges from 1 to 5, and this number increases with the advancement of pachytene substages. These subunits are present in recombination nodules of all the other avian species previously studied, and they may be present in other organisms as well. It is suggested that the particulate substructure of recombination nodules mirrors the multiplicity of multienzymatic complexes that are needed for the ordered series of reactions that occur at the molecular level in the sites of meiotic recombination

Análisis ultraestructural e inmunocitoquímico del complejo sinaptonémico al inicio de la sinapsis / Ultraestructual analysis and immunocytochemical of synaptonemal complex at begging of synapsis

Los complejos sinaptonémicos (CSs) son estructuras nucleares específicas de las meiosis. Juegan un papel central en el apareamiento de cromosomas homólogos, se consideran esenciales en los eventos de crossing over y la segregación cromosómica durante la primera división meiótica. Cuando finaliza su ensamble en el estadio paquiteno, cada complejo sinaptonémico se extiende a lo largo del bivalente uniendo sus extremos a la envoltura nuclear. Los CSs se caracterizan por la presencia de dos elementos laterales y una región central. Los elementos laterales son paralelos y equidistantes. La cromatina de los cromosomas homólogos, se unen en una serie de asas a estos elementos. La región central se localiza entre los elementos laterales. Está formada por las fibrillas latero-mediales y el elemento medial. Las primeras se orientan perpendicularmente al eje longitudinal de CS y conectan los elementos laterales con el elemento medial. Los nódulos de recombinación juegan un papel activo en los procesos de recombinación y formación de quiasmas, se asocian a intervalos con la región central entre los cromosomas homólogos. La localización y función de los ácidos nucleicos en la formación y apareamiento del complemento sinaptonémico es poco conocida, por lo que se buscan alternativas metodológicas para resolver este tipo de problemas. En el presente trabajo se estudió la distribución de ADN en ovocitos de pollo en citeno utilizando técnicas para icroscopía electrónica de inmuno-oro. Además se emplearon técnicas citoquímicas como: contraste preferencial para ADN o preferencial para ribonucleoproteínas (RNPs). La combinación de tinción preferencial para RNPs e inmunolocalización de ADN nos demuestran que la cromatina se acumula conujuntamente con las ribonucleoprotéinas en los elementos laterales no apareados y la presencia de numerosas fibrillas RNPs distribuidas laxamante alrededor de los elementos laterales. Se encontraron nódulos de recombinación entre los elementos laterales durante el apareamiento, estos nódulos son PTA positivos lo que nos indica la presencia de ADN en éstos y por lo tanto la presencia de ADN entre los elementos laterales. La presencia de un puente de fibrillas marcadas con oro coloidal (ADMN) uniendo a los elementos laterales no apareados, sugeriría al ADN como una especie de macromolécula formadora de sitios de sinapsis

Synaptonemal complex karyotyping in an oligospermic patient with heterochromatin duplication in chromosome n§ 9

Se ha realizado el análisis de complejos sinaptonépticos en espermatocitos de un paciente con oligospermia severa de etiologéa desconocida y portador de un polimorfismo de la heterocromatina paracentrométrica del cromosoma 9. La espermatogénesis del paciente está disminuida en las espermátidas, que presenta anormalidades ultraestructurales en especial en la condensación de la cromatina. En los espermatocitos en paquitene temprano hay un lazo muy visible y asimétrico en el bivalente 9, que en paquitene tardío desaparece frecuentemente, probablemente por un proceso de reajuste sináptico. El lazo es debido a que uno de los elementos es en promedio 7.02% mayor que el otro y que la media de los elementos 9 normales. Esta diferencia indica la presencia de un reordenamiento cromosómico en estado heterocigótico en la región paracentromérica del brazo largo del par 9, que corresponde probablemente a una duplicación en tánden de alrededor del 50% de la zona heterocromática normal. La extensión del lazo sugiere que puede sobrepasar el centrómero y ocupar un segmento del brazo corto. Si bien no es posible asegurar la existencia de una asociación causal entre la anomalía y la hipoespermatogénesis, esta observación se suma a otras sobre inversiones pericéntricas con lazos asinápticos en paquitene, en las cuales hay severa oligospermia o azoospermia. Sobre esta base se sugiere un estudio análogo en otros pacientes portadores de polimorfismos del 9

Recombination nodules, synaptonemal complexes and heterochromatin in the hemipteran Triatoma infestans

Se ha realizdo un estudio cuantitativo de la morfología, número y localización de los nódulos de recombinación (NR) en espermatocitos de Triatoma infestans, y se han correlacionado estos datos con las configuraciones quiasmáticas en diacinesis y en matafase 1. Además se han estudiado las relaciones cuantitativas entre cantidad de heterocromatina y longitud de complejo sinaptonémico (CS). En T. Infestans los três autosomas mayores tienen bloques grandes de heterocromatina, C, que corresponden a 61,4; 64,1 y 35,7% de sus longitudes mitóticas. Los CS correspondientes son proporcionalmente menores a los CS de los otros autosomas. Las ecuaciones de regresión lineal de longitud de CS en función de las longitudes mitóticas muestran una clara diferencia entre los bivalentes que contienen heterocromatina y aquéllos sin ella. Por ello, se propone que la heterocromatina está sub-representada en los CS. Los nódulos de recombinación son esféricos y siempre uno por bivalente. Su localización no es al azar. En los CS 1 y 2 hay una proporción más alta en las regiones mediales; y en el CS 10 hay una proporción alta cerca de los extremos. Los quiasmas de 20 células en diacinesis y 20 células en metafase 1 se clasificaron en intersticiales o terminales. No hay diferencias estadísticas significativas entre las medias de quiasmas terminales en diacinesis y en metafase 1. La distribución de localizaciones quiasmáticas en los bivalentes es similar a la de los nódulos de recombinación. En conclusión, no hay evidencia de un proceso de terminalización quiasmática en esta espécie