Biomedical subjects
Publications and source records attributed to K Simkiss.
1. Incubating eggs at reduced temperatures leads to a decline in the rate of embryonic development. 2. All tissues do not respond equally and the migration of primordial germ cells is delayed in time, but occurs at an earlier stage of development than for normally incubated eggs. 3. The results are interpreted in relation to the integrated development of the gonad.
A new helper cell line designated L3.07, has been used to package spleen necrosis virus (SNV)-based vectors, resulting in the production of high titres of replication defective retroviruses. One of these vectors, vSNO21 has been shown to infect avian primordial germ cells (PGCs).
Chicken primordial germ cells were infected with a defective retrovirus containing the Escherichia coli lacZ gene and injected into the heart of stage 15 embryos. DNA samples were isolated from various tissues of the injected embryos at different stages of development and were examined for the presence of the lacZ gene using the polymerase chain reaction. Integration of the retrovirus DNA was demonstrated with a 32P-labelled oligonucleotide in five-, 10- and 18-day embryos. This quick procedure provides an opportunity for the early detection of foreign DNA in small numbers of transfected cells and is a valuable tool in the detection of transgenic animals.
The chemosterilant drug busulphan (1, 4-butanediol dimethane sulphonate) has been applied to embryos of the domestic fowl at doses of from 1 to 500 micrograms after 48 hours incubation. Direct application caused a number of teratological effects. These could be avoided by injecting the drug in sesame oil directly into the yolk. Embryos treated in this way could be sterilised with an efficiency of over 95 per cent with minimal side effects to the young embryo. The technique provides a method for destroying primordial germ cells that will facilitate studies of germ cell/stroma interactions in the gonad and facilitate the production of transgenic birds.
Explore the source record for details and available documents.
1. Experiments were undertaken to attempt to sterilise fowl embryos with ultraviolet light. Such sterilised embryos would be useful as recipients of genetically manipulated germ cells. 2. The germinal crescents of embryos were exposed to a calibrated UV source at stages 4 and 8 to 10 of incubation for 30 s, 3 min and 10 min. Teratological and sterility effects were studied at periods up to 6 d of incubation. 3. Simply exposing embryos by opening the shell produced a number of abnormalities and mortalities. These decreased with the age of the embryo but increased with the dosage of irradiation. 4. Although there was abundant evidence for UV-induced cell damage, the sterility of the embryos was usually less than 75%.
1. A simple artificial diet was devised for larvae of Lucilia sericata Meigen. 2. A basic diet of 20 g/l agar with 20% horse blood and added yeast sustained normal growth and development, as compared with a lamb meat control. 3. When yeast was added to the blood agar diet at 50 g/l, both peak and final larval weights were increased by 25-50% at higher larval densities (2-8 larvae/g diet) and the hatchling-adult development period was reduced by about 3 days. 4. No adult insects emerged on an agar-yeast diet without blood. Increasing the concentration of blood from 10% to 20% increased adult weight at emergence by 50%, though developmental period was not significantly affected. 5. Increasing larval density significantly reduced the weights of pupae and emergent adults (by up to 50%), both on the blood-agar-yeast diet and the lamb meat control. Percentage survival fell from 80-90% to below 10% on the blood-agar-yeast diet at the highest densities of 4 or 8 larvae/g diet, though survival on lamb was not significantly affected by density.
Inorganic granules of the general type CaMgP2O7 are found within cells of a wide range of species. The granules are amorphous to X-rays and occur in membrane-bound compartments. They accumulate a variety of cations from the body fluids of these animals. The interaction of zinc ions with pyrophosphate granules from cells of the snail Helix aspersa have been studied in vivo and in vitro by X-ray absorption spectroscopy and X-ray diffraction. The in vivo deposits incorporate zinc and remain amorphous although the pyrophosphate is hydrolysed to orthophosphate. In this in vitro reaction the mineral becomes crystalline but there is little change in the form of the The results clearly indicate a role for the cellular system in maintaining the amorphous state and in the hydrolysis of pyrophosphate to orthophosphate. As such they provide a model system for some of the changes observed in precursors of bone mineral and in pathological changes in the calcification of cartilage.
1. The PCO2 and PO2 levels of oxygenated and deoxygenated embryonic blood were measured in normal and shell-less cultured embryos. 2. Embryos in shell-less culture were both hypoxic and hypocapnic, suggesting that wetting the respiratory membranes and the reduction in their functional area is distorting their normal function. 3. Despite this hypocapnia, there was evidence for an increase in base excess during incubation. This suggests that plasma bicarbonate is derived from renal sources rather than by resorbing the eggshell calcium carbonate, which is, of course, absent from shell-less cultures.
1. Oscillating temperatures cause an increase in 65Zn uptake into the digestive gland of M. edulis when compared with the effects of constant temperatures. 2. The increased uptake is associated with a change in the distribution of 65Zn onto cytoplasmic proteins. There is a fall in the percentage of metal on the greater than 70 K dalton fraction and a rise in the 3 K dalton fraction. 3. A possible hypothesis is produced to explain these effects in terms of heat lability of metal-protein ligands.
An equation is derived for quantifying the diffusion of gases through the funnel-shaped pores of eggshells. Calculations based on this approach indicate that diffusion in such pores is largely determined by the inner pore radius and that the thickness of the eggshell and its cuticle are relatively unimportant. The approach is extended to include other noncylindrical pores.
There is a critical period between 3 and 7 days of incubation when the absence of turning in eggs of the domestic fowl leads to increased mortality and decreased embryo growth. This critical period coincides with the time of subembryonic fluid formation, and it is suggested that the absence of turning leads to the presence of unstirred layer effects in fluid secretion. This fluid deficiency persists throughout the subsequent development of the embryo. Experiments on shell-less culture systems support this interpretation in preference to other explanations of embryo death in unturned eggs, which usually refer to chorion adhesion to shell membranes.
The diffusion of gases through the avian eggshell has usually been interpreted as an example of Fick's law, and this appears to be the best explanation for gas exchange through narrow long pores. Many eggshells, however, contain more elaborate pores, of which the funnel-shaped type is the most common. It is suggested that most of the resistance to diffusion through these types of pores is best explained by Stefan's law of diffusion through apertures. The implications of this theory to the understanding of pore functions are discussed.
Explore the source record for details and available documents.
We report the use of X-ray-absorption spectroscopy (x.a.s.) to study the local atomic environment of cations in intracellular granules from the hepatopancreas of Helix aspersa. Both the calcium K-edge in these concretions and the manganese K-edge in doped specimens were measured. Electron-microprobe measurements confirm that the introduced Mn2+ is concentrated in irregular growths on the surfaces of the granules. The near-edge structure (x.a.n.e.s.) of calcium is similar to that of manganese, indicating that the oxygen-co-ordination spheres of both cations share a similar symmetry. From the extended structure (e.x.a.f.s.) the metal-oxygen bond lengths of 0.230 nm (2.30A) for Ca-O and 0.218 nm (2.18A) for Mn-O [+/- 0.004 nm (0.04A)] were determined, reference being made to a variety of model compounds. The low density of the granules (2.07 g/cm3), together with the local atomic distribution, suggest an open hydrated structure for these phosphate deposits. Detailed analysis of the distribution of nearest-neighbour oxygen atoms demonstrates that this is asymmetric and considerably broader for Ca2+ than for Mn2+. Compared with the model compounds, the Ca2+ environment in the granules is similar to that observed in Ca2P2O7. I.r. spectra indicate the presence of condensed phosphate groups in the granules, with the strong possibility these are pyrophosphate (P2O7(4-) groups.
The ultrastructure of the hepatopancreas of the crayfish Austropotamobius pallipes (Lereboullet) is described in relation to its function in digestion. X-ray microprobe analyses of the cells of this tissue have been obtained after using a variety of fixatives and plasma oxygen etching. The distribution of metals in the digestive cells is considered in relation to the polarization of the cells and their ability to absorb materials across the apical and basal cell membranes.
Explore the source record for details and available documents.
Certain cells in the hepatopancreas of the common garden snail (Helix aspersa) contain intracellular granules that are sites of metal-ion accumulation. These granules have been extracted and investigated by u.v. and i.r. spectroscopy, atomic-absorption spectroscopy, X-ray microanalysis, thermogravimetric analysis, enzymic assay and microanalysis. The deposits contain about 18% (w/w) water, 5% (w/w) organic matter and 76% (w/w) inorganic material of which the main components are Ca2+, Mg2+ and P2O7(4)-. The possible origin of these granules is discussed, as is their role in detoxifying heavy-metal ions.