1219 INFORMAL CAREGIVERS OF PEOPLE WITH PARKINSONISM IN THE PRIME-UK CROSS-SECTIONAL STUDY

Introduction

Many people with parkinsonism require care as the disease progresses with much provided unpaid by family and friends. Caring for someone can have a negative impact on physical and psychosocial wellbeing. Caregiver burden can impact ability to continue this role, which can precipitate hospitalisation or institutionalisation of the recipient.

Methods

In this single-site study, primary, informal caregivers, defined as those providing any care or support, were enrolled alongside the person with parkinsonism or individually. Self-reported questionnaires included the 22-item Zarit Burden Interview (ZBI), which can range from 0-88, with higher scores representing greater burden. Linear regression was used to explore the association between recipient characteristics/need and caregiver burden.

Results

Of 1,032 eligible patients approached, 813 participants indicated whether they had an informal caregiver (708) or not (105). 376 caregivers consented (53.1%), of whom 321 have returned questionnaires, with patient data available for 296. The median age of caregivers was 73.0 (range 27.0- 91.1 years), 237 (73.8%) female. 274 (85.4%) were the spouse/partner of the patient. 215 (67.0%) were the sole caregiver. The median time per week spent caring was 21 hours (interquartile range 7, 41 hours). 18 (5.6%) of caregivers provided 24-hour care daily and 113 (35.2%) had provided support for over 5 years. Median ZBI score was 17, (interquartile range 7-29). The care recipient’s duration of parkinsonism was associated with higher burden score (0.38 increase per year of parkinsonism; 95% CI 0.07, 0.69; p value 0.015), as was the time per week spent caring (0.16 increase for each additional hour; 95% CI 0.11, 0.20; p value <0.0001).

Conclusions

Many informal caregivers in this study were the sole caregiver and many were themselves older adults. Burden increased with increasing duration of parkinsonism and as time spent caring increased. This highlights the ongoing need to improve support for this group.

697 PATIENTS WITH PARKINSONISM AND THEIR CAREGIVERS: A PROTOCOL FOR THE PRIME-UK CROSS-SECTIONAL STUDY

Introduction

People with parkinsonism (PwP) are a highly heterogeneous group and the condition encompasses a spectrum of motor and nonmotor symptoms which variably emerge and manifest across the disease course, fluctuate over time and negatively impact quality of life. Whilst parkinsonism is not directly the result of ageing, it is a condition that mostly affects older people, who may also be living with frailty and multimorbidity. This study aims to describe a broad range of PwP in relation to their symptomatology, disability, health needs, disease stage, comorbidities and sociodemographics.

Methods

In this cross-sectional study, performed at one site, PwP (excluding those with drug-induced parkinsonism) will be sent a study information pack for themselves and their primary informal caregiver, if relevant. Data are collected via questionnaire, with additional support if required to maximise participation. A specific strategy has been developed to target and proactively recruit patients lacking capacity to consent, including those in residential care settings, with input from a personal consultee prior to completion of a bespoke questionnaire by a representative. Caregivers are also recruited to look at various health outcomes.

Results

Our primary outcome is the frequency of various health outcomes (e.g. depression) and how they cluster together. Linear and logistic regression models will be used to test simple associations and interactions with gender, age group and socio-economic status.

Conclusion

It is necessary to consider the multifaceted problems that PwP experience, together with frailty and comorbidities, in order to fully appreciate the clinical complexity as well as the impact on caregiver well-being. This information is necessary to inform the development of a person-centered, individualised multicomponent intervention to target patients and caregivers most at risk of adverse outcomes. We hope that these findings will inform future intervention trials and improve accessibility to research participation.

Cholinesterase inhibitor to prevent falls in Parkinson's disease (CHIEF-PD) trial: a phase 3 randomised, double-blind placebo-controlled trial of rivastigmine to prevent falls in Parkinson's disease

BACKGROUND

Falls are a common complication of Parkinson's disease. There is a need for new therapeutic options to target this debilitating aspect of the disease. Cholinergic deficit has been shown to contribute to both gait and cognitive dysfunction seen in the condition. Potential benefits of using cholinesterase inhibitors were shown during a single centre phase 2 trial. The aim of this trial is to evaluate the effectiveness of a cholinesterase inhibitor on fall rate in people with idiopathic Parkinson's disease.

METHODS

This is a multi-centre, double-blind, randomised placebo-controlled trial in 600 people with idiopathic Parkinson's disease (Hoehn and Yahr stages 1 to 4) with a history of a fall in the past year. Participants will be randomised to two groups, receiving either transdermal rivastigmine or identical placebo for 12 months. The primary outcome is the fall rate over 12 months follow-up. Secondary outcome measures, collected at baseline and 12 months either face-to-face or via remote video/telephone assessments, include gait and balance measures, neuropsychiatric indices, Parkinson's motor and non-motor symptoms, quality of life and cost-effectiveness.

DISCUSSION

This trial will establish whether cholinesterase inhibitor therapy is effective in preventing falls in Parkinson's disease. If cost-effective, it will alter current management guidelines by offering a new therapeutic option in this high-risk population.

TRIAL REGISTRATION

REC reference: 19/SW/0043. EudraCT: 2018-003219-23.

ISCRTN

41639809 (registered 16/04/2019). ClinicalTrials.gov Identifier: NCT04226248 PROTOCOL AT TIME OF PUBLICATION: Version 7.0, 20th January 2021.

Public attitudes to the use of remote data collection in clinical research

Background/aims

Coronavirus Disease 2019 (COVID-19) has presented an unprecedented challenge for delivering clinical research. The use of technology-assisted data collection for clinical research is desirable for many practitioners, but the acceptability of use in the general population has not been assessed. The aim of the study was to assess attitudes towards using technology-assisted remote methods in the delivery of clinical research in the UK and to understand the barriers to taking part in research with respect to both remote assessments and traditional research methods across different age ranges.

Methods

The study was conducted as an online anonymous survey with a 4-part questionnaire, between August 2020 and December 2020. Participants living in the UK aged 18 years and above were eligible to take part.

Results

A total 351 completed the survey and are included in the data analysis. In all age groups, participants identified that use of online assignments, video calls and telephone calls would make them more likely to take part in clinical research. Overall, the largest barrier to taking part in research was time commitments and timing of the appointment. COVID-19 has had a small, positive influence on the confidence of using technology in the general population.

Conclusions

The study found that there is a large interest in taking part in research using online, telephone and video call appointments, which could facilitate research delivery in light of ongoing COVID-19-related restrictions and also improve the accessibility and inclusivity of research.

Prone Positioning of Older Adults with COVID-19: A Brief Review and Proposed Protocol

COVID-19 disproportionately affects older people, with higher rates of infection and a higher risk of adverse outcomes. A brief review of literature was undertaken to inform development of a protocol describing the indications and process of prone positioning to aid the management of COVID-19 infection in non-mechanically ventilated, awake older adults. PubMed was searched up to 14th January 2021 to identify English language papers that described prone positioning procedures used in non-mechanically ventilated patients. Data were pooled to inform the development of a prone positioning protocol for use in hospital ward environments. The protocol was trialled and refined during routine clinical practice. Screening of 146 articles yielded five studies detailing a prone positioning protocol. Prone positioning is a potentially feasible and tolerated treatment adjunct for hypoxaemia in older adults with COVID-19. Future studies should further establish the efficacy, safety, and tolerability in respiratory illnesses in non-intensive care settings.

Systematic review of the use of data from national childhood obesity surveillance programmes in primary care: a conceptual synthesis

This study reviewed the use in primary care of national surveillance data for children to determine the data's potential utility to inform policy and practice decisions on how to prevent and treat childhood obesity. We reviewed the 28 countries identified by the World Obesity Federation as having high-quality comparable body mass index data for children. Literature published from any period up to December 2013 was included. Peer review literature was searched using Web of Science (Core Collection, MEDLINE). Grey literature was searched using the Internet by country name, programme name and national health and government websites. We included studies that (i) use national surveillance obesity data in primary care, or (ii) explore practitioner or parent perspectives about the use of such data. The main uses of national surveillance data in primary care were to identify and recruit obese children and their parents to participate in school and general practice-based research and/or interventions, and to inform families of children's measurements. Findings indicate a need for school staff and practitioners to receive additional training and support to sensitively communicate with families. Translation of these findings into policy and practice could help to improve current uses of national child obesity surveillance data in primary care.

Developmentally-regulated cell surface N-linked oligosaccharides participate in intercellular cohesion in Dictyostelium discoideum

The ability of purified plasma membrane glycoconjugates to inhibit the EDTA-resistant agglutination between aggregation-stage cells of Dictyostelium discoideum has suggested that receptor binding of these glycoconjugates provides a basis for cell-cell cohesion during aggregation. This has been tested by analysis of a series of mutants with different defects in the assembly of N-linked oligosaccharides. Mutant HL241 lacks outer branch components of N-linked oligosaccharides and fails to aggregate or express EDTA-resistant cohesion. HL244 makes unsulphated but otherwise normal N-linked oligosaccharides, generates multiple tips on aggregated cell mounds in some clones, and shows abnormally strong EDTA-resistant cohesion. Two mutants that are temperature-sensitive for complete processing of N-linked oligosaccharides are also temperature-sensitive for expression of both aggregation ability and EDTA-resistant cohesion. A revertant that recovered essentially normal N-linked oligosaccharide processing at the restrictive temperature has also recovered its ability to aggregate and to agglutinate in EDTA.

Cell differentiation in Dictyostelium discoideum controls assembly of protein-linked glycans

The prestalk and prespore cells from the Dictyostelium discoideum multicellular slug stage of development differ in assembly of glycoconjugates. Prespore cells are 2- to 3-fold more active than prestalk cells in the assembly of N-linked glycans and 20-fold more active in their fucosylation. Only prespore cells synthesize an O-linked glycan consisting in part of Fuc alpha-linked to N-acetylglucosamine. Incorporation of fucose, glucosamine, mannose and galactose into large pronase-resistant glycoconjugates was almost exclusively into prespore cells. Such glucosamine-labelled glycoconjugates resist fragmentation by beta-elimination and include a glycoantigen dependent on the modB genetic locus. In contrast, large fucose-labelled glycoconjugates consisted of multiple, small, O-linked oligosaccharides on carrier peptides. The spore coat protein SP96 has several fucosylated O-linked oligosaccharides, one of which correlates with a fucose epitope previously shown to localize in prespore vesicles and the outer layer of the spore coat.

Home pass assessment in neurorehabilitation practice

The patient undergoing in-patient neurorehabilitation is often encouraged to go home with a family member or other carer for a short period when fit to do so. This home pass is helpful to both the family and the rehabilitation nursing staff in gauging how well the patient will function when discharged, but valuable feedback information can be lost. This study describes the experience of using a home pass assessment form to document the patients' performance and discusses the nursing staff and relative's perceptions of the usefulness of this instrument and the possible reasons for discrepancies between the nurses' assessment of the patient's abilities and the carers' reports.

Conditional intercellular cohesion in a Dictyostelium discoideum mutant which is temperature sensitive for correct processing of asparagine-linked oligosaccharides

Mutants of Dictyostelium discoideum have been isolated by a selection for cells with temperature-sensitive defects in the maturation of glycoprotein N-linked oligosaccharides. Here we describe a mutant, HT7, which is unable to aggregate at the restrictive temperature, but which aggregates and makes fruiting bodies at the permissive temperature. HT7 shows normal early developmental intercellular cohesion, but is temperature sensitive for expression of the ethylenediamine-tetraacetic acid (EDTA)-resistant cohesion characteristic of aggregation. The mutant initiates aggregation, but forms only loose cell mounds which later disperse. Metabolic labelling studies indicate that the thermolabile defect is not in protein synthesis, assembly of the lipid-linked precursor of N-linked oligosaccharides or transfer of the precursor to proteins. However, the defect does prevent assembly of fully processed N-linked oligosaccharides. Further, two glycopeptides, obtained from exhaustive Pronase digests of wild-type plasma membrane glycoproteins, inhibit intercellular cohesion of aggregation-stage wild-type cells. HT7 produces only approximately 50% of the wild-type level of these glycopeptides at the restrictive temperature and one of the glycopeptides has reduced cohesion inhibition ability. A revertant of HT7 was found to aggregate normally, to have restored EDTA-resistant cohesion, to have normal profiles of N-linked oligosaccharides and to express the two cohesion-inhibiting glycopeptides normally. These data strongly support a model in which cohesion during late aggregation is at least in part due to recognition between surface glycans and receptors on neighbouring cells.

Biochemical differentiation in a mutant of Dictyostelium discoideum defective in cyclic AMP chemotaxis and in intercellular cohesion

A temperature-sensitive mutant of Dictyostelium discoideum has been isolated based on its lack of chemotaxis toward cyclic AMP at the restrictive temperature, 27 degrees C. The mutant develops normally at the permissive temperature, 22 degrees C, but fails to aggregate or complete development at the restrictive temperature. The temperature-sensitive phenotype can be bypassed by allowing cultures to grown into late log phase or to starve for 60–90 min at 22 degrees C prior to a shift to 27 degrees C. At 27 degrees C, the mutant overproduces cell surface cyclic AMP receptors of both high and low affinity and is capable of spontaneous oscillations in light scattering in cell suspensions. Despite its complete lack of morphological development, the mutant undergoes extensive biochemical differentiation. At the onset of starvation, it shows increased levels of N-acetylglucosaminidase, it express cyclic AMP receptors at the normal time and, although somewhat slowly, suppresses those receptors as if aggregation had been achieved. Metabolic pulse labellings with [35S]methionine revealed that the mutant at 27 degrees C displays the same changes in the patterns of newly synthesized proteins observed during the vegetative-to-aggregation and the aggregation-to-slug stages of normal development. The only clear difference from wild type was the failure of the culmination-stage isozyme of beta-glucosidase to appear. The mutant is defective in establishment of intercellular cohesion mechanisms, correlated with poor agglutination by concanavalin A, at the restrictive temperature. The properties of the mutant place severe constraints on models regarding the role of chemoreception and intercellular cohesion in regulation of gene expression.

Differential regulation of glycoprotein sulfation and fucosylation during growth of Dictyostelium discoideum

During early starvation-induced development, amoebae of Dictyostelium discoideum have been previously shown to increase sulfation and fucosylation of glycoprotein-linked oligosaccharides to levels above those observed in axenically growing cells. We report here that the axenic broth culture itself induces generation of high levels of fucosylated glycoprotein-linked oligosaccharides at all stages in the growth curve. However, when grown on bacteria, amoebae of both the axenic strain and the wild type show dramatic depression in fucose incorporation during early exponential growth. In mid- and late-exponential stages of growth, fucosylation rises to the levels found at all stages of axenic culture. Sulfation also increases during early development, but, in contrast to fucosylation, oligosaccharide sulfation is not altered by growth in axenic medium and does not increase during growth on bacteria. Starvation of bacterially grown cells results in increased sulfation and a further rise in fucosylation, as is also characteristic of broth-grown cells. The ability of axenic culture to uncouple control of these two classes of glycan-modification steps suggests that the synchronous increases during early development actually reflect responses to different regulatory signals, even though they participate in the same metabolic process. The increase in in vivo fucosyltransferase activity, which can act on many substrate glycoproteins, may alter many characteristics of the cells.

Cell surface oligosaccharides participate in cohesion during aggregation of Dictyostelium discoideum

Plasma membrane glycoproteins from Dictyostelium discoideum amoebae at three stages of early development were digested with Pronase and endoglycosidase H and fractionated by gel filtration. This gave three classes of glycans (polysaccharides, endoglycosidase H-resistant glycopeptides, and endoglycosidase H-released oligosaccharides), which were tested for their ability to block agglutination of amoebae from vegetative, aggregation (8-hr), and late-aggregation (13-hr) stages of development. The endoglycosidase H-resistant glycopeptides from 8-hr cells inhibited agglutination of disaggregated 8-hr cells but not vegetative or 13-hr cells. The 8-hr polysaccharide and endo H-sensitive oligosaccharides did not inhibit. The glycopeptides from 8-hr cells were resolved into five species by electrophoresis in borate-containing buffer. Two of these had agglutination-inhibiting activity, and three did not. None of the glycan fractions from vegetative or 13-hr cells inhibited agglutination of vegetative, 8-, or 13-hr cells. These data implicate specific cell surface glycans in aggregation-stage intercellular cohesion and suggest that both these glycans and receptors for them are developmentally regulated.

Defective intercellular cohesion in glycosylation mutants of Dictyostelium discoideum

In order to identify the biological roles of protein-linked oligosaccharides, we have isolated mutants by a selection for amoebae with temperature-sensitive defects in glycan assembly and processing. Of these, 75% were also temperature sensitive for development [Boose and Henderson, 1986]. Two such mutants with distinct developmental phenotypes and glycosylation patterns are described. Mutant HT7 cannot complete aggregation at the restrictive temperature and is defective in expression of EDTA-resistant cohesion. The biochemical defect appears to be early in glycan processing. A revertant of HT7 has recovered aggregation capability, EDTA-resistant cohesion, and reverted almost totally to wild-type glycosylation. Mutant HT15 aggregates at the restrictive temperature but then disperses into a cell lawn. It is less deficient in EDTA-resistant cohesion than HT7 and has a different glycosylation profile. These results provide strong support for a role of protein N-linked oligosaccharides in aggregation-stage intercellular cohesion.

Altered cyclic-AMP receptor activity and morphogenesis in a chemosensory mutant of Dictyostelium discoideum

The functional properties of the cell-surface cyclic-AMP receptor that controls chemotaxis were found to be altered in an aggregation mutant of Dictyostelium discoideum. The mutant aggregated without stream formation and had a tenfold increased cell-density requirement for the initiation of aggregation. After aggregation, mounds formed multiple tips and subsequently subdivided to give multiple fruits that were small and abnormally proportioned. Cyclic-AMP-induced light-scattering changes in cell suspensions indicated that the mutant had a diminished response to external cyclic-AMP signals. Associated with these altered functional responses was a physical change in the cyclic-AMP sensory system. Cyclic-AMP-binding studies showed that the parent had two classes of cyclic-AMP binding sites, i.e., Kd = 32 and 110 nM. In contrast, the mutant had two- to threefold or more high-affinity sites (Kd = 25 nM) and altered low-affinity sites (Kd less than 3 microM). These results indicate that both affinity classes of binding site are independently mutable. This observation suggests that the two affinity classes can be interconverted by mutation, or the mutation alters a single molecular species and its equilibrium between binding sites with different affinities for cyclic AMP, as postulated in receptor cycling models.

Fluorographic detection of tritiated glycopeptides and oligosaccharides separated on polyacrylamide gels: analysis of glycans from Dictyostelium discoideum glycoproteins

Previous workers have shown that oligosaccharides and glycopeptides can be separated by electrophoresis in buffers containing borate ions. However, normal fluorography of tritium-labeled structures cannot be performed because the glycans are soluble and can diffuse during equilibration with scintillants. This problem has been circumvented by equilibration of the gel with 2,5-diphenyloxazole (PPO) prior to electrophoresis. The presence of PPO in the gel during electrophoresis does not alter mobility of the glycopeptides and oligosaccharides. After electrophoresis, the gel is simply dried and fluorography performed. This allows sensitive and precise comparisons of labeled samples in parallel lanes of a slab gel and, since mobilities are highly reproducible, between different gels. The procedure is preparative in that after fluorography the gel bands can be quantitatively eluted for further study, without any apparent modification by the procedure. In this report, the procedure is illustrated by fractionation of both neutral and anionic glycopeptides produced by the cellular slime mold Dictyostelium discoideum.

Sulfate suicide selection of Dictyostelium discoideum mutants defective in protein glycosylation

The assembly and processing of glycoprotein-linked oligosaccharides in Dictyostelium discoideum has been shown to generate a wide array of glycan structures which undergo dramatic developmental regulation. As late steps in processing of these oligosaccharides involve sulfation, a sulfate suicide selection procedure was developed to select for temperature-sensitive glycoprotein-processing mutants. Of 673 clones derived from the survivors of suicide selection, 99 were classified by replica-plating fluorography as temperature sensitive for sulfate transport or incorporation. Of these, 74 were unable to complete the developmental program to the fruiting body stage at the restrictive temperature, 29 being blocked in some aspect of aggregation and 45 being blocked at some postaggregation stage. Quantitative metabolic labeling experiments with representative clones showed that they incorporated wild-type levels of [35S]methionine but reduced levels of sulfate at the restrictive temperature. The specific incorporation patterns in the mutants suggest that distinct oligosaccharide-processing steps are involved in different developmental events.

Glycoprotein biosynthesis in dictyostelium discoideum: developmental regulation of the protein-linked glycans

The biosynthesis of glycoprotein N-linked oligosaccharides in D. discoideum is initiated by the transfer of a large precursor glycan from a carrier lipid. The subsequent processing of this precursor is dramatically dependent upon the stage of development. In early development processing retains the high mannose structure of the precursor and modifies some glycans by addition of fucose to core sugars and sulfate and phosphate to others. These reactions are coordinately lost during aggregation. Processing in late development extensively trims the precursor and adds fucose to peripheral mannose units of the smallest glycans. These reactions appear coincident with formation of tips on cell mounds. Experiments in which cells were starved in shaken suspension suggest that intercellular contacts and cyclic AMP signals may be sufficient to cause the controlled expression of these two alternate sets of processing enzymes.

Developmental regulation of Dictyostelium discoideum plasma membrane proteins

Developmental changes in the plasma membrane proteins of Dictyostelium discoideum have been studied using metabolic labeling with [35S]methionine and two-dimensional electrophoresis. Pulse labeling for 1 h at the early interphase, late interphase, aggregation, and tip formation stages of development showed that the profile of newly synthesized plasma membrane proteins changed dramatically over this interval. Only 14% of the polypeptide species were synthesized at all four stages at detectable levels; 86% of the species changed over this developmental interval according to the criterion that they were synthesized at some but not all of the four stages tested. Long-term labeling during vegetative growth followed by initiation of development showed that the "steady-state" levels of the plasma membrane proteins changed very little over the same period. The only changes were in minor species (33% overall change). Similar analyses of whole cell proteins showed 27 and 20% change, respectively. Cell surface radioiodination revealed 52 external proteins in the plasma membrane. Comparison with the uniform methionine labeling results showed that these proteins were, with one notable exception, minor membrane components. In these external proteins, also, developmental changes were limited and were observed in the less abundant species. These results demonstrate the existence of two general classes of plasma membrane proteins. The first is a population of high-abundance proteins that are present in vegetative cells and are largely conserved through development. These possibly serve "housekeeping" functions common to all stages. The second class consists of low-abundance species that are expressed in a highly stage-specific manner and which presumably participate in developmentally important functions.

Guanidine hydrochloride-induced shedding of a Dictyostelium discoideum plasma membrane fraction enriched in the cyclic adenosine 3',5'-monophosphate receptor

The cell surface cyclic AMP receptor of Dictyostelium discoideum is under study in a number of laboratories with respect to both its role in development of the organism and the physiology of excitation-response coupling. We report here that when starved amoebae are exposed to the chaotrope guanidine hydrochloride at 1.8 M, they shed a particulate cyclic AMP binding activity into the medium. This activity is due to membrane vesicles which originate from the cell surface. The vesicles are enriched up to 150-fold in cyclic AMP binding activity and up to 14-fold in phospholipid content when compared to the starting amoebae. The cyclic AMP binding activity of the membrane vesicles is identical to that of the cell surface receptor with respect to the following properties; (i) it is lacking in preparations from unstarved, vegetative amoebae; (ii) it is not inhibited by cyclic GMP and is stimulated by calcium ions; (iii) it has very rapid rates of association and dissociation of bound cyclic AMP; (iv) it has two classes of binding sites with dissociation constants similar to those of the surface receptors of whole amoebae. The binding activity of the isolated membranes is stable for several days at 4 degrees C and the lower affinity binding sites are stable up to several months when stored at -80 degrees C. Due to enrichment and stability of the receptor in this preparation, it should be highly suitable for many types of studies. The usefulness is enhanced by the fact that the preparation does not contain detectable cyclic AMP phosphodiesterase activity.

Thermosensitive development and tip regulation in a mutant of Dictyostelium discoideum

A thermosensitive developmental mutant of Dictyostelium discoideum identifies a gene product that is nonessential for cell multiplication but is continuously required during aggregation and the period when multicellular mounds are formed. After mounds form a tip, which has the properties of an embryonic organizer, this gene product may be nonessential. Surgical removal of the tip from a polarized developing multicellular structure (the slug) leads to emergence of a new tip at the permissive temperature but not at the restrictive temperature. The mutant continues to develop abnormally when mixed with wild-type cells; therefore, a cell-limited rather than an exchangeable factor is altered. Assays show that the mutant has a thermosensitive defect in chemotaxis toward cAMP. The mutation reduces the number of cell surface cAMP receptors expressed at the restrictive temperature without affecting their dissociation constants or their apparent thermostability. The expression of two developmentally regulated enzymes, N-acetylglucosaminidase and cAMP phosphodiesterase, is unaffected by the mutation.

Developmental regulation of glycoprotein biosynthesis in Dictyostelium

We have examined the glycoprotein-linked oligosaccharides assembled during the life cycle of Dictyostelium discoideum, and found their expression to be dramatically dependent upon the stage of development. During early development mature glycans have a high mannose character, and a substantial proportion acquire a fucose residue that correlates with endo-H resistance. One-third of the glycans also acquire sulfate residues. These glycans diminish in importance during aggregation. The mature glycans expressed during aggregation. The mature glycans expressed during late development contain fewer mannose residues, from five to ten mannose residues, and are characterized by the absence of sulfate residues and by the presence of fucose residues on endo-H-sensitive glycans. These glycans make their appearance coincident with the construction of tips on tight cell mounds. At this stage glycans characteristic of both early and late stages occur simultaneously. Developmental regulation of the wide array of protein-linked glycans expressed during the life cycle of Dictyostelium discoideum may be as simple as the controlled transition from a group of structures that are assembled by the vegetative cells to a group of structures that are assembled by the terminally differentiating cells. The potential biological significance of this transition is discussed.

The cyclic adenosine 3':5'-monophosphate receptor of Dictyostelium discoideum. Binding characteristics of aggregation-competent cells and variation of binding levels during the life cycle

Both cyclic guanosine 3':5'-monophosphate and dithiothreitol stimulate binding of cyclic adenosine 3':5'-monophosphate (cAMP) to aggregation-competent amoebae. Both compounds appear to function solely by preventing the hydrolysis of cAMP by the cell-bound phosphodiesterase. The dissociation constant for binding of cAMP is 36 nM. Both cAMP binding and membrane-bound phosphodiesterase activities increase dramatically as cells develop aggregation competence, reach a maximum at about 11 hours, and remain at high levels for up to 48 hours if cells are maintained in shaken suspension. When amoebae are allowed to aggregate and develop naturally, binding of cAMP increases during aggregation, decreases during tip formation, and disappears during culmination. Phosphodiesterase activity parallels binding activity except that the decreased level after tip formation is retained throughout culmination. Two N-6-modified cAMP derivatives compete with cAMP for binding sites. One derivative is fluorescent (1,N-6-etheno-cAMP); the other is photolyzable [N-6(ethyl-2-diazomalonyl)cAMP]. This result opens the possibilities of using fluorescence quenching for assay of in vitro binding and of affinity labeling of binding sites. Competition by the derivatives is only partial, indicating possible heterogeneity of binding sites. Both compounds inhibit hydrolysis of cAMP by the membrane-bound phosphodiesterase.