Ultrastructure of induced transitions in the chromatin organization of Drosophila polytene chromosomes

The structural changes taking place in the salivary chromosomes of Drosophila melanogaster after treatment with urea-sodium hydroxide solution were studied by light and electron microscopy. An essential effect of the treatment is the gradual disappearance of the chromosomal banding pattern due to uncoiling of the chromomeric fibrils. During this process a huge amount of very thin fibrillar network is detached from the salivary chromosomes, and the longitudinal interband fibrils become aggregated to form a distinct central axis. This gives apparent likeness to a lampbrush chromosome. Even though at the light microscope level certain regions of the axial core appear to have been lost, no signs of breaks in the linear coherence of the chromosome can be observed in the electron micrographs. Because uncoiling of the chromomeres does not interrupt the continuity of the linear fibres, these observations on induced transitions lend support to the idea that the chromomeric fibrils are to some extent independent and dissimilar as compared to the interchromomeric fibres.Dedicated to Professor Esko Suomalainen in honour of his 60th birthday on June 11, 1970.     

Chromosome organization revealed upon the decondensation of telophase chromosomes inAllium

Chromosomes of root tip cells ofAllium cepa andAllium sativum were studied in early, middle and late telophase to examine the organization of mitotic chromosomes, taking advantage of the naturally occurring chromosome dispersion during the process of decondensation in telophase. Longitudinal and transverse sections of telophase chromosomes viewed under the transmission electron microscope showed that mitotic chromosomes inAllium were composed of helically coiled 400–550 nm chromatin fibres. In some regions of the longitudinal sections, these chromatin fibres were seen to be orientated parallel to one another but formed roughly a right angle to the long axis of the chromosome. In transverse sections, the telophase chromosome appeared to have a hollow centre encircled by the 400–550 nm chromatin fibre which in turn was a hollow tube structure formed by the coiling of a thinner fibre of 170–200 nm. In addition, cross views of chromatin fibres of 170–200 nm and 50–70 nm were also identified in telophase chromosome preparations. These two organizational levels of chromatin fibres also showed a hollow centre. The process of decondensation of telophase chromosomes is described, and some morphological characteristics associated with the activities of chromosome decondensation are analysed. Based on the observations made onAllium chromosomes in this study, various models of chromosome organization are discussed.     

The structure of the chromosomes in human primordial oocytes

Primordial oocytes (oocytes in primordial follicles) from human ovaries aged 51/2 months post conception to 11 3/4 years post partum were examined in: (a) squash preparations of fresh and fixed tissue; (b) histological preparations; and (c) thin sections by electron microscopy, in order to study the structure of the chromosomes. — The light microscope shows that the chromosome consists of a thread bearing numerous fine lateral appendages. Cytochemical tests indicate that the thread contains DNA, and is surrounded by material containing RNA and protein. — The electron microscope shows that there are three main structural components in the chromosome: (i) an axis or core containing at least two longitudinal strands about 200 Å thick; (ii) a surrounding sheath composed of coiled fibrils which form symmetrically arranged columns and loops, and (iii) clusters of large granules which are associated with the outer parts of the sheath. Small nucleoli and other granular bodies are also present. — These observations indicate the presence of lampbrush chromosomes in the human oocyte. The significance of this type of chromosome in mammals is discussed in relation to the differential radiosensitivity of the oocytes, and to the form of chromosomes at the dictyate stage in rodents.     

Some facts concerning the nature and formation of axial core structures in spermatids of Gryllus domesticus

Examination of living spermatid nuclei of Gryllus domesticus has revealed the presence of the same structures, the X chromosome, the round body and the axial core structures, which have been described from electron microscopic observations. The outer ribbons of the axial core structures and the round body are composed of 100 Å fibres indiscernible from and often continuous with the fibres composing the X chromosome. That the outer ribbons of the axial core structures and the round body are chromosomal is further substantiated by the results of cytochemical examinations of formaldehyde fixed material which show that the axial core structures and the round body contain RNA, DNA and basic protein. Neither acetic acid-ethanol nor cold ethanol fixation preserve the round body and the axial core structures suggesting that a protein may be responsible for maintenance of the central core structure. The central core structures are always found in close association with condensed chromatin in regions where the chromosome elements are about 1000 Å apart, suggesting that the relative state of condensation of the chromatin and the spacial relationship between condensed regions may be two of the chief factors concerned in central core formation. Maintainance of the condensed state of the chromatin, however, may in turn depend upon central core integrity.Herrn Prof. J. Seiler zu seinem 80. Geburtstag gewidmet.     

Studies on the mitotic chromosome scaffold of Allium sativum

An argentophilic structure is present in the metaphase chromosomes of garlic(Allium sativum),Cytochemical studies indicate that the main component of the structure is non-histone proteins(NHPs).The results of light and electron microscopic observations reveal that the chromosme NHP scaffold is a network which is composed of fibres and granules and distributed throughout the chromosomes.In the NHP network,there are many condensed regions that are connected by redlatively looser regions.The distribution of the condensed regions varies in individual chromosomes.In some of the chromosomes the condensed regions are lognitudinally situsted in the central part of a chromatid while in others these regions appear as coillike transverse bands.At early metaphase.scaffolds of the sister chromatids of a chromosome are linked to each other in the centromeric region,meanwhile,they are connected by scafold materials along the whole length of the chromosome.At late metaphase,however,the connective scaffold materials between the two sister chromatids disappear gradually and the chromatids begin to separate from one another at their ends.but the chromatids are linked together in the centromeric region until anaphase.This connection seems to be related to the special structure of the NHP scaffold formed in the centromeric region.The morphological features and dynamic changes of the chromosome scaffold are discussed.     

Characterization of chromosome replication during S-phase with bromodeoxyuridine labelling in Chinese hamster ovary and HeLa cells

The same C-banded human polymorphic chromosomes were observed in the light microscope (LM) and then in the scanning electron microscope (SEM) to investigate the structural changes produced by the C-banding technique. C-banded regions, which stained positively in LM, were highly condensed with tightly packed chromatin fibres, resembling non-banded chromosomes. In striking contrast, adjacent non-C-banded regions were represented by loosely arranged fibres, resembling G-banded chromosomes. The significance of these observations in relation to current theories on the effects of C-banding on chromosome structure is discussed.     

Scanning electron microscopy of isolated Chironomus polytene chromosomes

Individual polytene chromosomes have been isolated from Chironomus stigmaterus for scanning electron microscope observations. The three dimensional ultrastructure of these chromosomes consists of a series of chromatin strands extended in the interbands and more tightly coiled or folded in the banded regions. The nucleolus is observed to be a dense disc or doughnut shaped structure surrounding the chromosome while the Balbiani Rings appear as diffuse regions consisting of both fibrillar and granular elements.     

The fine structure of striated muscles in teleosts

Summary The organization of skeletal and cardiac muscles of fishes described on the basis of observations carried out on several species of freshwater fishes (Tinca tinca, Misgurnus fossilis, Perca fluviatilis, Lebistes reticidatus) and marine fishes (Gobius minutus, Pleuronectes platessa, Ammodytes tobianus). Truncal, subcutaneous, extrinsic eye and cardiac muscles were used for study. Glutaraldehyde-fixed tissue was refixed in OsO₄, embedded in Epon and after polymerization, cut into ultra thin sections and examined by an electron microscope.White and red muscles were distinguished in the material examined. The latter was represented by subcutaneous muscles and small fibres of extrinsic eye muscles. Particular types of fibers differ from each other in their organization of the SR and localization of the T system tubules. In the most muscles the T system tubules are situated at the level of the Z line. In the small fibers of extrinsic eye muscles alone these tubules lie at the A-I junction.The myocardiac cells consist of a cylindrically shaped myofibril. In the middle of the cylinder is the nucleus, the remaining space being filled with numerous mitochondria. A loose sarcoplasmic network is twined around the myofibril.     

Variation of the folding and dynamics of the Escherichia coli chromosome with growth conditions

We examine whether the Escherichia coli chromosome is folded into a self‐adherent nucleoprotein complex, or alternately is a confined but otherwise unconstrained self‐avoiding polymer. We address this through in vivo visualization, using an inducible GFP fusion to the nucleoid‐associated protein Fis to non‐specifically decorate the entire chromosome. For a range of different growth conditions, the chromosome is a compact structure that does not fill the volume of the cell, and which moves from the new pole to the cell centre. During rapid growth, chromosome segregation occurs well before cell division, with daughter chromosomes coupled by a thin inter‐daughter filament before complete segregation, whereas during slow growth chromosomes stay adjacent until cell division occurs. Image correlation analysis indicates that sub‐nucleoid structure is stable on a 1 min timescale, comparable to the timescale for redistribution time measured for GFP–Fis after photobleaching. Optical deconvolution and writhe calculation analysis indicate that the nucleoid has a large‐scale coiled organization rather than being an amorphous mass. Our observations are consistent with the chromosome having a self‐adherent filament organization.     

The ultrastructure of G- and C-banded chromosomes

A method of visualizing chromosome bands by electron microscopy has been used to investigate the fine structural organization of G- and C-banded chromosomes. The following information has been obtained:

1. 1. G-bands, produced by trypsinization, were electron dense regions of highly packed chromatin fibres separated by regions in which the chromatin fibres were much less densely packed (interbands).

2. 2. Several degrees of chromatin dispersion were apparent in trypsinized chromosomes. Such dispersion was not a prerequisite for the initial visualization of G-bands, however the progressive pattern of dispersion indicated that the bands were relatively more resistant to dispersion than the interbands.

3. 3. After fixation and trypsinization, individual chromatin fibres measured 250 Å in diameter and appeared morphologically similar to control chromatin fibres seen by whole mount electron microscopy.

4. 4. In trypsinized chromosome complements, the chromosomes often appeared to be interconnected to one another by chromatin fibres. The evidence indicates that these interchromosomal fibres are artefacts produced by the overlapping of dispersed chromatin fibres.

5. 5. When the same metaphase chromosome was observed by both light and electron microscopy, some of the light microscopic G-bands were represented by two or more ultrastructural bands. The number of bands seen in metaphase chromosomes by electron microscopy appears to approach the increased number of bands generally seen in prometaphase chromosomes by light microscopy.

6. 6. C-banding methods (NaOH treatment or overtrypsinization) resulted in the extraction of variable amounts of chromatin from the non C-band regions of the chromosomes, however the constitutive heterochromatin remained highly condensed and resistant to extraction. This result supports the hypothesis that the mechanism of C-banding involves the selective loss of non C-band chromatin.

     

豌豆半无叶突变体性状的遗传及在育种上的利用

以半无叶类型、普通类型豌豆为试验材料,对卷须性状的特征特性、遗传规律及在育种上的利用进行了研究。结果表明：半无叶类型豌豆品种卷须极其发达,能够在株间相互缠绕,形成棚架结构,显著地提高了品种的抗倒伏能力,同时改善了群体通风透光性能,显著提高了新品种的产量,是豌豆抗倒伏育种的重要原始材料。半无叶类型属单基因质量性状遗传,显隐性完全,卷须基因af和子叶颜色基因i表现连锁,位于1号染色体上,交换值为5.72%。 Abstract:Using semi-leafless pea and common pea,the authors studied tendril character,its inheritance law and how to use it in pea breeding.The results were as follows:Semi-leafless pea had well developed tendrils;They twined with each other and formed an arbor structure.This ideal structure had greatly increased lodging resistance capability,improved canopy′s air and light level,and remarkably increased new varieties yield.So,semi-leafless pea was one of the most important materials in lodging resistance breeding.Tendril gene,af,and seed color gene i,in semi-leafless pea was linked on chromosome Ⅰ,and cross-over value was 5.72%.     

Structural and functional organization of the Ska complex, a key component of the kinetochore-microtubule interface

The Ska complex is an essential mitotic component required for accurate cell division in human cells. It is composed of three subunits that function together to establish stable kinetochore-microtubule interactions in concert with the Ndc80 network. We show that the structure of the Ska core complex is a W-shaped dimer of coiled coils, formed by intertwined interactions between Ska1, Ska2, and Ska3. The C-terminal domains of Ska1 and Ska3 protrude at each end of the homodimer, bind microtubules in vitro when connected to the central core, and are essential in vivo. Mutations disrupting the central coiled coil or the dimerization interface result in chromosome congression failure followed by cell death. The Ska complex is thus endowed with bipartite and cooperative tubulin-binding properties at the ends of a 350 ?-long molecule. We discuss how this symmetric architecture might complement and stabilize the Ndc80-microtubule attachments with analogies to the yeast Dam1/DASH complex.     

Observations with the Electron Microscope on the Cell Structure of the Antheridium and Spermatozoid of Sphagnum

Sectioned antheridia of Sphagnum have been investigated withthe electron microscope at magnifications up to 50, 000 diametersand anatomical features of the main protoplasmic organs in twotypes of cells are described and illustrated. In the parenchymatouscells of the antheridial wall the main components encounteredare: nucleus, starch-laden plastids, mitochondria, fat bodies,tubules, putative golgi areas, vesicles, membranes, and granules.In the coiled spermatozoid the main observations concern thecoiled nucleus, the vestigial plastid, putative mitochondriaat the two extremities of the cell, the distribution of vesiclesand fibres in the cytoplasm, and the structure and mode of attachmentof the two flagella. In a comparative discussion it is suggestedthat the parenchymatous cells show resemblance to cells of thehigher plants, notably in details of their plastids and mitochondria.The extreme specialization of the spermatozoid impedes closecomparisons with other plants but a homology is tentativelysuggested between a peculiar organ referred to here as the ‘fibrousband’ to which the nucleus and both flagella are attachedand certain intercalary fibres originating in a comparable positionbetween the bases of the flagella in green and brown algae.     

Electron microscopic map of surface-spread polytene chromosomes in Drosophila hydei

Surface-spread polytene (SSP) chromosomes of salivary glands from late third-instar larvae were used for the construction of an electron microscopic (EM) photo map of the entire genome of D. hydei. In comparison with the light microscopic chromosome map of Berendes (1963), based on squash preparations, the EM micrographs depict some 40%–50% more bands. — Two different types of chromosome constrictions are described. One type is assumed to be caused by differential distribution of chromosomal proteins; the other one appears to represent underreplicated sections in the salivary gland chromosomes.Dedicated to Prof. Dr. H.J. Becker on the occasion of his 60th birthday     

Behavior of the chromosome core in mitosis and meiosis

A simple method has been described for the visualization of chromosome cores with light microscopy in conventional chromosome preparations. The technique is relatively simple, highly reproducible and can be used effectively on fresh and aged slides. The following observations have been made: (1) a core existed in mitotic chromosomes in all the materials employed, confirming the findings of Howell and Hsu (1979). (2) The microchromosomes of the chicken and double minutes of a human carcinoma cell line also exhibited the core structure. (3) The core structure of meiotic chromosomes appear weak, disorganized, and disintegrating.     

Torus-shaped bands in polytene chromosomes of Drosophila. Relationship of toroidal structures and intercalary heterochromatin

Certain regions of the salivary gland polytene chromosomes of Drosophila auraria and its closely related species D. triauraria and D. quadraria, exhibit definite toroidal structures, as evidenced in routinely fixed and stained squash preparations under the light microscope. These toroids are associated with intercalary heterochromatin, as revealed by ectopic pairing and weak points. Similar observations on the giant chromosomes of D. melanogaster are discussed.     

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。     

Measurements of oxygen production rate in flowing Spirulina suspension

Summary The oxygen production rates for a cyanobacterial suspension flowing in straight and coiled tubes were measured to find a way of achieving higher efficiency of light utilization by means of convective mixing. The photosynthetic flow chambers were made of glass tubes and illumination was by fluorescent light. The cyanobacterium used was Spirulina platensis, which has a high growth rate. The oxygen production rate for fluid flow in straight and coiled tubes increase with the increase in Reynolds number. The maximum oxygen production rate was achieved at 30°C for both tube reactors, but the oxygen production rate was higher for the coiled tube unit than the straight tube unit at 30°C. Thus the convective mixing generated in the coiled tube reactor contributed to an increased in light utilization, which played an important part in improving the oxygen production rate. Offprint requests to: K. Tanishita     

The fine structure of the kinetochore of a mammalian cell in vitro

The chromosomes of Chinese hamster cells were examined with the electron microscope and the following observations were made concerning the structure and organization of the kinetochore. — The kinetochore consists of a dense core 200–300 Å in diameter surrounded hy a less dense zone 200–600 Å wide. The dense core consists of a pair of axial fibrils 50–80 Å in diameter which may be coiled together in a cohelical manner. The less dense zone about the axial elements is composed of numerous microfibrils which loop out at right angles to the axial fibrils. Together the structures comprise a lampbrush-like filament which extends along the surface of each chromatid. Some sections suggested that two such filaments may be present on each chromatid. The fine structure of kinetochores associated with spindle filaments was essentially the same as those free of filaments. The structure and organization of the kinetochore of these mammalian cells was compared to that of lampbrush chromosomes of certain amphibian oöcytes, dipteran polytene chromosome puffs, and the synaptinemal complex seen during meiotic prophase.The authors also wish to thank Dr. Arthur Cole of the Department of Physics for the use of his electron microscope facilities and for his helpful criticism.