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Biomedical subjects

F Young

Publications and source records attributed to F Young.

At least 19 recordsLinked to original sources
PubMed2000

COL5A1 haploinsufficiency is a common molecular mechanism underlying the classical form of EDS.

We have identified haploinsufficiency of the COL5A1 gene that encodes the proalpha1(V) chain of type V collagen in the classical form of the Ehlers-Danlos syndrome (EDS), a heritable connective-tissue disorder that severely alters the collagen-fibrillar structure of the dermis, joints, eyes, and blood vessels. Eight of 28 probands with classical EDS who were heterozygous for expressed polymorphisms in COL5A1 showed complete or nearly complete loss of expression of one COL5A1 allele. Reduced levels of proalpha1(V) mRNA relative to the levels of another type V collagen mRNA, proalpha2(V), were also observed in the cultured fibroblasts from EDS probands. Products of the two COL5A1 alleles were approximately equal after the addition of cycloheximide to the fibroblast cultures. After harvesting of mRNAs from cycloheximide-treated cultured fibroblasts, heteroduplex analysis of overlapping reverse transcriptase-PCR segments spanning the complete proalpha1(V) cDNA showed anomalies in four of the eight probands that led to identification of causative mutations, and, in the remaining four probands, targeting of CGA-->TGA mutations in genomic DNA revealed a premature stop at codon in one of them. We estimate that approximately one-third of individuals with classical EDS have mutations of COL5A1 that result in haploinsufficiency. These findings indicate that the normal formation of the heterotypic collagen fibrils that contain types I, III, and V collagen requires the expression of both COL5A1 alleles.

Alleles↗
PubMed2000

Normal isotype switching in B cells lacking the I mu exon splice donor site: evidence for multiple I mu-like germline transcripts.

Ig class switch recombination (CSR) in activated B cells is preceded by the generation of "switch" transcripts from the heavy chain constant region (CH) genes targeted for rearrangement. Switch transcripts include a sterile "I" exon spliced onto the first CH exon. Targeted mutations disrupting the expression or splicing of I exons severely hamper CSR to all tested CH loci, except mu. However, all mu switch transcript mutations tested so far have left the I mu exon splice donor site intact. To test the possibility that the residual CSR activity in I mu mutants could be due to splicing of a truncated I mu exon, we generated new mutants specifically lacking the I mu splice donor site. Surprisingly, normal CSR was observed in the I mu splice donor mutants even in the absence of detectable spliced I mu transcripts. In a search for potential alternative sources of switch-like transcripts in the mu locus, we identified two novel exons which map just upstream of the Smu region and splice onto the C mu 1 exon. Their expression is detectable from early B cell developmental stages, and, at least in hybridomas, it does not require the Emu enhancer. These studies highlight a unique structure for the mu locus I exon region, with multiple nested switch transcript-like exons mapping upstream of Smu. We propose that all of these transcripts directly contribute to mu class switching activity.

Animals↗
PubMed2000

Gene content and organization of a 281-kbp contig from the genome of the extremely thermophilic archaeon, Sulfolobus solfataricus P2.

The sequence of a 281-kbp contig from the crenarchaeote Sulfolobus solfataricus P2 was determined and analysed. Notable features in this region include 29 ribosomal protein genes, 12 tRNA genes (four of which contain archaeal-type introns), operons encoding enzymes of histidine biosynthesis, pyrimidine biosynthesis, and arginine biosynthesis, an ATPase operon, numerous genes for enzymes of lipopolysaccharide biosynthesis, and six insertion sequences. The content and organization of this contig are compared with sequences from crenarchaeotes, euryarchaeotes, bacteria, and eukaryotes.

Amino Acid Sequence↗
PubMed1999

Papilloedema secondary to acute purulent sinusitis.

Upper respiratory tract infections and sinusitis are common, but intracranial complications of sinusitis are rare in children and are often clinically unremarkable. Papilloedema secondary to purulent sinusitis is a complication previously not reported. We report two cases to highlight atypical manifestations of sinusitis in children.

Abscess↗
PubMed1998

Deletion of the IgH intronic enhancer and associated matrix-attachment regions decreases, but does not abolish, class switching at the mu locus.

The IgH locus intronic enhancer (Emu), located in the intron between the J(H) segments and the Cmu gene, and flanked by two matrix attachment regions (MAR), has been shown to be a major regulator of IgH gene transcription and VDJ recombination. To define the potential role of Emu plus MAR in class switch recombination (CSR), we generated IgG-expressing hybridomas from B cells heterozygous for mutations that delete all of these elements or replace them with a neo(r) gene and analyzed the switch status of the mutated IgH loci. Emu/MAR-deleted IgH loci displayed a highly significant, although not complete, decrease in CSR when compared to unmutated loci in normal hybridomas. Surprisingly, mutant loci with a pgk promoter-driven neo(r) gene replacing the Emu/MAR showed relatively normal switch frequency. These findings indicate that the Emu/MAR region plays a significant, but not necessary role in facilitating class switching at the mu locus. Potential mechanisms for these findings are discussed.

Age Factors↗
PubMed1998

Safety review of adult clinical trial experience with lamotrigine.

To date approximately 4000 adults > 12 years of age have been treated with lamotrigine in Glaxo Wellcome sponsored clinical trials. Review of the data from these trials shows lamotrigine to be effective and well tolerated in both add-on and monotherapy treatment. Safety of lamotrigine was comparable to that of other anticonvulsants in add-on controlled clinical trials. In addition, fewer than half the number of patients in monotherapy studies who were taking lamotrigine discontinued treatment because of adverse events compared to those taking carbamazepine and phenytoin. Most of the reported adverse events seen in lamotrigine treated patients in all studies were judged by the investigator to be mild or moderate in severity; few of the adverse events resulted in the withdrawal of patients from studies. Analysis of vital signs and clinical laboratory data have revealed no undesirable effect of lamotrigine on major systems of the body. The most concerning adverse event has been rash. In clinical trials, this has most often been limited to a simple morbilliform rash which is not associated with evidence of systemic involvement. The incidence of Stevens-Johnson syndrome (SJS) in clinical trials is approximately 1 in 1000. Rash associated with lamotrigine has typically occurred within the first 8 weeks of treatment. Data from clinical trials clearly point to exceeding currently recommended dosage guidelines of lamotrigine and co-administration of valproic acid (valproate sodium) as risk factors for rash. Early in 1997, Glaxo Wellcome strengthened existing warnings in the product label regarding the risk of rash and reinforced the importance of adherence to administration guidelines in an effort to reduce the incidence of rash.

Adolescent↗
PubMed1998

Normative Scottish data on the CELF-RUK: a pilot study.

There are relatively few standardised tests available for assessing language abilities in older children. A widely used test in Britain is the Clinical Evaluation of Language Fundamentals-Revised (CELF-R, Semel et al. 1987). One potential problem with its use in the UK is that the test has been standardised on American children. In this investigation, the CELF-RUK was administered to twenty Scottish language-normal children, aged 12;0-12;11 years. The results showed that the Scottish children's scores were significantly lower than the American standardisation sample scores for the expressive subtests but not significantly different for the receptive subtests. The results suggest that further research is needed before the test can be used confidently with Scottish children with language impairment.

Child↗
PubMed1997

Constitutive Bcl-2 expression during immunoglobulin heavy chain-promoted B cell differentiation expands novel precursor B cells.

To test for effects on B cell differentiation, we introduced immunoglobulin mu heavy chain (HC) and Bcl-2 transgenes, separately or together, into recombination-activating gene 2 (RAG-2)-deficient mice. Transgenic Bcl-2 expression led to increased numbers of RAG-deficient pro-B cells, but did not promote their further differentiation. Expression of the mu HC transgene promoted the differentiation of RAG-deficient pro-B cells into pre-B cells that also expressed certain differentiation markers characteristic of even more mature B cell stages. However, the extent of the mu HC-dependent differentiation effects was greatly enhanced by coexpression of the transgenic Bcl-2 gene, and a subset of pre-B cells from both HC and HC, Bcl-2-transgenic RAG-2-deficient animals expressed surface mu HCs that were functional as judged by cross-linking experiments. These experiments demonstrate that the pro-B to pre-B transition in vivo cannot be effected by the expression of Bcl-2 alone, and that nontransformed immature B-lineage cells are competent to receive signals through a surface mu complex.

Animals↗
PubMed1996

CD40 expression and function in murine B cell ontogeny.

The CD40 antigen, a member of the nerve growth factor/tumor necrosis factor receptor family, is expressed on all mature B lymphocytes and plays a crucial role in B cell activation, T cell-dependent antigen-driven isotype switching and germinal center formation. We have analyzed CD40 expression and function during mouse B cell development by examining B cell precursors in normal mice and in transgenic animals in which B cell development is frozen at discrete stages. These models included RAG-2-/- mice, and transgenic littermates that express a mu heavy chain and/or the bcl-2 proto-oncogene transgene. CD40 was undetectable at the pro-B cell stage, but was expressed, although at low levels, on pre-B cells. However, pre-B cells failed to respond to CD40 triggering either by expression of CD23 or by proliferation in the presence of IL-4. Overexpression of bcl-2 increased the density of CD40 expression on pre-B cells: these cells respond to CD40 ligation by expressing CD23 and by proliferating in the presence of IL-4.

Animals↗
PubMed1996

Organizational characteristics and information content of an archaeal genome: 156 kb of sequence from Sulfolobus solfataricus P2.

We have initiated a project to sequence the 3 Mbp genome of the thermoacidophilic archaebacterium Sulfolobus solfataricus P2. Cosmids were selected from a provisional set of minimally overlapping clones, subcloned in pUC18, and sequenced using a hybrid (random plus directed) strategy to give two blocks of contiguous unique sequence, respectively, 100,389 and 56,105 bp. These two contigs contain a total of 163 open reading frames (ORFs) in 26-29 putative operons; 56 ORFs could be identified with reasonable certainty. Clusters of ORFs potentially encode proteins of glycogen biosynthesis, oxidative decarboxylation of pyruvate, ATP-dependent transport across membranes, isoprenoid biosynthesis, protein synthesis, and ribosomes. Putative promoters occur upstream of most ORFs. Thirty per cent of the predicted strong and medium-strength promoters can initiate transcription at the start codon or within 10 nucleotides upstream, indicating a process of initial mRNA-ribosome contact unlike that of most eubacterial genes. A novel termination motif is proposed to account for 15 additional terminations. The two contigs differ in densities of ORFs, insertion elements and repeated sequences; together they contain two copies of the previously reported insertion sequence ISC 1217, five additional IS elements representing four novel types, four classes of long non-IS repeated sequences, and numerous short, perfect repeats.

Chromosomes, Bacterial↗
PubMed1995

Genomic organization and expression of a trypsin gene from the spruce budworm, Choristoneura fumiferana.

A 7 kb (kilobase) genomic fragment containing a trypsin gene from the spruce budworm Choristoneura fumiferana was isolated and sequenced. The coding sequence is interrupted by two introns; these occur at the same positions as the first two introns of mammalian trypsin genes. The three exons encode 256 amino acids. The deduced protein sequence displays all of the structural features that characterize trypsin enzymes in other eukaryotic organisms. Genomic Southern hybridization showed that there is only one copy of the trypsin gene in the Choristoneura genome. This gene is expressed in the insect midgut, where the pH is extremely high. The complete lack of Lysine residues may be an adaptation to the high pH conditions. Extensive sequencing of the flanking regions did not reveal the presence of any linked trypsin-encoding genes. Instead, several short repetitive sequences and a sequence homologous to a Drosophila reverse transcriptase gene was identified in this genomic region.

Amino Acid Sequence↗
PubMed1994

A class switch control region at the 3' end of the immunoglobulin heavy chain locus.

We replaced the IgH 3' enhancer (3'EH) region with a neomycin resistance gene in ES cells and generated chimeric mice in which all mature lymphocytes were either heterozygous (3'EH+/-) or homozygous (3'EH-/-) for the mutation. In vitro activated 3'EH-/- B cells responded similarly to 3'EH+/- B cells with respect to proliferation and secretion of IgM and IgG1 but were specifically deficient in IgG2a, IgG2b, IgG3, and IgE secretion. These isotype deficiencies correlated with a deficiency in accumulation of transcripts from and class switching to affected CH genes. In vivo, chimeric mice containing only 3'EH-/- B cells were deficient in serum IgG2a and IgG3. We propose that the 3'EH-/- mutation disrupts the activity of a regulatory region that influences heavy chain class switching to several different CH genes that lie as far as 100 kb upstream of the mutation.

Animals↗
PubMed1994

Influence of immunoglobulin heavy- and light-chain expression on B-cell differentiation.

To study the influence of immunoglobulin heavy-chain (HC) and light-chain (LC) expression in promoting B-cell differentiation, we have introduced functional immunoglobulin HC and/or LC transgenes into the recombinase activating gene-2-deficient background (RAG-2-/-). RAG-2-/- mice do not undergo endogenous V(D)J rearrangement events and, therefore, are blocked in B- and T-cell development at the early pro-B- and pro-T-cell stages. Introduction of immunoglobulin HC transgenes into the RAG-2-/- background promotes the development of a B-lineage cell population that phenotypically has the characteristics of pre-B cells. We have shown further that this population has altered growth characteristics as measured by interleukin-7 responsiveness in culture. Bone marrow cells from immunoglobulin HC transgenic RAG-2-/- mice have up-regulated expression of germ-line kappa LC gene transcripts and down-regulated expression of lambda 5 surrogate LCs (SLCs). Although mu HC/SLC complexes are detectable intracellularly in HC/RAG-2-/- pre-B-cell populations, HC expression is not readily detectable on the surface of these cells. lambda LC RAG-2-/- mice had a bone marrow B-lineage cell phenotype indistinguishable from that of RAG-2-/- littermates, indicating that LC expression by itself has no influence on pro-B cell differentiation. Strikingly, simultaneous introduction of mu HC and lambda LC transgenes into RAG-2-/- mice led to the generation of a substantial population of "monoclonal" peripheral B-cells that were functional with regard to immunoglobulin secretion, indicating that T cells or diverse immunoglobulin repertoires are not necessary for peripheral B-cell development.

Animals↗
PubMed1994

The expression of Vpre-B/lambda 5 surrogate light chain in early bone marrow precursor B cells of normal and B cell-deficient mutant mice.

Precursor B (pre-B) cells in bone marrow of normal and B cell-deficient mutant mice were analyzed for the expression of Vpre-B/lambda 5 surrogate light chain (SL). The surface expression of SL is confined to the early stages (pro-B and pre-B-I) of pre-B cell development and becomes undetectable once mu heavy chain (microH) is produced. The cell-cycle analysis revealed that cytoplasmic microH+ large cells (large pre-B-II), approximately 30% of which coexpressed SL in the cytoplasm, were most actively cycling, whereas cytoplasmic microH+ small cells (small pre-B-II) were SL- and not in cycle. The analysis of pre-B cells in B cell-deficient mice suggests that the large pre-B-II stage is a critical step for the selection and amplification of cells carrying functionally rearranged microH genes.

Animals↗
PubMed1994

Probing immune functions in RAG-deficient mice.

Inactivation of recombination activating gene (RAG)-1 or RAG-2 in mice results in the inability of developing lymphocytes to initiate V(D)J recombination, leading to the arrest of lymphocyte differentiation at a very early stage. Introduction of functionally assembled antigen-receptor genes or other potentially relevant genes into the RAG-deficient background can bypass the V(D)J recombination block and promote differentiation of the lymphocytes of RAG-deficient mice to various stages. This approach offers new means for analyzing the control of lymphocyte differentiation. In addition, generation of somatic chimeric mice by injecting mutant embryonic stem cells into the RAG-2-deficient blastocysts has also provided a powerful new method for assaying the potential roles of genes or regulatory elements in lymphocyte development or function.

Animals↗
PubMed1994

IL-2 receptor alpha chain expression during early B lymphocyte differentiation.

The IL-2/IL-2 receptor (IL-2R) has been studied intensively because of its potential function in the development and regulation of the immune system. The IL-2R alpha chain has been shown to be expressed on CD4-CD8- thymocytes and activated T and B cells. In this report, we show that IL-2R alpha is also expressed on precursor B cells in the bone marrow. Its expression is initiated by functional rearrangement and expression of Ig mu heavy chain gene and is down-regulated when immature B cells mature and express IgD. Its potential function in early B cell differentiation is discussed in comparison with its role in thymocyte differentiation.

Animals↗