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.
Animals ; Chromosome Segregation ; Meiosis/physiology* ; Synaptonemal Complex/physiology*

OBJECTIVETo analyze defective homologous chromosomal recombination in Han Chinese azoospermic patients.

METHODSTesticular 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.

RESULTSRespectively, 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.

CONCLUSIONDelayed 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.

Adult ; Asian Continental Ancestry Group ; Azoospermia ; genetics ; metabolism ; pathology ; Humans ; Male ; Meiosis ; genetics ; Middle Aged ; Recombination, Genetic ; Spermatocytes ; metabolism ; Synaptonemal Complex ; genetics ; Young Adult

In this study, the embryological characters of Pterocypsela formosana (Asteraceae) were investigated with the traditional paraffin section methods. The anther has 4 sporangiates, the anther wall development follows the dicotyledonous type and comprises of an epidermis, endothelium, a middle layer and a single-layered tapetum, the tapetum belongs to glandular type. Meiosis of the microspore mother cells is of the simultaneous type, for the formation of mostly tetrahedral tetrad, the mature pollen grains are 2 celled. The ovary is bicarpellate, unilocular, one ovule and basal placenta, the ovule is unitegmic, tenuinucellate, inverted campylotropous and with developed endothelium, archesporial cell of megaspore differentiates immediately below the nucellar epidermis and functions as megasporocyte after development and belongs to tenuinucellate ovule type. The megasporocyte undergoes meitotic to form a liner tetrad, only one chalazal megaspore becomes the functional megaspore which forms female gametophyte including 7-celled and 8-nucleated after three successive mitosis, the female gametophyte is of the Polygonum type. Two polar nuclei melt into a secondary nuclei before fertilization, the chalazal antipodal cells are ephemeral and degenerate shortly after forming. Fertilization is porogamous and belongs to premitotic type of syngamy. The division of the primary endosperm nucleus is earlier than the zygote, the endosperm is of the nuclear type with the presence of haustoria, and the embryogeny belongs to asterad type chicory variant. The developed suspensor on early stage has important significance to the embryo development.
Asteraceae ; embryology ; Meiosis ; Reproduction

Humans ; Meiosis/physiology* ; Mitosis/physiology*

Adult ; Chromatids/genetics* ; Chromosome Aberrations ; Humans ; Infertility, Male/genetics* ; Male ; Meiosis ; Metaphase/genetics* ; Spermatocytes/physiology*

OBJECTIVE: Previously, we identified that transketolase (Tkt), an important enzyme in the pentose phosphate pathway, is highly expressed at 2 hours of spontaneous maturation in oocytes. Therefore, this study was performed to determine the function of Tkt in meiotic cell cycle regulation, especially at the point of germinal vesicle breakdown (GVBD). METHODS: We evaluated the loss-of-function of Tkt by microinjecting Tkt double-stranded RNAs (dsRNAs) into germinal vesicle-stage oocytes, and the oocytes were cultured in vitro to evaluate phenotypic changes during oocyte maturation. In addition to maturation rates, meiotic spindle and chromosome rearrangements, and changes in expression of other enzymes in the pentose phosphate pathway were determined after Tkt RNA interference (RNAi). RESULTS: Despite the complete and specific knockdown of Tkt expression, GVBD occurred and meiosis was arrested at the metaphase I (MI) stage. The arrested oocytes exhibited spindle loss, chromosomal aggregation, and declined maturation promoting factor and mitogen-activated protein kinase activities. The modified expression of two enzymes in the pentose phosphate pathway, Prps1 and Rbks, after Tkt RNAi and decreased maturation rates were amended when ribose-5-phosphate was supplemented in the culture medium, suggesting that the Tkt and pentose phosphate pathway are important for the maturation process. CONCLUSION: We concluded that Tkt and its associated pentose phosphate pathway play an important role in the MI-MII transition of the oocytes' meiotic cell cycle, but not in the process of GVBD.
Cell Cycle ; Maturation-Promoting Factor ; Meiosis ; Metaphase ; Oocytes ; Pentose Phosphate Pathway ; Protein Kinases ; Ribosemonophosphates ; RNA Interference ; RNA, Double-Stranded ; Transketolase

OBJECTIVE: Oocyte-specific homeobox 4 (Obox4) is preferentially expressed in oocytes and plays an important role in the completion of meiosis of oocytes. However, the Obox4 expression pattern has not been reported yet. In this study, we investigated the subcellular localization of Obox4 using a green fluorescent protein (GFP) fusion expression system. METHODS: Three regions of Obox4 were divided and fused to the GFP expression vector. The partly deleted homeodomain (HD) regions of Obox4 were also fused to the GFP expression vector. The recombinant vectors were transfected into HEK-293T cells plated onto coated glass coverslips. The transfected cells were stained with 4',6-diamidino-2-phenylindol and photographed using a fluorescence microscope. RESULTS: Mutants containing the HD region as well as full-length Obox4 were clearly localized to the nucleus. In contrast, the other mutants of either the N-terminal or C-terminal region without HD had impaired nuclear localization. We also found that the N-terminal and C-terminal of the Obox HD contributed to nuclear localization and the entire HD was necessary for nuclear localization of Obox4. CONCLUSION: Based on the results of the present study, we demonstrated that the intact HD region of Obox4 is responsible for the nuclear localization of Obox4 protein in cells.
Fluorescence ; Genes, Homeobox ; Glass ; Meiosis ; Oocytes

OBJECTIVE: The aims of this study were to investigate whether fertilization could induce the resumption of meiosis in mouse oocytes arrested at metaphase I (MI) after in vitro maturation (IVM), and to investigate the effect of Ca²⁺ chelator treatment at the time of fertilization on the transition from MI to metaphase II (MII). METHODS: MII-stage and arrested MI-stage mouse oocytes after IVM were fertilized, and then embryonic development was monitored. Blastocysts from each group were transferred into 2.5 days post-coitum pseudo-pregnant ICR mice. MI oocytes after IVM were treated with a Ca²⁺ chelator to investigate the effect of Ca²⁺ oscillations on their maturation. RESULTS: As insemination time increased, the number of oocytes in the MI group that reached the MII stage also increased. The blastocyst rates and total cell numbers in the MII group were significantly higher than in the MI group. No pregnancy occurred in the MI group, but 10 pregnancies were achieved (10 of 12) in the MII group. The proportion of MI oocytes that matured to MII oocytes after fertilization was significantly higher in the non-treated group than in the Ca²⁺ chelator-treated group. CONCLUSION: The findings that a higher proportion of MI-arrested oocytes progressed to MII after fertilization and that the MI-to-MII transition was blocked by Ca2+ chelator treatments before fertilization indicate that the maturation of MI oocytes to MII oocytes is associated with intracellular Ca²⁺ oscillations driven by fertilization.
Animals ; Blastocyst ; Calcium Signaling ; Cell Count ; Embryonic Development ; Female ; Fertilization ; In Vitro Oocyte Maturation Techniques ; In Vitro Techniques* ; Insemination* ; Meiosis ; Metaphase* ; Mice* ; Mice, Inbred ICR ; Oocytes* ; Pregnancy ; Spermatozoa*

Retinoic acid (RA) is an oxidative metabolite of vitamin A (retinol, ROH) and plays an important role in the spermatogenesis (as in meiosis) of mammals. In mammalian testes, RA, in combination with its retinoic acid receptor (RAR), regulates the expressions of related target genes in various types of cells at different times. It activates meiosis by up-regulating the expressions of the genes that promote meiosis and down-regulate those that inhibit it during spermatogenesis in a specific stage. The results of researches on mammalian spermatogenesis have a great application value in reproductive biology, developmental biology, and reproductive engineering. Therefore, it is of considerable significance to study the signaling pathway of RA-induced meiosis during mammalian spermatogenesis. This article presents an introduction of the RA signal transduction system and its action mechanisms, as well as an overview on the signaling pathway of RA-activated meiosis during spermatogenesis.
Animals ; Humans ; Male ; Meiosis ; Signal Transduction ; Spermatogenesis ; Tretinoin ; metabolism

The development of female germ cells can be mainly divided into two stages: fetal germ cells and oocytes in folliculogenesis after puberty. Mitosis-meiosis transition, meiosis arrest and re-activation are the key phases of the development. Several phases may be characterized by their distinct molecular events, which involve precise regulation of gene expression and interaction with corresponding gonadal niche cells. In recent years, single-cell transcriptome studies have clarified phase-specific patterns of gene expression, signaling pathways and epigenetic modification during oogenesis and folliculogenesis. These works have provided important insights into the development of female germ cells and pathogenesis of germ-cell related diseases, which may promote clinical application of reproductive genetic research.
Female ; Germ Cells ; Humans ; Meiosis ; Oocytes ; Oogenesis/genetics* ; Signal Transduction