scholarly journals Positional information and pattern regulation in hydra: formation of the foot end

Development ◽  
1973 ◽  
Vol 30 (3) ◽  
pp. 727-740
Author(s):  
J. Hicklin ◽  
L. Wolpert
Keyword(s):  
Positional Information ◽  
Basal Disc ◽  
Time Required ◽  
Pattern Regulation

The time required for foot end formation increases with distance from the foot end. Using lateral grafting it was shown that both the peduncle and basal disc could induce a proximal axis when grafted into the gastric region. The time for foot end determination was shown to be about 4 h at the proximal end of the gastric region and to increase towards the head end. In general the determination of the foot end is similar to that of the head end.

Positional information and pattern regulation in Hydra. Dynamics of regions at the boundary

Development ◽  
1975 ◽  
Vol 33 (2) ◽  
pp. 499-510
Author(s):  
J. Hicklin ◽  
A. Hornbruch ◽  
L. Wolpert
Keyword(s):  
Positional Information ◽  
Boundary Region ◽  
The Times ◽  
Pattern Regulation ◽  
Cut Surface

The dynamics of boundary regions have been investigated mainly by axial grafting and with the emphasis on the head end. The time to lesist inhibition of head-end formation and the ability to inhibit head-end formation have been assayed under a variety of conditions. The times increase with distance from the head end. The times required by a boundary region to acquire the inhibitory properties of a head end are longer than those required to acquire resistance to inhibition. Determination of a head end is faster at a cut surface and at higher temperatures. The results are discussed in terms of a model involving two gradients. Some anomalous results are reported.

Nucleic acid and protein synthesis and pattern regulation in hydra

Development ◽  
1969 ◽  
Vol 21 (1) ◽  
pp. 55-70
Author(s):  
S. G. Clarkson
Keyword(s):  
Protein Synthesis ◽  
Dna Synthesis ◽  
Experimental Approach ◽  
Direct Evidence ◽  
Animal Cells ◽  
Rna And Protein Synthesis ◽  
Metabolic Activities ◽  
Time Required ◽  
Pattern Regulation

In a previous paper (Clarkson, 1969) data were presented which indicate that hypostome determination is accompanied by a large and rapid burst of RNA synthesis, a slight stimulation of protein synthesis, and no increase in DNA synthesis. More direct evidence concerning the relative importance of these metabolic activities in hypostome determination is reported in this paper. The experimental approach made use of the transplantation test of Webster & Wolpert (1966) in conjunction with some inhibitors of DNA, RNA and protein synthesis, the rationale being that if these metabolic activities play important roles in the determination of the hypostome, then their inhibition would be expected to have severe effects on the time required for this process. Regarding the inhibitors, hydroxyurea (HU) inhibits DNA synthesis in a variety of animal cells without altering rates of formation of RNA or protein (Young & Hodas, 1964; Yarbro, Kennedy & Barnum, 1965; Schwartz, Garofalo, Sternberg & Philips, 1965).

Studies on pattern regulation in hydra

Development ◽  
1966 ◽  
Vol 16 (1) ◽  
pp. 105-122
Author(s):  
Gerald Webster
Keyword(s):  
Detailed Analysis ◽  
Original Position ◽  
Axial Gradient ◽  
Characteristic Features ◽  
Time Required ◽  
Pattern Regulation

In a previous paper (Webster & Wolpert, 1966a) it was shown that during regulation the time required for the determination of the dominant region, the hypostome, was dependent on the original position of the hypostome-forming region on the linear axis. Hypostome determination occurred more quickly from distal than from proximal regions, suggesting an axial gradient. As Spiegelman (1945) has pointed out, a gradient in time for determination is not sufficient for limited realization to occur in a regulative system (Webster & Wolpert, 1966a). In addition, some mechanism for suppressing potentialities is required. One of the characteristic features of a dominant region is that it inhibits the formation of a new dominant region (Huxley & de Beer, 1934), and earlier work on hydra (Rand, Bovard & Minnich, 1926) has presented some evidence for inhibition of distal regeneration by distal structures. This paper will be concerned with a detailed analysis of the factors controlling hypostome formation.

The interaction of the organizing regions in hydra and its possible relation to the role of the cut end in regeneration

Development ◽  
1974 ◽  
Vol 31 (3) ◽  
pp. 541-555 ◽  
Author(s):  
Stuart A. Newman
Keyword(s):  
Cell Division ◽  
Pattern Formation ◽  
Positional Information ◽  
Regenerative Process ◽  
Basal Disc ◽  
Model Based ◽  
Pattern Regulation ◽  
Cut Surface

Regeneration in hydra does not necessarily involve cell division, so that the problem of pattern regulation is essentially one of finding the processes by which a given population of cells are assigned appropriate functions in the correct positions. The restoration and nature of the organizers or ‘dominant regions’ must also be explained. Lateral transplants of the two different organizer tissues (hypostome and basal disc) into the digestive regions of host animals unexpectedly antagonize one another's inductive ability, suggesting that the heretofore separately studied distal and proximal developmental fields may in fact be interconnected. A model based on this idea, incorporating the extinction results with classical findings, leads to the hypothesis of a role for leakage from the cut surface as a trigger for the regenerative process. This is tested using a ligature technique in which the cut surface is minimized when the hypostome is removed, and the degree of regeneration is found to be significantly lowered, in agreement with prediction. These results are discussed in relation to ‘positional information’ and ‘special substance’ models for pattern formation.

Mercury-204 Determination by Emission Spectroscopy

1965 ◽  
Vol 19 (3) ◽  
pp. 87-89 ◽  
Author(s):  
F. M. Smith
Keyword(s):  
Coefficient Of Variation ◽  
Isotope Shift ◽  
Emission Spectroscopy ◽  
Electrodeless Discharge ◽  
Discharge Lamp ◽  
Isotope Concentration ◽  
Single Determination ◽  
Time Required

The determination of mercury-204 was made by using the isotope shift of the 3984 A mercury line excited by electrodeless discharge. Densitometric traces were made from film recordings of the 3984 A line and the areas under the component peaks were determined. Ratios of each of these areas to the sum of the areas from all the line components are plotted against the isotope concentration to produce a working curve. The coefficient of variation for this method is approximately 11 percent The time required for a single determination (after fabrication of the discharge lamp) is about two hours.

scholarly journals THE EFFECTS ON BIOLOGICAL MATERIALS OF FREEZING AND DRYING BY VACUUM SUBLIMATION

1954 ◽  
Vol 100 (1) ◽  
pp. 81-88 ◽  
Author(s):  
Donald Greiff ◽  
Henry Pinkerton
Keyword(s):  
Influenza Virus ◽  
Biological Materials ◽  
Continuous Operation ◽  
Virus Suspension ◽  
Vacuum Sublimation ◽  
End Point ◽  
Different Temperatures ◽  
Time Required

A vacuum sublimation apparatus is described which will permit, (a) the removal of water from virus suspensions at temperatures ranging down to –80°C., (b) continuous operation with a minimum of attention from the investigator, (c) sealing off of samples at operating pressures (10–5 mm. Hg), (d) simultaneous lyophilization of aliquot samples at different temperatures, (e) isolation of a portion of the apparatus without disturbing the remainder of the system, and (f) determination of the end-point of sublimation without disturbing the samples. The time required for drying 0.1 ml. of influenza virus suspension was shown to increase markedly with decrease of temperature, 8 days being required for dehydration at –80°C. in contrast to 2 days at –30°C. and 1 day at 0°C.

Positional information and pattern regulation in hydra: enzyme profiles

Development ◽  
1975 ◽  
Vol 33 (4) ◽  
pp. 853-867
Author(s):  
Najma Zaheer Baquer ◽  
Patricia McLean ◽  
Amata Hornbruch ◽  
L. Wolpert
Keyword(s):  
Pentose Phosphate Pathway ◽  
Citrate Synthase ◽  
Positional Information ◽  
Pentose Phosphate ◽  
Basal Region ◽  
Redox Systems ◽  
Metabolic Pattern ◽  
Alternative Pathways ◽  
Redox States ◽  
Pattern Regulation

Certain key enzymes of alternative pathways of glucose metabolism, of amino acid metabolism and of redox systems have been measured in hydra and this profile compared with mammalian differentiated tissues with a view to locating pathways of specific importance in hydra. There was a marked constant proportionality in the major part of the enzymes investigated, the profile suggested a metabolic pattern geared to utilization of amino acids as a carbon source for biosynthesis and energy production and to the production and conservation of pyruvate. The importance of conversion to ionized forms was noted. The most notable specific proportion changes were the exceptionally low lactate dehydrogenase, malic enzyme and the relatively high citrate synthase. The proximal-distal gradients in hydra were examined and these gradients suggested a switch to a more anaerobic type of metabolism and an elevation of the pentose phosphate pathway as the basal region was approached. Measurements of the formation of 14CO2 from specifically labelled glucose provided additional evidence for the functional activity and polarity of the pentose phosphate pathway in hydra. The effect of oligomycin, which can reverse polarity in hydra, had a significant effect on gradients of enzymes eliminating all except that observed for G6P dehydrogenase. The profile suggested a movement towards a more anaerobic type of metabolism, in keeping with the known biochemical action of this inhibitor. It is suggested that redox states and/or phosphorylation states may be featured in the positional information of cells in hydra.

Rapid Measurement of Nutation NQR Spectra in Powders Using an RF Pulse Train

1996 ◽  
Vol 51 (5-6) ◽  
pp. 363-367 ◽  
Author(s):  
Nicolai Sinyavsky ◽  
Michał Ostafin ◽  
Mariusz Maćkowiak
Keyword(s):  
Asymmetry Parameter ◽  
Pulse Train ◽  
Pulse Action ◽  
Rf Pulses ◽  
Time Saving ◽  
Long Time ◽  
The Asymmetry ◽  
Rf Pulse ◽  
Time Required

Abstract The method of two-dimensional nutation NQR spectroscopy, introduced by Harbison in 1989, has been successfully used for determining of the asymmetry parameter of the EFG tensor for spin-3/2 nuclei in both powdered and monocrystal samples in the absence of an external magnetic field. The inconvenience inherent in the method, however, is the long time required, because data acquisition must be repeated for various RF pulse lengths. We discuss a method to reduce the time of the nutation experiment by using a sequence of identical short RF pulses of length r w and distance τ. It is shown that for an NQR frequency ω0 , frequency offset Δω, and pulse parameters satisfying the relation ω0τ + Δωtw = 2πk (k = 1, 2, 3,..., n) a synchronism of pulse action takes place and the nutation interferogram can be measured "stroboscopically" between the pulses. The maximum time saving factor that can be obtained as compared to the conventional nutation experiment is of the order of the number of pulses used in a pulse train. The method has been successfully applied for determination of the asymmetry parameter for one of the two 3 5 Cl sites in polycrystalline 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride).

DETERMINATION OF URANIUM IN FLOTATION CONCENTRATES AND IN LEACH LIQUORS BY X-RAY FLUORESCENCE

1959 ◽  
Vol 37 (1) ◽  
pp. 20-28 ◽  
Author(s):  
G. L. Smithson ◽  
R. L. Eager ◽  
A. B. VanCleave
Keyword(s):  
Direct Measurement ◽  
Pilot Plant ◽  
Internal Standard ◽  
Liquid Extraction ◽  
X Ray ◽  
Liquid Liquid Extraction ◽  
Northern Saskatchewan ◽  
Plant Operations ◽  
Time Required

X-Ray fluorescence has been applied to the analysis of flotation concentrates obtained from pegmatitic uranium ores occurring in Northern Saskatchewan. Approximate uranium analyses can be obtained by direct measurement on flotation concentrates but more accurate results are obtained by using an internal standard such as strontium or yttrium. The time required for an analysis, as compared to that of conventional chemical or fluorimetric methods, is considerably reduced and flotation pilot plant operations can therefore be more effectively controlled. The method has been extended to include the analysis of sulphate leach liquors obtained from the leaching of pegmatitic ores and their flotation concentrates. Organic phases obtained in liquid – liquid extraction studies can also be rapidly analyzed for uranium by X-ray fluorescence.

scholarly journals XXXIII.—I. On the Estimation of Carbon in Organic Substances by the Kjeldahl Method. II. Its Application to the Analysis of Potable Waters

1895 ◽  
Vol 37 (4) ◽  
pp. 743-757
Author(s):  
Charles Hunter Stewart
Keyword(s):  
Accurate Method ◽  
Great Accuracy ◽  
Organic Substances ◽  
Applied Chemistry ◽  
Carbon And Nitrogen ◽  
Kjeldahl Method ◽  
The Will ◽  
Time Required

An easy and yet accurate method of determining carbon and nitrogen in organic substances has long been a desideratum, especially among those engaged in the application of chemistry to biological, hygienic, and agricultural questions. For the determination of nitrogen the method of Dumas, with its numerous modifications, is still the only one applicable in all cases, but the time required for it, and the manipulative dexterity necessary, has prevented its wide application for the above-named purposes. The method of Will and Varrentrap, though less generally applicable, is easier, and, until the publication of Kjeldahl's method, was most frequently used in applied chemistry. Kjeldahl claims for his method the same applicability and as great accuracy as the Will and Varrentrap method, with the added advantage of greater ease in working.

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