Teaching the tutors: use of an OSTE to train medical students to be peer tutors.

First-year medical students are often challenged by the rapid pace and large volume of content that must be learned. Peer teaching has emerged as a supportive educational strategy. However, the most effective strategies for training peer tutors (PTs) for their role are not known. This paper examines the use of an Objective Structured Teaching Exercise (OSTE) to augment PT training sessions. Applying deliberate practice as a conceptual framework, an OSTE was used to provide tutors with an opportunity to practice their skills and receive feedback about their performance when meeting with a student presenting with a challenge. The newly trained PTs were required to assess a standardized student, determine challenge(s) being experienced, and present options to address the challenge(s). Standardized students evaluated the tutors' performance and a pre- and post-OSTE questionnaire was used to determine whether the OSTE was effective in increasing the confidence level of PTs to effectively assess and support students seeking help. Participants reported an increase in confidence in their ability to assess areas requiring improvement, understand the active learning strategies, and suggest appropriate active learning study strategies. Evaluations completed by standardized students documented that newly trained PTs accurately diagnosed the challenge presented in the OSTE and in most cases PTs asked all relevant questions to assess. Increased self-efficacy promotes PT's capacity to perform their work and feedback during an OSTE can further advance required skills. Aggregate OSTE results can also inform efforts to enhance the PT training program.NEW & NOTEWORTHY This novel application of the Objective Structured Teaching Exercise (OSTE) was done to enhance tutors' skills as valued members of our integrated academic support program. The OSTE provided feedback to the tutors and enabled us to identify a need for enhanced tutor training in active learning strategies. The OSTE can be adapted for use in other health science educational programs to enhance their training programs and to assess tutor's skills in preparation for their role.

The role of periostin in tissue remodeling across health and disease.

Periostin, also termed osteoblast-specific factor 2, is a matricellular protein with known functions in osteology, tissue repair, oncology, cardiovascular and respiratory systems, and in various inflammatory settings. However, most of the research to date has been conducted in divergent and circumscribed areas meaning that the overall understanding of this intriguing molecule remains fragmented. Here, we integrate the available evidence on periostin expression, its normal role in development, and whether it plays a similar function during pathologic repair, regeneration, and disease in order to bring together the different research fields in which periostin investigations are ongoing. In spite of the seemingly disparate roles of periostin in health and disease, tissue remodeling as a response to insult/injury is emerging as a common functional denominator of this matricellular molecule. Periostin is transiently upregulated during cell fate changes, either physiologic or pathologic. Combining observations from various conditions, a common pattern of events can be suggested, including periostin localization during development, insult and injury, epithelial-mesenchymal transition, extracellular matrix restructuring, and remodeling. We propose mesenchymal remodeling as an overarching role for the matricellular protein periostin, across physiology and disease. Periostin may be seen as an important structural mediator, balancing appropriate versus inappropriate tissue adaption in response to insult/injury.

Increased expression and serum levels of the stromal cell-secreted protein periostin in breast cancer bone metastases.

Periostin, a matricellular protein, is overexpressed in the stroma of several cancers. The aim of our study was to investigate more specifically whether periostin expression is associated with bone metastases from breast cancer and to determine its source in the affected bone. Nude mice were inoculated with human MDA-B02 breast cancer cells. Bone metastases-bearing mice were treated with zoledronic acid-an antiresorptive drug-or vehicle. Bone metastases were examined for tumor- and stroma-derived periostin expression by quantitative polymerase chain reaction with human- and mouse-specific primers and immunohistochemistry. Serum periostin and conventional bone turnover markers were also measured. MDA-B02 cells did not express periostin both in vitro and in vivo. However, mouse-derived periostin was markedly overexpressed (eightfold) in metastatic legs compared to noninoculated mice. Serum periostin levels were also markedly increased in metastatic mice and correlated with in situ expression levels. Immunostaining showed that periostin derived from the environing stromal cells of bone metastasis. Bone turnover blockade by zoledronic acid markedly decreased osteolytic lesions but only slightly modulated serum periostin levels. Bone metastases from breast cancer induce overexpression of periostin by surrounding stromal cells. Periostin could be a biochemical marker of the early stromal response associated to breast cancer bone metastasis formation.

Development of a new ELISA for serum periostin: evaluation of growth-related changes and bisphosphonate treatment in mice.

Periostin is a gamma-carboxyglutamic acid protein preferentially expressed in periosteum and bone mesenchymal stem cells. Lack of a precise assay for measuring circulating levels impairs the investigation of its biological significance. We developed a new ELISA and studied changes of periostin levels both locally at the bone site and systemically in circulating blood during growth and after bisphosphonate-induced inhibition of bone remodeling in the mouse. The ELISA we developed is based on an affinity-purified polyclonal antibody that was raised against the C-terminal sequence of mouse periostin. Reproducibility, repeatability, precision, and accuracy tests met standards of acceptance. Serum periostin and levels of the bone turnover markers osteocalcin, PINP, CTX-I, and TRAP5b were measured in (1) 4-, 6-, 8-, 10-, and 12-week-old wild-type female Balb/c mice and (2) adult ovariectomized female Balb/c mice treated with zoledronic acid or vehicle. Serum periostin decreased during growth and stabilized from 8 weeks and older, its levels correlating with bone turnover markers. Immunohistochemistry in bones from different growth stages showed that periostin localized specifically at the sites of endochondral and intramembranous ossification, especially at the periosteal envelopes. Zoledronic acid induced a marked decrease in bone remodeling markers but did not alter serum periostin levels or periostin immunostaining pattern. The novel ELISA is highly specific and allows accurate and precise measurements of serum periostin levels in mice.

Periostin-like-factor in osteogenesis.

Periostin-like-factor (PLF), an isoform related to Periostin, is expressed in bone, heart, and vascular smooth muscle cells. PLF was detected by immunostaining in mesenchymal cells in the periosteum and in osteoblasts lining trabecular bone, suggesting that PLF has a role in osteogenesis. PLF has a signal peptide and is also secreted from osteoblasts in vitro. To study the function of PLF in osteogenesis, we assessed the effect of PLF on osteoblast proliferation and differentiation in vitro and bone formation in vivo. First, to examine whether PLF regulates osteoblast proliferation in vitro, the CyQUANT cell proliferation assay was performed. PLF over-expression by adenovirus resulted in a significantly higher rate of cell proliferation compared to controls. This finding suggests that PLF promotes osteoblast proliferation in vitro. Second, to test whether PLF mediates osteoblast differentiation in vitro, differentiation markers of osteoblasts, were assessed, including alkaline phosphatase staining and activity, von Kossa staining and calcium deposition. Over-expression of PLF resulted in higher expression and activity of alkaline phosphatase and higher amounts of mineralization and calcium deposition compared to controls. These data suggest that PLF promotes osteoblast differentiation in vitro. Third, to investigate the role of PLF in bone formation in vivo, PLF adenovirus was injected into 6-week-old rat femur bone marrow. Over-expression of PLF resulted in increased bone formation within the marrow cavity. Lastly, in a model of fracture healing, PLF expression is robustly upregulated in callus osteoblasts at post-fracture days 7 and 14. Taken together, these findings suggests that PLF induces bone formation in vivo. We conclude that PLF stimulates bone formation in vivo possibly by promoting osteoblast proliferation and differentiation.

Immunolocalization of Periostin-like factor and Periostin during embryogenesis.

Periostin-like factor (PLF) and Periostin are alternatively spliced mRNAs. Our findings are the first to show similarities and differences between PLF and Periostin location using isoform-specific antibodies. The differences in when and where they are present during mouse embryogenesis suggest that they may have different functions. Using immunostaining techniques, we observed that PLF was highly expressed at 12.5 days postconception (dpc) in the intermediate and outer zones of most brain regions, spinal cord, cranial and spinal nerves, and chondrocytes in developing bone and in the heart wall. By 16.5 dpc, PLF was also present in ameloblasts and odontoblasts in developing teeth, and by 19.5 dpc, PLF was present at low levels only in vagal nerve bundles, discrete white matter bundles in the brain, and chondrocytes of developing ribs. Periostin, on the other hand, was absent at 12.5 dpc from dorsal spinal cord and from cranial and spinal nerves. By 16.5 dpc, Periostin was present in many spinal nerves, but absent thereafter, and at 19.5 dpc, Periostin was present in chondrocytes in developing bone but not in neural tissues. The different spatial and temporal location of PLF and Periostin in cartilage and bone cells suggests different roles for these proteins in endochondral bone formation. The early expression of PLF in brain differentiation zones and in developing axon bundles and nerves suggests that it may facilitate axon growth.

Cyclin-dependent kinase 4 expression is essential for neu-induced breast tumorigenesis.

Previous work has shown that cyclin D1 expression is required for neu- and ras-induced, but not wnt- or c-myc-induced, breast tumorigenesis in mice. Although cyclin D1 binds and activates cyclin-dependent kinase 4 (Cdk4), thereby mediating activation of a program of E2F-dependent gene expression, it has been suggested that the oncogenic activities of cyclin D1 are independent of Cdk4. To determine whether Cdk4 expression is required for breast tumorigenesis in mice, we have generated compound mice ectopically expressing the neu or wnt oncogenes in the mammary glands of wild-type and Cdk4-/- mice. Our results show that Cdk4 expression is required for efficient neu-induced tumorigenesis but is dispensable for wnt-induced breast tumorigenesis. In contrast to results previously observed in the mammary glands of cyclin D1-/- virgin females, our results show defects in mammary gland development in Cdk4-/- virgin females, suggesting differences in compensatory mechanisms in the absence of either subunit of the cyclin D1/Cdk4 complex. These results suggest that drugs targeted to inhibit Cdk4 activities could be developed to specifically treat certain breast tumors as Cdk4 is not essential for viability.

Periostin and periostin-like factor in the human heart: possible therapeutic targets.

BACKGROUND: Although numerous signaling pathways have been identified in adult heart disease, our ability to diagnose and treat human cardiomyopathies remains limited. A family of proteins, which includes periostin and periostin-like factor (PLF), has been identified during heart development and disease. Based on recent findings, these proteins are candidate therapeutic agents for heart disease. METHODS: Affymetrix GeneChip Expression Analysis as well as northern and western blot analyses were used to determine periostin and PLF expression in humans. Periostin-like factor levels were determined, by western blot analysis, in the rat animal model used to study myocardial loading and unloading. In vivo and in vitro effects of overexpressing PLF by infection with adenovirus were assessed by calculating cardiac myocyte cross-sectional area and determining the level of protein synthesis, respectively. RESULTS AND CONCLUSIONS: Our findings on PLF suggest that this periostin isoform plays a crucial role in adult cardiac myocyte growth following mechanical overload, thus, implicating its potential as a therapeutic target. In addition, we believe that the differences between the periostin and PLF are of functional significance.

Increased CCN2, substance P and tissue fibrosis are associated with sensorimotor declines in a rat model of repetitive overuse injury.

Key clinical features of cumulative trauma disorders include pain, muscle weakness, and tissue fibrosis, although the etiology is still under investigation. Here, we characterized the temporal pattern of altered sensorimotor behaviors and inflammatory and fibrogenic processes occurring in forearm muscles and serum of young adult, female rats performing an operant, high repetition high force (HRHF) reaching and grasping task for 6, 12, or 18 weeks. Palmar mechanical sensitivity, cold temperature avoidance and spontaneous behavioral changes increased, while grip strength declined, in 18-week HRHF rats, compared to controls. Flexor digitorum muscles had increased MCP-1 levels after training and increased TNFalpha in 6-week HRHF rats. Serum had increased IL-1beta, IL-10 and IP-10 after training. Yet both muscle and serum inflammation resolved by week 18. In contrast, IFNγ increased at week 18 in both muscle and serum. Given the anti-fibrotic role of IFNγ, and to identify a mechanism for the continued grip strength losses and behavioral sensitivities, we evaluated the fibrogenic proteins CCN2, collagen type I and TGFB1, as well as the nociceptive/fibrogenic peptide substance P. Each increased in and around flexor digitorum muscles and extracellular matrix in the mid-forearm, and in nerves of the forepaw at 18 weeks. CCN2 was also increased in serum at week 18. At a time when inflammation had subsided, increases in fibrogenic proteins correlated with sensorimotor declines. Thus, muscle and nerve fibrosis may be critical components of chronic work-related musculoskeletal disorders. CCN2 and substance P may serve as potential targets for therapeutic intervention, and CCN2 as a serum biomarker of fibrosis progression.

Characterization of cardiac muscle factor 1 sequence motifs: retinoblastoma protein binding and nuclear localization.

Cardiac muscle factor 1 (CMF1) is characterized as a protein important in cardiac and skeletal myocyte differentiation and is expressed in a developmentally regulated manner. Sequence analysis data showed that CMF1 has crucial protein-protein interaction domains, has a retinoblastoma protein-binding site which interacts with RB directly in vitro and in the embryo, has a functional nuclear localization signal and is highly homologous to other cell cycle regulatory proteins such as mitosin and centromere protein F, which suggests that CMF1 may be involved in regulating the cell cycle.

Performance of repetitive tasks induces decreased grip strength and increased fibrogenic proteins in skeletal muscle: role of force and inflammation.

BACKGROUND: This study elucidates exposure-response relationships between performance of repetitive tasks, grip strength declines, and fibrogenic-related protein changes in muscles, and their link to inflammation. Specifically, we examined forearm flexor digitorum muscles for changes in connective tissue growth factor (CTGF; a matrix protein associated with fibrosis), collagen type I (Col1; a matrix component), and transforming growth factor beta 1 (TGFB1; an upstream modulator of CTGF and collagen), in rats performing one of two repetitive tasks, with or without anti-inflammatory drugs. METHODOLOGY/RESULTS: To examine the roles of force versus repetition, rats performed either a high repetition negligible force food retrieval task (HRNF), or a high repetition high force handle-pulling task (HRHF), for up to 9 weeks, with results compared to trained only (TR-NF or TR-HF) and normal control rats. Grip strength declined with both tasks, with the greatest declines in 9-week HRHF rats. Quantitative PCR (qPCR) analyses of HRNF muscles showed increased expression of Col1 in weeks 3-9, and CTGF in weeks 6 and 9. Immunohistochemistry confirmed PCR results, and also showed greater increases of CTGF and collagen matrix in 9-week HRHF rats than 9-week HRNF rats. ELISA, and immunohistochemistry revealed greater increases of TGFB1 in TR-HF and 6-week HRHF, compared to 6-week HRNF rats. To examine the role of inflammation, results from 6-week HRHF rats were compared to rats receiving ibuprofen or anti-TNF-α treatment in HRHF weeks 4-6. Both treatments attenuated HRHF-induced increases in CTGF and fibrosis by 6 weeks of task performance. Ibuprofen attenuated TGFB1 increases and grip strength declines, matching our prior results with anti-TNFα. CONCLUSIONS/SIGNIFICANCE: Performance of highly repetitive tasks was associated with force-dependent declines in grip strength and increased fibrogenic-related proteins in flexor digitorum muscles. These changes were attenuated, at least short-term, by anti-inflammatory treatments.

Cooperativity of Cdk4R24C and Ras in melanoma development.

The importance of the CDK4 protein in human cancer first became evident following the identification of a germ line mutation in the Cdk4 locus that predisposes humans to melanoma. This mutation results in substitution of arginine with cysteine at position 24 (R24C). In an earlier study, we introduced the R24C mutation into the Cdk4 locus of mice using Cre-loxP-mediated "knock-in" technology and observed a very low incidence of spontaneous melanomas in Cdk4(R24C/R24C) mice. This suggested that additional oncogenic mutations might be required for development of melanomas. Here we report an increased incidence of spontaneous cutaneous melanoma in mice expressing the oncogene HRAS(G12V) in melanocytes on a Cdk4(R24C) background. Treatment of Tyr-HRas:Cdk4(R24C/R24C) mice with the carcinogen, DMBA/TPA resulted in a further increase in the number of nevi and melanomas developed when compared with Tyr-HRas:Cdk4(+/+) mice. In summary, in Tyr-HRas:Cdk4(R24C/R24C) mice, we observed that activated CDK4 cooperates with the oncogenic HRAS(G12V) protein to increase the susceptibility of melanoma development in vivo.

Requirement of Cdk4 for v-Ha-ras-Induced Breast Tumorigenesis and Activation of the v-ras-Induced Senescence Program by the R24C Mutation.

Activating mutations in CDK4 and inactivation of its key kinase inhibitor, p16INK4A, have been implicated in the genesis and progression of human cancer. Previous work has demonstrated that CDK4 expression is required for Neu-induced but not Wnt-induced breast tumorigenesis in mice. However, the role that CDK4 plays in ras-mediated breast tumor development is not well defined. To gain an understanding of the role of Cdk4 in ras-induced breast tumorigenesis, MMTV-v-Ha-ras transgenic mice were bred with Cdk4(+/neo) and Cdk4(R24C/R24C) mice to generate Cdk4(neo/neo):MMTV-v-Ha-ras, Cdk4(+/+):MMTV-v-Ha-ras, and Cdk4(R24C/R24C):MMTV-v-Ha-ras mice. The studies presented here demonstrate that Cdk4 expression is essential for Ras-mediated breast tumorigenesis. Surprisingly, the results also show that coexpression of mutant ras and Cdk4R24C genes in breast epithelial cells leads to an activation of senescent pathways that delay tumorigenesis. Analysis of the phosphorylated form of H2AX, a marker for DNA damage, indicated its increased presence in the tumors of Cdk4(R24C/R24C):MMTV-v-Ha-ras mice. These observations indicate that the increased apoptosis and senescence seen in breast tumors of these mice might be due to increased DNA damage response in cells expressing activated forms of ras and Cdk4(R24C).

Exposure-dependent increases in IL-1beta, substance P, CTGF, and tendinosis in flexor digitorum tendons with upper extremity repetitive strain injury.

Upper extremity tendinopathies are associated with performance of forceful repetitive tasks. We used our rat model of repetitive strain injury to study changes induced in forelimb flexor digitorum tendons. Rats were trained to perform a high repetition high force (HRHF) handle-pulling task (12 reaches/min at 60 +/- 5% maximum pulling force [MPF]), or a low repetition negligible force (LRNF) reaching and food retrieval task (three reaches/min at 5 +/- 5% MPF), for 2 h/day in 30 min sessions, 3 days/week for 3-12 weeks. Forelimb grip strength was tested. Flexor digitorum tendons were examined at midtendon at the level of the carpal tunnel for interleukin (IL)-1beta, neutrophil, and macrophage influx, Substance P, connective tissue growth factor (CTGF), and periostin-like factor (PLF) immunoexpression, and histopathological changes. In HRHF rats, grip strength progressively decreased, while IL-1beta levels progressively increased in the flexor digitorum peritendon (para- and epitendon combined) and endotendon with task performance. Macrophage invasion was evident in week 6 and 12 HRHF peritendon but not endotendon. Also in HRHF rats, Substance P immunoexpression increased in week 12 peritendon as did CTGF- and PLF-immunopositive fibroblasts, the increased fibroblasts contributing greatly to peritendon thickening. Endotendon collagen disorganization was evident in week 12 HRHF tendons. LRNF tendons did not differ from controls, even at 12 weeks. Thus, we observed exposure-dependent changes in flexor digitorum tendons within the carpal tunnel, including increased inflammation, nociceptor-related neuropeptide immunoexpression, and fibrotic histopathology, changes associated with grip strength decline.

Periostin-like-factor and Periostin in an animal model of work-related musculoskeletal disorder.

Work-related musculoskeletal disorders (WMSDs), also known as overuse injuries, account for a substantial proportion of work injuries and workers' compensation claims in the United States. However, the pathophysiological mechanisms underlying WMSDs are not well understood, especially the early events in their development. In this study we used an animal model of upper extremity WMSD, in which rats perform a voluntary repetitive reaching and pulling task for a food reward. This innovative model provides us an opportunity to investigate the role of molecules which may be used either as markers of early diagnosis of these disorders, and/or could be targeted for therapeutic purposes in the future. Periostin-like-factor (PLF), and Periostin were examined in this study. Both belong to a family of vitamin K-dependent gamma carboxylated proteins characterized by the presence of conserved Fasciclin domains and not detected in adult tissues except under conditions of chronic overload, injury, stress or pathology. The spatial and temporal pattern of PLF and Periostin localization was examined by immunohistochemistry and western blot analysis in the radius and ulna of animals performing a high repetition, high force task for up to 12 weeks and in controls. We found that PLF was present primarily in the cellular periosteum, articular cartilage, osteoblasts, osteocytes and osteoclasts at weeks 3 and 6 in all distal bone sites examined. This increase coincided with a transient increase in serum osteocalcin in week 6, indicative of adaptive bone formation at this time point. PLF immunoexpression decreased in the distal periosteum and metaphysis by week 12, coincided temporally with an increase in serum Trap5b, thinning of the growth plate and reduced cortical thickness. In contrast to PLF, once Periostin was induced by task performance, it continued to be present at a uniformly high level between 3 and 12 weeks in the trabeculae, fibrous and cellular periosteum, osteoblasts and osteocytes. In general, the data suggest that PLF is located in tissues during the early adaptive stage of remodeling but not during the pathological phase and therefore might be a marker of early adaptive remodeling.

Induction of periostin-like factor and periostin in forearm muscle, tendon, and nerve in an animal model of work-related musculoskeletal disorder.

Work-related musculoskeletal disorders (WMSDs), also known as repetitive strain injuries of the upper extremity, frequently cause disability and impairment of the upper extremities. Histopathological changes including excess collagen deposition around myofibers, cell necrosis, inflammatory cell infiltration, and increased cytokine expression result from eccentric exercise, forced lengthening, exertion-induced injury, and repetitive strain-induced injury of muscles. Repetitive tasks have also been shown to result in tendon and neural injuries, with subsequent chronic inflammatory responses, followed by residual fibrosis. To identify mechanisms that regulate tissue repair in WMSDs, we investigated the induction of periostin-like factor (PLF) and periostin, proteins induced in other pathologies but not expressed in normal adult tissue. In this study, we examined the level of PLF and periostin in muscle, tendon, and nerve using immunohistochemistry and Western blot analysis. PLF increased with continued task performance, whereas periostin was constitutively expressed. PLF was located in satellite cells and/or myoblasts, which increased in number with continued task performance, supporting our hypothesis that PLF plays a role in muscle repair or regeneration. Periostin, on the other hand, was not present in satellite cells and/or myoblasts.

Expression and function of periostin-like factor in vascular smooth muscle cells.

In injured blood vessels activated vascular smooth muscle cells (VSMCs) migrate from the media to the intima, proliferate and synthesize matrix proteins. This results in occlusion of the lumen and detrimental clinical manifestations. We have identified a novel isoform of the periostin family of proteins referred to as periostin-like factor (PLF). PLF expression in VSMCs was increased following treatment with mitogenic compounds, suggesting that PLF plays a role in VSMC activation. Correspondingly, proliferation of the cells was significantly reduced with anti-PLF antibody treatment. PLF expression increased VSMC migration, an essential cellular process leading to vascular restenosis after injury. PLF protein was localized to neointimal VSMC of rat and swine balloon angioplasty injured arteries, as well as in human arteries with transplant restenosis, supporting the hypothesis that PLF is involved in VSMC activation and vascular proliferative diseases. Taken together, these data suggest a role for PLF in the regulation of vascular proliferative disease.

CXCR3 surface expression in human airway epithelial cells: cell cycle dependence and effect on cell proliferation.

We recently demonstrated that human bronchial epithelial cells (HBEC) constitutively express the CXC chemokine receptor CXCR3, which when activated, induces directed cell migration. The present study in HBEC examined the relative expression of the CXCR3 splice variants CXCR3-A and -B, cell cycle dependence of CXCR3 expression, and the effects of the CXCR3 ligand, the interferon-gamma-inducible CXC chemokine I-TAC/CXCL11, on DNA synthesis and cell proliferation. Both CXCR3-A and -B mRNA, assessed by real-time RT-PCR, were expressed in normal HBEC (NHBEC) and the HBEC line 16-HBE. However, CXCR3-B mRNA was 39- and 6-fold greater than CXCR3-A mRNA in NHBEC and 16-HBE, respectively. Although most HBEC (>80%) assessed by flow cytometry and immunofluorescence microscopy contained intracellular CXCR3, only a minority (<40%) expressed it on the cell surface. In this latter subset of cells, most (>75%) were in the S + G(2)/M phases of the cell cycle. Stimulation of CXCR3 with I-TAC enhanced thymidine incorporation and cell proliferation and increased p38 and ERK1/2 phosphorylation. These data indicate that 1) human airway epithelial cells primarily express CXCR3-B mRNA, 2) surface expression of CXCR3 is largely confined to the S + G(2)/M phases of the cell cycle, and 3) activation of CXCR3 induces DNA synthesis, cell proliferation, and activation of MAPK pathways. We speculate that activation of CXCR3 exerts a mitogenic effect in HBEC, which may be important during airway mucosal injury in obstructive airway diseases such as asthma and chronic obstructive pulmonary disease.

Cell surface proteins of wholeXenopus embryos identified by radioiodination.

We have examined the proteins ofXenopus whole oocytes and embryos that are accessible to surface iodination. These cell surface proteins appear to undergo stagespecific modulation during development. The most pronounced changes were observed between oocytes and the 32-cell stage when the number of labelled proteins doubled, and between early and late gastrula when the complexity declined by two thirds. The simplification of the pattern during gastrulation may reflect changes in cell position as endodermal cells move inside leaving ectodermal cells at the external surface. The lectin binding patterns for NP-40 solubilized proteins extracted from oocytes and embryos also changed in a stage-dependent manner. Con A and WGA recognized a complex pattern of glycoproteins containing glucose and mannose residues. In contrast, SAB and RCA binding to galactose residues recognized far fewer glycoproteins. Many of the observed changes occurred during cleavage stages before embryonic gene transcription is initiated and may be due to post-translational modifications.