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PubMed2002

Workload of radiologists in the United States in 1998-1999 and trends since 1995-1996.

OBJECTIVE: This article measures the workload of radiologists in the United States in 1998-1999, its variation by practice characteristics, and changes since 1995-1996. MATERIALS AND METHODS: Data on procedures performed were collected from the American College of Radiology's 1999 Survey of Practices, and responses were weighted to make them representative of all radiologists in the United States. Workload measured as number of procedures per full-time equivalent diagnostic radiologist was tabulated by practice type, size, setting, and location and compared with corresponding survey results from 1995-1996. The independent effect of these factors on workload was measured using regression analysis. Changes in procedure complexity were calculated in terms of relative value units (RVUs) per procedure using Medicare files. RESULTS: In 1998-1999, the average workload per full-time equivalent diagnostic radiologist had increased 8.5% since 1995-1996 to 12,800 (standard error = 200) procedures annually, with substantial variation by group type. For example, the average workload was 9400 procedures in academic groups and 13,600 in nonacademic private radiology practices. Even in relatively homogeneous categories of practices, radiologists at the 75th percentile of workload were typically performing at least 50% more procedures than radiologists at the 25th percentile. Average RVUs per Medicare procedure increased by 4% between 1995 and 1998, mainly because of an increase in the share of more complex techniques such as MR imaging and CT in the procedure mix. CONCLUSION: The workload per radiologist measured in procedures and RVUs increased substantially between 1995-1996 and 1998-1999. Because much variation remains unexplained, averages or medians should not be used as norms.

Data Interpretation, Statistical↗

PubMed1999

A Double-Blind, Placebo-Controlled Trial of Secretin for the Treatment of Autistic Disorder.

OBJECTIVE: This study examines the efficacy of intravenous porcine secretin for the treatment of autism. METHODS: Using a randomized, double-blind, placebo-controlled crossover design, 20 subjects with autistic disorder received either a secretin or placebo infusion at baseline and the other substance at week 4. Subjects were given the Autism Diagnostic Interview-Revised, the Autism Diagnostic Observation Schedule-Generic (ADOS-G), and other pertinent developmental measures at baseline and at weeks 4 and 8 to assess drug effects. RESULTS: For the primary efficacy analysis, change of ADOS-G social-communication total score from week 0 to week 4, no statistically significant difference was obtained between placebo (-1.0 +/- 2.4) and secretin groups (-0.7 +/- 1.4; t 0.34, df 18, P less than.74). No significant differences were obtained for the other measures, including when all 20 subjects were compared by paired t-test from baseline to 4 weeks after secretin infusion. CONCLUSION: There was no evidence for efficacy of secretin in this preliminary randomized controlled trial. These data were collected as part of a multicenter study with the University of California-Irvine and the University of Utah.

Journal Article↗

PubMed1997

Three-dimensional endosonography for staging of rectal cancer.

OBJECTIVE: This prospective study was conducted to investigate the value of three-dimensional (3D) endosonography for staging of rectal cancer. SUMMARY BACKGROUND DATA: Transrectal ultrasound is the most sensitive technique for peroperative staging and follow-up of rectal cancer. Major limitations of this technique include the complexity of image interpretation and the inability to examine stenotic tumors or to identify recurrent rectal cancer. METHODS: Three-dimensional endosonography was performed in 100 patients with rectal tumors. Transrectal volume scans were obtained using a 3D multiplane transducer (7.5/10.0 MHz). Stenotic tumors were examined with a 3D frontfire transducer (5.0/7.5 MHz). The volume scans were processed and analyzed on a Combison 530 workstation (Kretztechnik, Zipf, Austria). RESULTS: The 3D endosonography and conventional endosonography were performed in 49 patients with nonstenotic rectal cancer. Display of volume data in three perpendicular planes or as 3D view facilitated the interpretation of ultrasound images and enhanced the diagnostic information of the data. The accuracy of 3D endosonography in the assessment of infiltration depth was 88% compared to 82% with the conventional technique. In the determination of lymph node involvement, 3D and two-dimensional endosonography provided accuracy rates of 79% and 74%, respectively. The 3D scanning allowed the visualization of obstructing tumors using reconstructed planes in front of the transducer. Correct assessment of the infiltration depth was possible in 15 of 21 patients with obstructing tumors (accuracy, 76%). Three-dimensional endosonography displayed suspicious pararectal lesions in 30 patients. Transrectal ultrasound-guided biopsy was extremely precise (accuracy, 98%) and showed malignancy in 10 of 30 patients. Histologic analysis changed the endosonographic diagnosis in 8 (27%) of the patients. CONCLUSIONS: The 3D endosonography permits examination of rectal cancer using previously unattainable planes and 3D views. The 3D imaging and ultrasound-guided biopsy seem capable to improve staging of rectal cancer and should be evaluated in further studies.

Endosonography↗

PubMed2002

Sequence requirements for terminators and antiterminators in the T box transcription antitermination system: disparity between conservation and functional requirements.

The T box transcription termination control system is used in Gram-positive bacteria to regulate expression of aminoacyl-tRNA synthetase and other amino acid-related genes. Readthrough of a transcriptional terminator located in the leader region of the target gene is dependent on a specific interaction between the nascent leader transcript and the cognate uncharged tRNA. This interaction is required for formation of an antiterminator structure in the leader, which prevents formation of a competing transcriptional terminator stem-loop. The antiterminators and terminators of genes in this family are highly conserved in both secondary structure and primary sequence; the antiterminator contains the T box sequence, which is the most highly conserved leader element. These conserved features were investigated by phylogenetic and mutational analysis. Changes at highly conserved positions in the bulge and in the helix above the bulge reduced function, while alteration of other positions that were as much as 96% conserved did not have a major effect. The disparity between sequence conservation and function may be due to the requirement for maintaining base pairing in both the antiterminator and terminator structures.

Bacillus subtilis↗

PubMed1998

Prediction of indications for valve replacement among asymptomatic or minimally symptomatic patients with chronic aortic regurgitation and normal left ventricular performance.

BACKGROUND: Optimal criteria for valve replacement are unclear in asymptomatic/minimally symptomatic patients with aortic regurgitation (AR) and normal left ventricular (LV) performance at rest. Moreover, previous studies have not assessed the prognostic capacity of load-adjusted LV performance ("contractility") variables, which may be fundamentally related to clinical state. Therefore, 18 years ago, we set out to test prospectively the hypothesis that objective noninvasive measures of LV size and performance and, specifically, of load-adjusted variables, assessed at rest and during exercise (ex), could predict the development of currently accepted indications for operation for AR. METHODS AND RESULTS: Clinical variables and measures of LV size, performance, and end-systolic wall stress (ESS) were assessed annually in 104 patients by radionuclide cineangiography at rest and maximal ex and by echocardiography at rest; ESS was derived during ex. During an average 7.3-year follow-up among patients who had not been operated on, 39 of 104 patients either died suddenly (n = 4) or developed operable symptoms only (n = 22) or subnormal LV performance with or without symptoms (n = 13) (progression rate=6.2%/y). By multivariate Cox model analysis, change (delta) in LV ejection fraction (EF) from rest to ex, normalized for deltaESS from rest to ex (deltaLVEF-deltaESS index), was the strongest predictor of progression to any end point or to sudden cardiac death alone. Unadjusted deltaLVEF was almost as efficient. Symptom status modified prediction on the basis of the deltaLVEF-deltaESS index. The population tercile at highest risk by deltaLVEF-deltaESS progressed to end points at a rate of 13.3%/y, and the lowest-risk tercile progressed at 1.8%/y. CONCLUSIONS: Currently accepted symptom and LV performance indications for valve replacement, as well as sudden cardiac death, can be predicted in asymptomatic/minimally symptomatic patients with AR by load-adjusted deltaLVEF-deltaESS index, which includes data obtained during exercise.

Aortic Valve Insufficiency↗

PubMed1993

Developmental profile of the gene expression of a Bombyx homolog of mammalian sorbitol dehydrogenase during embryogenesis in non-diapause eggs.

1. By using semi-quantitative PCR analysis, changes in the amount of the transcript for a Bombyx homolog of mammalian sorbitol dehydrogenase (BmSDH) were examined during embryogenesis in non-diapause eggs. 2. Occurrence of the transcript for BmSDH correlated with the two developmental phases, the growth of embryo and the formation of larval tissues. 3. In the first phase, an increase in the amount of the transcript for BmSDH resulted from embryonic cells rather than yolk cells. 4. In the second phase, the transcript was suggested to be abundant in fat-body cells of pharate larva, because it was abundant in fat-bodies of 5th instar larvae. 5. The difference in the expression of BmSDH gene between diapause and non-diapause eggs is discussed.

Animals↗

PubMed1995

Modulation of ras transformation affecting chromatin supraorganization as assessed by image analysis.

Changes in chromatin supraorganization defined in terms of patterns of chromatin texture were studied by video image analysis in Feulgen-stained revertants of LTR-ras-transformed NIH 3T3 cells and in cell lines obtained by transfection of these revertants with sense and antisense constructs of the lysyl oxidase gene (also named Lox or "ras recision gene"). The objective was to determine whether changes in expression of the Lox gene, which have been assumed to modulate cell transformation by ras, could also affect the chromatin supraorganization changes known to be elicited in NIH 3T3 cells by ras transformation. The image analysis results revealed that, although a nuclear phenotype visually similar to the most frequent one (III) in ras-transformed NIH 3T3 cells also appeared in the revertant, it contained a remarkably less tight chromatin packing state. This situation was also found in the revertant transfected with the sense construct of the Lox gene, but in the revertant transfected with the Lox antisense constructs the chromatin texture of the III phenotype was equal to or close to that of the ras-transformed cells. With regard to the nuclear phenotype characterized by abundant loosely packed chromatin and less represented in the transformed cell lines (I'), changes in the various cell lines, although detectable, were not as drastic as those reported for the III phenotype. The enhancement in chromatin condensation of the type III nuclei, which affects euchromatin, is probably associated with a limited transcription of the genome. Although the image analysis results are mostly in agreement with previously published data on the molecular biology and tumorigenicity of the same cell lines, it appears that the phenomenon of chromatin condensation once established in NIH 3T3 cells by LTR-ras transformation could not be totally reverted by simply affecting Lox expression.

3T3 Cells↗

PubMed2000

Comparative sequence analysis of the VP7 genes of G6, G8 and G10 bovine group A rotarviruses and further characterization of G6 subtypes.

We previously reported the relatively high prevalence (15%) of bovine G6 subtypes (G6s) in the field using RT-PCR and restriction fragment length polymorphism (RFLP) analysis (Chang et al., Arch. Virol. 141: 1727-39). In the present study, we report the nucleotide and antigenic characterization of a G6s strain (C-8336). We also sequenced the VP7 genes of four additional bovine rotavirus (BRV) strains: another G6s (MC27), G6 (IND), G8 (C-8008) and G10 (2292B) and compared these with other bovine and human rotavirus strains. The C-8336 and MC27 strains were confirmed as P[11]G6s by RT-PCR and RFLP analysis. The VP7 genes of the C-8336 and MC27 strains showed high homology to each other (approximately 98%) and with other bovine G6s strains (greater than 95% homology in nucleotide and amino acid sequence with KN-4[P[11]G6s]) and also showed lower, but substantial sequence homology with human G6s strains and prototype G6 BRV (79-87% in nucleotide and 88-91% in amino acid). Serologic analysis of the cell culture adapted C-8336 strain showed that it was neutralized by a G6 monoclonal antibody (MAb IC3) to similar titers as the reference NCDV and IND G6 strains. In two-way cross-neutralization tests, strain C-8336 showed 4- to 16-fold differences in antibody titers with NCDV and IND G6 BRV. Moreover polyclonal antiserum against strain C-8336 neutralized the NCDV and IND strains weakly. Genetic variability was also observed among G8 and G10 bovine and human group A rotaviruses: the VP7 genes of the bovine C-8008 (P[5]G8) and 2292 B (P[11]G10) strains showed from 10 to 17% nucleotide divergence with those of Cody 1801 (P[1]G8, bovine), A5 (P[1]G8, bovine), 69M (P[10]G8, human) and Hal 1166 (P[14]G8, human), and I321(P[11]G10, human) and MC35 (P[14]G10, human) rotaviruses, respectively. The divergence of VP7 genes among bovine and human G6, G8 and G10 strains appears related to host species origin and their combination with VP4 (P type). The data presented in this report confirms the genetic variability among homotypic bovine and human strains and highlights the importance of continued monitoring of BRV G and P types circulating in the field for the future development and monitoring of effective vaccines.

Animals↗

PubMed2001

Urinary adrenomedullin is related to ET-1 and salt intake in patients with mild essential hypertension. Salt Sensitivity Group of Italian Society of Hypertension.

Adrenomedullin (ADM) infusion increases salt excretion in the rat. However, there is no evidence that this substance is related to changes in salt intake in humans. In this study we sought whether the urinary excretion rate of this autacoid is related to salt intake and by the expected changes in arterial pressure in patients with mild essential hypertension. The influence of salt intake on the renal excretion of ADM was investigated in 55 hypertensive patients in a double blind, randomized and crossover study comparing a 2-week 50 mmol/day salt intake period with a 150 mmol/day salt intake period. Twenty-four-hour ADM and endothelin-1 (ET-1) excretion rate were measured by radioimmunoassay on preextracted urinary samples (intraassay confidence variable <8%). The antibodies used in these assays had minimal ADM-ET-1 cross-reactivity (<1%). Twenty-four-hour microalbuminuria was measured by nephelometry. On univariate analysis changes in urinary ADM were significantly related to those in salt excretion (r = 0.33, P = .01) as well as to changes in urinary ET-1 (r = 0.56, P = .0001). Furthermore, changes in urinary albumin excretion were related to those in urinary ET-1 (r = 0.26, P = .05), but were independent of those in urinary ADM (P = .19). In a multiple regression model including age, sex, body mass index, and changes in systolic pressure, plasma renin activity and plasma aldosterone and urine volume, salt excretion resulted as the stronger independent predictor of urinary ADM (r = 0.33, P = .01). However, changes in urinary salt lost prediction power (P = .11) for urinary ADM when urinary ET-1 was introduced into the model. In this model (multiple r = 0.31) urinary ET-1 resulted to be the only independent predictor of urinary ADM (beta = 0.56, P = .0001). This study is the first to show that the renal excretion of ADM is related to changes in salt intake and that it is tightly linked to that of ET-1. The data support the notion that these autacoids play a role in the regulation of sodium metabolism in patients with mild hypertension. The intercorrelations between ET-1, ADM, and microalbuminuria are compatible with the hypothesis that ET-1 is involved in a salt-induced increase in glomerular pressure and suggest that ADM may act as a counterregulatory factor in this situation.

Adrenomedullin↗

PubMed1996

Effect of the membrane biocompatibility on nutritional parameters in chronic hemodialysis patients.

Malnutrition is highly prevalent in chronic hemodialysis patients and is an important determinant of their morbidity and mortality. Several recent studies have suggested that the inflammatory response associated with the biocompatibility of the dialysis membranes is a potential contributing factor. In a prospective study of 159 new hemodialysis patients from two centers randomized to either a low-flux biocompatible (BCM) membrane or a low-flux bioincompatible (BICM) membrane, we measured the long-term effects of biocompatibility on several nutritional parameters, including estimated dry weight, serum albumin, insulin-like growth factor-1 (IGF-1), and prealbumin over 18 months. Our results show that the BCM group had a mean (+/- SD) increase in their dry weight of 2.96 +/- 6.88 kg at month 12 and 4.36 +/- 8.57 kg at month 18 (P < 0.05 vs. baseline for both), whereas no change in mean weight was observed in BICM group. Following initiation of hemodialysis, a significant increase was observed in serum albumin levels in both groups of patients. However, the biocompatible group had an earlier and more marked increase in serum albumin levels compared to the BICM group. The average increase in serum albumin compared to baseline was consistently greater than 0.25 g/dl after seven months in the BCM group, but did not reach this level until 12 months after initiation of dialysis in the BICM group. The difference between the groups was statistically significant at months 7, 8, and 10 (P < 0.05, higher in the BCM group). Furthermore, the overall difference in serum albumin concentration between the two groups was larger in the center where the dose of dialysis was equivalent (P < 0.001). A consistently higher value was also observed in IGF-1 levels for BCM patients compared to BICM group (P = NS). In a further analysis, changes in IGF-1 levels, but not prealbumin, predicted the subsequent changes in serum albumin. We conclude that biocompatible hemodialysis membranes favorably impact on the nutritional status of chronic hemodialysis patients, independently of the flux characteristics of the membranes, and that IGF-1 may be an early marker of nutritional status.

Adult↗

PubMed2002

Molecular epidemiology of influenza A(H3N2) virus reinfections.

Between 1979 and 1989, families enrolled in the Houston Family Study were prospectively monitored for influenza virus infections. Reinfection with the H3N2 subtype occurred in a number of family members, and 6 pairs of isolates (interval between collection of first and second isolate, 2-5 years) were available for molecular analysis. Changes in the hemagglutinin genes of pairs of viruses isolated from the same individuals were examined to determine the molecular basis for reinfection. The findings of this study indicate that reinfection of an individual by viruses of the same subtype may occur within a relatively short period of time when the paired strains have genetically distinct hemagglutinin genes in which amino acid changes are present in the defined antigenic sites.

Adolescent↗

PubMed1996

A 15-year longitudinal study of Halstead-Reitan neuropsychological test performance.

Using a two-stage growth curve analysis, change over time in performance on tests in the Halstead-Reitan Battery and Average Impairment Rating (AIR) was assessed for 53 individuals who varied in age and health status. In the first stage of the analysis, estimated slope and intercept values were calculated for each individual by regressing longitudinal data points on time. In the second stage, estimated slope and intercept values obtained in the first-stage analysis were regressed on age at entry into the study with statistical control for health status, education, occupation, and gender. Control for health status had an insignificant influence on magnitude of associations between age and test performance. Age-at-entry into the study was associated with statistically significant increasing change over time (poorer performance) for tests placing relatively heavy demands on speed of psychomotor performance and for AIR.

Adult↗

PubMed1997

Aortic valve replacement for aortic stenosis with severe left ventricular dysfunction. Prognostic indicators.

BACKGROUND: Aortic valve replacement for aortic stenosis (AS) carries an increased risk in the presence of left ventricular (LV) systolic dysfunction. Few data are available on the outcome of such patients. METHODS AND RESULTS: Between 1985 and 1992, 154 consecutive patients (107 men and 47 women) with LV systolic dysfunction (ejection fraction [EF] < or = 35%) underwent aortic valve replacement for AS. The mean preoperative characteristics included EF, 27 +/- 6%; aortic valve mean gradient, 44 +/- 18 mm Hg; aortic valve area, 0.6 +/- 0.2 cm2; and cardiac output, 4.1 +/- 1.5 L/min. Simultaneous coronary artery bypass graft surgery was performed in 78 patients (51%). Perioperative (30-day) mortality was 9% (14 of 154 patients). Fifty patients died during follow-up. Coronary artery disease (P = .002) and a reduced preoperative cardiac output (P = .03) were significantly related to reduced overall survival rate by multivariate analysis. Postoperative improvement occurred in most patients; 88% were New York Heart Association class III or IV before surgery versus 7% after surgery. Postoperative EF was assessed in 76% of survivors; 76% of these demonstrated improvement. By multivariate analysis, change in EF was inversely related to coronary disease (P = .002) and preoperative aortic valve area (P = .03). CONCLUSIONS: Despite LV dysfunction, the risk of aortic valve replacement for AS was acceptable and related to coronary artery disease and mean aortic gradient, and long-term survival was related to coronary disease and cardiac output. Improvement in symptoms and EF occurred in most patients.

Adult↗

PubMed1986

Hemodynamic effects of environmental hyperthermia in stage 18, 21, and 24 chick embryos.

Environmental hyperthermia is a hazard to the poikilothermic chick embryo. We studied effects of hyperthermia on mean vitelline arterial blood pressure and mean dorsal aortic blood flow in stage 18, 21, and 24 chick embryos. The pressure was measured with a servo-null micropressure system, and the blood flow was measured with a 20 MHz pulsed Doppler flowmeter. Temperature was monitored with a needle thermoprobe positioned adjacent to the embryo. Data were obtained at 37 degrees C, after warming to 40 degrees C, and then after cooling to 37 degrees C. At stage 21, the pressure increased from 0.96 +/- 0.05 (+/- SE) to 1.04 +/- 0.06 mm Hg on warming and returned from 1.05 +/- 0.04 to 0.87 +/- 0.04 mm Hg on cooling. Pressure measurements during warming and cooling were performed in two separate groups of embryos because of technical problems. The blood flow, studied using different groups of the embryo from the pressure study, also increased from 0.65 +/- 0.06 to 0.75 +/- 0.06 mm3/s on warming and returned to 0.56 +/- 0.05 mm3/s. The heart rate increased from 173 +/- 2 to 211 +/- 3 at 40 degrees C and returned to 170 +/- 3 at 37 degrees C. Stroke volume (flow/heart rate) did not change during the temperature variation. Vascular resistance, the quotient of pressure to blood flow obtained by a ratio analysis, changed from 1.53 +/- 0.33 (median +/- 95% confidence interval) to 1.42 +/- 0.29 mm Hg/mm3/s on warming and changed to 1.60 +/- 0.32 mm Hg/mm3/s on cooling. Similar results were obtained at stages 18 and 24.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1998

Ambulatory device for surface EMG recordings.

The principles of electromyographic (EMG) analysis can be divided into the following groups: signal or motor unit shape analysis, amplitude analysis, multi-channel or successive time difference analysis, signal frequency composition analysis, change of frequency time based analysis based on simultaneous amplitude or frequency based analysis or concentric and excentric work based shape and amplitude ratio analysis. The aim of this paper is to present an ambulatory portable device for surface EMG analysing both for integrated EMG and for spectral analysis. The reliability of surface EMG recordings have established. The recent new technology gets a possibility to measure by reliable way surface EMG on-line during exercise, rehabilitation or occupational conditions. Portable EMG measurement unit and analysing program seems to be suitable for documentation of the response of rehabilitation programs, effects of physiotherapy, analysing the muscle balance and activity of sportsman and for documentation of occupational health problems. Automatic interpretation and wide data base for patient data makes the system useful in daily practice.

Ambulatory Care↗

PubMed1992

Trend analysis of solar ultraviolet exposure of the Austrian population caused by holiday patterns since 1969.

Over the last few decades, a steady increase in the incidence of skin cancer has been observed. Solar ultraviolet (UV) exposure is undoubtedly one of the primary causes, and of these, holiday patterns are an intrinsic component. To assess solar UV exposure for this trend analysis, changes in holiday patterns were investigated. For Austrians, a preponderance of holidays are spent at the Mediterranean Sea. These holidays represent not only a potentially high UV exposure because of location but also because sun-intensive activities are preferred. The analysis shows an increase in solar UV exposure from all holidays of 1.6% per year. About 22% of the population spends holidays at the Mediterranean Sea, and UV exposure of the total population from these holidays has increased annually by about 3.3%. Because of the latency period, it is not possible to draw conclusions from the increase in UV exposure and the temporal trends in skin cancer. A longer time series would be necessary to do this. A direct comparison of data from other countries reporting increases in skin cancer does not seem appropriate, as levels of UV exposure vary greatly and such factors as genetic susceptibility are involved.

Austria↗

PubMed1985

Differential effects of exercise on serum lipid and lipoprotein levels seen with changes in body weight. A meta-analysis.

Ninety-five studies conducted between September 1955 and October 1983 measuring changes in human serum lipid and lipoprotein levels in response to exercise training were analyzed using meta-analysis. Change in body weight during exercise training may confound observed serum lipid and lipoprotein level changes; thus, data from these studies were partitioned into those where subjects gained body weight, maintained body weight, or lost body weight. Results showed differential changes in cholesterol, triglyceride, low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol, and cholesterol/high-density lipoprotein-cholesterol levels in the three body-weight categories. Where body weight did not change, cholesterol and LDL-C levels decreased significantly (7.3 mg/dL and 3.3 mg/dL, respectively). Where body weight decreased, cholesterol and LDL-C levels also decreased significantly (13.2 mg/dL and 11.1 mg/dL, respectively). However, with body-weight increase, cholesterol and LDL-C levels increased by 2.9 mg/dL and 3.0 mg/dL, respectively. These results suggest that reductions in cholesterol and LDL-C levels were greatest when exercise training was combined with body-weight losses.

Body Weight↗

PubMed1995

Alpha-2,3 sialylation differentiate the limbal and corneal epithelial cell phenotypes.

PURPOSE: The initial differentiation event for the corneal epithelial cell lineage occurs as the limbally localized stem cells yield, through mitosis, the highly proliferative, transiently amplifying corneal peripheral cells. This differentiation is characterized by the expression of tissue-specific cytokeratins, as well as the loss of alpha-enolase and pigmentation. All these are intracellular events. The aim of this study was to identify and characterize, through lectin analysis, changes in cell surface properties associated with differentiation. METHODS: Cryostat sections of the limbo-corneal area from freshly dissected pigmented rabbit corneas were stained with fluorescent lectins. RESULTS: Peanut lectin (PNA; binds to Ser/Threo-GalNAc-beta-1,3-Gal, if the Gal residue is not sialylated) stained the plasma membrane of all layers of the conjunctiva and limbus but was excluded from corneal cell membranes. Maakia amurensis agglutinin (MAA; binds to sialic acid attached to galactose through alpha-2,3 bonds in either N-glycans or O-glycans) stained exclusively corneal cell plasma membrane. After complete tissue desialylation, all corneal plasma membranes became PNA positive with equal stain intensity across both sides of the limbo-corneal margin. The binding of the agglutinins from Limax flavus (binds unselectively to sialic acid) and Sambucus nigra (binds to sialic acid attached through alpha-2,6 bonds) to the basement membrane displayed a large increase at the corneal side of limbo-corneal demarcation. CONCLUSIONS: Limbal (stem) cells express on the cell surface unsialylated galactose residues that are recognized by PNA and that lack any sialic acid bound through alpha-2,3 bonds. The initial differentiation involves sialylation of these residues and the concurrent appearance of alpha-2,3 sialic acid residues, suggesting expression or activation of alpha-2-3 sialytransferase. Changes in basement membrane composition, charge, or both may underpin this expression.

Animals↗