Haploid Amount Of DNA Research Articles

Megacycles of atmospheric carbon dioxide concentration correlate with fossil plant genome size

Tectonic processes drive megacycles of atmospheric carbon dioxide (CO(2)) concentration, c(a), that force large fluctuations in global climate. With a period of several hundred million years, these megacycles have been linked to the evolution of vascular plants, but adaptation at the subcellular scale has been difficult to determine because fossils typically do not preserve this information. Here we show, after accounting for evolutionary relatedness using phylogenetic comparative methods, that plant nuclear genome size (measured as the haploid DNA amount) and the size of stomatal guard cells are correlated across a broad taxonomic range of extant species. This phylogenetic regression was used to estimate the mean genome size of fossil plants from the size of fossil stomata. For the last 400 Myr, spanning almost the full evolutionary history of vascular plants, we found a significant correlation between fossil plant genome size and c(a), modelled independently using geochemical data. The correlation is consistent with selection for stomatal size and genome size by c(a) as plants adapted towards optimal leaf gas exchange under a changing CO(2) regime. Our findings point to the possibility that major episodes of change in c(a) throughout Earth history might have selected for changes in genome size, influencing plant diversification.

Geographical parthenogenesis, genome size variation and pollen production in the arctic-alpine species Hieracium alpinum

Hieracium alpinum L. (Asteraceae) is an arctic-alpine species distributed throughout Europe with both diploid and triploid cytotypes. We determined the ploidy levels of plants from 23 populations from Austria, Bosnia and Herzegovina, Finland, Italy, Norway, Romania, Slovakia, Switzerland and Ukraine. Data showed a non-overlapping pattern of cytotype distribution: sexually reproducing diploids (2n = 2x = 18) occur solely in the Eastern and Southern Carpathians, while apomictic triploids (2n = 3x = 27) cover the rest of the range. Such clear-cut allopatry is rather rare in vascular plants with geographical parthenogenesis. Comparison of absolute genome size indicates genome downsizing (by on average 3.7%) of haploid DNA amount in triploids relative to diploids. Genome size further correlated with longitude and latitude in the Alps, with decreasing absolute DNA content from west to east, and from south to north. While previously published data indicated complete male sterility of triploid plants, we found that plants from the Alps and Bosnia and Herzegovina commonly produced some pollen, whereas populations from the Western Carpathians and Scandinavia seemed to be almost completely pollen sterile. Scenarios about the evolution of geographical parthenogenesis in H. alpinum are discussed.

Cells of different ploidy are often present together in Cryptococcus neoformans strains.

We examined the ploidy of C. neoformans strains using both laser scanning cytometry and a fluorescence microscope equipped with a photomultiplier. Haploid strains consisted of normal-sized cells with a haploid DNA amount. In the cell population there were also large-sized cells with a diploid DNA amount. These large cells in haploid strains were isolated using a Skerman micromanipulator, cultivated, and were able to generate diploid clones. Even after only 3-5 transfers on slants, haploid cells were present in all the diploid clones examined. Conversely, haploid clones obtained by single-cell-isolation of normal-sized cells from haploid strains were also shown to contain diploid cells after 3-5 transfers. Fresh haploid isolates from the environment similarly contained diploid cells after 3-5 transfers. Thus, a cellular ploidy shift was shown to occur widely in C. neoformans strains.

Giant-Cell Transformation of Trophoblast Cells in Mice

During the early stages of pregnancy in the mouse, part of the trophectodermal cells undergo endoreplication and are transformed into trophoblastic giant cells (TGCs) that contain up to several hundred times the haploid amount of DNA per nucleus. TGCs, which position at the border between fetal and maternal tissues throughout mouse pregnancy, not only form the cell layer between fetal and maternal tissues, but they also secrete progesterone and several hormonal proteins structurally similar to prolactin and growth hormone. Thus, these cells play an important role in fetal-maternal interaction and tissue remodeling and function as endocrine cells essential for the maintenance of pregnancy. In this paper, we review current knowledge on the mechanisms of the TGC transformation of trophoblast cells and the biological function of TGCs in mouse placentation.

Evidence for haploidy in metacyclic forms of Trypanosoma brucei.

The parasitic flagellate Trypanosoma brucei undergoes a series of morphologic and metabolic changes during its passage in the digestive organs of its insect vector, a Glossina or tsetse fly. This morphogenesis ends by the differentiation, in the salivary gland of the fly, of the metacyclic form, which will be transmitted in the bloodstream of the mammalian host. On the basis of DNA microfluorometric measurements, we propose that these metacyclic trypanosomes have a haploid amount of DNA, compared to that of bloodstream forms and also of the proventricular forms, which initiate the invasion of the salivary glands. It can be inferred that trypanosomes undergo meiosis during their developmental cycle in the tsetse fly's salivary glands and syngamy shortly after cyclic transmission.

On the DNA content and ploidy of trypanosomes

We have determined the nuclear and kinetoplast DNA content of two trypanosomatids by quantitative absorption and fluorescence cytophotometry of individual Feulgen-pararosaniline stained cells. For the insect trypanosomatid Crithidia fasciculata we find nuclear and kinetoplast DNA contents of 0.095 and 0.032 pg per non-replicating cell. For the African trypanosome Trypanosoma brucei these values are 0.097 and 0.004 pg. A sub-population of T. brucei cells with two kinetoplasts and one nucleus was found to contain 0.181 pg/nucleus. The DNA values of bloodstream form T. brucei and the procyclic culture form were not significantly different. In DNA-DNA renaturation experiments the haploid amount of DNA in T. brucei was previously found to be 0.041 pg/nucleus (Borst, P., Fase-Fowler, F., Frasch, A.C.C., Hoeijmakers, J.H.J. and Weijers, P.J. (1980) Mol. Biochem. Parasitol. 1, 221–246). Our data, therefore, indicate that T. brucei is diploid. No sub-population of haploid cells was observed in T. brucei grown in rats or in culture.

Endomitosis and the effect of gibberellic acid in different Pisum sativum L. cultivars

The evolution of the total amount of DNA in epicotyls and of the amount of DNA per cell nucleus in epicotyl cortex cells during germination was followed in two closely related pea varieties, Pisum sativum cv. Finale and Pisum sativum cv. Rondo. Under etiolating conditions, growth of the cv. Rondo occurs only by cell elongation which is preceded by endomitotic DNA synthesis, while in the cv. Finale growth is the result of cell elongation accompanied by endomitotic DNA synthesis and cell division. The maximum C-level attained in both cultivars under etiolating conditions is 8 C (C=haploid amount of DNA in a gamete cell). Both the maximum C-level reached and the percentage of cells reaching this C-level seem to be under strict genetic control. In both cultivars, light inhibits the endomitotic DNA replication.Neither gibberellic acid (GA3), nor AMO 1618 alter the maximum C-level or the percentage distribution of the C-classes. Both growth regulators are effective, although in an opposite way, only in tissues where cell division occurs or where endomitotic DNA synthesis is blocked, as in light-grown pea epicotyls.

Polyploidization of extraembryonic tissues during mouse embryogenesis

It has recently been shown that visceral yolk-sac endoderm is derived from the primitive endoderm of the 4.5-day mouse blastocyst (Gardner & Papaioannou, 1975; Gardner & Rossant, 1979). During development, primitive endodermal cells acquire nuclei with more than four times the haploid amount of DNA. The finding of metaphases with multiple sets of chromosomes suggests that the diploid precursors of such endodermal giant cells become truly polyploid. Amniotic cells also contain giant nuclei but the mechanism by which these arise is uncertain. The giant-cell transformation therefore appears to be a general feature of mouse extraembryonic development rather than a phenomenon restricted solely to trophoblast. The basis and significance of these findings are discussed in relation to the development of other extraembryonic membranes both of plant and animal origin.

DNA Content and Chromosome Complement ofChromis Chromis(Pommacentridae, Perciformes)

SUMMARYSomatic and germinal chromosomes of Chromis chromis were analysed and the diploid number was determined to be 48, the same as its F. N. The haploid amount of DNA was estimated by Feulgen cytophotometry at 1, 2 pg. The karyotype and DNA content are discussed as a contribution to the understanding the evolution of this species inside the family. The study helps to establish the location of this family on the evolutionary scale within the teleosts.

Characterization of long and short repetitive sequences in the sea urchin genome

Long and short repetitive sequences were purified from the DNA of Paracentrotus lividus under conditions designed to optimize the yield of complete, end to end sequences. Double-stranded long repeat DNA prepared in this manner ranged in length from approximately 3000 to 15 000 nucleotide pairs with average sizes of approximately 6000 base pairs. In the electron microscope, long repeat DNA was observed to possess continuous sequences that often appeared to be terminated by one or more loops and/or fold backs. Long repeat DNA sequences, resheared to 300 base pairs, were found to have an average melting point identical to that for sheared native DNA. Thus, the reassociated duplexes of long repetitive DNA seem to possess very few mismatched base pairs. Reassociation kinetic analyses indicate that the majority of the long repeat sequences are reiterated only 4–7 times per haploid amount of DNA. Melt-reassociation analyses of short repetitive DNA, at several criteria, support the previously held concept that these sequences belong the sets or families of sequences which are inexact copies of one another. Our studies also support hypotheses suggesting that short repetitive sequences belong to families which may have arisen via distinct saltatory events. The relationships between long and short repetitive DNA sequences are considered with respect to widely held concepts of their sequence organization, evolution, and possible functions within eucaryotic genomes. A model for the possible organization of short repeats within long repetitive DNA sequences is also presented.

Ribonucleic acid from the higher plant Matthiola incana Molecular weight measurements and DNA · RNA hybridisation studies

The percentage of DNA from the crucifer Matthiola incana coding for different types of RNA was measured by filter saturation hybridisation experiments using RNA labelled in vivo. In addition, the melting curves of the various DNA · RNA hybrids formed and the buoyant densities of the DNA sequences complementary to different types of RNA were measured. 1. 1. The RNA preparations used were 25, 18, and 5 S rRNA and 4 S RNA, purified by gel electrophoresis, and poly(A)-containing RNA purified by oligo-(dT)-cellulose chromatography. The molecular weights of the 25 S and 18 S rRNAs, calculated from the mobility in formamide-acrylamide gels relative to Escherichia coli RNA, are 1.25 · 10 6 and 0.64 · 10 6. The rRNA precursor has a molecular weight of approx. 2.1 · 10 6 and the average molecular weight of the poly(A)-containing RNA from both cotyledons and roots is 4 · 10 5. 2. 2. The percentage of the genome, calculated on the basis of double-stranded DNA, coding for these RNAs and the estimated number of genes per haploid DNA amount are approximately 0.46% and 1100 for 25 S plus 18 S rRNA, 0.032% and 3600 for 5 S rRNA and 0.072% and 13 000 for 4 S RNA. In filter hybridisation experiments very little hybridisation of poly(A)-containing RNA was found. A rapidly-hybridising component is attributed to small amounts of contaminating rRNA. 3. 3. M. incana DNA has a main band at 1.697 g · ml −1 in CsCl and a satellite constituting approximately 3% of the DNA, at 1.708 g · ml −1. 25 and 18 S rRNA hybridise to DNA with a buoyant density of 1.701-2 g · ml −1. The buoyant density of 5 S DNA is slightly less at 1.700-1 g · ml −1. 4 S RNA hybridises to at least two separate regions, one within the main-band DNA and a second lighter component. None of the RNAs tested hybridised to the satellite DNA. The T m of the DNA · RNA hybrids in 1 × SSC is 89° C for 25 S rRNA, 85° C for 5 S rRNA and 82° C for 4 S RNA. 4. 4. 5 and 4 S RNA preparations contain fragments which hybridise to sequences complementary to high-molecular-weight rRNA. This spurious hybridisation can be eliminated by competition with unlabelled high-molecular-weight RNA.

Quantitation of nuclear DNA in Ascaris lumbricoides: DNA constancy and chromatin diminution.

SUMMARYThe DNA contents of nuclei during gametogenesis and embryogenesis inAscaris lumbricoideswere measured by Feulgen-microspectrophoto-metry. The variability in the mean value for the haploid amount of DNA in sperm from different males processed at different times was not significant when sperm cell samples were taken from the same region of the seminal vesicle. As the sperm mature, the extent of uptake of Feulgen dye decreases nonsystematically. A similar phenomenon occurs during embryogenesis, and as noted by others, primary oocytes in the terminal portion of the oviduct become Feulgen-negative. Feulgen-positive primary oocytes maintain a 4C DNA value without significant variation. Notwithstanding the differences in Feulgen-DNA values in certain types of nuclei, our evidence supports the view that inAscaris lumbricoidesthe amount of intraspecific DNA has a constant value between individual organisms and from one generation to the next. About 34% of the DNA of the zygote is lost through chromatin diminution at the third embryonic cleavage. This quantity represents 0·23 pg DNA per haploid equivalent.

The cellular DNA content of sharks, rays and some other fishes

1. 1. The haploid amount of DNA was determined for 31 species of elasmobranchs and 8 other non-teleost fishes. 2. 2. The elasmobranchs have a modal DNA amount of about 4 pg, compared to 1 pg for the teleosts. 3. 3. The DNA content of the other non-teleosts ranges from 1.2 at the low end to 142 pg for lungfishes that have been assayed. 4. 4. Several characteristics that are common to DNA distributions in many different groups of organisms, such as a skewed distribution and the positive correlation between specialization and a low amount of DNA, are apparent here. The lungfishes appear to be an exception to the latter characteristic.

Constancy in human sperm DNA content.

The frequency distribution of DNA content of human sperm was measured in an automated flow microfluorometer. The flow method measures the DNA content by quantifying the amount of fluorescence emitted by the fluorescent Feulgen stained DNA of single sperm cells suspended in microdroplets. The variability in the mean value for the haploid amount of DNA in sperm from 15 randomly chosen donors was less than 1%. Statistical tests on the observed frequency distribution data indicated that each sperm population probably consists of two homogenous components present in almost equal proportions but differing in mean DNA content. The difference in their modal values for DNA is within the range of known values of DNA difference between the two sex chromosomes. Sperm of donors segregating balanced translocations, when compared to the random samples as a class, showed greater variability in the mean DNA content.

Cytological studies on the organization of DNA in giant trophoblast nuclei of the mouse and the rat.

Giant trophoblast nuclei of the mouse and the rat, known to contain hundreds, or even thousands, of times the haploid amount of DNA, have been studied by a number of cytological techniques. These nuclei appear in two morphological states:“reticulate,” in which large numbers of chromatin threads of uniform size intermingle throughout the nucleus, often radiating from clumps of heterochromatin adjacent to the nucleoli, and “homogeneous,” in which the chromatin is more evenly dispersed and individual threads are more difficult to distinguish. Intermediate morphologies are also observed. In neither case were structures resembling polytene chromosomes discernible. — Centromeric heterohromatin as revealed by the Giemsa BSG technique has been quantitatively analyzed in giant versus diploid trophoblast nuclei. Although the median number of chromocenters is slightly greater in giant than in diploid nuclei, the range is similar. In both cases, the chromocenter number is usually less than the diploid number of chromosome pairs, indicating the attraction between centromeres not only of homologous, but also of heterologous, chromosomes. By scanning microdensitometry, we have observed a constant ratio of chromocenter area: total nuclear area in giant cells. This ratio, which likely reflects the ratio of chromocenter volume: total nuclear volume, is in good agreement with that of satellite DNA: total DNA.

Oogenesis in Tenebrio molitor: Histological and autoradiographical observations on pupal and adult ovaries

ABSTRACT Nurse cells and oocytes in the telotiophic ovary of Tenebrio molitor L. (Insecta, Coleoptera-Polyphaga) are differentiated in the larval stadium. During pupation DNA synthesis occurs in the nurse cells and is probably associated with polyploidy; some of them become multinucleate. The functional significance of these events is interpreted as preparation for subsequent massive RNA synthesis. The oviducts incorporate [3H]thymidine and undergo elongation due to mitoses. This ceases at eclosion. RNA synthesis in the pupal ovary is low, but increases in the nurse cells and follicle cells just prior to eclosion. In the adult ovary, once the growth phase has been initiated, a primary oocyte takes about six days to reach maturity. The nurse cells, though apparently lacking nucleoli, synthesize much stable RNA which reaches each oocyte via a trophic cord. The follicle cells undergo continuous DNA synthesis: some nuclei contain over 64 times the haploid amount of DNA. Replication is probably asynchronous within a nucleus: this may account for the phenomenon of simultaneous DNA and RNA synthesis in the follicle cells, which also lack nucleoli. Oogenesis has been divided into nine developmental stages, three of which are vitellogenic. The oocyte chromosomes are capable of RNA synthesis both when despiralized during early previtellogenesis and after karyosome formation, which occurs at stage 6. The protein content of the oocyte appears to have a dual origin: at least part of the ooplasmic proteins form in situ; while yolk proteins are derived from the haemolymph. The extra-ovarian protein reaches the oocyte via spaces which develop between the follicle cells. The nucleoplasm becomes more heavily labelled with proteins than the ooplasm. With [3H]leucine, methionine and phenylalanine but not with tryptophane or arginine, there is an increased incorporation into the karyosome. It is suggested that this karyosomeassociated protein may function in gene masking. The significance of these findings is discussed with reference to the literature.

Trophoblast giant cell differentiation in the mouse: Expression of glucose phosphate isomerase (GPI-1) electrophoretic variants in transferred and chimeric embryos

Trophoblast differentiation in the mouse embryo is characterized by the formation of giant cells whose nuclei contain as much as 500–1000 times the haploid amount of DNA. Three mechanisms which have been proposed to account for the increase in DNA include (1) endomitosis, (2) uptake of maternal nuclei or macromolecular DNA as the trophoblast cells invade the endometrium, and (3) the formation of syncytial trophoblast by cell fusion followed by the fusion of nuclei. We have used genetic variants of the dimeric isozyme glucose phosphate isomerase (GPI-1) to examine whether heterokarotypes are expressed in trophoblast tissue from transferred embryos (GPI-1A embryos to GPI-1B females) and chimeric embryos (GPI-1A↔GPI-1B). In the electrophoretic assay system we used, the GPI-1 phenotype of individual ectoplacental cones could be determined. We also established that different electrophoretic forms of GPI-1 could be discerned when one form comprises only 1% of the total GPI-1 activity of the sample. We found no evidence of heteropolymer (GPI-1AB) in electrophoretic assays of trophoblast from either the transferred or chimeric embryos. These data indicate that trophoblast cells do not functionally incorporate maternal DNA nor do they form syncytial heterokaryons by cell fusion. Our results are consistent with the proposal that DNA increases in trophoblast giant cells by endomitosis.

CYTOCHEMICAL STUDIES ON THE PROBLEM OF MACRONUCLEAR SUBNUCLEI IN TETRAHYMENA

DNA amounts in macronuclei and micronuclei of Tetrahymena pyriformis were measured by Feulgen microspectrophotometry. Assuming that the unreplicated micronucleus is diploid, the unreplicated macronucleus was found to contain approximately 45 times the haploid DNA amount. The relationship of these findings to the 45 independently assorting genetic subunits characterized by Allen and Nanney and their collaborators is discussed. The pattern of DNA synthesis in macro- and micronuclei during the cell cycle is also described.

A cytophotometric analysis of the DNA in the nucleus of the giant cell, R-2, in Aplysia.

DNA was cytophotometrically measured in Feulgen stained nuclei of R-2, the giant neuron of the abdominal ganglion in Aplysia. The data indicate that the nucleus hag a volume of more than 7 X 106 μ3 in large animals, and contains as much as 75000 times the haploid amount of DNA. To our knowledge, this is the most highly polyploid nucleus yet described. Furthermore, the amount of DNA increases with growth, going from approximately 2000 times the haploid amount in small animals to over 75000 times in large animals. The data suggest that the increase in DNA occurs in increments, each increment having approximately twice the DNA as the one before. Thus we suggest that the increase in DNA in the nucleus of R-2 results from the entire genome replicating without accompanying cell division.

Evolution of Cellular DNA Content in Teleost Fishes

The haploid amount of DNA in teleost fishes ranges from 0.40 to 4.4 picograms. Almost all the teleost groups with low amounts of DNA per cell are considered to be evolutionally advanced. Most of the groups with large amounts of DNA per cell are more primitive and more closely related to ancestral forms. It is proposed that evolution and specialization in the teleosts have been accompanied by loss of DNA.