bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of cell proliferation and cellular shape change in branching morphogenesis of the embryonic mouse lung: Analysis using aphidicolin and cytochalasins
Authors: Goldin Geoffrey V. , Hindman Heather M. , Wessells Norman K. 
Published: June 2005

AbstractThe formation of induced supernumerary buds in the embryonic mouse tracheal epithelium has been used as a model system to analyse the respective roles of cell proliferation and microfilament‐mediated cell shape change during branching morphogenesis. In order to analyse the mitotic events associated with the formation of epithelial buds, the induction of supernumerary tracheal buds by mesenchymal grafts was carried out with the inhibitor of DNA synthesis, aphidicolin, present in the culture medium for varying intervals of time during the 16‐hour inductive process. The presence of aphidicolin for 10 to 16 hours of the inductive period blocks the formation of induced tracheal buds, whereas the presence of the inhibitor for half of that time (either the first 8 hours or the last 8 hours) does not prevent this morphogenetic event from taking place, although smaller buds resulted from induction under these conditions. Both the inhibition of DNA synthesis and the recovery from 10 μM aphidicolin treatment, as measured by 3H‐thymidine incorporation, were found to occur rapidly. The addition of 2 μM dihydrocytochalasin B (or cytochalasin B) together with aphidicolin during the second half of the inductive period inhibits the formation of supernumerary buds and upon removal of the cytochalasin rapid formation of buds takes place. We conclude that the formation of epithelial buds during branching morphogenesis occurs as a result of enhanced localized cell proliferation coupled with epithelial cell shape change (or preservation of cell morphology) mediated by microfilaments, which have been observed in both the apical and basal cytoplasm of the epithelial cells in the region where branching of the trachea is taking place.
Structure‐Activity relations of LHRH in birds
Authors: Millar R. P. , King J. A. 
Published: June 2005

AbstractStructural requirements in LHRH for gonadotropin‐releasing activity were investigated by comparing the activity of the natural vertebrate LHRH structural variants and synthetic analogues. Substitution of Arg8 results in a loss of activity of LHRH in mammals, whilst a number of amino acid substitutions for Arg8 retain high gonadotropin‐releasing activity in the chicken. Thus Arg8 of LHRH comprises an integral part of the binding site of LHRH and/or contributes towards the conformation of the binding site for the mammalian receptor while this does not pertain in the bird. The possibility that relative conformational stabilization of LHRH is important for biological activity in mammals but not birds, was supported by the demonstration that a γ‐lactam conformationally constrained analogue of LHRH was more active than LHRH in the mammalian system but equipotent in the bird. The chicken LHRH receptor is also relatively undiscriminating with regard to amino acid substitutions in positions 5 and 7. A series of LHRH analogues with pure antagonist activity in rats exhibited a spectrum of activities, from pure agonist to mixed activity and pure antagonist, in the chicken. These differences in LHRH structural requirements of the mammalian and avian receptor are reflected by a difference in molecular size of the chicken receptor (67,000) and mammalian receptor (60,000). Nevertheless, like the mammalian pituitary, the chicken pituitary does exhibit “desensitization” on prolonged exposure to LHRH.
Growth hormone: Its physiology and control
Authors: Scanes Colin G. , Lauterio Thomas J. 
Published: June 2005

AbstractGrowth hormone (GH) is a protein hormone produced by the somatotrophs of the anterior pituitary gland of birds and other vertebrates. The secretion of GH in birds is under hypothalamic control; it involves three peptidergic releasing factors: growth hormone‐releasing factor (GRF) (stimulatory); thyrotropin‐releasing hormone (TRH) (stimulatory); and somatostatin (SRIF) (inhibitory). In addition, there is evidence for effects of biogenic amines (including serotonin and norepinephrine) and prostaglandins at the level of the hypothalamus and possibly also the pituitary gland. In all avian species examined, plasma concentrations of GH are high in young posthatching chicks but low in the adult and embryo. The difference in plasma concentrations of GH between young and adult birds is due to both greater GH secretion and reduced clearance. The lower secretion of GH in adult birds reflects fewer somatotrophs in the pituitary, changes in somatotroph structure, and reduced GH responses to TRH or GRF administration. There is only limited data on the role of GH in birds. GH appears to be required for normal growth; acting at least in part by increasing somatomedin production. However, plasma concentrations of GH do not necessarily correlate with growth rate. For instance, in chicks with reduced growth rate owing to either goitrogen or protein deficiency in the diet, plasma concentrations of GH are elevated. GH also can influence lipid metabolism by increasing lipolysis, decreasing lipogenesis, and stimulating the uptake of glucose by adipose tissue. The physiological significance of these actions is, however, not established. In addition, GH affects the secretion of other hormones, the immune system, and perhaps also the reproductive system.
Hormonal and environmental interactions on thyroid function in the chick embryo and posthatching chicken
Authors: Kühn E. R. , Decuypere E. , Rudas P. 
Published: June 2005

AbstractRecent research has focused on developmental changes in thyroxine (T4) metabolism as well as hormonal and environmental interactions upon peripheral monodeiodination. Toward the end of incubation and the time of air space membrane perforation, concentrations of 3,3′,5′‐triiodothyronine T3 increase more rapidly than T4, while reverse T3 (rT3) decreases. Administration of glucocorticoids or prolactin (hormones known to increase at the end of incubation) 2 to 3 days prior to air chamber perforation can induce this change in T4 metabolism. Attention has been focused on two major environmental factors that influence T4 concentrations in posthatch chicks. T4 disappearance rate and peripheral T4 conversion are adjusted during thermal acclimation. More T3 will be generated in cold‐exposed chickens, and more rT3 will be produced at higher ambient temperatures. Peripheral T4 metabolism acts as an independent regulation pathway but accompanies changes in hypothalamothyroid activity. Changes in thyroid hormone levels following ambient temperature changes, therefore, are the result of a balance between central and peripheral control mechanisms, depending on age of the animal and degree and duration of the temperature change. In the hen, feeding also plays an important role in the regulation of the absolute levels and daily rhythms of plasma thyroid hormones. Fasting results in an increase in circulating T4 levels, but a decrease in T3 levels, owing to a lower 5′deiodinase activity, and also abolishes the circadian circulating T3 rhythm.
Avian endocrine responses to environmental pollutants
Authors: Rattner Barnett A. , Eroschenko Victor P. , Fox Glen A. , Fry D. Michael , Gorsline Jane 
Published: June 2005

AbstractMany environmental contaminants are hazardous to populations of wild birds. Chlorinated hydrocarbon pesticides and industrial pollutants are thought to be responsible for population declines of several species of predatory birds through eggshell thinning. Studies have demonstrated that these contaminants have estrogenic potency and may affect the functioning of the gonadal and thyroidal endocrine subsystems. Petroleum crude oil exerts toxicity externally, by oiling of plumage, and internally, by way of ingestion of oil while feeding or preening. Extensive ultrastructural damage to the inner zone of the adrenal, diminished adrenal responsiveness to adrenocorticotrophic hormone, and reduced corticosterone secretion rate suggest that low levels of plasma corticosterone reflect a direct effect of petroleum on the adrenal gland. Suppressive effects of oil on the ovary and decreases in circulating prolactin have been associated with impaired reproductive function. Large‐scale field studies of free‐living seabirds have confirmed some of the inhibitory effects of oil on reproduction that have been observed in laboratory studies. Organophosphorus insecticides, representing the most widely used class of pesticides in North America, have been shown to impair reproductive function, possibly by altering secretion of luteinizing hormone and progesterone. Relevant areas of future research on the effects of contaminants on avian endocrine function are discussed.
Hypotensive action of parathyroid hormone in chicken
Authors: Pang Peter K. T. , Zhang R. H. , Yang May C. M. 
Published: June 2005

AbstractIn a recent series of studies, the hypotensive action of parathyroid hormone (PTH) was demonstrated in several vertebrate species. In mammals, the mechanism of this direct action on specific vascular beds was studied. An increase in intracellular cyclic AMP and an inhibition of entry of extracellular calcium into the vascular tissue was correlated with the vasorelaxing action of PTH. In the present report, PTH was found to relax chicken mesenteric vessels in vitro in the presence or absence of constriction with concentrated potassium chloride (KCl). PTH produced dose‐related inhibition of the chicken vessel constricted with 10, 20, 40, or 60 mM KCl. Extracellular calcium‐dependent constriction of the chicken mesenteric artery was also decreased by PTH. An inhibitory effect was also observed with D600, a known calcium‐entry inhibitor, in the above in vitro test systems. The low affinity lanthanum‐resistant pool of calcium, which supposedly reflects the rate of calcium entry into cells, was also decreased by PTH in the control or KCl‐stimulated chicken mesenteric artery. These data suggest that PTH may produce vasorelaxation in chicken mesenteric artery by inhibition of calcium entry into cells. This vessel from the chicken seems to have a high turnover rate of calcium and may be a good model for studying the effects of substances on calcium entry in vascular smooth muscle.
In Vitro synthesis of vitellin by the ovary of the fiddler crab, Uca pugilator
Authors: Eastman‐Reks Sarah B. , Fingerman Milton 
Published: June 2005

AbstractDeveloping ovaries of the fiddler crab, Uca pugilator, were incubated in vitro in labeled leucine, which was incorporated into the egg yolk protein, vitellin. Two primary vitellin subunits, having molecular weights of 100,600 and 123,500, were separated by SDS‐polyacrylamide gel electrophoresis. These results show that the ovary of this crab has the capacity to synthesize vitellin.
On the use of α‐amanitin as a transcriptional blocking agent in mouse embryos: A cautionary note
Authors: Kidder Gerald M. , Green A. Fred , McLachlin Jeanne R. 
Published: June 2005

AbstractWe have tested the effect of α‐amanitin at 10, 50, and 100 μg/ ml, on precursor uptake and incorporation into poly(A)+ RNA and poly(A)− RNA of mouse embryos on days 2, 3 and 4 of gestation. Embryos were pretreated with the inhibitor for 2 hr, then labeled for 2 hr in its continued presence. RNA fractions were separated by affinity chromatography on oligo(dT)‐cellulose. α‐Amanitin did not suppress uptake of RNA precursors at any of the concentrations tested in any stage. At 10 μg/ml, we could not detect any effect on incorporation into either RNA fraction in any stage. Only the highest concentration tested, 100 μg/ml, was effective in all stages in substantially suppressing incorporation into poly(A)+ RNA within 2 hr. Longer treatments increased the level of suppression to a maximum of about 80%. Incorporation into poly(A)− RNA was suppressed to roughly the same extent. Despite previously reported data, it cannot be assumed that α‐amanitin at concentrations less than 100 μg/ml brings about a quick interruption of mRNA synthesis in preimplantation mouse embryos.
Muscle function studies in amputated lathyritic rats
Authors: Yeager Vernon L. 
Published: June 2005

AbstractThis study is presented to compare two methods of evaluating changes in muscle function after amputation of the left leg at the knee. Rats were fed a 50% Lathyrus odoratus diet, which causes exostoses to develop at sites of attachment of certain muscles. The rats were on the experiment for 3, 6, or 9 weeks. Muscles of rats killed at 6 weeks were weighed to determine whether atrophy or hypertrophy had occurred. Sizes of exostoses were evaluated subjectively at each time period. The left adductor longus and quadratus femoris muscles underwent considerable atrophy and their exostoses were smaller than on the right side. The left iliopsoas increased in weight and had the larger exostosis. However, the left pectineus increased in weight but had the smaller exostosis. It is concluded that changes in muscle weights and changes in sizes of exostoses both reflect changes in muscle function, but because the two methods respond by different mechanisms, the results do not always agree.
Possible function of 17β‐hydroxysteroid dehydrogenase in preimplantation hamster embryos
Authors: Wu Jung‐Tsung , Matsumoto Paul S. 
Published: June 2005

Abstract17β‐Hydroxysteroid dehydrogenase (17β‐HSD) catalyzes the interconversion of estradiol‐17β (E2) and estrone (E1). The present study is designed to investigate the following: (1) the developmental stage of hamster embryos at which 17β‐HSD activity first becomes detectable, and (2) the E1 → E2 and E2 → E1 conversion rate in the preimplantation hamster embryo. Embryos obtained from superovulated hamsters on days 1–4 were cultured in medium containing 107 ng [3H]E1 or – E2/ml and the respective conversion product, [3H]E2 or – E1, was isolated and assayed. The results show that (1) E1 → E2 conversion was active in all embryos at the rate of 0.57, 0.66, 0.54 and 0.48 fmol/embryo/hr for day 1 (one‐cell), 2 (two‐cell), 3 (eight‐cell) and 4 (blastocyst), respectively, and (2) E2 → E1 conversion was not detectable in hamster embryos. In long‐term blastocyst culture, E2 → E1 conversion becomes detectable at 25 hours and increases sharply from 25 to 47 hours. These results suggest that (1) 17β‐HSD may function mainly to convert E1 into E2 in preimplantation hamster embryos and (2) E2 → E1 conversion may become active only during and after implantation.
Cortical reaction and zona hardening in mouse oocytes following exposure to ethanol
Authors: Gulyas Bela J. , Yuan Lydia C. 
Published: June 2005

AbstractMouse oocytes were treated with 8% ethanol for 3–6 min. The rate and pathways of parthenogenetic activation, occurrence of cortical reaction, and zona solubility changes were assessed in alcohol‐treated eggs. The incidence of parthenogenetic activation was greatest (91%) after 3–4‐min exposure, and it was reduced (84%) after 5–6‐min exposure to alcohol. Also, the rate of haploid single pronucleate parthenogenones decreased and the rate of fragmented ova increased with increase time of exposure to ethanol. Ultrastructural observations showed occurrence of cortical reaction, disappearance and subsequent reappearance of short microvilli. A slight damage occurred to the ER in alcohol‐exposed ova. The zona dissolution assay utilizing äL‐chymotrypsin demonstrated decreased solubility of the zonae pellucidae after exposure to alcohol. The zona dissolution t50 increased from 0.5–2.5 min in nontreated unfertilized oocytes to about 4 h in activated ova. The t50 of in vivo fertilized eggs was 4 1/2 h. Empty zonae exposed to alcohol lysed at the same rate as nontreated control zonae did. The results indicate that activation of mouse oocytes with alcohol initiates completion of meiosis and triggers the cortical reaction, which results in subsequent hardening of the zona pellucida.
Protein synthesis by isolated pachytene spermatocytes in the absence of sertoli cells
Authors: Jutte N. H. P. M. , Jansen R. , Grootegoed J. A. , Rommerts F. F. G. , van der Molen H. J. 
Published: June 2005

AbstractIsolated rat pachytene spermatocytes were incubated in chemically defined medium supplemented with pyruvate and lactate, which are known to be essential energy substrates for these germ cells. Protein synthesis by the isolated cells was investigated by means of two‐dimensional polyacrylamide gel electrophoresis. The electrophoretic patterns of (35S)‐labeled proteins, synthesized by the pachytene spermatocytes during incubation in the presence of (35S)methionine either from 0–2 h or from 24–26 h after isolation, were almost completely identical. The patterns of newly synthesized proteins of freshly isolated spermatocytes and spermatids, however, showed several stage‐specific proteins in addition to many proteins common to both spermatogenic cell types. Hence, it was concluded that a stage‐specific pattern of protein synthesis can be maintained by pachytene spermatocytes during incubation for a period of 24 h in the absence of Sertoli cells but in the presence of a proper energy source.
Decrease in the number of primordial germ cells following injection of the animal pole cytoplasm into the vegetal pole region of Xenopus Eggs
Authors: Sakata Susumu , Kotani Minoru 
Published: June 2005

AbstractEffects of the egg cytoplasm on the formation of primordial germ cells (PGCs) were examined through microinjection into the subcortical cytoplasm near the vegetal pole of Xenopus laevis eggs. Injection of vegetal pole cytoplasm and physiological saline did not reduce the number of PGCs. However, the average number of PGCs in tadpoles at stage 46 decreased to about 60% of that in normal controls when the animal pole cytoplasm of fertilized eggs was injected into the intact eggs. Similar effects were observed when the animal pole cytoplasm of fertilized or unfertilized eggs was injected into eggs irradiated with a low dose of ultraviolet light. These facts suggest the possibility that inhibitor(s) of PGC formation exists in the animal pole cytoplasm of both fertilized and unfertilized eggs.
Dissociation and reaggregation of cells of Chrysaora quinquecirrha (cnidaria, scyphozoa)
Authors: Black Robert E. , Riley Gayle K. 
Published: June 2005

AbstractCells of scyphistomae, strobilae, and ephyrae were dissociated with trypsin and reaggregated. Clumping was inhibited in low Ca+ + and by puromycin, but not by collagenase or sugars. Reaggregates from the oral end of the polyp developed tentacles and mouths first and basal structures later, whereas the opposite sequence occurred with cells from the lower gastric region. Nile‐blue‐stained cells from hypostome or peduncle did not form specific structures in the reconstructed polyp, but were distributed throughout the animal. Ephyra cell aggregates showed little morphogenesis, whereas cells from presumptive ephyra tissue gave rise to structures with tentacles and multiple oral openings. Mixed reaggregates containing equal proportions of polyp and ephyra cells formed irregular structures with transparent outer layer and opaque inner cell mass, suggesting stage‐specific sorting.
Appearance of autoantigens during gonad maturation in the rainbow trout (Salmo gairdneri)
Authors: Secombes Christopher J. , Lewis Andrew E. , Needham Edward A. , Laird Lindsay M. , Priede Imants G. 
Published: June 2005

AbstractMaturing rainbow trout were immunised with testis plus Freund's complete adjuvant (FCA) to determine when autoantigen(s) appear on germ cells during spermatogenesis. Only testes containing spermatozoa and spermatids developed lesions, and no other germ cell types appeared to be involved. This response was gonad specific, but showed little correlation with antibody titres to spermatozoa. The necessary conditions that allow the development of autoantigen(s) on postmeiotic cells are discussed.
Limited and specific proteolysis of the zona pellucida by acrosin
Authors: Urch Umbert A. , Wardrip Nathan J. , Hedrick Jerry L. 
Published: June 2005

AbstractThe proteolytic action of boar sperm acrosin on its natural substrate, the zona pellucida, was investigated. Acrosin exhibited substrate specificity for the zona pellucida and differentially hydrolyzed the glycoprotein families composing the zona pellucida. In contrast to acrosin, trypsin was a less‐specific protease in terms of zona pellucida hydrolysis.
Some determinants of cellular adhesiveness in an embryonic cell line from Drosophila melanogaster
Authors: Fausto‐Sterling Anne , Muckenthaler F. A. , Hsieh Lily , Rosenblatt Peter L. 
Published: June 2005

AbstractWe have examined, under a number of conditions, the aggregation behavior of Schneider Line 2 cells established originally from embryos of Drosophila melanogaster. The work presented in this paper 1) further establishes appropriate conditions for the study of cellular adhesion in Drosophila cell lines; 2) shows that the adhesive capacity of Drosophila cell line cells, under our experimental conditions, depends upon the presence of CA2+ but not Mg2+; 3) shows that Drosophila cell line cells will not aggregate in the cold; and 4) shows that trypsin treatment inhibits the aggregation of cell line cells, although high concentrations of calcium ions interfere with the action of trypsin.
cAMP in ovine oocytes: Localization of synthesis and its action on protein synthesis, phosphorylation, and meiosis
Authors: Crosby Ian M. , Moor Robert M. , Heslop John P. , Osborn Jeremy C. 
Published: June 2005

AbstractIn the first series of experiments, the source of cAMP in the sheep oocyte was studied. Cholera toxin was shown to be a potent stimulator of cAMP in isolated sheep oocytes, demonstrating the presence of adenyl cyclase. There was no evidence for transmission of cAMP from stimulated myocardial cell monolayers to cumulus‐enclosed oocytes even though the existence of a concentration gradient of cAMP and of intercellular communication were demonstrated. However, gonadotrophin‐stimulated follicle shells were able to induce a rise in the cAMP content of denuded or cumulus‐enclosed oocytes in the same dish, independently of cell contact. Further experiments were designed to study the effects of a cholera toxin‐stimulated rise in cAMP on the maturation of oocytes. When applied to cumulus‐oocyte complexes, cholera toxin did not block germinal vesicle breakdown (GVBD), nor the accompanying changes in protein synthesis and phosphorylation, although there was evidence for a delaying effect. There were, however, indications that the toxin was inducing abnormalities that became gross when the concentration was raised 1 μg/ml. This high concentration of cholera toxin was able to block the maturation of oocytes in intact, gonadotrophin‐treated follicles, although once again abnormalities were evident. We conclude that the role of cAMP in the maturation of the sheep oocyte is different from that proposed in the mouse.
Anhydrobiosis in nematodes: Control of carbon flow through the glyoxylate cycle
Authors: Madin Katherine A. C. , Loomis Stephen H. , Crowe John H. 
Published: June 2005

AbstractDuring induction of anhydrobiosis the nematode Aphelenchus avenae synthesizes large quantities of trehalose and free glycerol the carbon for which apparently originates from lipid. In the present paper we show that these worms possess a functional glyoxylate cycle by which lipid is converted to carbohydrate. Furthermore, we suggest a mechanism for regulation of the pathway during induction of anhydrobiosis.