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G Richards

Publications and source records attributed to G Richards.

At least 55 records · Page 3Linked to original sources
PubMed1994

Coincidental appearance of the alpha 1 subunit of the GABA-A receptor and the type I benzodiazepine receptor near birth in macaque monkey visual cortex.

The expression of subtypes of the GABA-A/benzodiazepine receptor complex has been studied during pre- and postnatal development of Macaca monkey visual cortex using complementary radioligand and immunocytochemical labeling. Type I benzodiazepine receptors were labeled directly by [3H]zolpidem. Type II receptors were determined by the amount of binding for [3H]flunitrazepam (FZ) persisting in the presence of the type I-specific ligand CL218872. Monoclonal antibody bd24 was used to label alpha 1 subunits and bd17 to label beta 2 and beta 3 subunits of the GABA-A receptor. Radioligand binding data and bd17 immunoreactivity indicated that type II benzodiazepine receptors were present by fetal day (Fd) 74 (44% of gestation). Immunoreactivity for the beta 2/beta 3 subunits increased until 3-6 weeks after birth, and then declined somewhat into adulthood. Neither radioligand labeling for type I receptors nor immunocytochemical staining for the alpha 1 subunit were apparent until mid-gestation. Both markers appeared shortly before birth in layer 4C, and then in other cortical layers after birth. Immunoreactivity for the alpha 1 subunit increased steadily after birth until it became more intense than that for beta 2/3 subunits in the adult. Quantitative densitometry of CL218872 competition for [3H]FZ binding showed that type I/II distribution was 22%/78% at Fd103; 42%/58% at Fd131; 67%/33% at 9 months; and 61%/39% in adult visual cortex. This "switch" between benzodiazepine receptor subtypes overlaps the postnatal critical period for geniculostriate development, suggesting that the change from type II to type I receptors and the appearance of alpha 1 subunits may play a decisive role in the maturation of geniculocortical axon terminations and cortical response properties. It remains to be shown whether this "switch" is dependent on functional visual input.

Animals↗
PubMed1993

Puffs and PCR: the in vivo dynamics of early gene expression during ecdysone responses in Drosophila.

The steroid hormone ecdysone orchestrates insect development by regulating gene networks. In Drosophila the most detailed description of ecdysone action is the sequential activation of early and late puffs in the polytene chromosomes of the late larval salivary gland. A number of these early puffs (2B5, 74EF and 75B) contain complex transcription units (Broad-Complex, E74 and E75 respectively) encoding families of regulatory proteins which are expressed in most if not all tissues. In vitro, transcripts of the different isoforms of these early genes as well as the ecdysone receptor (EcR) present varying dose response characteristics (Karim and Thummel, 1992, EMBO J. 11, 4083-4093). We have developed an in vivo approach using a reverse transcription-polymerase chain reaction assay (RT-PCR) so as to visualise these transcripts in the RNA extracted from a single salivary gland. Using one salivary gland lobe for developmental puff staging and the sister lobe for RT-PCR, we have obtained precise developmental profiles for these transcripts and have extended our study to other tissues and stages where puffing studies were not possible. In the salivary gland we have characterised three distinct ecdysone responses. For the mid and late third larval instar responses our results confirm and extend the conclusions of the in vitro studies concerning the temporal expression of the early gene isoforms. The relatively brief prepupal response contains elements in common with each of the larval responses and all three can be explained by the profiles of the respective ecdysone peaks. Interestingly EcR transcripts respond differently during each response. The analysis of different tissues of the same animal reveals subtle differences in the timing of the ecdysone response and isoform expression and suggests that this may reflect tissue differences in the ecdysone profiles. As these molecules have homologues in vertebrates, our analysis may have general implications for the organisation of hormonal responses in vivo.

Animals↗
PubMed1992

Acute adrenal insufficiency secondary to heparin-induced thrombocytopenia-thrombosis syndrome.

OBJECTIVE: To present a case of acute adrenal insufficiency secondary to heparin-induced thrombocytopenia-thrombosis syndrome (HITTS), an important though rare complication of heparin therapy. CLINICAL FEATURES: A 69-year-old woman developed HITTS secondary to low dose heparin administered subcutaneously as prophylaxis against deep venous thrombosis. This followed a revision of a knee replacement. The first manifestation of HITTS was the development of pulmonary emboli in the setting of a falling platelet count. Bilateral adrenal haemorrhages complicated her course resulting in acute adrenal insufficiency. Non-specific symptoms dominated the clinical picture, with fever, nausea, abdominal pain and vomiting. Symptomatic postural hypotension was noted later in the course of her illness. INTERVENTION AND OUTCOME: The diagnosis of adrenal insufficiency was confirmed by short Synacthen test plus computed tomographic scanning which demonstrated bilateral adrenal haemorrhages. Steroid replacement resulted in rapid clinical improvement. CONCLUSIONS: This case demonstrates one of the life threatening complications that may occur with heparin even in prophylactic doses. Regular platelet counts are essential to detect heparin-induced thrombocytopenia at an early stage.

Acute Disease↗
PubMed1992

Insect immunity: developmental and inducible activity of the Drosophila diptericin promoter.

Diptericins are 9 kDa inducible antibacterial peptides initially isolated from immune haemolymph of Phormia (Diptera). Following the isolation of a Drosophila cDNA encoding a diptericin homologue, we have now cloned a genomic fragment containing the Drosophila diptericin gene. To dissect the regulation of this gene, we have transformed flies with a fusion gene in which the reporter beta-galactosidase gene is under the control of 2.2 kb upstream sequences of the diptericin gene. We show that such a fusion gene is inducible by injection of live bacteria or complete Freund's adjuvant and respects the tissue specific expression pattern of the resident diptericin gene. Our analysis reveals at least four distinct phases in the regulation of this gene: young larvae, late third instar larvae, pupae and adults. This complexity may be related to the presence in the upstream sequences of multiple copies of response elements previously characterized in genes encoding acute phase response proteins in mammals (e.g. NK-kappa B, NF-kappa B related, NF-IL6 response elements).

Acute-Phase Proteins↗
PubMed1992

GEBF-I in Drosophila species and hybrids: the co-evolution of an enhancer and its cognate factor.

The activation of the Drosophila melanogaster salivary gland secretion protein gene Sgs-3 is marked by important changes in chromatin structure in the distal regulatory region at -600 bp from the Sgs-3 start site. A stage- and tissue-specific glue enhancer binding factor, GEBF-I, binds in vitro to sequences from this region. Previous studies have revealed considerable variation in the DNA sequences of comparable regions in the related Drosophila species, D. simulans, D. erecta and D. yakuba. We detected GEBF-I-like proteins in these species, which appear to evolve as rapidly as the corresponding DNA sequences, and studied in detail the binding characteristics of the GEBF-I proteins of the two most closely related species, D. melanogaster and D. simulans. In crosses between these species, certain strains produce hybrid larvae which, unexpectedly, synthesised a single intermediate form of the protein. This suggests that the factor is subject to species-specific post-transcriptional modifications. In these hybrid larvae, which carry one D. melanogaster and one D. simulans Sgs-3 gene, the hybrid GEBF-I protein appears equally effective in the induction of both target genes.

Animals↗
PubMed1991

Sgs-3 chromatin structure and trans-activators: developmental and ecdysone induction of a glue enhancer-binding factor, GEBF-I, in Drosophila larvae.

The transcription of the Drosophila melanogaster 68C salivary gland glue gene Sgs-3 involves the interaction of a distal and a proximal regulatory region. These are marked in vivo by a specific chromatin structure which is established sequentially during development, starting early in embryogenesis. The distal region is characterized by a stage- and tissue-specific DNase I hypersensitive site. A stage- and tissue-specific factor, GEBF-I, binds in this region and is missing in 2B5 mutant larvae which lack Sgs-3 transcripts. This binding involves the simultaneous interaction with two distinct DNA sequences which induces conformational changes in the protein. Salivary glands acquire competence to respond to ecdysone in the mid-third larval instar, whereafter the hormone rapidly induces both the GEBF-I protein and Sgs-3 transcription.

Age Factors↗
PubMed1991

Mary & Leroy.

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Adult↗
PubMed1989

Regulatory elements and interactions in the Drosophila 68C glue gene cluster.

We reviewed studies on the developmental regulation of the 68C glue gene cluster of Drosophila melanogaster. Extensive transformation analyses of Sgs-3 have shown that four regions necessary for normal expression can be distinguished. The first(+10 to -50) contains the transcription start site and TATA motif. This region can be replaced functionally by corresponding sequences from the hsp70 gene, but it is sensitive to point mutations in the TATA sequence. The second region (-50 to -98) contains more than one upstream sequence that, in combination with the other elements, leads to stage and tissue-specific expression. The third region (centered at -600) contains an element that enhances transcript levels some 20-fold. The final region (between -1.65 and -2.35 kb) contains elements having modest (twofold to threefold) effects on expression, one of which is contained in the coding sequences of Sgs-7, a second member of the cluster.

Animals↗
PubMed1989

Induction and repression of the Drosophila Sgs-3 glue gene are mediated by distinct sequences in the proximal promoter.

The normal developmental expression of the Drosophila salivary gland secretion protein gene Sgs-3 requires the interaction of a distal and proximal regulatory element. A deletion/replacement analysis of the proximal promoter in stably transformed lines shows that induction of an Sgs-3/Adh fusion gene is normal if sequences from +10 to -50 are replaced by those of the hsp70 gene. Sequences between -98 and -50 are necessary for this expression but there is internal redundancy within this region as two distinct upstream sequences of 18 and 22 bp respectively are sufficient for stage- and tissue-specific expression, albeit at reduced levels. A point mutation at -53 eliminates the ecdysone-mediated repression of the Sgs-3 promoter at pupariation. We report mosaicisms of expression within the salivary gland for a number of stably transformed lines.

Animals↗
PubMed1989

Drosophila Sgs3 TATA: effects of point mutations on expression in vivo and protein binding in vitro with staged nuclear extracts.

The Drosophila salivary gland secretion protein gene, Sgs3, has a consensus TATA sequence and gives rise to abundant stage and tissue-specific transcripts. Two TATA point mutations (TAAA and TAGA) reduce transcript levels approximately 50-fold when assayed in transgenic flies. This effect is reflected in vitro, in DNase I footprint and gel retardation assays where we observed TATA-probe-specific complexes that are not seen with TAAA, TAGA or non-specific probes. The binding patterns observed when using nuclear extracts from 0-2- and 0-20-h embryos (Sgs3 inactive) differ from those seen with extracts from third instar salivary glands (Sgs3 active). There are also differences in in vitro binding when using an hsp70 TATA fragment, previously shown to substitute in vivo for the Sgs3 TATA sequence, as probe. Together these observations suggest the possibility that more than one TATA box factor may be present in these extracts. We conclude that a wild-type TATA motif is crucial for the binding of a TATA box factor and all subsequent interactions with other factors bound to the proximal and distal regulatory sequences that are necessary for the normal expression of Sgs3.

Animals↗
PubMed1989

Quicker and sicker.

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Economics, Hospital↗
PubMed1988

Localization of calbindin D28 mRNA in rat tissues by in situ hybridization.

We investigated, by in situ hybridization histochemistry, the cellular localization of the mRNA encoding a vitamin D-dependent calcium-binding protein (calbindin D28) in rat brain and peripheral organs. Using a [35S]cRNA probe under high stringency conditions, specific mRNA was found in tissues well known for their calbindin D28 content, e.g. renal distal tubules, cerebellar Purkinje cells and dentate gyrus granule cells. Tissue devoid of this protein, such as liver, also lacked specific mRNA. In situ hybridization histochemistry allows the precise identification of cells expressing calbindin D28 and offers a new approach to study its regulation and possible role, e.g. in neuronal function.

Animals↗