Typisierung der Geschmacksknospen von Fischen

Zusammenfassung Im Epithel des Kopfdarms von Xiphophorus helleri Heckel (Poeciliidae, Cyprinodontiformes, Teleostei) kommen drei Typen von Geschmacksknospen vor, die in charakteristischer Weise über diesen Darmabschnitt verteilt sind: Organe des Typ I liegen in Epithelpapillen und überragen das durchschnittliche Epithelniveau deutlich. Sie finden sich an der Mundöffnung, speziell auf den Atemsegeln. Organe des Typ II sind nur wenig über das allgemeine Epithelniveau erhoben und kommen im Epithel von Mundhöhle, Gaumen und branchialem Vorderdarm vor. Geschmacksknospen des Typ III überragen das Epithelniveau nicht; sie liegen ausschließlich im verhornten Epithel des bezahnten metabranchialen Vorderdarms.Die Nervenfaserplexus der Geschmacksknospen des Typ I (und III) geben eine stärkere Reaktion auf Acetylcholinesterase (ACHE) als die des Typ II. Dagegen zeigen die Geschmacksknospen der Typen II und III eine deutlichere 5-Hydroxytryptamin (5-HT; Serotonin)-Fluoreszenz und eine stärkere Monoaminoxidase (MAO)-Aktivität als die des Typ I. Daraus wird geschlossen: 1) daß die elevierten Geschmacksknospen des Typ I neben der chemorezeptorischen möglicherweise auch eine ausschließlich cholinerg gesteuerte mechanorezeptorische Funktion haben, und 2) daß die nur wenig oder nicht über das Epithelniveau hinausragenden Geschmacksknospen der Typen II und III überwiegend chemorezeptorisch tätig sind (cholinerger Funktionsablauf unter aminerg-sympathischer Kontrolle).

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The types of taste buds in fishesI. Morphological and neurohistochemical investigations on Xiphophorus helleri heckel (poeciliidae, cyprinodontiformes, teleostei)

Summary In sword-tails (Xiphophorus helleri), the taste buds within the epithelium of the head gut can be classified into three types, which are characteristically distributed in this part of the gut: Organs belonging to type I are lying within epithelial papillae and rise distinctly above the normal level of the epithelium. They are found in the mouth region, especially on the breathing valves. Organs of type II rise only a little above the normal level of the epithelium. They occur within the oral cavity, the palate and the branchial part of the foregut (pharynx). Taste buds belonging to type III never rise above the level of the epithelium; they are exclusively situated within the keratinized and teeth-bearing metabranchial foregut.On their basal nerve plexus, the taste buds of type I (and type III) are more acetylcholine esterase (ACHE)-reactive than those of type II. In contrast to type I organs, type II and type III taste buds show a more distinct 5-hydroxytryptamine (5-HT; serotonine)-fluorescence and clearer evidence of monoamino oxidase (MAO)-activity. Therefore following conclusions can be drawn: 1) In addition to their chemoreceptor function, the elevated type I taste buds may also have a mechanoreceptor function, which works exclusively in a cholinergic manner. 2) Type II and type III taste buds, which are only a little elevated or not elevated at all, mainly act as chemoreceptors with a cholinergic impulse transmission which is controlled by the aminergic sympathetic system.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Giemsa banding of a human metacentric chromosome number 9

Summary Giemsa staining procedures have been used on human lymphocyte preparations to locate constitutive heterochromatin (C-bands) and to produce distinct banding patterns for each individual chromosome (G-bands). A metacentric C group chromosome has been shown by both techniques to be chromosome number 9.

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Zusammenfassung An menschlichen Lymphocyten wurde eine Giemsafärbung durchgeführt, mit dem Ziel, konstitutives Heterochromatin (C-Banden) zu lokalisieren und für jedes einzelne Chromosom besondere Bandmuster herauszuarbeiten (G-Banden). Beide Techniken erlaubten, ein metazentrisches C-Chromosom als Nr. 9 zu identifizieren.

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Supported by PHS grants RR-62 and 5-SO1-RRO-5411.     

Verteilung strahleninduzierter Brüche auf den Geschlechtschromosomen von Microtus agrestis

Zusammenfassung Fibroblastenkulturen von weiblichen und männlichen Tieren der Erdmaus Microtus agrestis wurden mit Röntgenstrahlen von 250 R bestrahlt, um Aufschluß über Verteilung und Häufigkeit strahleninduzierter Chromosomenaberrationen im Eu- und Heterochromatin zu erhalten, und zwar insbesondere unter dem Aspekt der Selektion über einen längeren Zeitraum. Die Kulturen wurden zwischen 12 Std und 42 Tagen nach Bestrahlung abgebrochen. An Chromosomenaberrationen fanden sich dizentrische Chromosomen, Ringchromosomen und Deletionen. Die Aberrationsraten waren 12 Std nach Bestrahlung mit 31,5% beim Weibchen und 25,9% beim Männchen gegenüber 1,9% in den Kontrollkulturen deutlich erhöht. Diese Raten sanken während des weiteren Beobachtungszeitraums langsam ab.Die Lokalisation der Brüche ergab 12 Std nach Bestrahlung eine annähernd gleichmäßige Verteilung über das gesamte Chromosom; zu späteren Beobachtungszeitpunkten bilden sich über einzelnen Chromosomenabschnitten Bruchmaxima aus. Faßt man jeweils die Brüche auf den euchromatischen und heterochromatischen Abschnitten zusammen, so ergibt sich 12 Std nach Bestrahlung ein Bruchverhältnis von Euchromatin zu Heterochromatin wie 1:3, was umgerechnet auf gleiche Längenanteile wiederum einer Zufallsverteilung entspricht. Mit fortschreitender Kulturdauer sinken die Bruchraten im Euchromatin sehr viel rascher ab als im Heterochromatin, was zu einer deutlichen Verschiebung des Bruchverhältnisses zugunsten des Heterochromatins führt. Beim Weibchen liegt das Verhältnis, bezogen auf gleiche Längenanteile, nach 42 Tagen bei 1:4,5 und beim Männchen nach 23 Tagen bei 1:5,7.Dieser Selektionsvorteil von Zellen mit Chromosomenbrüchen im Heterochromatin gegenüber im Euchromatin geschädigten Zellen bestätigt die These, daß der Verlust heterochromatischer Abschnitte nicht zu einer Beeinträchtigung der Zellfunktion führen muß, d. h., daß das Heterochromatin für die Funktion der Zelle nur eine untergeordnete Rolle spielt.

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Distribution of radiation-induced breaks in the sex chromosomes of Microtus agrestis

Summary Fibroblast cultures from male and female field voles, Microtus agrestis, were exposed to an x-irradiation of 250 R in order to obtain data on the distribution and frequency of radiation-induced chromosome aberrations in eu- and heterochromatin, especially under the aspect of selection over a longer period of observation. The cultures were harvested between 12 h and 42 days after exposure. Chromosonal aberrations, such as dicentrics, rings and deletions, were observed in the following frequencies: 12 h after irradiation 31,5% in female and 25,9% in male cultures against only 1,9% in the control cultures. Further observation exhibited a slow decrease in the percentage of aberrations.The localisation of the breaks (deletions) 12 h after irradiation showed an approximately random distribution over the whole chromosome. At the later observation period the development of breakage maxima on some chromosome parts was observed. Compiling the breaks in the euchromatic and heterochromatic regions respectively a breakage ratio of 1:3 was observed 12 h after irradiation; this, when related to equal proportions of chromosomal length, corresponds again to a random distribution. At the later observation period cells with breaks in the euchromatin disappear much faster than cells damaged in the heterochromatin, which alters the breakage ratio in favor of the heterochromatin 42 days after irradiation, the female shows a ratio of 1:4,5 (again related to equal parts of chromosomal length); the male shows a ratio of 1:5,7, 23 days after irradiation.This selective advantage of cells with chromosome breaks in the heterochromatin over cells damaged in the euchromatin confirms the hypothesis, that loss of heterochromatic portions of a chromosome must not lead to impairment of cell growth, i.e., the heterochromatin plays only a subordinate role in the cell function.

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Wesentliche Teile dieser Arbeit wurden von Herrn Claus Waldenmaier als Dissertation der Medizinischen Fakultät der Universität Freiburg i. Br. vorgelegt.     

Counterstained enhancement of TaqI resistant sites after distamycin A/diamidinophenylindole treatment

Numerous selective and differential staining techniques have been used to investigate the hierarchical organisation of the human genome. This investigation demonstrates the unique characteristics that are produced on fixed human chromosomes when sequential procedures involving restriction endonuclease TaqI, distamycin A (DA) and 4,6-diamidino-2-phenylindole (DAPI) are employed. TaqI produces extensive gaps in the heterochromatic regions associated with satellite II and III DNAs of human chromosomes 1, 9, 15, 16 and Y. DA/DAPI selectively highlights, as brightly fluorescent C-bands, the heterochromatin associated with the alpha, beta, satellite II and III DNAs of these chromosomes. When DA and DAPI are used on chromosomes before TaqI digestion, and then stained with Giemsa, the centromeric regions appear to be more resistant, producing a distinct C-banding pattern and gaps in the heterochromatin regions. Sequential use of the DA/DAPI technique after TaqI treatment produces a bright fluorescence on the remaining pericentromeric regions of chromosomes 1, 9, 16 and Y, which also displayed a cytochemically unique banding pattern. This approach has produced specific enhanced chromosomal bands, which may serve as tools to characterize genomic heterochromatin at a fundamental level.     

Localization of repetitive DNA in the chromosomes of Microtus agrestis by means of in situ hybridization

Heterochromatin in the European field vole, Microtus agrestis, was studied using a special staining technique and DNA/RNA in situ hybridization. The heterochromatin composed the proximal 1/4 of the short arm and the entire long arm of the X chromosome, practically the entire Y chromosome and the centromeric areas of the autosomes. By using the DNA/RNA in situ hybridization technique, repeated nucleotide sequences are shown to be in the heterochromatin of the sex chromosomes.Supported in part by Research Grants DRG-1061 and 269 from the Damon Runyon Memorial Fund for Cancer Research, G-373 and G-267 from the Robert A. Welch Foundation.     

Localization of repetitive DNA in the chromosomes of <Emphasis Type="Italic">Microtus agrestis</Emphasis> by means of <Emphasis Type="Italic">in situ</Emphasis> hybridization

Heterochromatin in the European field vole, Microtus agrestis, was studied using a special staining technique and DNA/RNA in situ hybridization. The heterochromatin composed the proximal 1/4 of the short arm and the entire long arm of the X chromosome, practically the entire Y chromosome and the centromeric areas of the autosomes. By using the DNA/RNA in situ hybridization technique, repeated nucleotide sequences are shown to be in the heterochromatin of the sex chromosomes.     

Distribution of constitutive heterochromatin in Hela and HEp-2 cell lines

Summary Despite the fact that HeLa and HEp-2 cell lines have been established respectively from a female and a male patient, the frequent loss of the Y chromosome makes it difficult to discriminate the two cell types. The technique of centromeric localization of heterochromatin, however, facilitates more definite identification of the two cell types. Giemsa positive centromeric constitutive heterochromatin blocks were induced within the intact metaphase chromosome preparations of Hela and HEp-2 cells. The Hela cell population had a single heterochromatin marker chromosome, whereas the HEp-2 cell line was found to possess two types of heterochromatin markers. The distinctive patterns of distribution of constitutive heterochromatin of these three chromosomes served as the guides in tracing the presumptive cytological pathways for their orgin.

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Zusammenfassung Trotz der Tatsache, daß Hela- und HEp-2-Zellinien jeweils von einem weiblichen und einem männlichen Patienten stammen, erschwert der häufige Verlust des Y-Chromosoms eine Unterscheidung der beiden Zelltypen. Der Nachweis des zentromernahen Heterochromatins jedoch ermöglicht eine zuverlässigere Erkennung dieser beiden Zelltypen. Die Hela-Zellpopulation hat ein einzelnes, durch das Heterochromation gekennzeichnetes Marker-Chromosom, während die HEp-2-Zellinie deren 2 besitzt. Das distinkte Verteilungsmuster des konstitutiven Heterochromatons dieser 3 Chromosomen dient dazu, die vermutliche cytologische Herkunft zu interpretieren.

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Supported in part by the Robert A. Welch Foundation, The National Foundation —March of Dimes and USPHS Grant No. FR-05425.     

Structural variability of human chromosome 9 in relation to its evolution

Summary Human chromosome 9 shows a high susceptibility for structural rearrangements, particularly pericentric inversions, which often are transmitted. Three types of pericentric inversions can be observed on No. 9: 1) Type I, showing the total constitutive heterochromatin in the short arm. 2) Type II with part of the C heterochromatin on the short arm, the rest located on the long arm proximal to the centromere. 3) Type III: a subtelocentric chromosome with part of the C heterochromatin in the very short arm and the rest located interstitially on the long arm. With these inversions as well as with other structural rearrangements, e.g. translocations, the break-points are located preferentially within the C heterochromatin or close to the heterochromatic-euchromatic junctions. These findings are in contrast to the findings in lymphocytes from 5 patients with Fanconi's anemia and after irradiation in vitro, reported in the literature. In lymphocytes break-points seem to be distributed more or less by chance. These observations together led us to speculate that human chromosome 9 primarily was an acrocentric chromosome; in morphology and at least in some functions similar to D-and G-group chromosomes. During evolution this acrocentric chromosome changed to a submetacentric one due to a pericentric inversion.The author is sponsored by the Deutsche Forschungsgemeinschaft.     

Karyotyp und Heterochromatinmuster des rumänischen Hamsters (Mesocricetus newtoni)

In the Romanian hamster (2n=38) a number of whole chromosome arms is heterochromatic. This offers the opportunity to test the effect of some recently developed differential staining techniques upon heterochromatin. It is shown that the late replicating segments are stained by the C-banding technique. A method for exclusively demonstrating centromeric heterochromatin is described. With this, only 8 autosome pairs and the X-chromosome show centric heterochromatin. There is a good agreement between the multiple banding pattern produced by fluorescent and Giemsa stain.

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Stipendiat der Alexander-von-Humboldt-Stiftung.     

Heterochromatin,repetitive DNS und Nukleolen in Leberzellen von Microtus agrestis

Zusammenfassung Die Zellstruktur von Leberzellen der Erdmaus, Microtus agrestis, wurde nach Giemsafärbung, Feulgenbehandlung, Behandlung mit Ribonuklease und nach Färbung des konstitutiven Heterochromatins untersucht. Das konstitutive Heterochromatin ist in Leberzellen nicht heteropyknotisch, das fakultative Heterochromatin ist im weiblichen Geschlecht als Sexchromatinkörperchen sichtbar. Bestimmungen des relativen DNS-Gehalts ergaben, daß die Zahl der Sexchromatinkörperchen der Ploidie der Zellkerne proportional ist. Die Nukleolen liegen in Hepatozyten oft randständig; in 59% der diploiden Zellkerne sind 2 Nukleolen enthalten. Nach Anfärbung der repetitiven DNS werden oft auch die Nukleolen gefärbt, nach Ribonukleasebehandlung tritt dieser Effekt nicht auf. Das konstitutive Heterochromatin wird in Form von 2 langen fädigen Strukturen sichtbar.

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Heterochromatin, repetitive DNA and nucleoli in liver cells of Microtus agrestis

Summary The nuclear structure of parenchymal liver cells of embryo and adult Microtus agrestis was studied in smear and section preparations after staining with Giemsa solution and treatment according to Feulgen, after treatment with ribonuclease and after specific staining of constitutive heterochromatin. In liver cell nuclei only the facultative heterochromatin is heteropycnotic, a sex chromatin body is observable in female but not in male animals. Constitutive heterochromatin is not heteropycnotic in liver cells. Measurements of the relative DNA content showed that nuclei with one sex chromatin body are diploid; tetraploid nuclei possess two and octoploid nuclei four sex chromatin bodies. Solely in the diploid cell nuclei of the intrahepatic gall ducts two large chromocenters are found. The nucleoli in hepatocytes often lie at the perimeter of the nucleus. 17% of the diploid nuclei contain one nucleolus, 59% two nucleoli, 23% three and 1% four. After staining of repetitive DNA, the nucleoli often become stained as well; after treatment with ribonuclease this effect does not occur. The constitutive heterochromatin becomes visible in form of two long, threadlike structures. After longer periods of dissociation the sex chromatin body ceases to be visible. Sex chromatin and constitutive heterochromatin are contiguous to the nucleoli.

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Mit dankenswerter Unterstützung durch das Bundesministerium für Bildung und Wissenschaft der Bundesrepublik Deutschland.     

Gestörte Granabildung in Chloroplasten einer Chlorina-Mutante von Arabidopsis thaliana (L.) Heynh.

Zusammenfassung Die Chloroplasten in Palisadenzellen aus Rosettenblättern von Arabidopsis thaliana wurden an der grünen Normalform und einer vitalen chlorina-Mutante (ch ₃) vergleichend licht-, fluorescenz- und elektronenmikroskopisch untersucht.Die Chloroplasten der grünen Normalform zeigen in Aufsicht licht-und fluorescenzmikroskopisch eine regelmäßige Granaverteilung. Elektronenmikroskopisch entspricht die Ausbildung der Grana- und Intergranabereiche in Profilansicht den Befunden an Chloroplasten anderer höherer Pflanzen.Bei der licht- und fluorescenzmikroskopischen Analyse der Chloroplasten der Mutante fehlt eine entsprechende Granaordnung. Elektronenmikroskopisch lassen sich drei verschiedene Chloroplastentypen nachweisen: Bei Typ I kann das Thylakoidsystem in den Chloroplasten weitgehend undifferenziert bleiben; bei Typ II erfolgt eine von der grünen Normalform abweichende Schichtenbildung in den Chloroplasten, wie sie bislang nur von Anthoceros bekannt ist; bei Typ III werden in Profilansicht Stapel mit vornehmlich konjunktiver Schichtung vom Aspekt normaler Grana erreicht.An Hand von kompletten Schnittserien wird die Stapelbildung für die komplizierteren Chloroplasten-Typen II und III in räumlichen Modellen dargestellt; ihre Entwicklung wird als Folge von Invaginations-und Überschiebungsprozessen gedeutet.

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Disturbed grana-formation in chloroplasts of a Chlorina-mutant of Arabidopsis thaliana (L.) Heynh.

Summary Chloroplasts in the palisade cells of rosette leaves of Arabidopsis thaliana have been compared in the green wild type and in a vital chlorina mutant (ch ₃) using light-, fluorescence-, and electron microscopy.In the chloroplasts of the wild type in face view a regular distribution of grana was revealed by light- and fluorescence microscopy. In side view under the electron microscope the formation of grana and intergrana regions corresponds to the reported chloroplast fine structure in other higher plants.In the chloroplasts of the mutant form this normal grana formation is not visible when analysed under the light- and fluorescence microscope. Under the electron microscope, three different types of chloroplasts have been distinguished: type I, in which the thylakoid system remains largely undifferentiated; type II, in which stacking processes take place comparable to those reported for the Anthoceros chloroplast but different from those of the wild type plastid in Arabidopsis; and type III, in which the stacking of thylakoids leads to a predominantly conjunctive arrangement which may reach the aspect of normal grana in side view.On the basis of complete series of cross sections spatial models have been constructed for the more complicated stacking in chloroplasts of type II and III, and their development has been explained by invagination and sliding over processes.

     

Location,structure and behaviour of C-heterochromatin during meiosis in Dichroplus silveiraguidoi (Acrididae-Orthoptera)

The constitutive heterochromatin of Dichroplus silveiraguidoi, a species which shows an exceptionally low chromosome number (2n=8), was studied at meiosis with a staining technique on normal and hypotonically treated specimens. The results showed: 1) an unusual behaviour of the heterochromatic blocks located in the so-called synaptic region of the sex bivalent (Neo Y-Neo X), which remains paired from early prophase through metaphase I; 2) in normal or in hypotonically treated cells a heterogeneous configuration of the C-heterochromatic blocks was observed. This configuration is characterized by the existence of small positive granules interconnected by euchromatic filaments and is enhanced by treatment with a low ionic strength solution; 3) A weakly positive stained (intermediate) material was demonstrated in the Neo X chromosome; 4) A large amount of heterochromatin is distributed in the form of granular material along the length of the autosomes and as telomeric and centromeric blocks in all chromosomes. The possible evolutionary mechanisms involved and the significance of the C-band heterochromatin demonstrated in this species are discussed.     

Kinetics of DNA replication in the Indian muntjac chromosomes as studied by quantitative autoradiography

DNA replication patterns of individual chromosomes and their various euchromatic and heterochromatic regions were analyzed by means of quantitative autoradiography. The cultured cells of the skin fibroblast of a male Indian muntjac were pulse labeled with ³H-thymidine and chromosome samples were prepared for the next 32 h at 1–2 h intervals. A typical late replication pattern widely observed in heterochromatin was not found in the muntjac chromosomes. The following points make the DNA replication of the muntjac chromosomes characteristics: (1) Heterochromatin replicated its DNA in a shorter period with a higher rate than euchromatin. (2) Two small euchromatic regions adjacent to centromeric heterochromatin behaved differently from other portions of euchromatin, possessing shorter Ts, higher DNA synthetic rates and starting much later and ending earlier their DNA replication. (3) Segmental replication patterns were observed in the chromosomes 2 and 3 during the entire S phase. (4) Both homologues of the chromosome 3 showed a synchronous DNA replication pattern throughout the S phase except in the distal portion of the long arms during the mid-S phase.     

Panspecies Small-Molecule Disruptors of Heterochromatin-Mediated Transcriptional Gene Silencing

Heterochromatin underpins gene repression, genome integrity, and chromosome segregation. In the fission yeast Schizosaccharomyces pombe, conserved protein complexes effect heterochromatin formation via RNA interference-mediated recruitment of a histone H3 lysine 9 methyltransferase to cognate chromatin regions. To identify small molecules that inhibit heterochromatin formation, we performed an in vivo screen for loss of silencing of a dominant selectable kanMX reporter gene embedded within fission yeast centromeric heterochromatin. Two structurally unrelated compounds, HMS-I1 and HMS-I2, alleviated kanMX silencing and decreased repressive H3K9 methylation levels at the transgene. The decrease in methylation caused by HMS-I1 and HMS-I2 was observed at all loci regulated by histone methylation, including centromeric repeats, telomeric regions, and the mating-type locus, consistent with inhibition of the histone deacetylases (HDACs) Clr3 and/or Sir2. Chemical-genetic epistasis and expression profiles revealed that both compounds affect the activity of the Clr3-containing Snf2/HDAC repressor complex (SHREC). In vitro HDAC assays revealed that HMS-I1 and HMS-I2 inhibit Clr3 HDAC activity. HMS-I1 also alleviated transgene reporter silencing by heterochromatin in Arabidopsis and a mouse cell line, suggesting a conserved mechanism of action. HMS-I1 and HMS-I2 bear no resemblance to known inhibitors of chromatin-based activities and thus represent novel chemical probes for heterochromatin formation and function.     

Arrangement of centromeres in mouse cells

Applying a staining procedure which reveals constitutive heterochromatin to cytological preparations of the mouse (Mus musculus), one detects heterochromatin pieces at the centromeric areas of all chromosomes except the Y. The Y chromosome is somewhat heteropyenotic in general but possesses no intensely stained centromeric heterochromatin. The arrangement of the centromeric heterochromatin in interphase cells is apparently specific for a given cell type. In meiotic prophase, centromeric heterochromatin may form clusters among bivalents. From the location of the centromeric heterochromatin of the X chromosome in the sex bivalent, it is concluded that the association between the X and Y (common end) in meiosis is limited to the distal portions of the sex elements.     

Banding in Human Chromosomes treated with Trypsin

THE differential staining properties of the Giemsa stain were first observed by Pardue and Gall¹. They were studying in situ hybridization between mouse satellite DNA and mouse chromosomes and observed that following certain pretreatment the centromeric regions of mouse chromosomes were more densely stained by Giemsa stain than other regions. The darkly stained regions were considered to consist of constitutive heterochromatin. Similar observations were later made on human chromosomes by Arrighi and Hsu² and Gagné et al.³. Through modifications of the original methods used in the DNA hybridization work, techniques have been developed which make each chromosome identifiable^4–6.     

Heterochromatic differentiation in barley chromosomes revealed by C- and N-banding techniques

Summary Heterochromatin distribution in barley chromosomes was investigated by analyzing the C- and N-banding patterns of four cultivars. Enzymatic maceration and air drying were employed for the preparation of the chromosome slides. Although the two banding patterns were generally similar to each other, a clear difference was observed between them at the centromeric sites on all chromosomes. Every centromeric site consisted of N-banding positive and C-banding negative (N⁺ C^–) heterochromatin in every cultivar examined. An intervarietal polymorphism of heterochromatin distribution was confirmed in each of the banding techniques. The appearance frequencies of some bands were different between the two banding techniques and among the cultivars. The heterochromatic differentiation observed is discussed with respect to cause.     

Human (Homo sapiens) and chimpanzee (Pan troglodytes) share similar ancestral centromeric alpha satellite DNA sequences but other fractions of heterochromatin differ considerably

The euchromatic regions of chimpanzee (Pan troglodytes) genome share approximately 98% sequence similarity with the human (Homo sapiens), while the heterochromatic regions display considerable divergence. Positive heterochromatic regions revealed by the CBG-technique are confined to pericentromeric areas in humans, while in chimpanzees, these regions are pericentromeric, telomeric, and intercalary. When human chromosomes are digested with restriction endonuclease AluI and stained by Giemsa (AluI/Giemsa), positive heterochromatin is detected only in the pericentromeric regions, while in chimpanzee, telomeric, pericentromeric, and in some chromosomes both telomeric and centromeric, regions are positive. The DA/DAPI technique further revealed extensive cytochemical heterogeneity of heterochromatin in both species. Nevertheless, the fluorescence in situ hybridization technique (FISH) using a centromeric alpha satellite cocktail probe revealed that both primates share similar pericentromeric alpha satellite DNA sequences. Furthermore, cross-hybridization experiments using chromosomes of gorilla (Gorilla gorilla) and orangutan (Pongo pygmaeus) suggest that the alphoid repeats of human and great apes are highly conserved, implying that these repeat families were present in their common ancestor. Nevertheless, the orangutan's chromosome 9 did not cross-hybridize with human probe. The euchromatic regions of chimpanzee (Pan troglodytes) genome share approximately 98% sequence similarity with the human (Homo sapiens), while the heterochromatic regions display considerable divergence. Positive heterochromatic regions revealed by the CBG-technique are confined to pericentromeric areas in humans, while in chimpanzees, these regions are pericentromeric, telomeric, and intercalary. When human chromosomes are digested with restriction endonuclease AluI and stained by Giemsa (AluI/Giemsa), positive heterochromatin is detected only in the pericentromeric regions, while in chimpanzee, telomeric, pericentromeric, and in some chromosomes both telomeric and centromeric, regions are positive. The DA/DAPI technique further revealed extensive cytochemical heterogeneity of heterochromatin in both species. Nevertheless, the fluorescence in situ hybridization technique (FISH) using a centromeric alpha satellite cocktail probe revealed that both primates share similar pericentromeric alpha satellite DNA sequences. Furthermore, cross-hybridization experiments using chromosomes of gorilla (Gorilla gorilla) and orangutan (Pongo pygmaeus) suggest that the alphoid repeats of human and great apes are highly conserved, implying that these repeat families were present in their common ancestor. Nevertheless, the orangutan's chromosome 9 did not cross-hybridize with human probe. © 1995 Wiley-Liss, Inc.     

Differential cell division in human X chromosome mosaics

Summary Fibroblasts were grown from skin explants of 3 human females who are sex chromosome mosaics. The 3 cultures had the following chromosome complements: 45,X/46,XX, 45,X/46,XXqi and 45,X/47,XXX. Using thymidine labelling and Colcemid accumulation of metaphases it was found that in all 3 mosaic cultures the 45,X cells had a faster cell cycle than the second cell population. The difference in cell cycle duration was attributed to the longer G₁ phase in the cells with 2 or 3 X chromosomes. The 2 populations of cells in the mosaic only differ in the number of heterochromatic X chromosomes and it is argued that heterochromatin has a retardative effect on cell division.

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Zusammenfassung Kulturen von Fibroblasten der Haut dreier weiblicher Individuen mit Sexchromatin-Mosaiks zeigten folgende chromosomale Zusammensetzung: 45,X/46,XX; 45,X/46XXqi und 45,X/47,XXX. Mit Hilfe von Thymidinmarkierung und Akkumulation von Metaphasen durch Colcemid konnte gezeigt werden, daß in allen 3 Mosaikkulturen die 45,X-Zellen einen schnelleren Zellcyclus haben als die zweite Zellpopulation. Der Unterschied in der Dauer des Zellcyclus beruht auf der längeren G₁-Phase der Zellen mit 2 oder 3 X-Chromosomen. Die 2 Zellpopulationen im Mosaik differieren nur in der Zahl der heterochromatischen X-Chromosomen, so daß angenommen werden könnte, daß Heterochromatin einen retardierenden Effekt ausübt.

     

Meiotic events at the centromeric heterochromatin: histone H3 phosphorylation, topoisomerase IIα localization and chromosome condensation

Mechanisms of chromosome condensation and segregation during the first meiotic division are not well understood. Resolution of recombination events to form chiasmata is important, for it is chiasmata that hold homologous chromosomes together for their oppositional orientation on the meiotic metaphase spindle, thus ensuring their accurate segregation during anaphase I. Events at the centromere are also important in bringing about proper attachment to the spindle apparatus. This study was designed to correlate the presence and activity of two proteins at the centromeric heterochromatin, topoisomerase II alpha (TOP2A) and histone H3, with the processes of chromosome condensation and individualization of chiasmate bivalents in murine spermatocytes. We tested the hypothesis that phosphorylation of histone H3 is a key event instigating localization of TOP2A to the centromeric heterochromatin and condensation of chromosomes as spermatocytes exit prophase and progress to metaphase. Activity of topoisomerase II is required for condensation of chromatin at the end of meiotic prophase. Histone H3 becomes phosphorylated at the end of prophase, beginning with its phosphorylation at the centromeric heterochromatin in the diplotene stage. However, it cannot be involved in localization of TOP2A, since TOP2A is localized to the centromeric heterochromatin throughout most of meiotic prophase. This observation suggests a meiotic function for TOP2A in addition to its role in chromatin condensation. The use of kinase inhibitors demonstrates that phosphorylation of histone H3 can be uncoupled from meiotic chromosome condensation; therefore other proteins, such as those constituting metaphase-promoting factor, must be involved. These results define the timing of important meiotic events at the centromeric heterochromatin and provide insight into mechanisms of chromosome condensation for meiotic metaphase.