FURTHER EVIDENCE FOR A MEMBRANE-BOUND ENDOSYMBIONT WITHIN THE DINOFLAGELLATE PERIDINIUM FOLIACEUM1

The fine structure of the binucleate, fucoxanthin-containing dinoflagellate Peridinium foliaceum (Stein) Biechler was re-examined for evidence of an endosymbiout. The eucaryotic nucleus, chloroplasts and associated ribosome-dense cytoplasm were separated by a single invaginating membrane from the rest of the dinoflagellate cell. The triple membrane-enclosed eyespot, mesocaryotic nucleus, trichocysts and accumulation bodies resided in the dinoflagellate cytoplasm. These observations suggest that P. foliaceum contains a membrane-bound endosymbiont, similar to that already described for the closely related species. P. balticum (Levander) Lemmermann.     

ULTRASTRUCTURAL STUDIES ON TWO KINDS OF MESOCARYOTIC DINOFLAGELLATE NUCLEI

The nucleus of the mesocaryotic dinoflagellate has unusually distinctive features as seen under the light and electron microscope. An electron microscope study of 7 species has demonstrated two kinds of dinoflagellate nuclei. One type, characteristic of Amphidinium and most other dinoflagellates and called here the dinocaryotic type, is distinguished by the presence of discrete chromosomes visible throughout the entire cell cycle. The other type, found in vegetative cells of Noctiluca and called here the nocticaryotic type, is characteristically devoid of evident chromosomes at least during interphase. Questions are raised regarding the distinction between the nucleoplasm, chromosomes, and nucleolus of dinoflagellates. As the Heliozoa and Radiolariahave typically eucaroytic nuclei, they should not be considered as part of the Mesocaryota, as has been previously suggested.     

Isolation and Properties of Isolated Nuclei from the Florida Red Tide Dinoflagellate Gymnodinium breve (Davis)1

A simple and rapid method is described for the isolation of nuclei from the Florida red tide dinoflagellate Gymnodinium breve. The nuclei are free of cytoplasmic contamination and are active in endogenous RNA synthesis. The ratio of DNA: RNA: acidsoluble protein: acid-insoluble protein is 1:0.39:0.13:0.63, respectively, and each nucleus contains ca. 113 picograms of DNA. Electrophoretic analysis of the acid-soluble proteins reveals the presence of two histone-like proteins with molecular weights of 12,000 and 13,000.     

Ultrastructure of the nuclear apparatus of the lower ciliateRemanella granulosa Kahl (Karyorelictida)

Summary The nuclear apparatus ofRemanella granulosa has been investigated using conventional TEM methods and Bernhard's technique of preferential RNP staining. This species has two (rarely three) macronuclei and a single micronucleus (rarely two micronuclei). The nuclei always form a single group.The macronuclei contain a fibro-granular matrix resistant to EDTA destaining, and several nucleoli and chromatin bodies. The chromatin bodies are readily bleached with EDTA and are often clustered, or even fused, forming chromocenters. The nuclei are of the compact concentric type. Some macronuclei contain nuclear bodies, as finely fibrous spheres or bundles of coarse fibers, or both. Neither type of nuclear body is destained with EDTA. The spheres are frequently associated with nucleoli. There is no evidence of any transition between the two types of nuclear bodies. The macronuclear envelope contains numerous pore complexes and is strengthened with an electron dense layer. The micronucleus is filled with spongy condensed chromatin and surrounded by an envelope with occasional pores. This nucleus lacks nucleoli and nuclear bodies.     

Les ultrastructures nucléaires de la Noctiluque (Dinoflagellé libre) au cours de la sporogenèse

The trophozoït of Noctiluca miliaris has a large nucleus (30 ) with several nucleoli of considerable size that contain DNA fibrillae lying in the interspaces. — Before and during the first sporogenetic divisions, the nucleoli disintegrate, releasing towards the cytoplasma numerous groups of ribonucleic granules passing through the nuclear ampullae. At the end of the sporulation, there are no nucleoli visible in the nuclei and no ampullae. — The nucleoplasm diminishes, as the DNA filaments are built up, to form the meshes of a network which limit the masses of chromatic material that take the shape of chromosomes characterized by regular fibrillar arches, at the 8–16 nuclei stage. In their centre, there is an axial structure which remains intact during the chromosomal segregation; its function during mitosis seems to be important: supplementary layers of arches appear at this level. — The progressive condensation of the chromosomes is correlated to the sporogenetic evolution of the nuclei, not to the different phases of the mitotic cycle. — The karyokinesis is brought about, during early stages, by mere splitting of the chromatic mass and of its envelope, and later one by separation into two lots of chromosomes. The segregation of these chromosomes is effected by partial intervention and growth of the envelope of the nucleus; there is no centromeric structure visible. At the end of divisions, the nucleus is almost entirely formed by its chromosomes. — The nucleolar structure, the karyokinesis, the structure of the nuclear envelope and the chromosomal cycle show the particularly high evolution of Noctiluca, within the Dinoflagellata.     

Number of nucleoli in various cell types of the mouse

The nucleoli of cells of the adult mouse were examined by staining with toluidine blue after removal of deoxyribonucleic acid from tissue sections by deoxyribonuclease treatment. The nuclei of each cell type examined contained one or more nucleoli. This was observed even in lymphocytes and neuroglia, although these cells have occasionally been described as anucleolated. In mature spermatids and spermatozoa, however, it was not possible to detect a nucleolus. The distribution of the number of nucleoli in many diploid cells exhibited a mode of two or three nucleoli per nucleus, and a range from 1 to 6 nucleoli. In presumedly diploid hepatic nuclei, the maximum number of nucleoli was six; but in presumedly tetraploid hepatic nuclei, it was 11. Thus, nearly twice as many nucleoli are present when the chromosome number is doubled. In view of this observation, it is suggested that six nucleolar organizers are present in the diploid chromosomal complement of the mouse. However, through failure of some nucleolar organizers or more probably through fusion of nucleoli, the number of these organelles in most nuclei is less than six.     

煤绒菌Fuligo septica显型原质团细胞核及菌核的超微结构

从煤绒菌显型原质团中提纯细胞核、核仁,诱导原质团形成菌核,并在透射电镜下观察。研究结果表明:细胞核具有中央核仁,核仁可以看到明显的纤维中心、致密纤维中心和颗粒结构。原质团中存在大量的黏液颗粒。菌核具有双层膜,内含有细胞器及脂滴。     

煤绒菌Fuligo septica显型原质团细胞核及菌核的超微结构

从煤绒菌显型原质团中提纯细胞核、核仁,诱导原质团形成菌核,并在透射电镜下观察。研究结果表明:细胞核具有中央核仁,核仁可以看到明显的纤维中心、致密纤维中心和颗粒结构。原质团中存在大量的黏液颗粒。菌核具有双层膜,内含有细胞器及脂滴。     

A chromosome rearrangement in Neurospora that produces segmental aneuploid progeny containing only part of the nucleolus organizer

In translocation T(ILVL)OY321 of Neurospora crassa a distal portion of the nucleolus organizer chromosome, including ribosomal DNA sequences and the nucleolus satellite, is interchanged with a long terminal segment of IL. When OY321 is crossed by Normal sequence, one-fourth of the meiotic products are segmental aneuploids that contain two copies of the long IL segment and that are deficient for the distal portion of the organizer. Each such product forms a nucleolus and is viable. The complementary aneuploid products are deficient for the IL segment and are therefore inviable. — In crosses of OY321xOY321, each product is capable of making two nucleoli; nucleoli formed by the separated nucleolus organizer parts usually fuse, but most 8-spored asci contain some nuclei in which two separate nucleoli can be seen. One nucleolus is then terminal on its chromosome while the second is interstitial and somewhat smaller. — In crosses of OY321 x Normal, half of the meiotic products are capable of making two nucleoli. However, only about 15% of 8-spored asci have one or more nuclei containing separate nucleoli. At pachytene and later in prophase I, the single fusion nucleolus is associated with three bivalent chromosome segments. Each nucleus of every ascus contains at least one nucleolus, even in asci where some nuclei display two nucleoli. — Crosses of Aneuploid x Normal are usually semibarren, producing a reduced number of ascospores, some of which are inviable. Some aneuploid cultures become fully fertile by reverting to a quasinormal sequence lacking a satellite. In some crosses of Aneuploid x Normal, individual asci may show at prophase I either complete loss, partial loss, or pycnosis of the translocated IL segment. This observation of pycnosis suggests chromosome inactivation. — Growth from aneuploid ascospores is initially slow, but can accelerate to the wild-type rate.     

Nucleolar behaviour in Triticum

The maximum number of major nucleoli (macronucleoli) per nucleus of hexaploid, tetraploid and diploid wheat, Aegilops speltoides and Ae. squarrosa corresponded to the number of satellited chromosomes of each species. Smaller nucleoli (micronucleoli) were rare or absent in all of these species except the hexaploid, in which they were predominantly organized on chromosome arm 5D^s. — Fewer than the maximum number of macronucleoli in a mitotic interphase nucleus resulted from fusion of developing nucleoli. Enforced proximity of nucleolus-organizing regions resulted in more frequent fusion of nucleoli. — Analyses of related interphase nuclei showed that nucleoli, and hence probably chromosomes, undergo limited movement during mitotic interphase. These observations also indicate that specific chromosomes do not occupy specific sites in the interphase nucleus.     

NUCLEAR BASIC PROTEINS FROM THE BINUCLEATE DINOFLAGELLATE PERIDINIUM FOLIACEUM (PYRROPHYTA)1

Histories of the endosymbiont nucleus of the binucleate dinoflagellate Peridinium foliaceum Stein were prepared from isolated nuclei and analyzed by peptide mapping, ammo acid composition, and two-dimensional gel electrophoresis. Using these criteria, we identified the presence of two HI-like histories and the core histones H3, H2A, H2B, and H4. These histones are similar but not identical to those of the endosymbiont nucleus of the bi-nucleate dinoflagellate Peridinium balticum Levander.     

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.     

Gene amplification in oocytes with 8 germinal vesicles from the tailed frog Ascaphus truei Stejneger

In the last 3 oogonial mitoses in Ascaphus truei all daughter nuclei remain in the same cell. The oocyte is 8-nucleate at the start of meiotic prophase and remains so until late in oogenesis when 7 of the nuclei disappear. All 8 nuclei in a single oocyte resemble one another with respect to size and chromatin distribution at all stages of meiotic prophase. Much of the Feulgen-positive material in pachytene nuclei is concentrated into one region of the nucleus. — All of the 8 germinal vesicles of yolky oocytes have a full set of lampbrush diplotene bivalents. Germinal vesicles from oocytes of up to 0.8 mm diameter have less than 100 nucleoli, some of which are multiple nucleoli in the sense that they have more than one core region. Each of the 8 nuclei in oocytes from one animal had about the same volume of nucleolar material. — Two values have been obtained for the amount of DNA in a diploid nucleus from Ascaphus. A biochemical estimate utilizing erythrocyte nuclei and the diphenylamine reaction yielded a value of 7.1 pg per nucleus. Microphotometry of erythrocyte nuclei stained with Feulgen's reagent gave a value of 8.2 pg per nucleus. — Microphotometric measurements of Feulgen-stained nuclei at various stages of meiotic prophase up to diplotene indicate that each nucleus synthesizes up to 5 pg of extrachromosomal DNA during and immediately after pachytene. This DNA is considered to be nucleolar. Autoradiography of nuclei from oocytes which had been incubated for 6h in ³H thymidine showed silver grains over pachytene and early diplotene nuclei only. In pachytene nuclei the silver grains overlaid that part of the nucleus where Feulgen-positive material was most concentrated. Most of the chromosomal material was unlabelled. — The significance of the 8-nucleate condition in Ascaphus oocytes is discussed, and the amount of nucleolar DNA synthesized at pachytene and of nucleolar material present in germinal vesicles is compared with corresponding situations in other amphibians.     

The Problem of Nucleolar Number in Cell Nuclei and in Sections of Cell Nuclei

In this paper the mean number N of nucleoli of cell nuclei and the relative frequency PN of cell nuclei with N nucleoli are investigated. To solve the first problem, the stereological model of convex shaped nuclei and nucleoli and the assumption of randomly-isotropically distributed objects in space are used. The model is developed for non-vanishing thickness T of tissue sections. The relationship between the unknown number N of nucleoli in cell nuclei and the mean number n of nucleoli in nuclear sections determined by counting is N = n (D+T)/(d + T). Here D and d are the mean values of caliper diameter for nuclei and for nucleoli, resp. The second problem is illustrated by means of some biomedical examples: The relative frequency PN of cell nuclei with N nucleoli can be approximated by a generalized Poisson distribution in all investigated cases. Therefore the mean nucleolar number N is the essential parameter to describe the frequencies of cell nuclei with different numbers of nucleoli.     

Pyramidodinium spinulosum sp. nov. (Dinophyceae), a sand‐dwelling non‐motile dinoflagellate from the seafloor (36 m deep) off Mageshima Island,Kagoshima, Japan

A new species of benthic marine dinoflagellate, Pyramidodinium spinulosum Horiguchi, Moriya, Pinto & Terada is described from the deep (36 m) seafloor off Mageshima Island, Kagoshima Prefecture, Japan in the subtropical region of the northwest Pacific. The life cycle of the dinoflagellate consists of a dominant, attached, dome‐shaped, vegetative form and short‐lasting, motile cell. Asexual reproduction takes place by the formation of two motile cells within each non‐motile cell. The released motile cells swim only for a short period and transform directly into the dome‐shaped vegetative form. The duration of the cell cycle varies and can be extremely long, ranging 5–38 days under culture conditions. The non‐motile cell is enclosed by a cell wall and its surface is covered with many (80 – 130) spines of various length. The dinoflagellate is photosynthetic and contains many (more than 50) discoidal chloroplasts. Phylogenetic analysis reveals that the dinoflagellate is closely related to the type species of the genus Pyramidodinium, P. atrofuscum which also possesses a dominant, attached, non‐motile form. However, P. spinulosum can be clearly distinguished from P. atrofuscum by the cell shape (dome‐shaped vs. pyramid‐shaped) and surface ornamentation (spines vs. wart‐like processes) of the non‐motile form. Based on these morphological differences together with molecular evidence, it was concluded that this organism from a deep water sand sample should be described as a second species of the genus Pyramidodinium, P. spinulosum.     

A NOVEL ASSOCIATION BETWEEN AN ENDEMIC STICKLEBACK AND A PARASITIC DINOFLAGELLATE. 2. MORPHOLOGY AND LIFE CYCLE1

An unusual dinoflagellate has been discovered in association with an endemic population of stickleback, Gasterosteus (L.), from the Queen Charlotte Islands, Canada. The dinoflagellate spends most of its life cycle as a coccoid vegetative cyst, not as a parasitic trophont. The vegetative cyst is unique in containing a rigid fenestrated matrix, which is penetrated by cytoplasmic process that emanate from a central area containing the dinokaryotic nucleus and associated chloroplasts. Some pores in the matrix are filled by oil droplets or starch granules. Intracellular bacteria are found throughout the cyst, sometimes in association with the nucleus. The cytoplasm contains accumulation bodes, microbodies, polyhedral crystals, chloroplasts and polyvesicular bodes. The encysted dinoflagellate has several potential strategies. It can 1) shed its wall and become amoeboid; 2) undergo sporogenesis and give rise to both regular and resistant spores; 3) divide mitotically, with a gradual reduction in the size of daughter cells down to 20 μm; and 4) apparently form a resting cyst, during which it secretes a thick outer wall composed of five layers. Taxonomically, this unusual dinoflagellate appears to be a new member of the Blastodiniales, although its position will become clearer when details of the motile stage are known.     

An ultrastructural study of early endosperm development and synergid changes in unfertilized cotton ovules

Excised, unfertilized cotton (Gossypium hirsutum L.) ovules were cultured for 1–5 days postanthesis and embryo-sac development was studied with the electron microscope. In some ovules the two polar nuclei fuse and the diploid endosperm nucleus goes through a limited number of free nuclear divisions after 2–3 days in culture. Each nucleus has two nucleoli, in contrast to nuclei of fertilized triploid endosperm which have three nucleoli. Precocious cell walls form between the endosperm nuclei on the 3rd day in culture. The morphology of the plastids, mitochondria, rough endoplasmic reticulum (RER), dictyosomes and microbodies, and the amount of starch and lipid in the diploid cellular endosperm are similar to those of the central cell. A few large helical polysomes appear close to plastids and mitochondria. After 2 days in culture, one of the two synergids in the unfertilized cultured ovules shows degenerative changes which in fertilized ovules are associated with the presence of the pollen tube, i.e., increase in electron density, collapse of vacuoles, irregular darkening and thickening of mitochondrial and plastid membranes, disappearance of the plasmalemma and the membranes of the plasmalemma and the membranes of the RER. The second synergid remains unchanged in appearance. The egg cell does not shrink or divide or show structural changes characteristic of the cotton zygote. Embryo-sac development is arrested on the 4th and 5th days in culture. The nucellus continues growth and at 14 days crushes the degenerate embryo sac.     

Localised uptake of63nickel into dinoflagellate chromosomes: An autoradiographic study

Summary The uptake of⁶³Ni into cells of the binucleate dinoflagellateGlenodinium foliaceum was investigated using insoluble compound light and electron microscope autoradiography. Cells labelled over a period of 2 hours showed active uptake throughout the whole population, with an increase in mean cell grain count when the labelling period was extended to 4 hours and 24 hours. The mean grain count did not vary with type of fixation (glutaraldehyde, paraformaldehyde or acetic alcohol) suggesting that retention of⁶³ Ni is not a specific fixation-binding artefact. At light microscope level, silver grains were not localised to any major cell component, but with the greater resolution of electron microscope autoradiography, a high degree of localisation was demonstrated in the typical dinoflagellate (dinocaryotic) nucleus-which contained about 83% of the cell label (cytoplasm 16%, supernumerary nucleus 1%). Silver grain distribution within the dinocaryotic nucleus was consistent with some degree of localisation to the condensed chromatin.The autoradiographic results corroborate previous X-ray microanalytical data which demonstrated high levels of transition metals in dinoflagellate nuclei. The distinction between the two types of nucleus inGlenodinium is further emphasised, giving additional support to the concept of a separate phyllogenetic origin of the supernumerary nucleus.     

Nuclear thyroid hormone receptors: evidence for association with nucleolar chromatin.

When hypothyroid rat liver nuclei labeled $\text{in vivo}$ with [125 I]L-triiodothyronine are incubated with micrococcal nuclease, the nuclear chromatin is digested and chromatin particles are released into the medium. The nuclease-treated nuclei contain intact nucleoli and a residual chromatin fraction. When this residual chromatin is purified, it contains only a small percentage of the initial nuclear DNA but is strikingly enriched in [125 I]L-triiodothyronine. This chromatin fraction has many of the characteristics of nucleolar chromatin including a high protein to DNA ratio, an abundance of nonhistone proteins, and a relatively high RNA to DNA ratio. An association of thyroid hormone receptors with a nucleolar component implicates this organelle in the early events of thyroid hormone action.