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Biomedical subjects

J R Collier

Publications and source records attributed to J R Collier.

At least 19 recordsLinked to original sources
PubMed2000

A cell cycle model for somitogenesis: mathematical formulation and numerical simulation.

After many years of research, the mechanisms that generate a periodic pattern of repeated elements (somites) along the length of the embryonic body axis is still one of the major unresolved problems in developmental biology. Here we present a mathematical formulation of the cell cycle model for somitogenesis proposed in Development105 (1989), 119-130. Somite precursor cells in the node are asynchronous, and therefore, as a population, generate continuously pre-somite cells which enter the segmental plate. The model makes the hypothesis that there exists a time window within the cell cycle, making up one-seventh of the cycle, which gates the pre-somite cells so that they make somites discretely, seven per cycle. We show that the model can indeed account for the spatiotemporal patterning of somite formation during normal development as well as the periodic abnormalities produced by heat shock treatment. We also relate the model to recent molecular data on the process of somite formation.

Animals↗
PubMed1998

Shell differentiation and engrailed expression in the Ilyanassa embryo.

We have used in situ hybridization and immunocytochemistry to study the expression of the engrailed-related gene, Ily-en in embryos of the marine mud snail Ilyanassa obsoleta. We find that Ily-en is only expressed in shell gland cells. Only mRNAs localized in the shell gland hybridize to an antisense probe of the Ily-en homeobox. Similarly, only shell gland cells or shell-forming cells are stained by the monoclonal antibody 4D9, which was raised to the engrailed-class protein from Drosophila. Ilyanassa embryos made deficient in vegetal cytoplasm by removing the third polar lobe fail to differentiate an organized external shell. They do however make some randomly oriented internal shell fragments in which Ily-en is expressed. Because Ily-en is expressed in shell gland cells of both normal and lobeless embryos, we conclude that the determinant(s) required for Ily-en expression are not exclusively localized in the polar lobe.

Animals↗
PubMed1996

Pattern formation by lateral inhibition with feedback: a mathematical model of delta-notch intercellular signalling.

In many developing tissues, adjacent cells diverge in character so as to create a fine-grained pattern of cells in contrasting states of differentiation. It has been proposed that such patterns can be generated through lateral inhibition--a type of cell-cell interaction whereby a cell that adopts a particular fate inhibits its immediate neighbors from doing likewise. Lateral inhibition is well documented in flies, worms and vertebrates. In all of these organisms, the transmembrane proteins Notch and Delta (or their homologues) have been identified as mediators of the interaction--Notch as receptor, Delta as its ligand on adjacent cells. However, it is not clear under precisely what conditions the Delta-Notch mechanism of lateral inhibition can generate the observed types of pattern, or indeed whether this mechanism is capable of generating such patterns by itself. Here we construct and analyse a simple and general mathematical model of such contact-mediated lateral inhibition. In accordance with experimental data, the model postulates that receipt of inhibition (i.e. activation of Notch) diminished the ability to deliver inhibition (i.e. to produce active Delta). This gives rise to a feedback loop that can amplify differences between adjacent cells. We investigate the pattern-forming potential and temporal behaviour of this model both analytically and through numerical simulation. Inhomogeneities are self-amplifying and develop without need of any other machinery, provided the feedback is sufficiently strong. For a wide range of initial and boundary conditions, the model generates fine-grained patterns similar to those observed in living systems.

Animals↗
PubMed1993

Localized expression of the H-ras proto-oncogene during Ilyanassa development.

We have immunostained Ilyanassa embryos with an antibody to the ras protein and shown that the ras gene (1) is not expressed from early cleavage through the gastrula stage, but (2) is expressed during organogenesis by both normal and lobeless embryos, (3) that the ras protein is first synthesized from the third day of development in the normal embryo and from the fifth day of development in the lobeless embryo, and (4) that the expression of the ras protein is localized in mesodermal lineages of both normal and lobeless embryos.

Animals↗
PubMed1985

Midline granuloma.

Explore the source record for details and available documents.

Granuloma, Lethal Midline↗
PubMed1983

Protein synthesis during Ilyanassa organogenesis.

The proteins labeled by normal and lobeless embryos of Ilyanassa obsoleta incubated in [35S]methionine during early and late organogenesis were shown by two-dimensional electrophoresis to be qualitatively equivalent. It is concluded that these polypeptides are part of the ubiquitous proteins required for cellular maintenance and that they are not uniquely associated with the differentiation of any specific organ or structure.

Animals↗
PubMed1978

Immunity to Lancefield's group E. streptococcus: flank inoculation of susceptible and immune swine.

Healthy swine flank inoculated with Lancefield's group E Streptococcus sp developed characteristic signs of streptococcal lymphadenitis of swine; however, abscesses were found in prefemoral lymph nodes rather than in cervical lymph nodes. After 6 months, swine (recovered from the cervical form of streptococcal lymphadenitis of swine caused by oral exposure to group E Streptococcus) were flank inoculated with group E Streptococcus sp. Only transitory signs of diseases developed and abscesses did not develop in the prefemoral lymph nodes.

Abscess↗
PubMed1978

Immunity to Lancefield's group E Streptococcus: passive protection of swine.

Healthy swine from one source were randomly allotted to 3 groups of 3 pigs each. Troup I and II pigs were parenterally dosed with serum obtained from swine in the convalescent stage of streptococcic lymphadenitis of swine. Group III pigs were contact controls. The swine of all groups were orally exposed to Lancefield's group E Streptococcus sp. During the next 3 weeks, the controls evidenced little resistance to the development of streptococcic lymphadenitis of swine, whereas the principals evidenced considerable resistance to development of the disease.

Agglutinins↗
PubMed1976

Evaluation of a vaccine for control of streptococcic lymphadenitis of swine.

Three tirals were conducted to evaluate the use of a vaccine for control of streptococcic lymphadenitis of swine. Clinically normal swine were vaccinated orally, according to the manufacturer's instructions. Unvaccinated controls and the vaccinated pigs were subsequently inoculated with a virulent strain of the etiologic agent, group E Streptococcus, serotype IV. At necropsy, 47 of the 51 vaccinated pigs (92.1%) were free of cervical abscesses, whereas 20 of the 21 control pigs (95.2%) developed cervical abscesses.

Abscess↗
PubMed1976

Shipping fever pneumonia in yearling feedlot cattle.

During each week of 1974, we surveyed, for illnesses and deaths, a continually changing population of yearling feedlot cattle that, for the year, totaled 407,000 animals. About 5.1% of the cattle sickened and, of these, 18.9% died. From the 3,943 fatalities, 1,988 necropsies were made. About 75% of the clinical diagnoses and 64% of the necropsy diagnoses were respiratory tract diseases; of the fatalities from respiratory tract diseases, 75% were attributed to shipping fever pneumonia. Nearly 72% of fatal cases of shipping fever pneumonia occurred during the first 45 days on feed. In the lungs of most cattle with shipping fever pneumonia, bronchiolitis, fibrinous exudate, colonies of microorganisms, lymphatic clots, intravascular clots, thromboses, and foci of necrosis were found. Pasteurella spp, Mycoplasma spp, and infectious bovine rhinotracheitis virus were isolated from pneumonic tissues. It was hypothesized that pathogenic Pasteurella spp and other microorganisms in nasal secretions transfer from the nasopharynx into the lungs by draining along the tracheal floor into ventral bronchi, bronchioles, and alveoli, and that pasteurella endotoxin, formed in infected lobules, thromboses and occludes lymphatics, capillaries, and veins and thereby causes ischemic necrosis.

Animals↗
PubMed1976

An electrophoretic analysis of RNA synthesis in normal and lobeless Ilyanassa embryo.

RNA from pulse-labelled normal and lobeless Illyanassa embryos was analysed by electrophoresis on polyacrylamide gels. The proportional distribution of radioactivity among the RNAs made by these two types of embryos was compared statistically. It was shown that removal of the third polar lobe from the Ilyanassa egg at first cleavage did not produce any change in the proportion of several size classes of RNA transcribed during the first day od development. The post-gastrular lobeless embryo did show a significant deviation from the normal pattern of RNA synthesis, though it is not clear that this was a direct effect on transcription by the polar lobe cytoplasm.

Animals↗