Arrangement of nucleosomes in condensed chromatin fibres

Summary Condensed chromatin shows globules of 300 Å formed by 8 to 10 nucleosomes. Each globule might be an uncoiled turn of a supercoil. This supercoil forms major coils along the fibre.This work was supported by grants from Brazilian CNPq, FAPESP and FEDIB.We thank Dr A. Brunner Jr for the permission to use the electron microscope.     

Structural characteristics and distribution of satellite cells along crayfish muscle fibers

The distribution of satellite cells (sc) in long-sarcomere muscle fibers from the carpopod extensor muscle of the crayfish (Astacus fluviatilis) has been studied electron-microscopically. The sc are spindle-shaped and are oriented parallel to the long axis of a fiber. The mean lengths of sc nuclei (17.00 m) and that of myonuclei (18.35 m) differ non-significantly. In older animals, the mean ratio of the number of sc nuclei to the total number of nuclei (sc nuclei + myonrclei) is 0.0716, 0.0848, and 0.034 for the tendon, central and shell segments, respectively. The corresponding values for younger animals are 0.158, 0.166, and 0.081. The mean numbers of sc nuclei per mm of a fiber are 94, 117, and 47 (older animals), and 164, 117, and 94 (younger animals) for the tendon, central and shell segments, respectively. The high incidence of sc per unit fiber length in crayfish may be related to the fact that crayfish muscle fibers have a much larger diameter than vertebrate muscle cells.     

Large scale preparation of calf liver nuclei by continuous flow centrifugation

Summary Large scale purification and preparation of calf liver nuclei was accomplished by high speed centrifugation of a fraction enriched in nuclei (nuclear homogenate) through 1.8 M sucrose by means of a Beckman CF-32 Ti continuous flow rotor. In comparison with methods involving the use of conventional high capacity rotors, larger volumes of homogenate could be processed. This method was used to prepare nuclei from calf liver for the preparation of DNA-dependent RNA polymerases. The use of continuous flow ultracentrifugation avoids time-consuming manipulations, thus allowing handling of large quantities of tissue.Acknowledgments. The authors wish to thank Professor J. Brachet for his interest and fruitful discussion. They also thank Ms J. Gilder for secretarial assistance.     

Über die Zytologie der Parthenogenese und der Geschlechtsbestimmung bei der GallmückeOligarces paradoxus Mein

Summary InOligarces paradoxus, the chromosomal behaviour was compared during pedogenetic development of and . The -egg undergoes a single non-reductional maturation division, the -egg shows two divisions which result in reduced nuclei. After maturation in the -egg, the number of chromosomes is restored by endomitosis. The nuclei of germ-line cells contain a high number of chromosomes (: 74\2-82; : at least 58) in both sexes. In somatic nuclei, the number is diminished by elimination to 10 in , to 5 in .     

Heavy incorporation of3H-prostaglandin F2α in the neoplastic cells as revealed by autoradiographic studies

Summary A marked uptake (9-fold) of the³H-PGF₂ was found specifically over heterochromatin in the nuclei of neoplastic cells. Lower but significant uptakes of³H-PGF₂ were also found in the nuclei of control epidermal cells, which indicate the presence of nuclear receptors in the epidermal neoplastic cells.     

Unusual high volume of sarcoplasmic reticulum in a wasp leg muscle

Summary Ultrastructural and morphometric examination of a wasp leg muscle showed that it contained a high volume of sarcoplasmic reticulum (volume fraction=0.35, surface density=21.4 m²/m³). As well as being arranged in double or triple layers between the myofibrils, the SR was found in large multilayered accumulations around the nuclei and in the subsarcolemmal space. Fibres of adjacent muscles had the normal volume and arrangement of SR.     

The morphology of cytoplasts and karyoplasts produced by cytochalasin D

Summary The denucleation of L cells and human lymphocytes in suspension was carried out by incubation with cytochalasin D25 and 50 g/ml and with ultracentrifugation over a discontinuous Ficoll gradient. Ultrastructural examination of the separate layers confirmed the presence of the anucleate cytoplasm (cytoplasts) with intact membrane and the separated nuclei (karyoplasts).This work was supported by a grant from the National Cancer Institute of Canada.     

Riesenzellen im Chorion laeve des Kaninchens

Summary The avascular chorion adjacent to the placenta of the rabbit has been suggested as a site of transport or resorption of protein and antibodies. In this chorion giant cells are found. These cells are about 60 in diameter and contain between 5 and 150 nuclei, sometimes even more.     

Fine structural correlations between the muscle pathology of amyotrophic lateral sclerosis (ALS) patients and experimental Ca−Mg deficient rats

Summary Nonspecific myofibrillar changes such as streaming of the Z-line, formation of rod-like structures, satellitosis, proliferation of sarcolemmal nuclei and papillary projection of the sarcolemma were recognized as a disorganization of the muscle itself. In addition, fine structural pathology in ALS specimens showed characteristically a pig-tail formation-Zopfformation-which has been considered to have a neurogenic origin.     

Localisation of acetylcholinesterase in rat myotubes in the presence of β-endorphin and β-endorphin-(1-27)

Summary In rat embryo skeletal myotubes, acetylcholinesterase is present, as multiple forms, and can be detected in deposits at the cell surface. Myotubes cultured in the presence of -endorphin, exhibit an increased predominance of the globular (precursor) forms of the enzyme, which are largely restricted to intracellular sites associated with nuclei. In the presence of -endorphin-(1-27), the relative proportions of the different forms of acetylcholinesterase is similar to that seen in the controls, but the enzyme is intracellular and has a characteristic focal localisation in the myotube.     

Selective activation of noradrenergic neurons in the brainstem and spinal cord of young spontaneously hypertensive rats

Summary In young spontaneously hypertensive rats (SHR), dopamine -hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) activities were examined in the brainstem nuclei. Activation of noradrenergic neurons in the locus coeruleus, A2 and spinal intermediolateral cell areas, resulting in enhanced sympathetic nervous activity in the periphery, initiates hypertension. Adrenergic neurons, unchanged in these and A1 cell areas of young SHR, are not involved in the development of hypertension in SHR.     

Presence of specific binding sites for [3H]sarcophytol-A in cultured human skin fibroblasts

Summary The presence of specific binding sites for [³H]sarcophytol-A in human skin fibroblasts was examined using biochemical and morphological methods. The displacement studies clearly revealed that high (K_D=31.0 nM) and low (K_D=6.05 M) affinity sites were present in the intact cells. Moreover, autoradiographic studies using light microscopy revealed that the specific binding sites may exist in boththe cytoplasm and the nuclei.     

Hemmung der Azetylierungsfunktion des Coenzyms A

Summary It is demonstrated that the acetylation of sulfanilamide and of p-amino-azobenzene, in the presence of pigeon liver extract and coenzyme A, is not only inhibited by -phenyl fatty acids but also by a considerable number of other substances. The most effective inhibitors contain at least two benzene nuclei and one acidic group (phenolic hydroxyl or a carboxyl group).     

Paradoxical effect of 1-β-D-arabinofuranosyl cytosine triphosphate on bleomycin-induced unscheduled DNA synthesis in permeable sarcoma cells

Summary 1--D-Arabinofuranosyl cytosine-5-triphosphate (araCTP), an inhibitor of DNA synthesis, paradoxically enhanced unscheduled DNA synthesis (USD) induced by bleomycin in permeable mouse sarcoma cells. A greater enhancing effect of araCTP on bleomycin-induced USD was observed with lower concentrations of dCTP in the assay mixture. USD measured without bleomycin in nuclei isolated from mouse sarcoma cells was not enhanced, but inhibited by araCTP.Acknowledgments. The authors wish to thank Nippon Kayaku Co. (Tokyo, Japan) for providing copper-free bleomycin A₂. This research was supported in part by a grant from the Japan Ministry of Education, Science and Culture.     

High salt effect on RNA synthesis in Krebs ascites tumor cells

Summary The incubation of Krebs ascites tumor cells in medium with a high salt concentration resulted in a partial inhibition of nuclear RNA synthesis. The residual RNA polymerase activity in such nuclei was only slightly inhibited by low concentrations (50 nM) of -amanitin. This finding suggested an inhibition of RNA polymerase II activity under conditions of medium hypertonicity. Indeed, RNA polymerase II, isolated from the nuclei of cells exposed to hypertonicity, revealed only half of the control activity. On the other hand, RNA polymerase I was not affected by hypertonicity. Moreover, chromatin fractions isolated from cells incubated in hypertonic or isotonic medium were equally template-active in RNA synthesis.This investigation was supported by the Turkish Scientific and Technical Research Council (TÜBITAK), Project No. TAG 339.     

Effect of a brain-specific protein (S-100 protein) on the nucleolar RNA polymerase activity in isolated brain nuclei

Riassunto Una proteina specifica del sistema nervoso, chiamata S-100, stimola la RNA polimerase nucleolare in nuclei isolati da encefalo immaturo di pollo (11 giorni di incubazione). La proteina non ha alcum effetto sulla RNA polimerase nucleoplasmica del medesimo sistema sperimentale. La stimolazione della S-100 sulla RNA polimerase nucleolare è -amanitina resistente ed è parzialmente antagonizzata dalla actinomicina. Ulteriori ricerche potranno chiarire il ruolo della proteina S-100 sulla espressione genetica del sistema nervoso.     

Lesions in suprachiasmatic nuclei simulate effects of pinealectomy on prolactin release in ovariectomized and sulpiride-treated female rats

Summary Previous studies indicate that the pineal gland alters prolactin secretion, and it was suggested that at least part of the effect of the pineal hormone melatonin on prolactin release may be mediated by the hypothalamic structures. In this study, pinealectomy and lesions of the suprachiasmatic nuclei were found to alter serum levels of prolactin in the same direction, an effect that was counteracted by daily afternoon melatonin administration. Melatonin, but not other pineal indoles, also prevented sulpiride-induced prolactin secretion in pinealectomized or suprachiasmatic nuclei-lesioned and ovariectomized rats, which suggested that the pineal gland can modulate prolactin secretion by acting through a dopamine mechanism independent of hypothalamic suprachiasmatic structures.The authors thank Ms Karen Shashok for revising the English style. This work was supported in part by a grant GG85-0168 from the Comisión Asesora de Investigación Cientifica y Ténica. The NIAMDD, through the National Pituitary Agency, supplied the radioimmunoassay materials for prolactin determinations.     

DNA-dependent-DNA-polymerase: Possible limiting influence on cell reproduction during viral leukemogenesis

Summary Evidence is presented that during viral leukemogenesis spleen cell nuclei show an increase in labelling index and mean grain count, that is not accompanied by any changes in the nuclear level of DNA-polymerase-. It is suggested that polymerase production remains under the control of the normal cell mechanisms and the virus may affect cell proliferation by altering the primer-template levels.Acknowledgment. This work was supported in part by NIH-NCI grant No. 1-PO₂-CA-10438 and by USERDA contract No. E (11-1) 3097, P.G.B. was also supported by contract NCI-CB-43899.     

Chromatin circles in amphibian previtellogenic oocytes

Summary Previtellogenic oocytes ofOdontophrynus americanus display hundreds of chromatin circles. Electron microscopy of spread preparations of isolated nuclei shows that the circles originate from the chromatin. The circles change their morphology and form new copies. The length of the DNA packed in the nucleosomal circles is about 2.5–3.5 m or multiples of this value. Assuming that histones need not be removed from chromatin before DNA replication³ we suggest that the circles might belong to the process of rDNA amplification.This work was supported by grants from the Brazilian CNPq, FAPESP and FEDIB.We thank Dr A. Brunner Jr for the use of the electron microscope and Dr N. Leon for his valuable help.     

Sulla struttura microscopica dei cromosomi

Conclusioni Numerosissime osservazioni sulla struttura dei cromosomi in materiali diversissimi dimostrano concordemente che i cromatidi sono avvolti secondo un'elicoide.Questa disposizione spaziale ha un'importanza fondamentale nei processi di riproduzione e di trasformazione dei cromosomi («internal mechanics» diDarlington); ma, in molti particolari di importanza notevole, le opinioni dei citologi sono contrastanti.L'esame comparativo delle trasformazioni cromosomiche, sopratutto nella spermatogenesi e nell'oogenesi, che sono state qui esposte, ci permette di dare un'interpretazione generale sulla struttura cromatidica e sulla disposizione spaziale dei cromatidi nella mitosi e nella meiosi.I cromatidi sarebbero costantemente avvolti secondo un'elicoide «minor». Lo svolgimento di tale elicoide si osserverebbe soltanto in alcuni casi, ad es. nei nuclei degli oociti in accresimento. In questi sono visibili i veri cromomeri. I cromomeri comunemente descritti sarebbero invece giri dell'elicoide «minor», distribuiti irregolarmente lungo l'asse del cromosoma in relazione forse alla distribuzione dei veri cromomeri ed alle caratteristiche della matrice.La costanza dell'avvolgimento elicoidale «minor» ed il fatto che l'autoriproduzione cromatidica avviene nell'interfase, rendono molto verosimile che nei cromosomi a due o quattro cromatidi si formino sempre degli avvolgimenti paranemici. La stessa disposizione spaziale dei cromatidi si avrebbe in seguito all'appaiamento meiotico.Questo tipo di struttura nella maggior parte dei casi è confermato dalle trasformazioni cromosomiche, che precedono la separazione meta-anafasica dei cromosomi figli, ed è quella che probabilmente meglio concorda coi meccanismi di riproduzione cromosomica.

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Summary Very many observations of the structure of the chromosomes in various materials show, without exception, that the chromatids are coiled like springs.This spatial arrangements is of fundamental importance in processes of reproduction and changes in chromosomes (internal mechanics ofDarlington), but in many important particulars the opinions of cytologists differ.The comparative study of changes in chromosomes, especially during spermatogenesis and oögenesis, which are described here, permits us to give a general interpretation of the chromatid structure and of the spatial distribution of the chromatids in mitosis and meiosis.The chromatids should be constantly coiled in a minor spiral. The uncoiling of such spirals could be observed in some cases only, e.g., in nuclei of growing oöcytes. In this the chromomeres are visible. The chromomeres commonly described should be the coils of the minor spiral, distributed irregularly along the axis of the chromosomes, perhaps in relation to the distribution of true chromomeres and to the characteristics of the matrix.The constancy of the minor coil and the fact that chromatid reproduction takes place at the interphase, makes it very likely that in chromosomes with two or four chromatids there is always paranemic coil. The same spatial arrangement of the chromatids should have followed meiotic pairing.In most cases this type of structure is confirmed by the changes in the chromosomes, which precede the separation of the daughter chromosomes at meta-anaphase, and it is in better agreement with the mechanisms of chromosomes reproduction.