The Bone Sialoprotein RGD Domain Modulates and Maintains Periodontal Development

Bone sialoprotein (gene: Ibsp; protein: BSP) is a multifunctional extracellular matrix protein present in bone, cementum, and dentin. Accumulating evidence supports BSP as a key regulator of mineralized tissue formation via evolutionarily conserved functional domains, including a C-terminal integrin-binding Arg-Gly-Asp (RGD) domain implicated in extracellular matrix-cell signaling. Ablation of Ibsp in mice (Ibsp-/-) results in impaired bone growth and mineralization and defective osteoclastogenesis, with effects in the craniofacial region including reduced acellular cementum formation, detachment of the periodontal ligament (PDL), alveolar bone hypomineralization, and severe periodontal breakdown. We hypothesized that BSP-RGD plays an important role in cementum and alveolar bone formation and mineralization, as well as periodontal function. This hypothesis was tested by replacing the RGD motif with a nonfunctional Lys-Ala-Glu (KAE) sequence in (IbspKAE/KAE) mice and OCCM.30 murine (IbspKAE) cementoblasts. The RGD domain was not critical for acellular or cellular cementum formation in IbspKAE/KAE mice. However, PDL volume and thickness were increased, and significantly more tartrate-resistant acid phosphatase-positive osteoclasts were found on alveolar bone surfaces of IbspKAE/KAE mice versus wild type mice. PDL organization was disrupted as indicated by picrosirius red stain, second harmonic generation imaging, dynamic mechanical analysis, and decreased asporin proteoglycan localization. In vitro studies implicated RGD functions in cell migration, adhesion, and mineralization, and this was confirmed by an ossicle implant model where cells lacking BSP-RGD showed substantial defects as compared with controls. In total, the BSP-RGD domain is implicated in periodontal development, though the scale and scope of changes indicated by in vitro studies indicate that other factors may partially compensate for and reduce the phenotypic severity of mice lacking BSP-RGD in vivo.

MO1044: Understanding Perception of Pregnancy Risk in Women with Chronic Kidney Disease

BACKGROUND AND AIMS

Women with chronic kidney disease (CKD) are at increased risk of adverse pregnancy and renal outcomes, including preterm birth and progression of kidney disease. Women's risk perceptions of pregnancy impact behaviours and decisions including engagement with prenatal care, mode of delivery choices and adherence to medical advice, therefore, it is important that women perceive and understand their risk accurately. Pre-pregnancy counselling is recommended for all women with CKD, but it is unknown how women with CKD understand their pregnancy risk and if pre-pregnancy counselling affects women's perceptions. The aim of this study was to understand how a large cohort of diverse women with CKD perceive their pregnancy risk and compare differences in risk perceptions between those who have and have not received pre-pregnancy counselling.

METHOD

The ‘Perception of Pregnancy Risk Questionnaire’ (PPRQ;1) and ‘Desire to Avoid Pregnancy Questionnaire’ (2) were used to measure risk perception and pregnancy intention respectively. The PPRQ was adapted to assess risk perceptions in women with CKD including the severity of kidney disease. Content validity of the adapted PPRQ was confirmed by a panel of 21 experts including nephrologists, midwives, psychologists and obstetricians. Women aged between 18 and 50 years with CKD stages 1–5 were recruited from nine renal units in the United Kingdom and asked to complete an online survey (October 2020–December 2021). Clinical data were extracted from local databases. Data were analysed descriptively.

RESULTS

A total of 322 women completed the survey, mean age of 34.9 (SD 7.1) years. Women's obstetric history and pregnancy perspectives are described in the Table. Half of the respondents already had children (172/322; 54.1%) and three-quarters perceived pregnancy to be important or very important to themselves (241/322; 75.8%) and two-thirds (218/322; 66.7%) perceived pregnancy to be important or very important to their family. Only 109/321 (34%) of women with CKD had previously attended pre-pregnancy counselling, but those who had attended had a higher perception of pregnancy risk [51.4 (SD 21.4) versus 41.9 (SD 23.8); P < 0.0001] (0: not very severe to 100: extremely severe) and severity of kidney disease [51.3 (SD 24.9) versus 43.7 (SD 28.6); P = 0.014] compared to women who had not attended pre-pregnancy counselling.

CONCLUSION

This large multi-centre questionnaire study identified that risk perceptions of pregnancy for women with CKD appear to be higher than those of women with an uncomplicated pregnancy [PPRQ scores of 24.0 (SD 14.5)] [1]. However, women who had received pre-pregnancy counselling had a significantly higher perception of pregnancy risk and perceived severity of kidney disease. Limitations include a lack of measurement before and after attending a pre-pregnancy counselling clinic. Further assessment of the relationship between severity of kidney disease and perceived pregnancy risk and pregnancy intentions is needed.

Statewide implementation of child trauma-focused practices using the community-based learning collaborative model

A significant number of youth in the United States experience traumatic events that substantially increase the risk of physical and behavioral health problems across the life span. This public health concern warrants concerted efforts to promote trauma-informed, evidence-based practices that facilitate recovery. Although youth-focused trauma-specific treatments exist, determining effective ways to disseminate and implement these services-so that they are available, accessible, and sustainable-poses an ongoing challenge. This paper describes a comprehensive model for such implementation, the community-based learning collaborative (CBLC), developed as part of Project BEST, a four-phase statewide initiative to promote trauma-focused practices. The CBLC augments the learning collaborative model by including clinical and nonclinical (i.e., broker) professionals from multiple service organizations within a targeted community. CBLCs aim to build capacity for sustained implementation of trauma-focused practices by promoting interprofessional collaboration among those involved in the coordination and provision of these services. This paper describes the iterative development of the CBLC by examining participant completion data across the three completed phases of Project BEST (N = 13 CBLCs; 1,190 participants). Additionally, data from Project BEST's third phase (N = 6 CBLCs; 639 participants) were used to evaluate changes in the frequency of specific practices, pre- to post-CBLC, and post-CBLC perceived utility of CBLC components. High participant completion rates, significant increases in reported trauma-focused practices, and positive ratings of the CBLC's utility provisionally support the feasibility and efficacy of the model's final iteration. Implications for implementation and CBLC improvements are discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Community-Based Learning Collaboratives and Participant Reports of Interprofessional Collaboration, Barriers to, and Utilization of Child Trauma Services

Given the high prevalence and severe consequences of child trauma, effective implementation strategies are needed to increase the availability and utilization of evidence-based child trauma services. One promising strategy, the Community-Based Learning Collaborative (CBLC), augments traditional Learning Collaborative activities with a novel set of community-focused strategies. This prospective, observational study examined pre-to post-changes in CBLC participant reports of interprofessional collaboration (IPC), barriers to, and utilization of evidence-based child trauma treatment in their communities. Participants of five CBLCs from a statewide dissemination initiative, comprising 572 child abuse professionals (296 clinicians, 168 brokers, and 108 senior leaders), were surveyed pre-and post-CBLC participation. Results suggested that CBLCs significantly decreased barriers to child trauma treatment and significantly increased IPC and perceived utilization of evidence-based child trauma treatment. Further, changes in barriers partially mediated this relationship. Finally, small to medium differences in participants' reports were detected, such that senior leaders perceived significantly greater IPC than clinicians and brokers did, while brokers perceived significantly greater barriers to child trauma treatment than clinicians and senior leaders did. Collectively, these preliminary findings suggest the CBLC implementation model-which augments traditional Learning Collaborative models with a focus on fostering IPC-can reduce barriers and increase the utilization of evidence-based mental health treatment services.

Attachment of Algal Cells to Zwitterionic Self-Assembled Monolayers Comprised of Different Anionic Compounds

The influence of zwitterionic self-assembled monolayers on settlement and removal of algae was studied. The monolayers were constructed either from zwitterionic thiols or from solutions of positively and negatively charged thiols. The cationic component was composed of quaternary ammonium terminated thiols and the anionic component contained sulfate or carboxylate termination. During assembly, all surfaces showed a strong tendency for equilibration of the surface charge. Settlement and adhesion assays with zoospores of Ulva linza and the diatom Navicula incerta, and field tests of the initial surface colonization revealed the relevance of charge equilibration for the biological inertness of the prepared surfaces.

A single genetic unit specifies two transposition functions in the maize element activator

The self-mobile maize transposable element Ac (Activator) displays two trans-acting genetic functions: it induces transposition of the element Ds (Dissociation) but, as its dosage is increased, it also inhibits transposition. Previous work has shown that the 4563 base pair (bp)-long Ac element contains three open reading frames (ORF's) and that a deletion in ORF 1 in wx-m9(Ds), a Ds derivative from Ac isolated at the wx (waxy) locus, results in loss of transposition. The Ds element in the bronze allele bz-m2(DI) is shown to have arisen from Ac by a 1312-bp deletion that is located almost entirely within ORF 2 and does not affect ORF 1. The Ds elements in wx-m9(Ds) and bzm2(DI), defective in ORF 1 and ORF 2, respectively, do not complement genetically to restore the transposition function of Ac; therefore, this function must be specified jointly by ORF's 1 and 2. Furthermore, since bz-m2(DI) does not contribute to Ac's inhibitory dosage effect, both Ac properties result from the expression of the same genetic functional unit.

Detection and imaging of non-contractile inclusions and sarcomeric anomalies in skeletal muscle by second harmonic generation combined with two-photon excited fluorescence

The large size of the multinucleated muscle fibers of skeletal muscle makes their examination for structural and pathological defects a challenge. Sections and single fibers are accessible to antibodies and other markers but imaging of such samples does not provide a three-dimensional view of the muscle. Regrettably, bundles of fibers cannot be stained or imaged easily. Two-photon microscopy techniques overcome these obstacles. Second harmonic generation (SHG) by myosin filaments and two-photon excited fluorescence (2PEF) of mitochondrial and lysosomal components provides detailed structural information on unstained tissue. Furthermore, the infrared exciting light can penetrate several layers of muscle fibers and the minimal processing is particularly valuable for fragile biopsies. Here we demonstrate the usefulness of SHG, combined with 2PEF, to reveal enlarged lysosomes and accumulations of non-contractile material in muscles from the mouse model for the lysosomal storage disorder Pompe disease (PD), and in biopsies from adult and infant PD patients. SHG and 2PEF also detect sarcomeric defects that may presage the loss of myofibrils in atrophying muscle and signify loss of elasticity. The combination of SHG and 2PEF should be useful in the analysis and diagnosis of a wide range of skeletal muscle pathologies.

Blood vessels and desmin control the positioning of nuclei in skeletal muscle fibers

Skeletal muscle fibers contain hundreds to thousands of nuclei which lie immediately under the plasmalemma and are spaced out along the fiber, except for a small cluster of specialized nuclei at the neuromuscular junction. How the nuclei attain their positions along the fiber is not understood. Here we show that the nuclei are preferentially localized near blood vessels (BV), particularly in slow-twitch, oxidative fibers. Thus, in rat soleus muscle fibers, 81% of the nuclei appear next to BV. Lack of desmin markedly perturbs the distribution of nuclei along the fibers but does not prevent their close association with BV. Consistent with a role for desmin in the spacing of nuclei, we show that denervation affects the organization of desmin filaments as well as the distribution of nuclei. During chronic stimulation of denervated muscles, new BV form, along which muscle nuclei align themselves. We conclude that the positioning of nuclei along muscle fibers is plastic and that BV and desmin intermediate filaments each play a distinct role in the control of this positioning.

Golgi complex reorganization during muscle differentiation: visualization in living cells and mechanism

During skeletal muscle differentiation, the Golgi complex (GC) undergoes a dramatic reorganization. We have now visualized the differentiation and fusion of living myoblasts of the mouse muscle cell line C2, permanently expressing a mannosidase-green fluorescent protein (GFP) construct. These experiments reveal that the reorganization of the GC is progressive (1-2 h) and is completed before the cells start fusing. Fluorescence recovery after photobleaching (FRAP), immunofluorescence, and immunogold electron microscopy demonstrate that the GC is fragmented into elements localized near the endoplasmic reticulum (ER) exit sites. FRAP analysis and the ER relocation of endogenous GC proteins by phospholipase A2 inhibitors demonstrate that Golgi-ER cycling of resident GC proteins takes place in both myoblasts and myotubes. All results support a model in which the GC reorganization in muscle reflects changes in the Golgi-ER cycling. The mechanism is similar to that leading to the dispersal of the GC caused, in all mammalian cells, by microtubule-disrupting drugs. We propose that the trigger for the dispersal results, in muscle, from combined changes in microtubule nucleation and ER exit site localization, which place the ER exit sites near microtubule minus ends. Thus, changes in GC organization that initially appear specific to muscle cells, in fact use pathways common to all mammalian cells.

Glycogen synthase localization and activity in rat skeletal muscle is strongly dependent on glycogen content

1. The influence of muscle glycogen content on glycogen synthase (GS) localization and GS activity was investigated in skeletal muscle from male Wistar rats. 2. Two groups of rats were obtained, preconditioned with a combination of exercise and diet to obtain either high (HG) or low (LG) muscle glycogen content. The cellular distribution of GS was studied using subcellular fractionation and confocal microscopy of immunostained single muscle fibres. Stimulation of GS activity in HG and LG muscle was obtained with insulin or contractions in the perfused rat hindlimb model. 3. We demonstrate that GS translocates from a glycogen-enriched membrane fraction to a cytoskeleton fraction when glycogen levels are decreased. Confocal microscopy supports the biochemical observations that the subcellular localization of GS is influenced by muscle glycogen content. GS was not found in the nucleus. 4. Investigation of the effect of glycogen content on GS activity in basal and insulin- and contraction-stimulated muscle shows that glycogen has a strong inhibitory effect on GS activity. Our data demonstrate that glycogen is a more potent regulator of glycogen synthase activity than insulin. Furthermore we show that the contraction-induced increase in GS activity is merely a result of a decrease in muscle glycogen content. 5. In conclusion, the present study shows that GS localization is influenced by muscle glycogen content and that not only basal but also insulin- and contraction-stimulated GS activity is strongly regulated by glycogen content in skeletal muscle.

Golgi complex, endoplasmic reticulum exit sites, and microtubules in skeletal muscle fibers are organized by patterned activity

The Golgi complex of skeletal muscle fibers is made of thousands of dispersed elements. The distributions of these elements and of the microtubules they associate with differ in fast compared with slow and in innervated compared with denervated fibers. To investigate the role of muscle impulse activity, we denervated fast extensor digitorum longus (EDL) and slow soleus (SOL) muscles of adult rats and stimulated them directly with patterns that resemble the impulse patterns of normal fast EDL (25 pulses at 150 Hz every 15 min) and slow SOL (200 pulses at 20 Hz every 30 sec) motor units. After 2 weeks of denervation plus stimulation, peripheral and central regions of muscle fibers were examined by immunofluorescence microscopy with regard to density and distribution of Golgi complex, microtubules, glucose transporter GLUT4, centrosomes, and endoplasmic reticulum exit sites. In extrajunctional regions, fast pattern stimulation preserved normal fast characteristics of all markers in EDL type IIB/IIX fibers, although inducing changes toward the fast phenotype in originally slow type I SOL fibers, such as a 1.5-fold decrease of the density of Golgi elements at the fiber surface. Slow pattern stimulation had converse effects such as a 2.2-fold increase of the density of Golgi elements at the EDL fiber surface. In junctional regions, where fast and slow fibers are similar, both stimulation patterns prevented a denervation-induced accumulation of GLUT4. The results indicate that patterns of muscle impulse activity, as normally imposed by motor neurons, play a major role in regulating the organization of Golgi complex and related proteins in the extrajunctional region of muscle fibers.

The organization of the Golgi complex and microtubules in skeletal muscle is fiber type-dependent

Skeletal muscle has a nonconventional Golgi complex (GC), the organization of which has been a subject of controversy in the past. We have now examined the distribution of the GC by immunofluorescence and immunogold electron microscopy in whole fibers from different rat muscles, both innervated and experimentally denervated. The total number of GC elements, small polarized stacks of cisternae, is quite similar in all fibers, but their intracellular distribution is fiber type-dependent. Thus, in slow-twitch, type I fibers, approximately 75% of all GC elements are located within 1 micrometer from the plasma membrane, and each nucleus is surrounded by a belt of GC elements. In contrast, in the fast-twitch type IIB fibers, most GC elements are in the fiber core, and most nuclei only have GC elements at their poles. Intermediate, type IIA fibers also have an intermediate distribution of GC elements. Interestingly, the distribution of microtubules, with which GC elements colocalize, is fiber type-dependent as well. At the neuromuscular junction, the distribution of GC elements and microtubules is independent of fiber type, and junctional nuclei are surrounded by GC elements in all fibers. After denervation of the hindlimb muscles, GC elements as well as microtubules converge toward a common pattern, that of the slow-twitch fibers, in all fibers. Our data suggest that innervation regulates the distribution of microtubules, which in turn organize the Golgi complex according to muscle fiber type.

A simple method to enrich an Agrobacterium-transformed population for plants containing only T-DNA sequences

A simple modification to standard binary vector design has been utilized to enrich an Agrobacterium-transformed population for plants containing only T-DNA sequences. A lethal gene was incorporated into the non-T-DNA portion of a binary vector, along with a screenable marker. The resulting class of vectors is designated as NTL T-DNA vectors (non-T-DNA lethal gene-containing T-DNA vectors). The lethal gene used here is a CaMV 35S-barnase gene with an intron in the coding sequence (barnase-INT); the screenable marker is a pMAS-luciferase gene with an intron in the coding sequence (LUC-int). To evaluate the utility of this vector design, tobacco plants were transformed with either the NTL T-DNA vector or a control vector from which most of the barnase-INT gene was deleted. Populations of 50 transgenic plants were scored for LUC expression. The results indicated a dramatic reduction in the presence of non-T-DNA sequences in the transgenic population using the NTL T-DNA vector. Only one transgenic plant was found to be LUC+ using the NTL vector, compared with 42 of 50 plants using the control vector. Importantly, the efficiency with which transformed tobacco plants was obtained was reduced by no more than 30%. The reduction in LUC+ transgenics was partially reversed when a barstar-expressing tobacco line was transformed, indicating that barnase expression was responsible for the reduced frequency of incorporating non-T-DNA sequences. Similar transformation results were obtained with tomato and grape. The incorporation of a barnase-INT gene outside the left border appears to provide a generally applicable tool for enriching an Agrobacterium-transformed population for plants containing only T-DNA sequences.

Caveolin-3 is associated with the T-tubules of mature skeletal muscle fibers

Caveolae are abundant in skeletal muscle and their coat contains a specific isoform of caveolin, caveolin-3. It has been suggested that during muscle development, caveolin-3 is associated with the T-tubules, but that in adult muscle it is found on the plasma membrane only. We have studied the distribution of caveolin-3 in single skeletal muscle fibers from adult rat soleus by confocal immunofluorescence and by immunogold electron microscopy. We found that caveolin-3 occurs at the highest density on the plasma membrane but is also present in the core of the fibers, at the I-band/A-band interface where it is associated with the T-tubules. In neither domain of the muscle surface does caveolin-3 colocalize with the glucose transporter GLUT4 and there is no evidence for internalization of the caveolae in muscle.

Ribosome association contributes to restricting mRNAs to the cell body of hippocampal neurons

In neurons, mRNAs are differentially sorted to axons, dendrites, and the cell body. Recently, regions of certain mRNAs have been identified that target those mRNAs for translocation to the processes. However, the mechanism by which many, if not most mRNAs are retained in the cell body is not understood. Total inhibition of translation, by puromycin or cycloheximide, results in the mislocalization of cell body mRNAs to dendrites. We have examined the effect of translational inhibitors on the localization of ferritin mRNA, the translation of which can also be inhibited specifically by reducing iron levels. Using nonisotopic in situ hybridization, ferritin mRNA is found restricted to the cell body of cultured rat hippocampal neurons. Following treatment with either puromycin or cycloheximide, it migrates into dendrites. Control experiments reveal that the drugs affect neither the viability of the neuronal cultures, nor the steady-state level of ferritin mRNA. When transcription and protein synthesis are inhibited simultaneously, ferritin mRNA is found in the dendrites of puromycin, but not of cycloheximide-treated neurons. However, the localization of ferritin mRNA is unaffected by changes in iron concentration that regulate its translation rate specifically. We propose a model whereby cell body-restricted mRNAs are maintained in that location by association with ribosomes and with another cell component, which traps mRNAs when they are freed of ribosome association. The release of all mRNA species, as happens after total protein synthesis inhibition, floods the system and allows cell body mRNAs to diffuse into dendrites. In contrast, the partial release of the single ferritin mRNA species does not saturate the trapping system and the mRNA is retained in the cell body.

Molecular mechanisms involved in GLUT4 translocation in muscle during insulin and contraction stimulation

Studies in mammalian cells have established the existence of numerous intracellular signaling cascades that are critical intermediates in the regulation of various biological functions. Over the past few years considerable research has shown that many of these signaling proteins are expressed in skeletal muscle. However, the detailed mechanisms involved in the regulation of glucose transporter (GLUT4) translocation from intracellular compartments to the cell surface membrane in response to insulin and contractions in skeletal muscle are not well understood. In the present essay we report three different approaches to unravel the GLUT4 translocation mechanism: 1. specific pertubation of the insulin and/or contraction signaling pathways; 2. characterization of the protein composition of GLUT4-containing vesicles with the expectation that knowledge of the constituent proteins of the vesicles may help in understanding their trafficking; 3. degree of co-immunolocalization of the GLUT4 glucose transporters with other membrane marker proteins assessed by immunofluorescense and electron microscopy.

Analysis of GLUT4 distribution in whole skeletal muscle fibers: identification of distinct storage compartments that are recruited by insulin and muscle contractions

The effects of insulin stimulation and muscle contractions on the subcellular distribution of GLUT4 in skeletal muscle have been studied on a preparation of single whole fibers from the rat soleus. The fibers were labeled for GLUT4 by a preembedding technique and observed as whole mounts by immunofluorescence microscopy, or after sectioning, by immunogold electron microscopy. The advantage of this preparation for cells of the size of muscle fibers is that it provides global views of the staining from one end of a fiber to the other and from one side to the other through the core of the fiber. In addition, the labeling efficiency is much higher than can be obtained with ultracryosections. In nonstimulated fibers, GLUT4 is excluded from the plasma membrane and T tubules. It is distributed throughout the muscle fibers with approximately 23% associated with large structures including multivesicular endosomes located in the TGN region, and 77% with small tubulovesicular structures. The two stimuli cause translocation of GLUT4 to both plasma membrane and T tubules. Quantitation of the immunogold electron microscopy shows that the effects of insulin and contraction are additive and that each stimulus recruits GLUT4 from both large and small depots. Immunofluorescence double labeling for GLUT4 and transferrin receptor (TfR) shows that the small depots can be further subdivided into TfR-positive and TfR-negative elements. Interestingly, we observe that colocalization of TfR and GLUT4 is increased by insulin and decreased by contractions. These results, supported by subcellular fractionation experiments, suggest that TfR-positive depots are only recruited by contractions. We do not find evidence for stimulation-induced unmasking of resident surface membrane GLUT4 transporters or for dilation of the T tubule system (Wang, W., P.A. Hansen, B.A. Marshall, J.O. Holloszy, and M. Mueckler. 1996. J. Cell Biol. 135:415-430).

Altered subcellular localization patterns of ferritin and beta-actin mRNAs in muscle cultures, resulting from incomplete penetration of digoxigenin-labelled riboprobes

Protocols for in situ hybridization (ISH) of cultured cells often include storage in alcohol at -20 degrees C between fixation of the cultures and the ISH procedure. In experiments aimed at localizing ferritin mRNA in C2 muscle cultures by ISH with digoxigenin-labelled riboprobes, we have noticed that omission of the ethanol storage dramatically changed the pattern of mRNA localization. In cultures stored in 50%, 70%, or 90% ethanol for at least 15 min, ferritin signal was stronger on myotubes than myoblasts but was uniformly distributed over both. In untreated cultures, the signal was patchy, concentrated on the extremities of the elongated myoblasts and very sparse in myotubes. Similar results were obtained with a probe to beta-actin used as a control, except that signal was higher in myoblasts in all conditions. When the probes were reduced in size to approximately 100 bases from 561 for ferritin and 1150 for actin, the pattern became uniform, regardless of prehybridization treatment. The patchy pattern disappeared when cells were treated with RNase A following hybridization, suggesting that it is non-specific, despite its absence in cultures hybridized with a sense probe. We conclude that incomplete access of RNA probes can result not only in a reduced ISH signal but also in artefactual patterns of mRNA localization.

Pre-embedding staining of single muscle fibers for light and electron microscopy studies of subcellular organization

Skeletal muscle fibers are large, multinucleated cells which pose a challenge to the morphologist. In the course of studies of the distribution of the glucose transporter GLUT4, in muscle, we have compared different preparative procedures, for both light (LM) and electron microscopy (EM) immunocytochemistry. Here we show that pre-embedding staining of single teased fibers, or of single enzymatically dissociated fibers, has several advantages over the use of sections for observing discrete patterns that extend over long distances in the cells. We report on an optimization study carried out to establish fixation and permeabilization conditions for EM immunogold labeling of the fibers. We find that a simple fixation with depolymerized paraformaldehyde alone, followed by permeabilization with 0.01% saponin, offers the best compromise between the conflicting demands of unhindered tissue penetration and morphology preservation.

Nuclear domains in skeletal myotubes: the localization of transferrin receptor mRNA is independent of its half-life and restricted by binding to ribosomes

The retention of mRNAs near the nuclei that synthesize them may be an important feature of the organization of multinucleated skeletal myotubes. Here, we assess the possible role of two factors in this localization. First, we examine the role of mRNA half-life, by studying the distribution of the mRNA for the transferrin receptor (TfR), whose half-life can be manipulated in culture by changing the availability of iron. In situ hybridization of myotubes of the mouse muscle cell line C2 shows that TfR mRNA is concentrated in the core of the myotubes. Its distribution around the nuclei is often asymmetric and its concentration changes abruptly. Stable transcripts display the same asymmetric localization as unstable ones, suggesting that half-life does not determine subcellular localization of TfR mRNA. Differential effects of the protein synthesis inhibitors puromycin and cycloheximide suggest that the mRNA is retained in position by its association with ribosomes. We then examine the distribution of the rough endoplasmic reticulum (RER) and find it to be broader than the distribution of TfR mRNA. In contrast to TfR mRNA, the mRNA for a secreted immunoglobulin kappa light chain has a more uniform distribution. Taken together, the results suggest that TfR mRNA may associate with RER subdomains by specific targeting.

Expression of the adrenoleukodystrophy protein in the human and mouse central nervous system

The gene mutated in X-linked adrenoleukodystrophy (ALD), a progressive demyelinating disease, codes for a protein (ALDP) involved in very-long-chain fatty acid (VLCFA) transport. The expression of ALDP and of two peroxisomal enzymes involved in beta-oxidation of VLCFA, acyl-CoA oxidase, and catalase was studied in human and mouse brain. The pattern of expression was similar in both species. While acyl-CoA oxidase and catalase are found in all types of CNS cells, including neurons and oligodendrocytes, ALDP expression is restricted mostly to the white matter and endothelial cells. ALDP is highly expressed in astrocytes and microglial cells in vivo and in regenerating oligodendrocytes in vitro. In contrast, in vivo, ALDP is detected in much fewer oligodendrocytes and quantitative Western blot analysis confirmed the lower abundance of ALDP in these cells than in astrocytes. Only oligodendrocytes localized in corpus callosum, internal capsules, and anterior commissure express ALDP at levels comparable to those seen in astrocytes. In ALD, demyelination is first detected in these white matter regions, suggesting that the ALD gene mutation selectively affects those oligodendrocytes strongly expressing ALDP. Because of their failure to express ALDP, microglia and astrocytes may also contribute to demyelination in ALD patients.

GLUT4 in cultured skeletal myotubes is segregated from the transferrin receptor and stored in vesicles associated with TGN

There is little consensus on the nature of the storage compartment of the glucose transporter GLUT4, in non-stimulated cells of muscle and fat. More specifically, it is not known whether GLUT4 is localized to unique, specialized intracellular storage vesicles, or to vesicles that are part of the constitutive endosomal-lysosomal pathway. To address this question, we have investigated the localization of the endogenous GLUT4 in non-stimulated skeletal myotubes from the cell line C2, by immunofluorescence and immunoelectron microscopy. We have used a panel of antibodies to markers of the Golgi complex (alpha mannosidase II and giantin), of the trans-Golgi network (TGN38), of lysosomes (lgp110), and of early and late endosomes (transferrin receptor and mannose-6-phosphate receptor, respectively), to define the position of their subcellular compartments. By immunofluorescence, GLUT4 appears concentrated in the core of the myotubes. It is primarily found around the nuclei, in a pattern suggesting an association with the Golgi complex, which is further supported by colocalization with giantin and by immunogold electron microscopy. GLUT4 appears to be in the trans-most cisternae of the Golgi complex and in vesicles just beyond, i.e. in the structures that constitute the trans-Golgi network (TGN). In myotubes treated with brefeldin A, the immunofluorescence pattern of GLUT4 is modified, but it differs from both Golgi complex markers and TGN38. Instead, it resembles the pattern of the transferrin receptor, which forms long tubules. In untreated cells, double staining for GLUT4 and transferrin receptor by immunofluorescence shows similar but distinct patterns. Immunoelectron microscopy localizes transferrin receptor, detected by immunoperoxidase, to large vesicles, presumably endosomes, very close to the GLUT4-containing tubulo-vesicular elements. In brefeldin A-treated cells, a network of tubules of approximately 70 nm diameter, studded with varicosities, stains for both GLUT4 and transferrin receptor, suggesting that brefeldin A has caused fusion of the transferrin receptor and GLUT4-containing compartments. The results suggest that GLUT4 storage vesicles constitute a specialized compartment that is either a subset of the TGN, or is very closely linked to it. The link between GLUT4 vesicles and transferrin receptor containing endosomes, as revealed by brefeldin A, may be important for GLUT4 translocation in response to muscle stimulation.

Physicians' attitudes and beliefs about deaf patients

BACKGROUND

We wanted to validate reports that deaf persons have difficulty obtaining medical care by comparing physicians' attitudes towards these patients with physicians' attitudes toward their patients in general.

METHODS

Two questionnaires were randomly distributed to physicians attending continuing medical education conferences at the University of Michigan during a 3-month period. The questionnaires were identical except that one asked about deaf patients and the other about patients in general. The questions assessed the respondent's perceptions of communication with patients, attitudes toward their patients, knowledge of current information about deaf people, and demographics.

RESULTS

One hundred sixty-five physicians responded, 94 to the general questionnaire and 71 to the deaf questionnaire. The two physician groups were similar demographically, but 165 differed significantly in communication and attitude variables. Physicians receiving the questionnaire focusing on deaf patients reported greater difficulties in understanding (P < 0.001) and maintaining free-flowing conversations (P < 0.001), and that these patients had more difficulty understanding them (P < 0.001), trusted them less (P < 0.001), asked them to repeat statements more often (P < 0.001) and were less likely to understand the diagnosis and recommended treatments (P < 0.001). Physicians also reported feeling less comfortable with deaf patients (P < 0.001) and that they asked fewer questions (P < 0.001). Physicians were more likely to say that deaf patients rely on interpreters (P = 0.040), get frustrated easily (P < 0.001), and are harder to communicate with (P < 0.001). There were no significant differences between the two groups in knowledge about deaf people. All physicians, however, displayed ignorance about their legal obligations under the Americans with Disabilities Act to provide interpreters for their deaf patients.

CONCLUSIONS

Physicians surveyed about deaf patients reported significantly greater difficulties communicating with and different attitudes toward these patients than physicians surveyed about their patients in general. All physicians were unaware of their obligations under the Americans with Disabilities Act to provide interpreters for deaf patients. Research is needed to determine whether physician attitudes and beliefs affect the actual quality of care they deliver to deaf patients.

Improved lipid-mediated gene transfer into primary cultures of hippocampal neurons

We have examined lipids as transfection agents to introduce recombinant plasmids into primary cultures of rat hippocampal neurons. By modifying the protocol for transfection mediated by the commercial reagent DOTAP, we were able to achieve a transfection efficiency of about 3%. Expression of various transfected gene products was sustained for several weeks in culture, the neurons developed normally and the transfected gene products were targeted to the appropriate subcellular compartment.

Directed tagging of the Arabidopsis FATTY ACID ELONGATION1 (FAE1) gene with the maize transposon activator

The FATTY ACID ELONGATION1 (FAE1) gene of Arabidopsis is required for the synthesis of very long chain fatty acids in the seed. The product of the FAE1 gene is presumed to be a condensing enzyme that extends the chain length of fatty acids from C18 to C20 and C22. We report here the cloning of FAE1 by directed transposon tagging with the maize element Activator (Ac). An unstable fae1 mutant was isolated in a line carrying Ac linked to the FAE1 locus on chromosome 4. Cosegregation and reversion analyses established that the new mutant was tagged by Ac. A DNA fragment flanking Ac was cloned by inverse polymerase chain reaction and used to isolate FAE1 genomic clones and a cDNA clone from a library made from immature siliques. The predicted amino acid sequence of the FAE1 protein shares homology with those of other condensing enzymes (chalcone synthase, stilbene synthases, and beta-ketoacyl-acyl carrier protein synthase III), supporting the notion that FAE1 is the structural gene for a synthase or condensing enzyme. FAE1 is expressed in developing seed, but not in leaves, as expected from the effect of the fae1 mutation on the fatty acid compositions of those tissues.

Expression of the synaptic vesicle proteins VAMPs/synaptobrevins 1 and 2 in non-neural tissues

The VAMPs/synaptobrevins (Vp/Sybs) are small integral membrane proteins. Two isoforms, Vp/Syb 1 and Vp/Syb 2, are considered to be specific to neural tissue. They are associated with synaptic vesicles and are believed to play an important role in neurotransmitter release. A third isoform, cellubrevin, has recently been found in non-neural tissues. We now report that the distribution of Vp/Syb 1 and Vp/Syb 2 is wider than previously thought. RNA transcripts for both Vp/Syb 1 and Vp/Syb 2 were found in rat skeletal muscle and in several other rat non-neural tissues, and antibodies specific for Vp/Syb 2 detected a protein in the endoplasmic reticulum-Golgi area of skeletal muscle. Thus Vp/Sybs 1 and 2 are not restricted to the nervous system but appear to be co-expressed with cellubrevin in many different tissues. This redundancy of Vp/Sybs in a single cell may be required to control the specificity of vesicle-target interaction in the several pathways of intracellular vesicle traffic that are operative within each cell.

Distribution of unlinked receptor sites for transposed Ac elements from the bz-m2(Ac) allele in maize

We have shown before that the Ac element from the maize bz-m2(Ac) allele, located in the short arm of chromosome 9 (9S), transposes preferentially to sites that are linked to the bz donor locus. Yet, about half of the Ac transpositions recovered from bz-m2(Ac) are in receptor sites not linked to the donor locus. In this study, we have analyzed the distribution of those unlinked receptor sites. Thirty-seven transposed Ac (trAc) elements that recombined independently of the bz locus were mapped using a set of wx reciprocal translocations. We found that the distribution of unlinked receptor sites for trAs was not random. Ten trAcs mapped to 9L, i.e., Ac had transposed to sites physically, if not genetically, linked to the donor site. Among chromosomes other than 9, the Ac element of bz-m2(Ac) appeared to have transposed preferentially to certain chromosomes, such as 5 and 7, but infrequently to others, such as 1, the longest chromosome in the maize genome. The seven trAc elements in chromosome 5 were mapped relative to markers in 5S and 5L and localized to both arms of 5. We also investigated the transposition of Ac to the homolog of the donor chromosome. We found that Ac rarely transposes from bz-m2(Ac) to the homologous chromosome 9. The clustering of Ac receptor sites around the donor locus has been taken to mean that a physical association between the donor site and nearby receptor sites occurs during transposition. The preferential occurrence of 9L among chromosomes harboring unlinked receptor sites would be expected according to this model, since sites in 9L would tend to be physically closer to 9S than sites in other chromosomes. The nonrandom pattern seen among the remaining chromosomes could reflect an underlying nuclear architecture, i.e., an ordering of the chromosomes in the interphase nucleus, as suggested from previous cytological observations.

Tagging and Cloning of a Petunia Flower Color Gene with the Maize Transposable Element Activator

We report here the use of the maize transposable element Activator (Ac) to isolate a dicot gene. Ac was introduced into petunia, where it transposed into Ph6, one of several genes that modify anthocyanin pigmentation in flowers by affecting the pH of the corolla. Like other Ac-mutable alleles, the new mutation is unstable and reverts to a functional form in somatic and germinal tissues. The mutant gene was cloned using Ac as a probe, demonstrating the feasibility of heterologous transposon tagging in higher plants. Confirmation that the cloned DNA fragment corresponded to the mutated gene was obtained from an analysis of revertants. In every case examined, reversion to the wild-type phenotype was correlated with restoration of a wild-type-sized DNA fragment. New transposed Acs were detected in many of the revertants. As in maize, the frequency of somatic and germinal excision of Ac from the mutable allele appears to be dependent on genetic background.

Changes in architecture of the Golgi complex and other subcellular organelles during myogenesis

Myogenesis involves changes in both gene expression and cellular architecture. Little is known of the organization, in muscle in vivo, of the subcellular organelles involved in protein synthesis despite the potential importance of targeted protein synthesis for formation and maintenance of functional domains such as the neuromuscular junction. A panel of antibodies to markers of the ER, the Golgi complex, and the centrosome were used to localize these organelles by immunofluorescence in myoblasts and myotubes of the mouse muscle cell line C2 in vitro, and in intact single muscle fibers from the rat flexor digitorum brevis. Antibodies to the ER stained structures throughout the cytoplasm of both C2 myoblasts and myotubes. In contrast, the spatial relationship between nucleus, centrosome, and Golgi complex was dramatically altered. These changes could also be observed in a low-calcium medium that allowed differentiation while preventing myoblast fusion. Muscle fibers in vivo resembled myotubes except that the ER occupied a smaller volume of cytoplasm and no staining was found for one of the Golgi complex markers, the enzyme alpha-mannosidase II. Electron microscopy, however, clearly showed the presence of stacks of Golgi cisternae in both junctional and extrajunctional regions of muscle fibers. The perinuclear distribution of the Golgi complex was also observed in live muscle fibers stained with a fluorescent lipid. Thus, the distribution of subcellular organelles of the secretory pathway was found to be similar in myotubes and muscle fibers, and all organelles were found in both junctional and extrajunctional areas of muscle.

Restricted distribution of mRNA produced from a single nucleus in hybrid myotubes

Although the proteins encoded by a single nucleus in multinucleated myotubes have a wide range of distributions within the myofiber, little is known about the distributions of their mRNAs. We have used hybrid myotubes in which one or a few nuclei are derived from myoblasts that express nonmuscle proteins to investigate this question. We find that three different mRNAs, encoding proteins that are, respectively, nuclear, cytoplasmic, and targeted to the ER, have similar distributions within myotubes. Each is confined to an area within approximately 100 microns of the nucleus that expresses it.

Cooperation between the products of different nuclei in hybrid myotubes produces localized acetylcholine receptor clusters

Cultured myotubes form clusters of acetylcholine receptors (AChRs) spontaneously and at sites of nerve-muscle contact. To investigate the cellular mechanisms by which spontaneous clusters are formed, we have made hybrid myotubes between a mouse muscle cell variant, S27, that does not cluster AChRs, and one that does not make AChRs. We have also made hybrid myotubes using S27 and quail muscle cells. In both cases, clusters of AChRs were found near the non-S27 nuclei; in the case of the interspecific hybrids, mouse AChRs were associated with extracellular matrix components contributed by the quail nuclei. Our results suggest that AChRs made by one nucleus can be clustered by localized extracellular matrix produced by a different nucleus and provide an example of nuclear cooperation between the products of different nuclei within multinucleated muscle fibers.

Variable Patterns of Transposition of the Maize Element Activator in Tobacco

The strategy to be followed in a transposon tagging experiment will be determined largely by the transposition pattern of the transposon in question. With a view to utilizing the maize element Activator (Ac) as a transposon tag in heterologous systems, we investigated the pattern of Ac transposition from six different loci in transgenic tobacco. We isolated germinal revertants from plants carrying mutable alleles of the antibiotic-resistant gene streptomycin phosphotransferase (SPT) and mapped the location of the transposed Ac (trAc) elements relative to the donor SPT gene. A comparison of the distributions of trAcs among the six loci revealed that, although the receptor sites for trAcs tend to be linked to the donor locus, the pattern of Ac transposition in tobacco displays surprising locus-to-locus variation. Some trAc distributions showed the same tight clustering around the donor locus previously seen in maize, whereas others were more dispersed. The possible meaning of these findings and their implication for transposon tagging in heterologous systems are discussed.

Preferential transposition of the maize element Activator to linked chromosomal locations in tobacco

The autonomous maize transposon Activator (Ac) has been used in maize for gene isolation by tagging and may prove similarly useful in other species. To test the feasibility of gene tagging with heterospecific transposons, we have examined three key genetic properties of a slightly modified Ac in tobacco. First, we show that frequencies of germinal excision of this Ac element from the antibiotic resistance gene streptomycin phosphotransferase can be comparable with or slightly lower than in maize. Second, we show that about half of the progeny carrying a germinal excision product also carry a transposed Ac. Last, we have mapped transposed Ac locations relative to the streptomycin transferase gene excision product and have shown that as in maize Ac in tobacco preferentially transposes to genetically linked sites.

Chromosome-breaking structure in maize involving a fractured Ac element

Chromosome breakage in maize can result from an interaction between certain transposable elements. When an Ac (Activator) element and a state I Ds (Dissociation) element are present together in the genome, either linked or unlinked, breaks occur regularly at the locus of the Ds element. We show here that breaks occur with high frequency at or near the locus of a structure consisting of a 2.5-kilobase (kb) terminally deleted or fractured Ac element very tightly linked to a second, intact 4.6-kb Ac element. This structure has the features of a macrotransposon and may behave like one. Loss of the tight linkage abolishes chromosome breakage. A model based on transposition of the macrotransposon is proposed to explain the chromosome-breaking properties of Ac and Ds.

Intracellular and surface distribution of a membrane protein (CD8) derived from a single nucleus in multinucleated myotubes

We have investigated the contribution of an individual nucleus to intracellular and surface membranes in multinucleated muscle fibers. Using a retroviral vector, we introduced the gene encoding the human T-lymphocyte antigen CD8 into C2 mouse muscle cells to form a stable line expressing the human protein on its surface. The intracellular and surface distributions of the protein were then investigated by immunocytochemistry in hybrid myotubes containing a single nucleus expressing CD8. We show that the intracellular distribution of CD8 is limited to a local area surrounding the nucleus encoding it and several neighboring nuclei. On the cell surface, however, the protein is distributed over the entire myotube. Widespread distribution of a surface membrane protein in multinucleated myotubes can thus result from localized synthesis and processing.

Acetylcholine receptor in a C2 muscle cell variant is retained in the endoplasmic reticulum

We have examined the properties and intracellular localization of acetylcholine receptors in the C2 muscle cell line and in a variant (T-) that accumulates AChR intracellularly. On immunoblots, the subunit structures of the AChR from wild-type and T- cells were similar except that the gamma and delta subunits of the variant AChR had altered mobilities. Digestion with endoglycosidases H and F demonstrated that this difference results from a failure of high-mannose N-linked oligosaccharides on AChR subunits to be processed to complex forms in the variant. N-linked glycosylation of other proteins in the variant was normal. When examined by immunocytochemistry, the distribution of internal AChR in wild-type cells was consistent with a location both in the endoplasmic reticulum and in the Golgi. Variant cells, however, showed no evidence of Golgi staining. Subcellular fractionation experiments also demonstrated AChR in the Golgi fractions of wild-type cells, but not in those derived from T- cells. We conclude that in T- myotubes most of the AChR fails to be transported out of the endoplasmic reticulum.

Transfer of a protein encoded by a single nucleus to nearby nuclei in multinucleated myotubes

Specialized regions of muscle fibers may result from differential gene expression within a single fiber. In order to investigate the range of action of individual nuclei in multinucleated myotubes, C2 myoblasts were transfected to obtain stable cell lines that express a reporter protein that is targeted to the nucleus. Hybrid myotubes were then formed containing one or a few transfected nuclei as well as a large number of nuclei from the parental strain. In order to determine how far the products of a single nucleus extend, transfected nuclei were labeled with [3H]thymidine before fusion and the myotubes were stained to identify the reporter protein. In such myotubes the fusion protein was not confined to its nucleus of origin, but was restricted to nearby nuclei.

Clusters of 43-kDa protein are absent from genetic variants of C2 muscle cells with reduced acetylcholine receptor expression

Genetic variants of the C2 muscle cell line were used to investigate the relation between acetylcholine receptor (AChR) clustering and clustering of the 43-kDa protein. Two variants that express severely reduced amounts of the alpha subunit of the AChR and consequently lack AChR clusters were found also to lack clusters of the 43-kDa protein. The amount of 43-kDa protein in the variants measured by immunoassay was reduced to about one-third the levels found in wild-type cells. The beta subunit of the AChR was reduced to a similar extent. Northern blot analysis showed that neither the 43-kDa protein mRNA nor the beta subunit mRNA was reduced in the variants. Taken together, these results suggest that the amounts of beta subunit and 43-kDa protein may be regulated coordinately by a post-transcriptional mechanism.

Topological mapping of acetylcholine receptor: evidence for a model with five transmembrane segments and a cytoplasmic COOH-terminal peptide

Antibodies were raised against two synthetic peptides whose sequences correspond respectively to the COOH-terminal end (residues 501-516) of the protein encoded by the gene for the delta chain and to a proposed cytoplasmic region (residues 350-358) of the beta chain of the acetylcholine receptor from Torpedo californica. Binding of the COOH-terminal antibody to the acetylcholine receptor in intact, receptor-rich vesicles was tested by radioimmunoassay and by precipitation with immobilized protein A. In both cases, binding was detected only after treatment of the vesicles with detergent, suggesting that the segment of the receptor that is recognized by this antibody is on the cytoplasmic side of the membrane. Electron microscopy of tissue from Torpedo electric organ labeled with colloidal gold-conjugated second antibodies established that both anti-receptor antibodies bind to the cytoplasmic surface of the postsynaptic membrane. These experiments give ultrastructural evidence that the COOH-terminal segment of the delta chain as well as residues 350-358 of the beta chain are on the cytoplasmic surface. They strongly support a model in which each of the receptor subunits crosses the membrane five times in which one transmembrane segment of each chain contributes to the formation of a central ion channel.

Interactions of clathrin coat with model lipid membranes

The interaction of coat proteins from coated vesicles with model lipid membranes was examined using small unilamellar vesicles of dipalmitoylglycerophosphocholine as model membranes. Changes in membrane permeability were measured by the leakage of entrapped fluorescent dye, carboxyfluorescein. Both clathrin and the 55000-Da protein were found to be active. Density gradient centrifugation showed the formation of an irreversible protein-lipid complex. Dynamic light-scattering measurements showed that this complex is significantly larger than the original vesicles, suggesting that fusion is induced. The effects of pH, urea, Tris and ionic strength were studied and the possible biological relevance of the results is discussed.