The morphological sequence of XY pairing in the Norway rat Rattus norvegicus

The sequence of XY pairing at meiotic prophase in the Norway rat, Rattus norvegicus, has been studied in spread preparations of spermatocytes obtained from pubertal males. As in most mammals, sex chromosome pairing is delayed in relation to that of the autosomes. At one stage in pachytene, the Y is fully paired in synaptonemal complex association with about one-third of the X. Observation in spread preparations at pachytene and diplotene and in air-dried metaphase I preparations indicates that the long arm of the Y pairs with the short arm of the X. Pairing of the Y with both ends of the X is seen in about 4% of pachytene spermatocytes. The possibility that XY pairing in the rat may be nonhomologous (Ashley 1983) is considered, and the view is expressed that the XY synaptonemal complex may be incomplete in fine structural detail, thus not providing for the effective pairing required in true reciprocal recombination. The same mechanism that excludes crossing over from heterochromatic regions of autosomes may also operate to minimize or prevent crossing over in the sex pair of mammals.     

Meiosis in a sterile male mouse with an isoYq marker chromosome

A male mouse with a metacentric Y chromosome of twice the normal size has been studied chromosomally in bone marrow mitoses, spermatogonial mitoses, and diakinesis-metaphase I primary spermatocytes. A low frequency of nondisjunction for this chromosome (2%) was noted in both bone marrow and spermatogonial mitoses. In spermatogonial mitoses, loss of the Y chromosome had occurred to the extent that 12% of spermatogonia were XO, resulting in 17% XO primary spermatocytes. Hardly any stages beyond the primary spermatocyte stage were encountered, which agrees with testis weights of approximately 30% of normal. Surface-spread pachytene spermatocytes yielded few cells that were analyzable for their total complement of synaptonemal complexes. The Y chromosome showed complete fold-back pairing and was located far away from the X chromosome. X and Y chromosomes were paired in 14.5% of the diakinesis-MI spermatocytes that contained a Y chromosome. The origin of this chromosome is discussed against the background of localization of the gene for the testis-determining factor on the short arm of the mouse Y chromosome.     

Immunocytochemical labelling of the kinetochore of human synaptonemal complexes,and the extent of pairing of the X and Y chromosomes

An immunocytochemical method was used to label the kinetochores on human synaptonemal complexes. Synaptonemal complex spreads were labelled with autoimmune CREST serum, followed by a second antibody labelled with colloidal gold, and examined by electron microscopy. Clusters of gold particles were found at discrete sites which were identified as kinetochores on the autosomal synaptonemal complexes, as well as on the XY pair. This method was used to investigate the extent of pairing of the human X and Y chromosomes at pachytene. Our observations confirm earlier work, based purely on measurements, that the pairing of the sex chromosomes sometimes extends beyond the centromere of the Y chromosome into the long arm. At the same time we showed that the centromeric indices of the X and Y at pachytene are highly variable, so that measurements alone are not sufficient to estimate the degree of pairing of the sex chromosomes.     

Heterochromatin and nucleolus-organizer-region behaviour at male pachytene of Sus scrofa domestica

In the domestic pig (2n=38) two types of constitutive heterochromatin can be differentiated by fluorescence counterstaining techniques. All 24 biarmed autosomes and the X chromosome have chromomycin A₃-positive centromeric C-bands, whereas all 12 acrocentric chromosomes exhibit DA-DAPI-positive centromeric heterochromatin. Fluorescence analysis of male pachytene nuclei revealed that the DA-DAPI-positive C-bands form one or two large chromocentres per cell, while the chromomycin A₃-bright C-material is well scattered. Hence, the bivalents formed by the acrocentric chromosome pairs are centromerically associated, whilst the submetacentric bivalents are not. —Counce-Meyer spreading techniques were used to study the structure of synaptonemal complexes (SCs) both by light and electron microscopy. In general, the SCs of the domestic pig resemble those described for other mammals. The SC formed by the X and the Y may include up to 94.5% of the Y chromosome. In silver-stained microspreads each of the bivalents (nos. 8 and 10) bearing the nucleolus-organizer-regions (NORs) is connected to a pair of nucleoli, indicating that all four NORs are active during early meiotic stages. By contrast, in the majority of mitotic metaphases of phytohaemagglutinin-stimulated lymphocytes only one pair (no. 10) exhibited Ag-NOR staining. — The significance of the chromosome disposition in the pachytene nucleus is discussed with regard to heterochromatin composition and karyotype evolution.This paper is dedicated to Prof. Hans Bauer on the occasion of his 80th birthday     

Ultrastructure and behavior of the achiasmatic,telosynaptic XY pair of the sand rat (Psammomys obesus)

The behavior of the X and Y chromosomes in somatic and testicular cells of the sand rat (P. obesus) has been investigated with light and electron-microscope procedures. The Y chromosome has been identified as the fourth longest of the complement, both by C-banding and by its meiotic behavior. The X chromosome is the longest of the complement and carries two major C-heterochromatic blocks, one in the distal part of the long arm and the other forming most of the short arm. During presynaptic stages in spermatocytes, separate C-heterochromatic blocks, representing the sex chromosomes, are observed in the nuclei. An XY body is regularly formed at pachytene. During first meiotic metaphase the X and Y chromosomes show variable associations, none of them chiasmatic. Second meiotic metaphases contain, as in other mammals, a single sex chromosome, suggesting normal segregation between the X and the Y. — Electron microscopic observations of the autosomal synaptonemal complexes (SCs) and the single axes of the X and Y chromosomes during pachytene permit accurate, statistically significant identification of each of the largest chromosomes of the complement and determination of the mean arm ratios of the X and Y axes. The X and Y axes always lie close to each other but do not form a SC. The ends of the X and Y axes are attached to the nuclear envelope and associate with each other in variable ways, both autologously (X with X or Y with Y) and heterologously (X with Y), with a tendency to form a maximum number (four) of associated ends. Analysis of 36 XY pairs showed no significant preference for any single specific attachment between arm ends. The eighth longest autosomal bivalent is frequently partially asynaptic during early pachytene, and only at that time is often near or touching one end of the X axis. — It is concluded that while axis formation and migration of the axes along the plane of the nuclear envelope proceed normally in the X and Y chromosomes, true synapsis (with SC formation) does not occur because the pairing region of the X chromosome has probably been relocated far from the chromosome termini by the insertion of distal C-heterochromatic blocks.     

The pachytene synaptonemal complex complement of the cat

Surface spreads of pachytene spermatocyte nuclei from two cats were used to construct a synaptonemal complex karyotype for the cat. It was possible to recognise the 18 autosomal synaptonemal complexes by reference to a published light microscopic banded somatic karyotype. Some variation from the somatic karyotype was noted, presumably as a result of differential contraction during prophase I. The X and Y chromosome axes were joined by a synaptonemal complex in many of the nuclei, but the structure of the unpaired portion of the X axis was quite variable. In some nuclei it was highly contracted, while in others it was extended and often was split into two or more axes. In most nuclei the autosomal synaptonemal complexes had numerous axial twists.     

棕色田鼠罗伯逊易位的研究（简报）

The type of chromosome No. 1 and chromosome number from 53 individuals of Microtus mandarinus have been studied and compared in three sex types: XY, XX, XO. We found that the first pair of autosomes are very unstable, and there are three types: (1) M, M (With a double metacentric chromosome), (2) M, T, T, (With single metacentric chromosome). (3) T, T, T, T (Without metacentric chromosome). The chromosome number of the same sex individuals changes regularly with the type change of chromosome No. 1, that is, the increase of one chromosome in 2n number is always accompanied by the increase of two T and the decrease of one M, and vice versa. The synaptonemal complexes (SCs) of spermatocyte in pachytene nuclei from the males (2n = 51) were analysed by the electron microscopy. The SCs studies demonstrate that there are 23 fully paired autosomal bivalents, XY-bivalent and an autosomal trivalent. This trivalent is formed by one metacentric and two telocentric elements and characterized by the presence of two short side-arms. Meanwhile, all trivalents are in a cis configuration. The study of G-banding also demonstrates that the No. 1 autosome polymorphism is caused by Robertsonian translocation. Robertsonian fission is the main reason of the polymorphism of chromosome No. 1 and of variation of chromosome number in M. mandarinus.     

棕色田鼠罗伯逊易位的研究(简报)

棕色田鼠(Microtus mandarinus Milne-Edwards,1871)又称北方田鼠,主要分布于我国。前苏联、蒙古的少数地区亦有分布,前苏联学者称该鼠为中国田鼠。关于该鼠的染色体研究国内外已有报道。仅推测罗伯逊易位是引起该鼠第一对常染色体多态及其染色体数目多态的主要原因。本文详细研究了该鼠第一对常染色体多态类型与个体染色体数目之间的一一对应关系、性个体(2n=51)的G带带型及其联会复合作中三价体的存在,完全证实了     

Meiosis in gray voles of the subgenus microtus (rodentia, arvicolinae) and in their hybrids

The results of light and electron microscopic (EM) studies of meiosis in Microtus arvalis males of the karyoform "arvalis" (2n = 46, NFa = 80), in hybrids between the chromosomal forms arvalis and obscurus (2n = 46, NFa = 68), in M. rossiaemeridionalis voles (2n = 54, NFa = 54), and in a hybrid between the species M. rossiaemeridionalis and M. kermanensis (2n = 54, NFa = 54) are presented. SC (synaptonemal complex) karyotypes of the parental forms and the hybrids were constructed on the basis of measurements of the length ofautosomal SCs revealed by the EM analysis in spermatocytes at the stage of middle pachytene. The SC karyotypes of M. arvalis and the hybrids female obscurus x male arvalis consist of 22 synaptonemal complexes of autosomal bivalents and the axial elements of the synaptonemal complexes of the sex chromosomes X and Y. The SC karyotypes of M. rossiaemeridionalis and the hybrid M. rossiaemeridionalis x M. kermanensis consist of 26 synaptonemal complexes of autosomal bivalents and a sex bivalent; they differ only in the length of the Y chromosome axis (Y chromosome in the hybrid was inherited from M. kermanensis). Asynaptic configurations of the autosomal SCs were not observed in the hybrids. The SC axial elements of the X and Y chromosomes in the parental forms and in the hybrids were located close to each other throughout pachytene, but they did not form a synaptic region. The normal synapsis in sterile hybrids (M. rossiaemeridionalis x M. kermanensis) and the behavior of the sex chromosomes in meiosis in fertile and sterile hybrids are discussed in the context of specific features of meiosis and reproductive isolation.     

Silver-Stained accessory structures on human sex chromosomes

Summary Using a combination of silver-staining and light microscopic techniques on human male meiotic preparations, it is feasible to study the morphology and behavior of both autosomal synaptonemal complexes and sex chromosome axes. During leptotene and early zygotene, the X and Y chromosomes are separate; their axes appearing as thin, filamentous structures. During late zygotene/early pachytene, the sex chromosomes come close to each other and a distinct sex vesicle is formed. We confirm the existence of a short synaptonemal complex between the terminal ends of the X and Y chromosomes. In our preparations, a number of accessory structures can be seen along the axes of the sex chromosomes. These structures appear to be similar in morphology to those previously observed in several other mammalian species.     

江豚的染色体核型研究

江豚(Neophocaena phocaenoides)是鲸目(Cetacea)鼠海豚科(Phocaenidae)的一种小型齿鲸,在淡水和海洋中均有分布。关于江豚染色体的研究,国外文献中尚未见记载,国内亦无报道。Pilleri和Gihr(1972,1975)根据江豚的形态解剖学的研究,认为我国产的江豚和印度洋的及日本海的江豚不属同一个种,但国际上对此尚有不同意见。因此,搞清江豚染色体的核型,将可有助于澄清江豚属的的分类问题。本文就我国长江产江豚的染色体核型作初步探讨。     

Morphology and behavior of the sex chromosomes in meiosis in four vole species of the genus Microtus]

Morphology and behaviour of the X and Y chromosomes of four species of genus Microtus were studied at pachytene, metaphase I and meiotic metaphase. The X chromosomes of the species varied with respect to their size and location of heterochromatic blocks. The axes of X and Y chromosomes of these species as well as Microtus agrestis never formed true synaptonemal complexes at any sub-stage of the pachytene. They approached each other at the start of the pachytene throughout to metaphase I, getting situated closely. At the end of the pachytene, they formed sex vesicle. The X and Y chromosomes kept their proximity during metaphase I, but never formed true bivalents. It is suggested that lack of synapsis of the X and Y chromosomes in the genus Microtus is the final step of evolutionary trend to reduction of the size of the pseudo-autosomal region. The abolition of restrictions on homology between the X and Y chromosomes is supposed to be a cause for the fast divergence in morphology of sex chromosomes in the genus.     

Dependence on genic balance for synaptonemal complex formation in Drosophila melanogaster

Electron microscopic examination of gonads of Drosophila melanogaster with different genotypes, including a metafemale 3X;2A and an intersex XXY;3A have revealed that the formation of synaptonemal complexes is controlled by the genic balance, i.e., the ratio of X chromosomes to autosomes. The Y chromosome is not involved in the genetic control of the formation of precursors of the central element of synaptonemal complexes in males, nor does it disturb their formation in XXY females. Hyperploidy for sections 1-3A and 18A-20 of the X chromosome does not lead to the appearance of synaptonemal complexes in males and does not interfere with their formation in females. Females hyperploid for extensive regions of the X chromosome (sections 1-11A, 11A-20, and 8C-20) are fertile and show apparently normal formation of synaptonemal complexes. Hyperploidy for sections 8C-11A of the X results in a sharp decrease in the viability of females, in abnormal differentiation of ovary cells, and in the lack of synaptonemal complexes. These data suggest a possible important role for the sections 8C-11A in the genic balance controlling the formation of synaptonemal complexes in D. melanogaster. The lack of synaptonemal complexes in hypoploid females may be the result of abnormal cell differentiation in gonads.     

中国刺猬的染色体研究

本文采用全血培养和骨髓染色体制片法,对分布于我国南京市郊和济南市郊的刺猬染色体进行了组型、C-带、G-带和银染色的观察分析,并与东欧、西欧两种刺猬比较,它们之间的核型及带型差异显著;又将南京、济南及金清波(1985)报道的河南新乡三地分布的刺猬进行比较,它们的核型及带型也显示出一定差异,这种多态性在分类和进化上有一定的意义。     

臭鼩染色体的研究

本文采用骨髓染色体制片法,对捕自我国浙江萧山市的臭鼩进行了组型、G-带、C-带和核仁组织区银染的观察分析。结果表明,我国臭鼩染色体数目为2n=40,组型为8(m)+2(sm)+10(st)+18(t),性染色体为,(?):X(m或sm),Y(m或sm);♀:XX(m或sm)。G-带较为丰富,每一对染色体都有其特定的带型,较易于辨别与配对。在C-带方前,4对中间着丝粒染色体与5对亚端着丝粒染色体均具有不同程度的着丝粒带,1对亚中着丝粒染色体与9对端着丝粒染色体缺乏C-带物质,性染色体具丰富的远端带及中间带.银染的结果显示,第5、12和13对染色体具银染物质。     

Electron microscopic observations on the synaptonemal complex of spermatocytes of the Giant Panda (Ailuropoda melanoleuca)

Surface-spread and silver-stained preparations of spermatocytes from a giant panda were observed by electron microscopy for synaptonemal complex karyotyping. Ten pachytene spermatocyte nuclei were selected for length quantitation of SC. The mean relative lengths and centromeric indices of each SC agreed closely with those of the mitotic chromosomes. The pairing between lateral elements of autosomal chromosomes starts at early zygotene and leads progressively along their length to complete pairing at pachytene. The whole Y is paired with 1/3 length of X at mid-pachytene. The morphology of X and Y chromosome axes and the nonhomologous pairing of X and Y is discussed.