四种猕猴属动物精母细胞联会复合体的比较研究

本工作采用去污剂微铺展——硝酸银染色技术研究熊猴、平顶猴、藏酋猴、恒河猴及其亚种毛耳猴的精母细胞联会复合体（SC）核型、SC的结构及其在减数分裂中的行为。结果表明这几种动物的SC核型以及SC的发育过程基本一致。SC的形成开始于偶线期,成熟于粗线期,解体于双线期。在减数分裂前期,性染色体轴呈强嗜银性,配对明显落后于常染色体。根据减数分裂前期性染色体的形态和行为,性染色体的配对可分为五种类型。此外,本文还对XY染色体的同源性和侧轴加粗等现象进行了讨论。     

起源于花药培养的水稻同源不联会三倍体的细胞遗传学研究

本文报道了由花药培养获得的两株同源不联会三倍体水稻减数分裂的染色体行为。观察表明双线期以后的各个时期染色体均无联会发生,在浓缩期及中期Ⅰ呈现出36个单价染色体,表明它们是Asyndetic三倍体。其减数分裂时的异常行为表现在纺锤体在形态及数目上的异常;中期Ⅰ时出现合胞体;四分体时期小孢子,继续分裂;形成从一分体到八分体的异常小孢予;花粉完全败育而不结实。作者联系到稻属三基三倍体杂种F_1(ABC及ACD)减数分裂的染色体行为进行了讨论,并推测在花药培养时发生不联会三倍体的可能途径。     

聚合草的小孢子发生

本文研究了聚合草(Symphytum officinale L.)花粉母细胞减数分裂时染色体的行为。双线期和终变期染色体完全不形成交叉,中期I的染色体大部分以单价体形式存在,少数染色体次级联会。在减数分裂过程中有落后染色体,单价体提早分离,染色体桥,多极分裂与不均等分裂,形成单分体到十分体等不正常的小孢子,作者认为聚合草是一个远缘杂种,减数分裂染色体行为不正常是其不结实的重要原因。并且,观察到两种类型的减数分裂再组,认为聚合草的部分能育性是由于减数分裂再组时产生的不减数配子引起的。     

濒危植物矮沙冬青减数分裂期染色体行为的观察

用涂片法和酶解法,观察了濒危植物矮沙冬青的减数分裂过程。在减数分裂双线期末或终变期初,可以观察到9个二价体,在中期Ⅰ末至后期Ⅰ初,同源染色体基本排列在赤道板上,然后在纺锤丝的牵引下二价体的两条同源染色体分开,分别移向两极,每一极有9条染色体,从而确认该属植物的染色体基数为x=9。在矮沙冬青减数分裂过程中,没有发现染色体有异常行为,认为其小孢子形成过程正常。因此认为矮沙冬青濒危不是染色体行为异常和小孢子发育不正常而造成的。     

草菇减数分裂和担孢子形成细胞核行为

本文用苏木精染色和双苯并咪唑(Hoechst 33258)染色法,从草菇子实体“纽期”菌褶分化完开始,每3小时对同一个子实体连续切取菌褶进行染色观察。结果表明草菇子实体“纽期”菌褶形成时,约10％的担子发生了核配;在子实体发育过程中,尤其是子实体成熟期后,不断有少量新的双核担子产生,并发生核配,使草菇减数分裂的同步性不高;草菇从菌褶分化完成(此时已有10％担子发生核配)到子实体完全成熟,菌褶变成深粉红至褐色(此时约70％担子完成减数分裂)需要28—30小时;担子减数分裂的持续时间为18小时,其中细线期和偶线期5.9小时、粗线期6.2小时、双线期和终变期3.4小时、中期10.5小时、后期Ⅰ到四分体2小时;经过对粗线期、双线和终变期以及中期Ⅰ染色体条数的多次反复观察,认为草菇的染色体条数为11(n=11);减数分裂后,4个子核分别进入4个担孢子中,留下无核的担子;绝大部分担孢子是单核的,有约5％的担孢子是双核的。     

甜瓜花粉母细胞减数分裂及雄配子体的细胞学研究

以薄皮和厚皮类型甜瓜为试材,采用改良的染色体制片方法,系统观察了甜瓜花粉母细胞的减数分裂及雄配子体发育的过程,结果表明:(1)甜瓜细胞核减数分裂的同步性较高,细胞质是同时型分裂,在细胞核分裂的过程中,核仁在前期Ⅰ到中期Ⅰ逐渐消失,在前期Ⅱ再次出现,随后消失,染色体在前期Ⅰ到中期Ⅰ逐渐收缩,变得清晰,至末期Ⅰ变得模糊,在前期Ⅱ再次清晰;(2)2种类型甜瓜终变期的染色体构型都以环状二价体为主;(3)在后期Ⅱ,观察到染色体的垂直和平行2种分离方式;(4)在前期Ⅰ和前期Ⅱ,伽师瓜"形成了多个较小的核仁,呈现一定的特殊性;(5)雄配子体发育经历了单核期和双核期,最后形成了成熟的花粉粒.研究表明,薄皮和厚皮类型甜瓜减数分裂的染色体行为基本一致,没有明显差异;伽师瓜"的核仁数量表现特殊可能与其长期的生态适应性有关.     

紫斑牡丹栽培品种小孢子发育过程的细胞遗传学研究

本文对紫斑牡丹栽培品种的花平细胞减数分裂过程进行了系统研究,结果发现紫斑牡丹品种约６８．９６％的花平细胞在减数分裂过程表现正常,约有３１．０４％的花粉母细胞在减数分裂的比线期、中期Ⅰ、后期Ⅰ、中期Ⅱ、后期Ⅱ及四分体时期观察到染色体行为异常。本实验表明,在小孢子形成过程中,多数小孢子发育政党,但有约３１．０４％的花粉母细胞减数分裂异常,导致了花粉的败育。     

2012年《遗传》第12期封面说明

蝗虫材料易得,染色体大,染色体数目相对较少,双线期和终变期交叉明显,可以用于分析染色体交叉的结构、分布和频率,是观察减数分裂过程中染色体动态变化的理想材料。在蝗虫的曲细精管中同时存在精子发生的3个过程,即精原细胞有丝分裂,初/次级精母细胞减数分裂及精子形成。     

黄瓜花粉母细胞减数分裂行为的研究

研究了华北型、华南型和西南型黄瓜花粉母细胞的减数分裂行为,发现黄瓜细胞核减数分裂的同步性较高,细胞质是同时型分裂。在细胞核分裂的过程中,核仁在前期Ⅰ到中期Ⅰ逐渐消失,在前期Ⅰ再次出现,随后消失;染色体在前期Ⅰ到中期Ⅰ逐渐收缩,变得清晰,至末期Ⅰ解螺旋,变得模糊,在前期I再次清晰。不同生态型黄瓜终变期的染色体构型均以环状二价体为主。在前期Ⅰ和前期Ⅰ,西双版纳黄瓜的核仁都相应地比另外两种生态型黄瓜品种的多,在后期Ⅰ还偶尔出现染色体桥,显示了西双版纳黄瓜变种的特殊性。研究还发现寒冷的气候条件下栽培黄瓜都能够形成高频率的多分体,推测其形成很可能与低温逆境有关。     

普通小麦联会复合体发育过程的电镜观察

以改进的去污剂微铺展技术制备普通小麦减数分裂联会复合体标本,并对联会复合体发育的全过程作了详细的电镜观察和描述。结果表明,小麦SC以多点式起始方式于偶线期开始形成;随SC的发育,新的SC形成和已有SC片断的延伸并存;此外,在同一核内不同二价体之间,染色体配对和SC形成并不同步;SC成熟于粗线期,而以破碎方式解体,消失于双线期。在偶线期还观察到由同祖配对形成的多价体,但在随后阶段中这些多价体消失。对Ph基因的可能作用机制作了分析和讨论。     

Synaptonemal complexes in insects

The synaptonemal complex (SC) is the key nuclear element formed in meiotic prophase I to join 2 homologous chromosomes at the pachytene bivalent. It is a highly conserved structure that is universally present in eukaryotes. The SC is presented as a tripartite protein structure, which consists of 2 lateral elements and a central region. In insects, the central region is particularly distinct and highly ordered. This made it possible to describe the fine structure of the central region and propose a model of its architecture. Chromatid DNA is arranged in chromatin loops extending radially from the SC. The loops appear to consist of a basic chromatin fiber with a diameter of 20–30 nm. In many insect species, synaptonemal polycomplexes occur in postpachytene cells. They represent one of the possible ways of SC degradation. Another process, which occurs beyond pachytene, is the formation of proteinaceous chromatid axis, the silver-stained chromatid core. Based on results in insect models, the chromatid cores have been related to the structure and formation of the SC. Research on insect models significantly contributed to understanding individual steps of the SC formation and temporal sequence of chromosome pairing. These include the formation of lateral elements of the SC, pairing initiation, interlocking of chromosomes, and synapsis of homologous chromosomes. Attention is also given to non-homologous pairing, including synaptic adjustment, correction of pairing, and pairing of sex chromosomes. In the next section, chiasmatic and achiasmatic modes of meiosis are compared with respect to the SC formation. In the chiasmatic mode, the SCs display recombination nodules that are believed to mediate the process of recombination. These nodules were discovered in insects, and indirect evidence for their role comes from insects. Two different examples of achiasmatic meiosis, occurring in the heterogametic sex of several insect orders, are given: one involves the SC formation, whereas in the other, SCs are absent. Finally, the potential of SC karyotyping for analysis of the insect genome is discussed.     

Meiotic chromosome structure. Kinetochores and chromatid cores in standard and B chromosomes of Arcyptera fusca (Orthoptera) revealed by silver staining.

The behaviour of two chromosome structures in silver-stained chromosomes was analyzed through the first meiotic division in spermatocytes of the acridoid species Arcyptera fusca. Results showed that at diakinesis kinetochores and chromatid cores are individualized while they associate in bivalents of metaphase I; only kinetochores and distal core spots associate in the sex chromosome. Metaphase I is characterized by morphological and localization changes of both kinetochores and cores which define the onset of anaphase I. These changes analyzed in both autosomes and in the sex chromosome allow us to distinguish among three different substages in metaphase I spermatocytes. B chromosomes may be present as univalents, bivalents, or trivalents. Metaphase I B univalents are characterized by separated cores except at their distal ends and individualized and flat sister kinetochores. At anaphase I sister kinetochores of lagging B chromatids remain connected through a silver-stained strand. The behaviour of cores and kinetochores of B bivalents is identical with that found in the autosomal bivalents. The differences in the morphology of kinetochores of every chromosome shown by B trivalents at metaphase I may be related to the balanced forces acting on the multivalent. The results show dramatic changes in chromosome organization of bivalents during metaphase I. These changes suggest that chromatid cores are not involved in the maintenance of bivalents. Moreover, the changes in morphology of kinetochores are independent of the stage of meiosis but correlate with the kind of division (amphitelic-syntelic) that chromosomes undergo.     

Immunocytology of chiasmata and chromosomal disjunction at mouse meiosis

Immunocytological and in situ hybridization evidence supports the hypothesis that at meiosis of chiasmate organisms, chromosomal disjunction and reductional segregation of sister centromeres are integrated with synaptonemal complex functions. The Mr 125,000 synaptic protein, Syn1, present between cores of paired homologous chromosomes during pachytene of meiotic prophase, is lost from synaptonemal complexes coordinately with homolog separation at diplotene. Separation is constrained by exchanges between non-sister chromatids, the chiasmata. We show that the Mr 30,000 chromosomal core protein, Cor1, associated with sister chromatid pairs, remains an axial component of post-pachytene chromosomes until metaphase I. We demonstrate that at this time the chromatin loops are still attached to their cores. A reciprocal exchange event between two homologous non-sister chromatids is therefore immobilized by anchorage of sister chromatids to their respective cores. Cores thus contribute to the sister chromatid cohesiveness required for maintenance of chiasmata and proper chromosomal disjunction. Cor1 protein accumulates in juxtaposition to pairs of sister centromeres during metaphase I. Presumably, independent movement of sister centromeres at anaphase I is restricted by Cor1 anchorage. That reductional separation of sister centromeres is mediated by Cor1, is supported by the dissociation of Cor1 from separating sister centromeres at anaphase II and by its absence from mitotic anaphases.     

Localization and development of kinetochores and a chromatid core during meiosis in grasshoppers

Positive staining of kinetochores and a chromatid core has been achieved using a simplified silver staining method in squash preparations from meiotic chromosomes of grasshoppers. This technique permits the exact localization of kinetochores on the chromosomes whether metacentric, acrocentric or ‘telocentric’. The sister kinetochores can be observed from mid-diplotene stages but they are not differentiated during first meiotic metaphase. However they can be observed again at the onset of anaphase 1. The existence of a positively stained chromatid core in meiotic divisions is also reported. This core appears well defined inside each chromatid from diplotene to the end of the second meiotic division. The visualization of these cores in first meiotic metaphase clearly shows the points at which the chiasmata took place.     

红翅皱膝蝗减数分裂染色体的螺旋与轴结构

用低渗处理和苯酚品红染色,在经过卡诺液(甲醇3∶冰醋酸1)固定和未经固定的红翅皱膝蝗减数分裂染色体上都看到了螺旋结构。观察和测量结果表明,每条染色单体都是由430nm左右的染色线螺旋形成的。由染色线到染色体的压缩率为4∶1。低渗处理后固定的材料经过银染,则显示了染色体轴结构。同样,未经低渗处理直接固定的材料银染时也出现了轴结构。银染的轴结构位于每个染色单体的中央,并贯穿整个染色单体。在光镜下,这个轴并不是直径均一的棒状结构,而似乎是由许多大小相近的颗粒相连而成。本文对染色体结构的有关模型、骨架和轴结构的真实性以及轴和螺旋的关系等问题进行了讨论。     

Involvement of chromatid cohesiveness at the centromere and chromosome arms in meiotic chromosome segregation: A cytological approach

Kinetochores and chromatid cores of meiotic chromosomes of the grasshopper species Arcyptera fusca and Eyprepocnemis plorans were differentially silver stained to analyse the possible involvement of both structures in chromatid cohesiveness and meiotic chromosome segregation. Special attention was paid to the behaviour of these structures in the univalent sex chromosome, and in B univalents with different orientations during the first meiotic division. It was observed that while sister chromatid of univalents are associated at metaphase I, chromatid cores are individualised independently of their orientation. We think that cohesive proteins on the inner surface of sister chromatids, and not the chromatid cores, are involved in the chromatid cohesiveness that maintains associated sister chromatids of bivalents and univalents until anaphase I. At anaphase I sister chromatids of amphitelically oriented B univalents or spontaneous autosomal univalents separate but do not reach the poles because they remain connected at the centromere by a long strand which can be visualized by silver staining, that joins stretched sister kinetochores. This strand is normally observed between sister kinetochores of half-bivalents at metaphase II and early anaphase II. We suggest that certain centromere proteins that form the silver-stainable strand assure chromosome integrity until metaphase II. These cohesive centromere proteins would be released or modified during anaphase II to allow normal chromatid segregation. Failure of this process during the first meiotic division could lead to the lagging of amphitelically oriented univalents. Based on our results we propose a model of meiotic chromosome segregation. During mitosis the cohesive proteins located at the centromere and chromosome arms are released during the same cellular division. During meiosis those proteins must be sequentially inactivated, i.e. those situated on the inner surface of the chromatids must be eliminated during the first meiotic division while those located at the centromere must be released during the second meiotic division.by D.P. Bazett-Jones     

Differential immunolocalization of a putative Rec8p in meiotic autosomes and sex chromosomes of triatomine bugs

Hemipteran chromosomes are holocentric and show regular, special behavior at meiosis. While the autosomes pair at pachytene, have synaptonemal complexes (SCs) and recombination nodules (RNs) and segregate at anaphase I, the sex chromosomes do not form an SC or RNs, divide equationally at anaphase I, and their chromatids segregate at anaphase II. Here we show that this behavior is shared by the X and Y chromosomes of Triatoma infestans and the X(1)X(2)Y chromosomes of Triatoma pallidipennis. As Rec8p is a widely occurring component of meiotic cohesin, involved in meiotic homolog segregation, we used an antibody against Rec8p of Caenorhabditis elegans for immunolocalization in these triatomines. We show that while Rec8p is colocalized with SCs in the autosomes, no Rec8p can be found by immunolabeling in the sex chromosomes at any stage of meiosis. Furthermore, Rec8p labeling is lost from autosomal bivalents prior to metaphase I. In both triatomine species the sex chromosomes conjoin with each other during prophase I, and lack any SC, but they form "fuzzy cores", which are observed with silver staining and with light and electron microscopy during pachytene. Thin, serial sectioning and electron microscopy of spermatocytes at metaphases I and II reveals differential behavior of the sex chromosomes. At metaphase I the sex chromosomes form separate entities, each surrounded by a membranous sheath. On the other hand, at metaphase II the sex chromatids are closely tied and surrounded by a shared membranous sheath. The peculiar features of meiosis in these hemipterans suggest that they depart from the standard meiotic mechanisms proposed for other organisms.     

Meiotic sister chromatid cohesion in holocentric sex chromosomes of three heteropteran species is maintained in absence of axial elements

It has been suggested that in species with monocentric chromosomes axial element (AE) components may be responsible for sister chromatid cohesion during meiosis. To test this hypothesis in species with holocentric chromosomes we selected three heteropteran species with different sex-determining mechanisms. We observed in surface-spreads and sections using transmission electron microscopy that the univalent sex chromosomes form neither AEs nor synaptonemal complexes (SCs) during pachytene. We also found that a polyclonal antibody recognizing SCP3/Cor1, a protein present at AEs and SC lateral elements of rodents, labels the autosomal SCs but not AEs or SC stretches corresponding to the sex chromosomes. Cytological analysis of the segregational behaviour of the sex univalents demonstrates that although these chromosomes segregate equationally during anaphase I they never show precocious separation of sister chromatids during late prophase I or metaphase I. These results suggest that AEs are not responsible for sister cohesion in sex chromosomes. The segregational behaviour of these chromosomes during both meiotic divisions also indicates that different achiasmate modes of chromosome association exist in heteropteran species. Received: 22 September 1999; in revised form: 20 December 1999 / Accepted: 21 December 1999     

Synaptonemal complex damage in relation to meiotic chromosome aberrations after exposure of male mice to cyclophosphamide

The genetic implications of induced synaptonemal complex (SC) damage are not known. However, on theoretical grounds, such aberrations could be involved in mechanisms leading to potentially heritable defects. Cyclophosphamide (CP), a chemical reported to cause structural and numerical chromosomal aberrations in the mouse, was used to determine if SC damage observed in meiotic prophase is related to subsequent metaphase chromosomal aberrations. Male mice were injected i.p. with CP. In some instances, mice were also injected simultaneously with tritiated thymidine to label DNA so that cells could be tracked autoradiographically through spermatogenesis. Prophase, primary metaphase (M1), and secondary metaphase (M2) samples were sequentially harvested at appropriate times from the same individual, and nuclei were examined for aberrations. Correlation coefficients between SC and metaphase chromosome aberrations were calculated. The inclusion of tritium labeling increased the number and significance of positive correlations. Positive correlations were found between (1) dose-dependent total SC damage and damage to M1, and to a lesser extent, M2 chromosomes; (2) SC breaks/fragments and M1 chains/rings as well as isochromatid breaks/fragments; (3) SC asynapsis and M1 chromatid breaks/fragments; (4) SC multi-axial configurations and M1 chains/rings as well as isochromatid and chromatid breaks/fragments; and (5) SC multi-axial configurations and M2 hyperploidy. These correlations do not define mechanistic or causal relationships between SC and chromosomal damage. However, taken together with the observation that induced SC damage is many times greater than ensuing metaphase chromosome damage, they substantiate SC analysis as a highly sensitive indicator of potentially heritable effects of this (and presumably other) genotoxic agents.     

The distribution of synaptonemal complex material in metaphase I bivalents of Locusta and Chloealtis (Orthoptera: Acrididae)

At metaphase I synaptonemal complex (SC) material is located in a continuous but irregularly shaped bundle between sister chromatids. Only at the site of a chiasma is it present between homologous chromosomes. When the chromosomes pull apart at anaphase I the SC material becomes rearranged into poly-SCs which dissociate from the chromosomes. The observations agree with previous reports that modified SCs may function in meiotic chromosome disjunction.