2,137 research outputs found
Coupling of growth rate and developmental tempo reduces body size heterogeneity in C. elegans.
No full textAnimals increase by orders of magnitude in volume during development. Therefore, small variations in growth rates among individuals could amplify to a large heterogeneity in size. By live imaging of C. elegans, we show that amplification of size heterogeneity is prevented by an inverse coupling of the volume growth rate to the duration of larval stages and does not involve strict size thresholds for larval moulting. We perturb this coupling by changing the developmental tempo through manipulation of a transcriptional oscillator that controls the duration of larval development. As predicted by a mathematical model, this perturbation alters the body volume. Model analysis shows that an inverse relation between the period length and the growth rate is an intrinsic property of genetic oscillators and can occur independently of additional complex regulation. This property of genetic oscillators suggests a parsimonious mechanism that counteracts the amplification of size differences among individuals during development
The modernist angel: Art at the Limits of the Human in D. H. Lawrence, H. D. and Mina Loy
No full textPhDThe subject of this thesis is a figure that might provisionally be called the *modemist
angel'. Focusing on modernist literature, and more particularly on the work of D. H.
Lawrence, H. D. and Mina Loy, it aims to isolate from the many angels found in all periods
and all types of art a historically specific and intellectually coherent paradigm: an angel of
and for its modernist times. A figure of precisely this type could be said to exist in the
form of Walter Benjamin's 'angel of history'. Critics who address the question of the
modern angel in texts by Franz Kafka and Rainer Maria Rilke often do so in conjunction
with the problem posed by the angel of history. Beginning with a chapter on Benjamin,
this thesis nevertheless follows a different trajectory. Over five chapters, it explores a
modernist landscape formed not only by Lawrence, H. D. and Loy, but also by European
and American writers such as A. R. Orage, Allen Upward, Ezra Pound, Wallace Stevens,
Havelock Ellis, Edward Carpenter, Sigmund Freud and Friedrich Nietzsche. Although the
angel that emerges from this investigation might, in some respects, be said to anticipate
Benjamin's later version, this figure is also very different, standing for a project that is
distinctively, and recognisably, modernist in nature. He/she (the sex of the modernist
angel is often open to question) represents an attempt to reconcile the divine
responsibilities of the artist with the material and gendered conditions of being,
specifically of being human, in the modem world. This thesis looks again at the clash of
intellectual paradigms in the early-twentieth century - notably, the confrontation of the
Romantic view of art as a superhuman or sacred undertaking with the psychoanalytical or
evolutionary idea that all human endeavour is underpinned by sub-human motives - and
suggests the angel as a new and instructive figure through which to think the perilous
limits between the human and the divine in modernist literature
Public worship and practical theology in the work of Benjamin Keach (1640-1704)
No full textThe late seventeenth century was a critical and fruitful period
for the Particular Baptists of England. Severely persecuted following
the Restoration, toleration in 1689 brought its own perils.
Particular Baptists were fortunate in having several strong leaders,
especially the London trio of Hanserd Knollys, William Kiffin, and
Benjamin Keach. Such a small and severely persecuted group as the
Baptists could afford little time for academic pursuits, thus of
necessity most of their theology was practical in nature.
Benjamin Keach (1640-1704) was the most outstanding practical
theologian among the English Particular Baptists of the late
seventeenth century. This dissertation is a study of Keach, in
particular his writings on public worship and practical theology.
Although Keach was a prolific author, he has been almost completely
neglected by scholars.
After a biographical sketch of Keach, this study considers his
writings on public worship and practical theology. In the area of
worship, Keach made two outstanding contributions: First, he was the
most vocal apologist for Baptist views on Baptism of his period.
Secondly, and more importantly, his hymn writing and defense of hymn
singing broke new ground, not just for Baptists, but for English
Protestantism, in general. In addition to his contributions in these
areas, he also dealt with the laying on of hands and the sabbath day
worship controversy.
Keach's contributions to practical theology fall into two main
groups: his writings that concern religious education and those that
deal with polity. In addition to these, Keach's vigorous advocacy of
a high Calvinist soteriology are also considered under the rubric of
practical theology. Keach's most important (although not his most
positive) contribution in this area were his soteriological writings.
Although well within the bounds of orthodoxy, some of the tendencies
in Keach's soteriology were taken up by the following generation of
Baptist leaders and developed into a stultifying hyper-Calvinism that
handicapped Baptist evangelism and missions.
In the conclusion, Keach's contributions to a theory of practical
theology are considered
The nuclear envelope-a scaffold for silencing?
No full textAn increasing number of studies indicate that chromosomes are spatially organized in the interphase nucleus and that some genes tend to occupy characteristic zones of the nuclear volume. FISH studies in mammalian cells suggest a differential localization of active and inactive loci, with inactive heterochromatin being largely perinuclear. Recent genome-wide mapping techniques confirm that the nuclear lamina, which lies beneath the nuclear envelope, interacts preferentially with silent genes. To address the functional significance of spatial compartmentation, gain-of-function assays in which chromatin is targeted to the nuclear periphery have now been carried out. Such experiments yielded coherent models in yeast; however, conflicting results in mammalian cells leave it unclear whether these concepts apply to higher organisms. Nevertheless, the recent discovery that evolutionarily conserved inner nuclear membrane proteins support the peripheral anchoring of yeast heterochromatin suggests that certain principles of nuclear organization may hold true from yeast to man
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Glucose becomes one of the worst carbon sources for E.coli on poor nitrogen sources due to suboptimal levels of cAMP
No full textIn most conditions, glucose is the best carbon source for E. coli: it provides faster growth than other sugars, and is consumed first in sugar mixtures. Here we identify conditions in which E. coli strains grow slower on glucose than on other sugars, namely when a single amino acid (arginine, glutamate, or proline) is the sole nitrogen source. In sugar mixtures with these nitrogen sources, E. coli still consumes glucose first, but grows faster rather than slower after exhausting glucose, generating a reversed diauxic shift. We trace this counterintuitive behavior to a metabolic imbalance: levels of TCA-cycle metabolites including α-ketoglutarate are high, and levels of the key regulatory molecule cAMP are low. Growth rates were increased by experimentally increasing cAMP levels, either by adding external cAMP, by genetically perturbing the cAMP circuit or by inhibition of glucose uptake. Thus, the cAMP control circuitry seems to have a ‘bug’ that leads to slow growth under what may be an environmentally rare condition
The formation and sequestration of heterochromatin during development: delivered on 7 September 2012 at the 37th FEBS Congress in Sevilla, Spain.
No full textChromatin is not randomly positioned in the nucleus, but is distributed in subdomains based on its degree of compaction and transcriptional status. Recent studies have shed light on the logic of chromatin distribution, showing that tissue-specific promoters drive distinct patterns of gene positioning during cell-type differentiation. In addition, the sequestration of heterochromatin at the nuclear envelope has been found to depend on lamin and lamin-associated proteins. On the chromatin side, H3K9 monomethylation, dimethylation and trimethylation were shown to be the critical signals for perinuclear anchoring in worm embryonic nuclei. Downregulation of an equivalent histone methyltransferase, G9a, in human cells has a similar effect. In worms, the sequestration of the terminal methyltransferase by repressed chromatin may facilitate the propagation of a heterochromatin compartment, much as the sequestration of the silent information regulatory complex does at telomeric foci in budding yeast. These results argue for conserved logic in eukaryotic nuclear organization
Mechanisms of heterochromatin subnuclear localization.
No full textTranscriptionally repressed heterochromatin becomes the dominant form of chromatin in most terminally differentiated cells. Moreover, in most cells, at least one class of heterochromatin is positioned adjacent to the nuclear lamina. Recent approaches have addressed the mechanism of heterochromatin localization, in order to determine whether spatial segregation contributes to gene repression. Findings in worms and human cells confirm a role for histone H3K9 methylation in heterochromatin positioning, identifying a modification that is also necessary for gene repression of worm transgenic arrays. These pathways appear to be conserved, although mutations in mammalian cells have weaker effects, possibly due to redundancy in positioning mechanisms. We propose a general model in which perinuclear anchoring is linked to an epigenetic propagation of the heterochromatic state, through histone modification
'If I should die tonight' poem
No full textHumorous poem copied by Harrison Kerr and written by Benjamin Franklin King ca. 1890. The poem, titled "If I should die tonight," jokes about money owed to the author and the shock he would experience at being repaid upon his death. It was written as a parody of a serious contemporary poem of the same title.
Harrison Henry Kerr (1839-1901), born in North Georgetown, Ohio, served along with his brother, Ezra, as a private in Company D of the 58th Ohio Volunteer Infantry. He was taken prisoner at the Battle of Chickasaw Bayou, Mississippi, on December 29, 1862., and held for three months before being exchanged and returning to his regiment. He was discharged on January 14, 1865. Following the war, he was married to Elizabeth (Rettig) Kerr. The two lived in Cleveland and had one son, Harrison McKinley Kerr. In 1888, he joined the Memorial Post No. 141, Grand Army of the Republic. He is buried in North Georgetown Cemetery
Substrate specificity of [alpha]-proteobacterial N-end rule adaptors
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis. "June 2016." In title on title page [alpha] appears as lower case Greek letters.Includes bibliographical references (pages 103-118).by Benjamin J. Stein.Ph. D
A Bacterial Growth Law out of Steady State.
No full textBacterial growth follows simple laws in constant conditions. However, bacteria in nature often face fluctuating environments. We therefore ask whether there are growth laws that apply to changing environments. We derive a law for upshifts using an optimal resource-allocation model: the post-shift growth rate equals the geometrical mean of the pre-shift growth rate and the growth rate on saturating carbon. We test this using chemostat and batch culture experiments, as well as previous data from several species. The increase in growth rate after an upshift indicates that ribosomes have spare capacity (SC). We demonstrate theoretically that SC has the cost of slow steady-state growth but is beneficial after an upshift because it prevents large overshoots in intracellular metabolites and allows rapid response to change. We also provide predictions for downshifts. The present study quantifies the optimal degree of SC, which rises the slower the growth rate, and suggests that SC can be precisely regulated
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