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C Dean

Publications and source records attributed to C Dean.

At least 37 records · Page 2Linked to original sources
PubMed2000

Environmental-dependent acceleration of a developmental switch: the floral transition.

The transition from vegetative growth to reproductive growth in plants in which flowers are produced requires the activation of specific genes. Simpson and Dean discuss two recent reports that characterize the FLOWERING LOCUS T (FT) gene in Arabidopsis, which is part of the floral transition pathway. Unlike many of the known genes that initiate flower production, the FT gene appears to encode a membrane-associated protein that could function in signaling from the cell surface.

Adaptation, Biological↗
PubMed2000

Integrated cytogenetic map of chromosome arm 4S of A. thaliana: structural organization of heterochromatic knob and centromere region.

We have constructed an integrated cytogenetic map of chromosome arm 4S of Arabidopsis thaliana. The map shows the detailed positions of various multicopy and unique sequences relative to euchromatin and heterochromatin segments. A quantitative analysis of the map positions at subsequent meiotic stages revealed a striking pattern of spatial and temporal variation in chromatin condensation for euchromatin and heterochromatin. For example, the centromere region consists of three domains with distinguishable structural, molecular, and functional properties. We also characterized a conspicuous heterochromatic knob of approximately 700 kb that accommodates a tandem repeat and several dispersed pericentromere-specific repeats. Moreover, our data provide evidence for an inversion event that relocated pericentromeric sequences to an interstitial position, resulting in the heterochromatic knob.

Arabidopsis↗
PubMed2000

Neurochemical transmission of baroreceptor input in the nucleus tractus solitarius.

Baroreceptor activation has been found to produce different types of discharge patterns in neurons in the nucleus tractus solitarius (NTS). The contribution of different glutamate receptor subtypes, neuropeptide modulators and input from different baroreceptor subtypes to the generation of firing patterns in NTS barosensitive neurons was examined in a series of studies. Results from these studies indicate that both subtypes of ionotropic glutamate receptors contribute to discharge in barosensitive neurons, and the role of each subtype can vary for different neurons. The neuropeptide neurotensin was found to modulate baroreceptor control of BP and discharge of central barosensitive neurons, both through modulation of baroreceptor afferent input and possibly through release of neurotensin by baroreceptor afferent fibers in the NTS. Finally, selective modulation of input from baroreceptor subtypes indicates that there is some degree of divergent baroreceptor innervation of NTS neurons that could contribute to initiation of their different discharge patterns in response to baroreceptor input.

Animals↗
PubMed2000

Modulation of the carotid baroreceptor reflex by substance P in the nucleus tractus solitarius.

Previous studies have shown that administration of substance P (SP) into the nucleus tractus solitarius (NTS) can evoke a depressor response similar to that produced by activation of the arterial baroreceptors. In addition, some studies have suggested that SP increases the reflex responses to activation of baroreceptor input. The present study was performed to determine the effects of SP on the carotid sinus baroreceptor reflex at the level of the NTS by examining the effects of both exogenous SP microinjected into different rostrocaudal locations in the NTS and blockade of the effects of endogenous SP, through the microinjection of a substance P antagonist (SPa; [D-Pro, D-Trp]-substance P). Changes in pressure in an isolated carotid sinus in anesthetized dogs were used to evoke baroreflex changes in arterial blood pressure (BP) before and after microinjection of SP (0.5 microM) or SPa (10 microM) into barosensitive regions of the NTS. Microinjection of SP or its antagonist did not alter baseline, resting BP but did produce significant changes in baroreflex sensitivity. Microinjection of SP into different rostrocaudal regions of the NTS produced different responses, with rostral and caudal NTS microinjections producing significant increases in sensitivity. No effects on baroreflex sensitivity were obtained in response to SP microinjections into the intermediate NTS. Unlike SP, microinjection of the SPa significantly decreased baroreflex sensitivity at all rostrocaudal levels of the NTS. These data demonstrated that SP has the capability to modulate the carotid baroreflex at the level of the NTS and support a physiological role for endogenously released SP.

Animals↗
PubMed2000

Potentiation of non-N-methyl-D-aspartate receptor-induced changes in blood pressure by substance P in rats.

Central release of substance P (SP) in the nucleus tractus solitarius (NTS) may potentiate the reflex responses evoked by baroreceptor afferent input to this medullary nucleus. The mechanism is not known but may involve modulation of responses produced by release of glutamate, the putative primary baroreceptor transmitter, at neurons within the NTS. The principal glutamate receptor subtype proposed to transmit baroreceptor afferent input at second-order neurons is the non-N-methyl-D-aspartate (NMDA) receptor. The present study examined the effects of microinjection of SP into barosensitive regions of the NTS on the depressor and bradycardic response induced by activation of non-NMDA receptors in the NTS by subsequent microinjection of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), a non-NMDA receptor agonist. Substance P potentiated the non-NMDA receptor-induced depressor response to AMPA in the NTS, evoking a significantly larger change in blood pressure over the same time period. These data suggest that SP may modulate a non-NMDA-miediated component of the baroreflex to influence the control of arterial blood pressure by increasing the sensitivity of the baroreceptor reflex.

Animals↗
PubMed2000

Mutations causing defects in the biosynthesis and response to gibberellins, abscisic acid and phytochrome B do not inhibit vernalization in Arabidopsis fca-1.

The roles of gibberellins, abscisic acid and phytochrome B in the vernalization response were investigated by combining mutations causing defects in their biosynthesis and response with the Arabidopsis thaliana (L.) Heynh. fca-1 mutation. The fca-1 mutation confers a very late-flowering phenotype which can be reversed to wild-type flowering if the seedlings are vernalized. Vernalization was unaffected in ga1-3, gai, abi1-1, abi2-1, abi3-1 and phyB-1 backgrounds, suggesting that gibberellin action mediated via GA1 and GAI, abscisic acid action mediated through ABI1 and ABI2, and phytochrome B, function independently of vernalization. However, the mutations did interact with fca-1 to change flowering time in the absence of vernalization. The abi1 fca-1 and abi2 fca-1 double mutants flowered earlier than fca-1 implying a role for abscisic acid in floral repression. Combination of ga1-3 or gai with fca-1 unexpectedly resulted in opposite interactions, with gai partially suppressing the late flowering of fca-1.

Abscisic Acid↗
PubMed2000

Progress in understanding hominoid dental development.

Teeth preserve a record of the way they grow in the form of incremental markings in enamel, dentine and cementum. These make it possible to reconstruct cellular activity and the timing of dental development in living and fossil primates, including hominids. They also provide a way of exploring the mechanisms that underlie morphological change during evolution and the nature of the relationship between ontogeny and phylogeny. All living great apes are dentally mature by about 11 y, irrespective of their body mass. While the early period of root formation in living great apes is shorter than in modern humans, enamel takes approximately the same time to form, irrespective of how thick it is. In general, differences in the total time taken to form enamel seem not to be due to differences in the rate at which enamel and dentine are secreted, but rather to faster or slower rates of differentiation of ameloblasts and odontoblasts and therefore to the number of secretory cells active at any one time during tooth formation. Tooth size, especially height, may influence the sequence of appearance of tooth mineralisation stages. The space available in the jaws may also have an influence on both the timing of tooth bud/crypt appearance and the sequence of gingival emergence. When each of these potential influences on dental development are carefully considered, and incremental markings used to calibrate key events, the developing dentition can provide an estimate of the period of dental maturation in fossil hominoids. However, the influence of body mass on the period of dental development among primates remains unclear. The earliest hominoids, dated at around 18 Mya, may still have had modern monkey-like maturational profiles, and the earliest hominids, dated between 1.8 and 3.7 Mya, modern great ape-like maturational profiles. Exactly when the extended or prolonged modern human-like maturational profile first appeared remains debatable, but the most secure suggestion might be at the time of the appearance of the earliest archaic Homo sapiens, when brain size and body mass were finally both within the ranges known for modern humans. But at present we should not reject the hypothesis that an extended, modern human-like, maturational profile arose more than once during human evolution in parallel with an increase in brain size.

Animals↗
PubMed2000

Effects of inter-alpha-inhibitor and several of its derivatives on calcium oxalate crystallization in vitro.

The bikunin peptide chain of the protease inhibitor inter-alpha-inhibitor (IalphaI) has been reported to be an inhibitor of calcium oxalate (CaOx) crystallization, and hence has been proposed as having a role in CaOx kidney stone formation. However, further experimental evidence is required to assess if fragments of IalphaI other than bikunin may play a role in the regulation of crystallization events in stone formation. The aim of the present study was to assess the effects of IalphaI and several of its derivatives on CaOx crystallization in a seeded inorganic system and to compare these effects with those of a known inhibitor of crystallization, prothrombin. IalphaI was purified from a preparation of human plasma and fragmented by alkaline hydrolysis, and two of its peptide chains, bikunin and heavy chain 1 (H1), were purified further by HPLC. Their purity was confirmed by SDS/PAGE. Using Coulter counter and [(14)C]oxalate analysis and scanning electron microscopy, IalphaI, its H1 chain and bikunin from urine and from plasma were shown to be relatively weak inhibitors of CaOx crystallization in vitro at expected physiological concentrations. It was concluded that members of the IalphaI family may not be as important in kidney stone formation as has been generally proposed, although further studies are required before a possible role for IalphaI and its fragments in stone formation can be unambiguously discounted.

Alpha-Globulins↗
PubMed1999

Role of glutamate receptors in transmission of vagal cardiac input to neurones in the nucleus tractus solitarii in dogs.

1. Vagal afferent input from cardiac mechanoreceptors excites neurones in the nucleus tractus solitarii (NTS), but discharge patterns evoked by physiological activation of pressure-sensitive cardiac mechanoreceptors have not been studied in vivo. The role of glutamate receptor subtypes in transmission of afferent activity to the NTS neurones has not been determined. The present study therefore has two aims: first, to characterise the discharge patterns of neurones in the NTS that receive pressure-sensitive vagal cardiac receptor input and second, to determine the roles of ionotropic glutamate receptor subtypes in the transmission of this putative cardiac mechanoreceptor-related activity to NTS neurones. 2. Pulse-synchronous activity of neurones in the NTS evoked by vagal afferent input was recorded extracellularly in an anaesthetised dog model using multibarrel glass electrodes, which allowed picoejection of the glutamate receptor antagonists NBQX or AP5 to block either non-NMDA or NMDA receptors, respectively, during the neuronal recording. Pressure sensitivity of the recorded neurones was examined by monitoring their response to a small increase in arterial blood pressure. Selective pressure activation of carotid sinus baroreceptors in an isolated sinus or selective denervation of aortic baroreceptors were used to test for convergent excitation of the neurones by arterial baroreceptors. 3. Pulse-synchronous cardiac-related neuronal activity recorded from neurones in both the right and left NTS was eliminated following section of the left (n = 17) or right (n = 1) vagus nerves. No spontaneous, non-pulsatile activity was observed in these neurones before or after vagotomy. Activity transmitted via left vagal afferents was found to be sensitive to changes in arterial blood pressure. In these neurones, activity was blocked in 13 of 17 neurones by picoejection of NBQX, with the remainder requiring both NBQX and AP5. None of the cardiac-related neurones responded to activation of carotid baroreceptors or denervation of aortic baroreceptors, indicating no convergence of activity from carotid baroreceptors or aortic baroreceptors with pressure thresholds of approximately 130 mmHg or less. 4. The results suggest that vagal pressure-sensitive afferent input from cardiac mechanoreceptors is transmitted primarily by left vagal afferent fibres via non-NMDA receptors to neurones in both the ipsilateral and contralateral NTS. NMDA receptors were also found to have a role in the activation of a small subpopulation of neurones.

Animals↗
PubMed1999

Bdp, a new member of a family of DNA-binding proteins, associates with the retinoblastoma gene product.

We have cloned a gene, BDP, encoding a protein with homology to the retinoblastoma-binding proteins Rbp1 and Rbp2. It also has homology to DNA-binding proteins such as Bright, a B-cell-specific trans-activator, and the Drosophila melanogaster dead ringer gene product. Like MyoD, Bdp binds to the COOH-terminal region of pRb through its conserved region and to hypophosphorylated pRb. It also binds to the MAR of the immunoglobulin heavy-chain locus. Thus Bdp may contribute to the transcriptional regulation of genes involved in differentiation and tissue-specific expression.

Amino Acid Sequence↗
PubMed1999

Modulation of sympathetic nerve activity by microinjection of the 5-HT1A receptor agonist 8-OH-DPAT into the rostroventrolateral medulla.

In the present study, renal sympathetic nerve activity was recorded simultaneously with sympathetic nerve activity to skeletal muscle vasculature to determine if the sympatho-inhibition evoked by microinjection of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)teralin (8-OH-DPAT) into the rostroventrolateral medulla (RVLM) was uniform or regional. Three patterns of sympatho-inhibition were observed in these sympathetic outflows and the type of response depended upon location of microinjection within the subretrofacial nucleus (SRF). Inhibition of renal nerve activity only was elicited by microinjections at rostral sites at the caudal pole of the facial nucleus. In contrast, inhibition of muscle sympathetic nerve activity was evoked from more caudal injections at the rostral pole of the inferior olives. Microinjection in the area between these two regions produced inhibition of both sympathetic outflows. This study demonstrates that differential inhibition of regional sympathetic outflows can be elicited by microinjection of the 5-HT1A receptor agonist 8-OH-DPAT into the RVLM. These data suggests that this modulation is due to differences in anatomical arrangement of the medullary neurons rather than differences in neuron sensitivity to the serotonergic agonist.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1999

Presence of glutamate receptor subtypes on barosensitive neurons in the nucleus tractus solitarius of the dog.

Afferent baroreceptor information is transmitted to the nucleus tractus solitarius (NTS) in the dorsal medulla where glutamate is thought to be the primary neurotransmitter. However, the subtypes of glutamate receptors involved in the baroreflex remain to be established. The present study compared the distribution of immunohistochemically labeled ionotropic receptor subtypes to the distribution of physiologically stimulated barosensitive neurons in the NTS of the dog and also identified ionotropic receptor subtypes located on barosensitive neurons. Both NMDA and non-NMDA receptors were located in barosensitive areas and on barosensitive neurons, suggesting that both may be involved in the baroreflex.

Animals↗
PubMed1999

Sitting balance I: trunk-arm coordination and the contribution of the lower limbs during self-paced reaching in sitting.

The effects of reach distance and type of task on the functional relationship between the trunk, upper limb segments and the lower limbs during self-paced reaching in sitting were examined. Two-dimensional kinematic, kinetic and electromyography (EMG) data were collected as six healthy subjects reached forward under three distance (60, 100, 140% arm's length) and two task (reaching to press a switch, reaching to grasp a glass) conditions. The results demonstrate that type of task affected primarily the temporal aspects of coordination, with the grasp task taking consistently longer than the press task. In contrast, reach distance affected both the spatio-temporal aspects of coordination between the trunk and arm segments and the active contribution of the lower limbs. As reach distance increased, the magnitude of trunk and upper-arm segmental motion increased, whereas forearm segmental motion decreased. However, at each reach distance the path of the hand was relatively straight and there was remarkable consistency in the relationship between trunk and arm segments both within and between subjects suggesting that despite the presence of redundant degrees of freedom, the individual uses a parsimonious coordinative pattern. The vertical ground reaction force (GRF) and EMG data demonstrated that the lower limbs actively contributed to support the body mass when the object was located at 140% arm's length.

Adult↗
PubMed1999

The arabinose kinase, ARA1, gene of Arabidopsis is a novel member of the galactose kinase gene family.

The arabinose-sensitive ara1-1 mutant of Arabidopsis is deficient in arabinose kinase activity. A candidate for the ARA1 gene. ISA1, has been previously identified through the Arabidopsis genome sequencing initiative. Here we demonstrate that (1) the ARA1 gene coincides with ISA1 in a positional cloning strategy; (2) there are mutations in the ISA1 gene in both the ara1-1 mutant and an intragenic suppressor mutant; and (3) the ara1-1 and suppressor mutant phenotypes can be complemented by the expression of the ISA1 cDNA in transgenic plants. Together these observations confirm that ISA1 is the ARA1 gene. ARA1 is a member of the galactose kinase family of genes and represents a new substrate specificity among this and other families of sugar kinases. A second gene with similarities to members of the galactose kinase gene family has been identified in the EST database. A 1.8 kb cDNA contained an open reading-frame predicted to encode a 496 amino acid polypeptide. The GAL1 cDNA was expressed in a galK mutant of Escherichia coli and in vitro assays of extracts of the strain expressing GAL1 confirmed that the cDNA encodes a galactose kinase activity. Both GAL1 and ARA1 cross-hybridise at low stringency to other sequences suggesting the presence of additional members of the galactose kinase gene family.

Amino Acid Sequence↗
PubMed1999

Genome-wide mapping with biallelic markers in Arabidopsis thaliana.

Single-nucleotide polymorphisms, as well as small insertions and deletions (here referred to collectively as simple nucleotide polymorphisms, or SNPs), comprise the largest set of sequence variants in most organisms. Positional cloning based on SNPs may accelerate the identification of human disease traits and a range of biologically informative mutations. The recent application of high-density oligonucleotide arrays to allele identification has made it feasible to genotype thousands of biallelic SNPs in a single experiment. It has yet to be established, however, whether SNP detection using oligonucleotide arrays can be used to accelerate the mapping of traits in diploid genomes. The cruciferous weed Arabidopsis thaliana is an attractive model system for the construction and use of biallelic SNP maps. Although important biological processes ranging from fertilization and cell fate determination to disease resistance have been modelled in A. thaliana, identifying mutations in this organism has been impeded by the lack of a high-density genetic map consisting of easily genotyped DNA markers. We report here the construction of a biallelic genetic map in A. thaliana with a resolution of 3.5 cM and its use in mapping Eds16, a gene involved in the defence response to the fungal pathogen Erysiphe orontii. Mapping of this trait involved the high-throughput generation of meiotic maps of F2 individuals using high-density oligonucleotide probe array-based genotyping. We developed a software package called InterMap and used it to automatically delimit Eds16 to a 7-cM interval on chromosome 1. These results are the first demonstration of biallelic mapping in diploid genomes and establish means for generalizing SNP-based maps to virtually any genetic organism.

Arabidopsis↗
PubMed1999

Genetic interactions of the Arabidopsis flowering time gene FCA, with genes regulating floral initiation.

The genes controlling the timing of the transition from vegetative to reproductive growth are likely candidates for regulators of genes initiating floral development. We have investigated the interaction of one particular gene controlling flowering time, FCA, with the meristem identity-genes TERMINAL FLOWER 1 (TFL1), APETALA 1 (AP1) and LEAFY (LFY) and the floral repression gene EMBRYONIC FLOWER 1 (EMF1). Double mutant combinations were generated and the phenotypes characterized. The influence of strong and intermediate fca mutant alleles on the phenotype conferred by a 35S-LFY transgene was also analysed. The results support a model where FCA function promotes flowering in multiple pathways, one leading to activation of LFY and AP1, and another acting in parallel with LFY and AP1. Only the latter pathway is predicted to be non-functional in the intermediate fca-4 allele. The results are also consistent with AP1 and TFL1 negatively regulating FCA function. Combination of Columbia fca and emf1 mutant alleles confirmed that FCA is required for the early flowering of emf1. EMF1 and FCA are therefore likely to operate in different floral pathways.

Alleles↗