Biomedical subjects
A Stoker
Publications and source records attributed to A Stoker.
Sticking to their routes
Explore the source record for details and available documents.
Consolidating motor neuron identity.
Explore the source record for details and available documents.
Phosphotyrosine signalling as a regulator of neural crest cell adhesion and motility.
We demonstrate that neural crest cell-cell adhesion, cell-substrate adhesion, and ultimately cell motility, are highly dependent on the balanced action of tyrosine kinases and tyrosine phosphatases. Neural crest cell migration on fibronectin is diminished in the presence of the tyrosine phosphatase inhibitor vanadate or tyrosine kinase inhibitor herbimycin A, while cadherin-rich cell-cell adhesions are significantly increased. In contrast, cells treated with the kinase inhibitor genistein have decreased motility, rearrange rapidly and reversibly into a pavement-like monolayer, but have no increase in cadherin interactions. Genistein-sensitive tyrosine kinases may therefore abrogate a latent sensitivity of neural crest cells to contact-mediated inhibition of movement. Furthermore, we show that the activity of herbimycin A-sensitive kinases is necessary for focal adhesion formation in these cells. Moreover, the size and distribution of these adhesions are acutely sensitive to the actions of tyrosine phosphatases and genistein-sensitive kinases. We propose that in migrating neural crest cells there is a balance in phosphotyrosine signalling which minimises both cell-cell adhesion and contact inhibition of movement, while enhancing dynamic cell-substrate interactions and thus the conditions for motility.
Retinotectal ligands for the receptor tyrosine phosphatase CRYPalpha.
The cell adhesion molecule-like tyrosine phosphatase CRYPalpha is localized on retinal axons and their growth cones. We present evidence that two isoforms of this type IIa phosphatase, CRYPalpha1 and CRYPalpha2, have extracellular ligands along the developing retinotectal pathway. Using alkaline phosphatase fusion proteins containing the CRYPalpha1 ectodomain, we detect a prominent ligand on basement membranes of the early retina, optic stalk, and chiasm. A second ligand is observed in the endfeet region of radial processes in the developing stratum opticum, the site of initial retinal axon invasion. This latter ligand binds CRYPalpha2 preferentially. Further ligand interactions are detected for both CRYPalpha protein isoforms in retinorecipient tectal laminae and on retinal fibers themselves. CRYPalpha thus has cell- and matrix-associated ligands along the entire retinotectal projection. Moreover, these ligands appear to be heterotypic and interact with CRYPalpha through both its immunoglobulin and fibronectin type III regions. The anteroposterior levels of the ligands are relatively uniform within the retina and tectum, suggesting that the CRYPalpha protein within retinal axons does not directly recognise topographically graded guidance cues. We propose that CRYPalpha may have a permissive role in promoting retinal axon growth across the eye and tectum and that its functions are modulated temporally and spatially by isoform-specific interactions with cell- and matrix-associated ligands.
Protein tyrosine phosphatases and neural development.
During neural development, cells interact dynamically with each other and with the extracellular matrix, using cell signaling to control differentiation, axonogenesis, and survival. Enzymes that regulate protein tyrosine phosphorylation often lie at the core of such cell signaling. Protein tyrosine phosphatases (PTPases) are recognized as being of central importance here, and a growing family of PTPases are now known to be expressed in embryonic neurons and glia. Both receptor-like and cytoplasmic enzymes have been identified. The receptor family includes immunoglobulin superfamily members that influence cell-cell adhesion, proteoglycans that control neurite growth, and enzymes in Drosophila that regulate axon guidance and target cell recognition. Cytoplasmic PTPases are implicated in nerve cell commitment and potentially in the regulation of cell survival. This review outlines what we currently know about PTPases in the nervous system and presents concepts concerning their possible modes of action.
The expression of receptor tyrosine phosphatases is responsive to sciatic nerve crush.
Given the importance of phosphotyrosine signaling in growth cone dynamics, we have examined the embryonic and adult expression of receptor-like protein tyrosine phosphatases in sensory neurons and studied their responsiveness to nerve lesions in young adult animals. The phosphatases LAR, PTPsigma, and PTPalpha are expressed in most neurons of E14 and E18 rat embryo dorsal root ganglia, while BEM-1 is expressed in a more restricted subset of these neurons. These phosphatases continue to be expressed in young adult animals, suggesting that they have roles in mature as well as in developing dorsal root ganglia neurons. After an experimental sciatic nerve crush, the expression of the phosphatase genes was significantly and differentially altered in these neurons. PTPsigma mRNA was increased by 50% after 3 days, while LAR and PTPalpha expression dropped by 50 and 20%, respectively. BEM-1 mRNA levels were unaltered. These data show that mRNA levels of specific tyrosine phosphatase genes are highly responsive to nerve damage and may be reset to a new and potentially optimal pattern of expression more conducive for nerve regeneration. We propose that tyrosine phosphatases are not only involved in primary axonogenesis but can also now be implicated in the molecular control of adult nerve repair.
Perceived family relationships in drug abusing adolescents.
A group of 15- to 16-year-old adolescents were asked to report on their perception of their own family relationships, previous family experiences and their perceptions of their relationships with their fathers and with their mothers. They were also asked to report on their use of psychoactive drugs. Drug users were more likely than non-users to perceive their families as distant and less involved, with poor communications, mistrusting and punitive. Fathers were more likely perceived to be ineffective, and less significant than mothers. Drug users reported more parental separation, divorce, re-marriage and bereavement.
A novel Bacillus thuringiensis gene encoding a Spodoptera exigua-specific crystal protein.
Only one of the four lepidoptera-specific crystal protein subclasses (CryIC) Bacillus thuringiensis was previously shown to be highly toxic against several Spodoptera species. By using a cryIC-derived nucleotide probe, DNA from 25 different strains of B. thuringiensis was screened for the presence of homologous sequences. A putative crystal protein gene, considerably different from the cryIC gene subclass, was identified in the DNA of strain 4F1 (serotype kenyae) and cloned in Escherichia coli. Its nucleotide sequence was determined and appeared to contain several features typical for a crystal protein gene. Furthermore, the region coding for the N-terminal part of the putative toxic fragment showed extensive homology to subclass cryIA sequences derived from gene BtII, whereas the region coding for the C-terminal part appeared to be highly homologous to the cryIC gene BtVI. With an anti-crystal protein antiserum, a polypeptide of the expected size could be demonstrated in Western immunoblots, onto which a lysate of E. coli cells harboring the putative gene, now designated as BtXI, had been transferred. Cells expressing the gene appeared to be equally toxic against larvae of Spodoptera exigua as recombinant cells expressing the BtVI (cryIC)-encoded crystal protein. However, no toxicity against larvae of Heliothis virescens, Mamestra brassicae, or Pieris brassicae could be demonstrated. The nucleotide sequence analysis and the toxicity studies showed that this novel crystal protein gene falls into a new cryl gene subclass. We propose that this subclass be referred to as cryIE.
Pharmaceuticals and health policy: an Indian example.
The production and consumption of allopathic medicines in less developed countries has far-reaching effects. In particular, the legitimization of allopathic medicine endows professional groups and sectors of industry with a special status, supports some patterns of healthcare, and neglects others. Research in India demonstrates that people equate "more drugs' with "a better situation' and this is seen as the most "appropriate' solution to India's pharmaceuticals problems. The belief is expressed in matters such as Government policy on the pharmaceutical industry and the development of health services. However, these dominant assumptions, and the equation of drug prescription with medical practice, have a negative effect on health.
Plain film analysis in sigmoid volvulus.
Explore the source record for details and available documents.
20 years with the certifying board.
Explore the source record for details and available documents.
Mercury bichloride and tumor recurrence in colon anastomosis.
Explore the source record for details and available documents.
Don't forget prostatic carcinoma in abdominal carcinomatosis.
An incarcerated hernia containing peritoneal secondaries from carcinoma of the prostate is presented. Abdominal carcinomatosis may be due to a prostatic primary and will benefit from hormonal treatment.