Biomedical subjects

Spencer Brown

Publications and source records attributed to Spencer Brown.

8 recordsLinked to original sources

PubMed2006

Arabidopsis PASTICCINO2 is an antiphosphatase involved in regulation of cyclin-dependent kinase A.

PASTICCINO2 (PAS2), a member of the protein Tyr phosphatase-like family, is conserved among all eukaryotes and is characterized by a mutated catalytic site. The cellular functions of the Tyr phosphatase-like proteins are still unknown, even if they are essential in yeast and mammals. Here, we demonstrate that PAS2 interacts with a cyclin-dependent kinase (CDK) that is phosphorylated on Tyr and not with its unphosphorylated isoform. Phosphorylation of the conserved regulatory Tyr-15 is involved in the binding of CDK to PAS2. Loss of the PAS2 function dephosphorylated Arabidopsis thaliana CDKA;1 and upregulated its kinase activity. In accordance with its role as a negative regulator of the cell cycle, overexpression of PAS2 slowed down cell division in suspension cell cultures at the G2-to-M transition and early mitosis and inhibited Arabidopsis seedling growth. The latter was accompanied by altered leaf development and accelerated cotyledon senescence. PAS2 was localized in the cytoplasm of dividing cells but moved into the nucleus upon cell differentiation, suggesting that the balance between cell division and differentiation is regulated through the interaction between CDKA;1 and the antiphosphatase PAS2.

Arabidopsis↗

PubMed2005

Arabidopsis anaphase-promoting complexes: multiple activators and wide range of substrates might keep APC perpetually busy.

The anaphase-promoting complex (APC), a multisubunit E3 ubiquitin ligase, is an essential regulator of the cell cycle from metaphase until S phase in yeast and metazoans. APC mediates degradation of numerous cell cycle-related proteins, including mitotic cyclins and its activation and substrate-specificity are determined by two adaptor proteins, Cdc20 and Cdh1. Plants have multiple APC activators and the Cdh1-type proteins, in addition, are represented by two subclasses, known as Ccs52A and Ccs52B. The Arabidopsis genome contains five cdc20 genes as well as ccs52A1, ccs52A2 and ccs52B. In Schizosaccharomyces pombe, expression of the three Atccs52 genes elicited distinct phenotypes supporting nonredundant function of the AtCcs52 proteins. Consistent with these activities, the AtCcs52 proteins were able to bind both to the yeast and the Arabidopsis APCs. In synchronized Arabidopsis cell cultures the cdc20 transcripts were present from early G2 until the M-phase exit, ccs52B from G2/M to M while ccs52A1 and ccs52A2 were from late M until early G2, suggesting consecutive action of these APC activators in the plant cell cycle. The AtCcs52 proteins interacted with different subsets of mitotic cyclins, in accordance with their expression profiles, either in free- or CDK-bound forms. Expression of most APC subunits was constitutive, whereas cdc27a and cdc27b, corresponding to two forms of apc3, and ubc19 and ubc20 encoding E2-C type ubiquitin-conjugating enzymes displayed differences in their cell cycle regulation. These data indicate the existence of numerous APC(Cdc20/Ccs52/Cdc27) forms in Arabidopsis, which in conjunction with different E2 enzymes might have distinct or complementary functions at distinct stages of the cell cycle.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2005

Cell and plastid division are coordinated through the prereplication factor AtCDT1.

The cell division cycle involves nuclear and cytoplasmic events, namely organelle multiplication and distribution between the daughter cells. Until now, plastid and plant cell division have been considered as independent processes because they can be uncoupled. Here, down-regulation of AtCDT1a and AtCDT1b, members of the prereplication complex, is shown to alter both nuclear DNA replication and plastid division in Arabidopsis thaliana. These data constitute molecular evidence for relationships between the cell-cycle and plastid division. Moreover, the severe developmental defects observed in AtCDT1-RNA interference (RNAi) plants underline the importance of coordinated cell and organelle division for plant growth and morphogenesis.

Arabidopsis↗

PubMed2004

The N-myristoylated Rab-GTPase m-Rabmc is involved in post-Golgi trafficking events to the lytic vacuole in plant cells.

We report on the sub-cellular localisation and function of m-Rab(mc), a N-myristoylated plant-specific Rab-GTPase previously characterised at the molecular level and also by structural analysis in Mesembryanthemum crystallinum. By confocal laser scanning microscopy, we identified m-Rab(mc) predominantly on the prevacuolar compartment of the lytic vacuole but also on the Golgi apparatus in various plant cell types. Two complementary approaches were used immunocytochemistry and cyan fluorescent protein (CFP)/yellow fluorescent protein (YFP)-fusion proteins. Co-localisation studies of m-Rab(mc) with a salinity stress modulated integral calcium-ATPase suggest involvement of m-Rab(mc) in a plant-specific transport pathway to the prevacuolar compartment of the lytic vacuole. This hypothesis was strengthened by the inhibition of the transport of aleurain fused to green fluorescent protein (GFP), a marker of the lytic vacuole, in the presence of the dominant negative mutant m-Rab(mc)(N147I) in Arabidopsis thaliana protoplasts. The inhibitory effect of m-Rab(mc)(N147I) was specific for the transport pathway to the lytic vacuole, since the transport of chitinase-YFP, a marker for the neutral vacuole, was not hindered by the mutant.

Arabidopsis↗

PubMed2003

The tobacco A-type cyclin, Nicta;CYCA3;2, at the nexus of cell division and differentiation.

Although most of the components of the cell cycle machinery are conserved in all eukaryotes, plants differ strikingly from animals by the absence of a homolog of E-type cyclin, an important regulator involved in G1/S-checkpoint control in animals. By contrast, plants contain a complex range of A-type cyclins, with no fewer than 10 members in Arabidopsis. We previously identified the tobacco A-type cyclin Nicta;CYCA3;2 as an early G1/S-activated gene. Here, we show that antisense expression of Nicta;CYCA3;2 in tobacco plants induces defects in embryo formation and impairs callus formation from leaf explants. The green fluorescent protein (GFP)-Nicta;CYCA3;2 fusion protein was localized in the nucleoplasm. Transgenic tobacco plants overproducing GFP-Nicta;CYCA3;2 could not be regenerated from leaf disc transformation, whereas some transgenic Arabidopsis plants were obtained by the floral-dip transformation method. Arabidopsis plants that overproduce GFP-Nicta;CYCA3;2 showed reduced cell differentiation and endoreplication and a dramatically modified morphology. Calli regenerated from leaf explants of these transgenic Arabidopsis plants were defective in shoot and root regeneration. We propose that Nicta;CYCA3;2 has important functions, analogous to those of cyclin E in animals, in the control of plant cell division and differentiation.

Antisense Elements (Genetics)↗

PubMed2003

Identification and localization of a beta-COP-like protein involved in the morphodynamics of the plant Golgi apparatus.

This paper examines the molecular machinery involved in membrane exchange within the plant endomembrane system. A study has been undertaken on beta-COP-like proteins in plant cells using M3A5, an antibody raised against the conserved sequence of mammalian beta-COP proteins. In mammalian cells, beta-COP proteins are part of a complex named the coatomer, which probably recruits some specific areas of the endomembrane system. Immunofluorescence analyses by confocal laser scanning microscopy showed that beta-COP-like proteins marked predominantly the plant Golgi apparatus. Other proteins known to be part of a potential machinery for COPI vesicle formation (gamma-COP, beta'-COP and Arf1 proteins) were immunolocalized on the same membraneous structures as beta-COP. Moreover, beta-COP and other COPI antibodies stained the cell plate in dividing cells. It is further shown that, in maize root cells, and in contrast to observations upon mammalian cells, the drug Brefeldin A (BFA) does not induce the release of beta-COP and Arf1 proteins from the Golgi membrane into the cytosol. These data clearly demonstrate that the antibody M3A5 is a valuable marker for studies on trafficking events in plant cells. They also report for the first time the location of COP components in plant tissue at the light level, especially on a model well known for secretion, i.e. the maize root cells. They also suggest that the membrane recruitment machinery may function in a plant-specific way.

Animals↗

PubMed2003

Incidence of breast and chest wall asymmetry in breast augmentation: a retrospective analysis of 100 patients.

Although much is written concerning breast augmentation, few authors have addressed preoperative chest wall analysis as it pertains to postoperative outcome. In the present study, 100 patients were randomly selected, underwent bilateral augmentation, and were examined retrospectively by four independent physicians using standardized preoperative photographs. Each patient was examined for ptosis and asymmetry of the nipples, breast mound, and chest wall. Results revealed significant asymmetries in all parameters. Nipple-areola complex asymmetry was present in 24 percent (nipple/areola size) and 53 percent (nipple position) of the women. Mound asymmetry was noted in 44 percent (volume), 29 percent (base constriction), and 30 percent (inframammary fold position) of the women, and finally, 29 percent of the women had grade I to III ptosis. Chest wall asymmetry was observed in 9 percent of the women. Overall, 88 percent of the women had some degree of asymmetry, and 65 percent of the women had more than one parameter of asymmetry. These findings underscore the importance of developing a systematic preoperative breast and chest wall analysis that can be individualized for each patient. The resulting asymmetries should then be discussed with the patient, along with the potential for continued or even more pronounced asymmetry postoperatively.

Breast↗

PubMed2002

Urea as a passive transport marker for arthritis biomarker studies.

OBJECTIVE: To develop a method to correct for the unknown dilution of synovial fluid that occurs during lavage of a joint, we evaluated the utility of urea, a molecule that is neither synthesized nor metabolized by joint tissues, as a means of correcting for the dilutional effects of lavage procedures and effusions. METHODS: Joint fluids were obtained from normal canine joints by direct aspiration (n = 41) and lavage (n = 10). Acute joint injury was induced in 4 joints by intraarticular injection of chymopapain. Serum and joint fluid levels of urea and joint fluid concentrations of glucose, lactate, cartilage oligomeric matrix protein (COMP), and keratan sulfate (KS) were measured in these 55 joints. RESULTS: Urea concentrations in joint fluid were directly proportional to those in serum throughout a wide range of concentrations in normal joints. From this relationship, the dilution factor introduced by joint lavage was determined. This method was applied to quantify biomarker concentrations in synovial lavage fluid and was found to successfully correct for lavage-induced dilution of glucose, lactate, COMP, and KS to levels equivalent to those in samples aspirated directly. In the context of chymopapain-induced joint effusion, urea concentrations continued to be proportional to serum concentrations, but were much lower, enabling an estimation of the change in the volume of distribution (V(d)) of a marker due to a change in joint water content in the setting of inflammation characterized by effusion. Lactate and KS levels rose markedly in response to chymopapain. After adjustment for the V(d), the glucose concentration in the chymopapain-injected joints did not change. CONCLUSION: Urea provides a robust method of quantifying and correcting for the dilution of synovial fluid due to joint lavage or inflammation. This method is potentially applicable to surrogate marker studies in human arthritis.

Animals↗