Paediatrics (RCH) - Research Publications
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ItemCentromere protein B null mice are mitotically and meiotically normal but have lower body and testis weights(ROCKEFELLER UNIV PRESS, 1998-04-20)CENP-B is a constitutive centromere DNA-binding protein that is conserved in a number of mammalian species and in yeast. Despite this conservation, earlier cytological and indirect experimental studies have provided conflicting evidence concerning the role of this protein in mitosis. The requirement of this protein in meiosis has also not previously been described. To resolve these uncertainties, we used targeted disruption of the Cenpb gene in mouse to study the functional significance of this protein in mitosis and meiosis. Male and female Cenpb null mice have normal body weights at birth and at weaning, but these subsequently lag behind those of the heterozygous and wild-type animals. The weight and sperm content of the testes of Cenpb null mice are also significantly decreased. Otherwise, the animals appear developmentally and reproductively normal. Cytogenetic fluorescence-activated cell sorting and histological analyses of somatic and germline tissues revealed no abnormality. These results indicate that Cenpb is not essential for mitosis or meiosis, although the observed weight reduction raises the possibility that Cenpb deficiency may subtly affect some aspects of centromere assembly and function, and result in reduced rate of cell cycle progression, efficiency of microtubule capture, and/or chromosome movement. A model for a functional redundancy of this protein is presented.
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ItemRegulation of L-selectin-mediated rolling through receptor dimerization(ROCKEFELLER UNIV PRESS, 1998-10-05)L-selectin binding activity for its ligand expressed by vascular endothelium is rapidly and transiently increased after leukocyte activation. To identify mechanisms for upregulation and assess how this influences leukocyte/endothelial cell interactions, cell-surface dimers of L-selectin were induced using the coumermycin-GyrB dimerization strategy for cross-linking L-selectin cytoplasmic domains in L-selectin cDNA-transfected lymphoblastoid cells. Coumermycin- induced L-selectin dimerization resulted in an approximately fourfold increase in binding of phosphomanan monoester core complex (PPME), a natural mimic of an L-selectin ligand, comparable to that observed after leukocyte activation. Moreover, L-selectin dimerization significantly increased (by approximately 700%) the number of lymphocytes rolling on vascular endothelium under a broad range of physiological shear stresses, and significantly slowed their rolling velocities. Therefore, L-selectin dimerization may explain the rapid increase in ligand binding activity that occurs after leukocyte activation and may directly influence leukocyte migration to peripheral lymphoid tissues or to sites of inflammation. Inducible oligomerization may also be a common mechanism for rapidly upregulating the adhesive or ligand-binding function of other cell-surface receptors.
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ItemCollagen II is essential for the removal of the notochord and the formation of intervertebral discs(ROCKEFELLER UNIV PRESS, 1998-11-30)Collagen II is a fibril-forming collagen that is mainly expressed in cartilage. Collagen II-deficient mice produce structurally abnormal cartilage that lacks growth plates in long bones, and as a result these mice develop a skeleton without endochondral bone formation. Here, we report that Col2a1-null mice are unable to dismantle the notochord. This defect is associated with the inability to develop intervertebral discs (IVDs). During normal embryogenesis, the nucleus pulposus of future IVDs forms from regional expansion of the notochord, which is simultaneously dismantled in the region of the developing vertebral bodies. However, in Col2a1-null mice, the notochord is not removed in the vertebral bodies and persists as a rod-like structure until birth. It has been suggested that this regional notochordal degeneration results from changes in cell death and proliferation. Our experiments with wild-type mice showed that differential proliferation and apoptosis play no role in notochordal reorganization. An alternative hypothesis is that the cartilage matrix exerts mechanical forces that induce notochord removal. Several of our findings support this hypothesis. Immunohistological analyses, in situ hybridization, and biochemical analyses demonstrate that collagens I and III are ectopically expressed in Col2a1-null cartilage. Assembly of the abnormal collagens into a mature insoluble matrix is retarded and collagen fibrils are sparse, disorganized, and irregular. We propose that this disorganized abnormal cartilage collagen matrix is structurally weakened and is unable to constrain proteoglycan-induced osmotic swelling pressure. The accumulation of fluid leads to tissue enlargement and a reduction in the internal swelling pressure. These changes may be responsible for the abnormal notochord removal in Col2a1-null mice. Our studies also show that chondrocytes do not need a collagen II environment to express cartilage-specific matrix components and to hypertrophy. Furthermore, biochemical analysis of collagen XI in mutant cartilage showed that alpha1(XI) and alpha2 (XI) chains form unstable collagen XI molecules, demonstrating that the alpha3(XI) chain, which is an alternative, posttranslationally modified form of the Col2a1 gene, is essential for assembly and stability of triple helical collagen XI.
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ItemDNA vaccines for bacterial infections(BLACKWELL SCIENCE, 1997-08-01)DNA vaccines are an exciting development in vaccine technology which may have a special role in preventing viral infections and as 'theracines' for cancer. Their use in preventing bacterial infections has, by comparison, been less well documented. While it is unlikely that traditional, highly successful and cheap vaccines for diseases such as diphtheria will be replaced by DNA vaccines, naked DNA may be particularly appropriate for preventing bacterial infections where cytotoxic T cells confer protection, or where a Th1 type T cell response mediates resistance. For example, DNA vaccines containing different mycobacterial antigens have been shown to inhibit overt infections by Mycobacterium tuberculosis in rodent models. The use of DNA vaccines in bacterial infections may be complicated by fundamental differences between prokaryotic and eukaryotic genes and gene products, including mRNA stability, codon bias, secondary structures surrounding native start sequences and glycosylation. These problems can be solved by re-synthesis of bacterial genes to produce 'new' sequences which are more highly expressed by eukaryotic cells.
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ItemNo Preview AvailableCHROMOSOME TESTING IN CHILDREN WITH DEVELOPMENTAL DELAY IN WHOM THE ETIOLOGY IS NOT EVIDENT CLINICALLY(BLACKWELL SCIENCE, 1993-10-01)A review was carried out to establish the value of chromosome testing in children with significant developmental delay, where the aetiology was not evident clinically. During 1990, 315 children had been assessed at a child development clinic and found to be significantly delayed in one or more areas of development; in 256, the aetiology was not evident clinically. Chromosome testing of these children revealed an abnormality in 10 (3.9%). Thirty children had dysmorphic features; six (20%) of these had an abnormal karyotype. Four (2%) of the 226 who had no dysmorphic features had a chromosome abnormality. One hundred and fifty-five children had intellectual disability; eight (5%) of these had an abnormal karyotype. Two (2%) of 101 who had a specific delay in their development had a chromosome abnormality. The advantages of chromosome testing in children with developmental delay in whom the aetiology is not evident clinically are discussed.
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ItemNo Preview AvailableLONG-TERM NEUROLOGIC CONSEQUENCES OF NUTRITIONAL VITAMIN-B12 DEFICIENCY IN INFANTS(MOSBY-ELSEVIER, 1992-11-01)A review of the clinical findings in six infants with nutritional vitamin B12 deficiency seen during the last 10 years was undertaken and an attempt made to obtain long-term neurologic follow-up. There was a consistent clinical pattern in vitamin B12-deficient infants; irritability, anorexia, and failure to thrive were associated with marked developmental regression and poor brain growth. Two of the four patients who qualified for long-term review had a poor intellectual outcome. Although early response to treatment is satisfying, the long-term consequences of nutritional vitamin B12 deficiency in infants emphasize the need for prevention or early recognition of this syndrome.