Maternal vitamin D, DNA methylation at imprint regulatory regions and offspring weight at birth, 1 year and 3 years.

BACKGROUND/OBJECTIVE: Vitamin D deficiency during pregnancy is associated with poor birth outcomes in some studies, but few have examined weight beyond birth. In addition, little is known about how vitamin D influences DNA methylation of regulatory regions known to be involved in growth, as possible mediators to weight status in offspring. SUBJECTS/METHODS: We conducted linear regressions to assess maternal plasma 25-hydroxyvitamin D (25(OH)D) by quartile and birth weight for gestational age z-score, 1-year weight-for-length z-score and 3-year body mass index (BMI) z-score among 476 mother/infant dyads from a prospective cohort. We assessed maternal 25(OH)D and infant DNA methylation at nine differentially methylated regions (DMRs) of genomically imprinted genes with known functions in fetal growth, including H19, IGF2, MEG3, MEG3-IG, MEST, NNAT, PEG3, PLAGL1 and SGCE/PEG10. RESULTS: Mean (standard deviation, s.d.) maternal 25(OH)D was 41.1 (14.2) nmol l-m at a mean (s.d.) of 13.2 (5.5) weeks gestation. After adjustment for potential confounders, the first (Q1) and second (Q2) quartiles of 25(OH)D, compared to the fourth (Q4), were associated with lower birth weight for gestational age z-scores (-0.43 units; CI: -0.79, -0.07; P=0.02 for Q1 and -0.56 units; CI: -0.89, -0.23; P=0.001 for Q2). Q1 compared to Q4 was associated with higher 1-year weight-for-length z-scores (0.78 units; 0.08, 1.54; P=0.04) and higher 3-year BMI z-scores (0.83 units; 0.11, 0.93; P=0.02). We did not observe associations between maternal 25(OH)D and methylation for any of the nine DMRs after correcting for multiple testing. CONCLUSIONS: Reduced maternal 25(OH)D was associated with lower birth weight for gestational age z-scores but higher 1-year weight-for-length and 3-year BMI z-scores in offspring. However, 25(OH)D does not appear to be operating through the regulatory sequences of the genomically imprinted genes we examined.

Disparities in Cervical Cancer Incidence and Mortality: Can Epigenetics Contribute to Eliminating Disparities?

Screening for uterine cervical intraepithelial neoplasia (CIN) followed by aggressive treatment has reduced invasive cervical cancer (ICC) incidence and mortality. However, ICC cases and carcinoma in situ (CIS) continue to be diagnosed annually in the United States, with minorities bearing the brunt of this burden. Because ICC peak incidence and mortality are 10-15 years earlier than other solid cancers, the number of potential years of life lost to this cancer is substantial. Screening for early signs of CIN is still the mainstay of many cervical cancer control programs. However, the accuracy of existing screening tests remains suboptimal. Changes in epigenetic patterns that occur as a result of human papillomavirus infection contribute to CIN progression to cancer, and can be harnessed to improve existing screening tests. However, this requires a concerted effort to identify the epigenomic landscape that is reliably altered by HPV infection specific to ICC, distinct from transient changes.

Obesity and prostate cancer-specific mortality after radical prostatectomy: results from the Shared Equal Access Regional Cancer Hospital (SEARCH) database.

BACKGROUND: At the population level, obesity is associated with prostate cancer (PC) mortality. However, few studies analyzed the associations between obesity and long-term PC-specific outcomes after initial treatment. METHODS: We conducted a retrospective analysis of 4268 radical prostatectomy patients within the Shared Equal Access Regional Cancer Hospital (SEARCH) database. Cox models accounting for known risk factors were used to examine the associations between body mass index (BMI) and PC-specific mortality (PCSM; primary outcome). Secondary outcomes included biochemical recurrence (BCR) and castration-resistant PC (CRPC). BMI was used as a continuous and categorical variable (normal <25 kg/m2, overweight 25-29.9 kg/m2 and obese ⩾30 kg/m2). Median follow-up among all men who were alive at last follow-up was 6.8 years (interquartile range=3.5-11.0). During this time, 1384 men developed BCR, 117 developed CRPC and 84 died from PC. Hazard ratios were analyzed using competing-risks regression analysis accounting for non-PC death as a competing risk. RESULTS: On crude analysis, higher BMI was not associated with risk of PCSM (P=0.112), BCR (0.259) and CRPC (P=0.277). However, when BMI was categorized, overweight (hazard ratio (HR) 1.99, P=0.034) and obesity (HR 1.97, P=0.048) were significantly associated with PCSM. Obesity and overweight were not associated with BCR or CRPC (all P⩾0.189). On multivariable analysis adjusting for both clinical and pathological features, results were little changed in that obesity (HR=2.05, P=0.039) and overweight (HR=1.88, P=0.061) were associated with higher risk of PCSM, but not with BCR or CRPC (all P⩾0.114) with the exception that the association for overweight was no longer statistical significant. CONCLUSIONS: Overweight and obesity were associated with increased risk of PCSM after radical prostatectomy. If validated in larger studies with longer follow-up, obesity may be established as a potentially modifiable risk factor for PCSM.

Baseline subject characteristics predictive of compliance with study-mandated prostate biopsy in men at risk of prostate cancer: results from REDUCE.

BACKGROUND: Study compliance is crucial when the study outcome is determined by an invasive procedure, such as prostate biopsy. To investigate predictors of compliance in study-mandated prostate biopsies, we analyzed demographic, clinical and reported lifestyle data from the REDUCE trial. METHODS: We retrospectively identified 8025 men from REDUCE with at least 2 years of follow-up, and used multivariable logistic regression to test the association between baseline demographic and clinical characteristics and undergoing the study-mandated prostate biopsy at 2 years. We then examined whether missing any of these data was associated with undergoing a biopsy. RESULTS: In REDUCE, 22% of men did not undergo a 2-year biopsy. On multivariable analysis, the non-North American region was predictive of 42-44% increased likelihood of undergoing a 2-year biopsy (P⩽0.001). Being enrolled at a center that enrolled >10 subjects (2nd and 3rd tertile) was associated with a 42-48% increased likelihood of undergoing a 2-year biopsy (P<0.001). In addition, black race predicted 44% lower rate of on-study 2-year biopsy (odds ratio (OR)=0.56; P=0.001). Finally, missing one or more baseline variables was associated with a 32% decreased likelihood of undergoing a 2-year biopsy (OR=0.68; P<0.001). CONCLUSIONS: In REDUCE, men outside North America, those at higher volume centers and those with complete baseline data were more likely to undergo study-mandated 2-year biopsies. Given prostate biopsy is becoming increasingly utilized as an endpoint in trials that are often multi-national, regional differences in compliance should be considered when designing future trials. Likewise, efforts are needed to ensure compliance in low-volume centers or among subjects missing baseline data.

Genotoxic potential of leaf extracts of Jatropha gossypiifolia L.

Jatropha gossypiifolia L. (Euphorbiaceae) is widely used in popular medicine. However, further toxicological studies are necessary for its reliable use. The present study aimed to evaluate the cytotoxic, genotoxic, and mutagenic effects of ethanolic and aqueous leaf extracts of J. gossypiifolia, using the test system Allium cepa. In addition, the phytochemical profile of the extracts was also obtained. Seeds of A. cepa were subjected to different concentrations of the two extracts (0.001, 0.01, 0.1, 1, and 10 mg/mL). Distilled water was used for the negative control and methyl methanesulfonate (4 x 10(-4) M) and trifluralin (0.84 ppm) for the positive controls. The values of mitotic index at all concentrations of ethanolic extract and at 0.1, 1, and 10 mg/mL aqueous extract showed a significant decrease. Alterations, such as chromosome adherence, C-metaphases, chromosome bridges, nuclear buds, and micronuclei were verified in both extracts but chromosome loss indicating genotoxic activity was observed only in the ethanolic extract. Presence of micronuclei on administration of the extracts, also indicated mutagenic action at the chromosome level. In the ethanolic extract, aneugenicity seemed to be the main activity, probably as a result of the action of terpenes and/or flavonoids, whereas in the aqueous extract, clastogenic action appeared to be the principal activity, presumably as a consequence of the effect of flavonoids and/or saponins. Thus, we suggest that the extracts of this species should be used with great caution for medicinal purpose.

Newborns of obese parents have altered DNA methylation patterns at imprinted genes.

BACKGROUND: Several epidemiologic studies have demonstrated associations between periconceptional environmental exposures and health status of the offspring in later life. Although these environmentally related effects have been attributed to epigenetic changes, such as DNA methylation shifts at imprinted genes, little is known about the potential effects of maternal and paternal preconceptional overnutrition or obesity. OBJECTIVE: We examined parental preconceptional obesity in relation to DNA methylation profiles at multiple human imprinted genes important in normal growth and development, such as: maternally expressed gene 3 (MEG3), mesoderm-specific transcript (MEST), paternally expressed gene 3 (PEG3), pleiomorphic adenoma gene-like 1 (PLAGL1), epsilon sarcoglycan and paternally expressed gene 10 (SGCE/PEG10) and neuronatin (NNAT). METHODS: We measured methylation percentages at the differentially methylated regions (DMRs) by bisulfite pyrosequencing in DNA extracted from umbilical cord blood leukocytes of 92 newborns. Preconceptional obesity, defined as BMI ⩾30 kg m(-2), was ascertained through standardized questionnaires. RESULTS: After adjusting for potential confounders and cluster effects, paternal obesity was significantly associated with lower methylation levels at the MEST (ß=-2.57; s.e.=0.95; P=0.008), PEG3 (ß=-1.71; s.e.=0.61; P=0.005) and NNAT (ß=-3.59; s.e.=1.76; P=0.04) DMRs. Changes related to maternal obesity detected at other loci were as follows: ß-coefficient was +2.58 (s.e.=1.00; P=0.01) at the PLAGL1 DMR and -3.42 (s.e.=1.69; P=0.04) at the MEG3 DMR. CONCLUSION: We found altered methylation outcomes at multiple imprint regulatory regions in children born to obese parents, compared with children born to non-obese parents. In spite of the small sample size, our data suggest a preconceptional influence of parental life-style or overnutrition on the (re)programming of imprint marks during gametogenesis and early development. More specifically, the significant and independent association between paternal obesity and the offspring's methylation status suggests the susceptibility of the developing sperm for environmental insults. The acquired imprint instability may be carried onto the next generation and increase the risk for chronic diseases in adulthood.

PEG1/MEST and IGF2 DNA methylation in CIN and in cervical cancer.

INTRODUCTION: Although most invasive cervical cancer (ICC) harbor <20 human papillomavirus (HPV) genotypes, use of HPV screening to predict ICC from HPV has low specificity, resulting in multiple and costly follow-up visits and overtreatment. We examined DNA methylation at regulatory regions of imprinted genes in relation to ICC and its precursor lesions to determine if methylation profiles are associated with progression of HPV-positive lesions to ICC. MATERIALS AND METHODS: We enrolled 148 controls, 38 CIN and 48 ICC cases at Kilimanjaro Christian Medical Centre from 2008 to 2009. HPV was genotyped by linear array and HIV-1 serostatus was tested by two rapid HIV tests. DNA methylation was measured by bisulfite pyrosequencing at regions regulating eight imprinted domains. Logistic regression models were used to estimate odd ratios. RESULTS: After adjusting for age, HPV infection, parity, hormonal contraceptive use, and HIV-1 serostatus, a 10 % decrease in methylation levels at an intragenic region of IGF2 was associated with higher risk of ICC (OR 2.00, 95 % CI 1.14-3.44) and cervical intraepithelial neoplasia (CIN) (OR 1.51, 95 % CI 1.00-2.50). Methylation levels at the H19 DMR and PEG1/MEST were also associated with ICC risk (OR 1.51, 95 % CI 0.90-2.53, and OR 1.44, 95 % CI 0.90-2.35, respectively). Restricting analyses to women >30 years further strengthened these associations. CONCLUSIONS: While the small sample size limits inference, these findings show that altered DNA methylation at imprinted domains including IGF2/H19 and PEG1/MEST may mediate the association between HPV and ICC risk.

Associations between antibiotic exposure during pregnancy, birth weight and aberrant methylation at imprinted genes among offspring.

OBJECTIVES: Low birth weight (LBW) has been associated with common adult-onset chronic diseases, including obesity, cardiovascular disease, type II diabetes and some cancers. The etiology of LBW is multi-factorial. However, recent evidence suggests exposure to antibiotics may also increase the risk of LBW. The mechanisms underlying this association are unknown, although epigenetic mechanisms are hypothesized. In this study, we evaluated the association between maternal antibiotic use and LBW and examined the potential role of altered DNA methylation that controls growth regulatory imprinted genes in these associations. METHODS: Between 2009-2011, 397 pregnant women were enrolled and followed until delivery. Prenatal antibiotic use was ascertained through maternal self-report. Imprinted genes methylation levels were measured at differentially methylated regions (DMRs) using bisulfite pyrosequencing. Generalized linear models were used to examine associations among antibiotic use, birth weight and DMR methylation fractions. RESULTS: After adjusting for infant gender, race/ethnicity, maternal body mass index, delivery route, gestational weight gain, gestational age at delivery, folic acid intake, physical activity, maternal smoking and parity, antibiotic use during pregnancy was associated with 138 g lower birth weight compared with non-antibiotic use (ß-coefficient=-132.99, s.e.=50.70, P=0.008). These associations were strongest in newborns of women who reported antibiotic use other than penicillins (ß-coefficient=-135.57, s.e.=57.38, P=0.02). Methylation at five DMRs, IGF2 (P=0.05), H19 (P=0.15), PLAGL1 (P=0.01), MEG3 (P=0.006) and PEG3 (P=0.08), was associated with maternal antibiotic use; among these, only methylation at the PLAGL1 DMR was also associated with birth weight. CONCLUSION: We report an inverse association between in utero exposure to antibiotics and lower infant birth weight and provide the first empirical evidence supporting imprinted gene plasticity in these associations.

Phosphorylation of histone H3S10 in animal chromosomes: is there a uniform pattern?

Phosphorylation of serine 10 in histone H3 (H3S10ph) has been extensively analyzed and appears to be a conserved chromatin change associated with chromosome condensation in different eukaryotic organisms. In this work, we report the distribution of H3S10ph during meiosis in monocentric and holokinetic chromosomes of 6 insect species and in mitotic chromosomes of 7 mammalian species, aiming to investigate the labeling patterns in phylogenetically distant groups. The results indicated a very similar phosphorylation timing and distribution pattern among insects. The sex chromosomes of insects analyzed were always undercondensed and hypophosphorylated. Similarly, the micro chromosomes of the bug Pachylis aff pharaonis were also undercondensed and hypophosphorylated. Holokinetic chromosomes of bugs and monocentric chromosomes of grasshoppers and beetles displayed identical phosphorylation pattern in spite of the difference in the centromere type. Among mammals, a uniform chromosome phosphorylation was observed in marsupials, whereas bat chromosomes displayed a longitudinal banding pattern. These data indicate that, in general, the intensity of H3S10 phosphorylation in animal chromosomes is variable among the distinct chromosome types and associated with the degree of chromatin condensation at metaphase, but it may vary between different groups of animals.

Different chromatin fractions of tomato (Solanum lycopersicum L.) and related species.

Conventional chromosome staining has suggested that more than 75% of the tomato chromosomes are constituted by heterochromatin. In order to determine whether more deeply stained proximal regions are classic heterochromatin, the distributions of C-bands and chromomycin A(3) (CMA) bands, and the prophase condensation patterns, were analysed in tomato. In this and most other species of the tomato clade, the 5S and 45S rDNA sites were also localised. In tomato, CMA banding was similar to C-banding. After conventional staining, all species displayed large condensed heteropycnotic regions that did not correspond to C-bands or CMA bands. Analyses of the CMA banded karyotypes revealed a low heterochromatin content. Around 12-17% of the chromatin of tomato was CMA(+) and 1/4 to 1/5 of this heterochromatin corresponded to 45S rDNA. In other species, the CMA(+) heterochromatin showed extensive variation (8-35%), but was never near the values found in the literature for tomato. These data suggest the existence of three principal fractions of chromatin in tomato and related species: the late condensed euchromatin corresponding to the terminal regions of the chromosomes, the precocious condensed euchromatin that occupies the major part of the chromosomes and the constitutive heterochromatin that represents those regions revealed by C-bands.

A simple chromosomal marker can reliably distinguishes Poncirus from Citrus species.

Several chromosome types have been recognized in Citrus and related genera by chromomycin A(3 )(CMA) banding patterns and fluorescent in situ hybridization (FISH). They can be used to characterize cultivars and species or as markers in hybridization and backcrossing experiments. In the present work, characterization of six cultivars of P. trifoliata ("Barnes", "Fawcett", "Flying Dragon", "Pomeroy", "Rubidoux", "USDA") and one P. trifoliata x C. limonia hybrid was performed by sequential analyses of CMA banding and FISH using 5S and 45S rDNA as probes. All six cultivars showed a similar CMA(+) banding pattern with the karyotype formula 4B + 8D + 6F. The capital letters indicate chromosomal types: B, a chromosome with one telomeric and one proximal band; D, with only one telomeric band; F, without bands. In situ hybridization labeling was also similar among cultivars. Three chromosome pairs displayed a closely linked set of 5S and 45S rDNA sites, two of them co-located with the proximal band of the B type chromosomes (B/5S-45S) and the third one co-located with the terminal band of a D pair (D/5S-45S). The B/5S-45S chromosome has never been found in any citrus accessions investigated so far. Therefore, this B chromosome can be used as a marker to recognize the intergeneric Poncirus x Citrus hybrids. The intergeneric hybrid analyzed here displayed the karyotype formula 4B + 8D + 6F, with two chromosome types B/5S-45S and two D/5S-45S. The karyotype formula and the presence of two B/5S-45S chromosomes clearly indicate that the plant investigated is a symmetric hybrid. It also demonstrates the suitability of karyotype analyses to differentiate zygotic embryos or somatic cell fusions involving trifoliate orange germplasm.

Chromosomal markers distinguish hybrids and non-hybrid accessions of mandarin.

Mandarin is the common name of a heterogeneous group of Citrus species with a large range of variation in morphological and molecular characters as well as in number of species. Aiming to identify chromosome markers and to clarify the relationship within this group, the karyotype of 13 mandarin accessions were analyzed using CMA/DAPI staining and in situ hybridization with 5S and 45S rDNA probes. The CMA band pattern together with the position of rDNA sites revealed that mandarins can be separated karyologically into three groups: a) C. sunki and C. reshni; b) the Mediterranean mandarin, C. deliciosa, and the closely related C. tangerina cv. Dancy and C. reticulata cv. Cravo; c) the remaining cultivars, which are cytologically heterozygous and most probably interspecific hybrids. The former two groups are assumed to be pure species together with C. medica and C. grandis. A chromosome marker for mandarin species was identified and the relationship among the pure species and some hybrids is discussed.

Mitotic microtubule development and histone H3 phosphorylation in the holocentric chromosomes of Rhynchospora tenuis (Cyperaceae).

In the present work we report the phosphorylation pattern of histone H3 and the development of microtubular structures using immunostaining techniques, in mitosis of Rhynchospora tenuis (2n = 4), a Cyperaceae with holocentric chromosomes. The main features of the holocentric chromosomes of R. tenuis coincide with those of other species namely: the absence of primary constriction in prometaphase and metaphase, and the parallel separation of sister chromatids at anaphase. Additionaly, we observed a highly conserved chromosome positioning at anaphase and early telophase sister nuclei. Four microtubule arrangements were distinguished during the root tip cell cycle. Interphase cells showed a cortical microtubule arrangement that progressively forms the characteristic pre-prophase band. At prometaphase the microtubules were homogeneously distributed around the nuclear envelope. Metaphase cells displayed the spindle arrangement with kinetochore microtubules attached throughout the entire chromosome extension. At anaphase kinetochoric microtubules become progressively shorter, whereas bundles of interzonal microtubules became increasingly broader and denser. At late telophase the microtubules were observed equatorially extended beyond the sister nuclei and reaching the cell wall. Immunolabelling with an antibody against phosphorylated histone H3 revealed the four chromosomes labelled throughout their entire extension at metaphase and anaphase. Apparently, the holocentric chromosomes of R. tenuis function as an extended centromeric region both in terms of cohesion and H3 phosphorylation.

Mitotic instability in wheat x Thinopyrum ponticum derivatives revealed by chromosome counting, nuclear DNA content and histone H3 phosphorylation pattern.

To evaluate the mitotic stability of Triticum aestivum x Thinopyrum ponticum derivatives (BC(2)F(7) and BC(2)F(5) doubled haploids), chromosome counting by both conventional and immunostaining techniques, and measurement of DNA content were performed. The wheat progenitor line, PF 839197, the wheat recurrent parent CEP 19 and the control Chinese Spring were also investigated. In the hybrid derivatives, chromosome number ranged from 2n=36 to 60, with a predominance of chromosome numbers higher than 2n=42, that was confirmed by determination of nuclear DNA content. Chinese Spring' and PF 839197 were stable, but CEP 19 showed chromosome number variation (20%). Analyses of non-pretreated cells revealed the presence of anaphase bridges, lagging chromatids, chromosome fragments and micronuclei. Immunostaining with an antibody recognizing histone H3 phosphorylated showed dicentric chromatids forming anaphase bridges and pericentromeric phosphorylation at centric chromosome fragments but not at lagging chromatids. The possible causes of the observed mitotic instability are discussed.

The relationships among lemons, limes and citron: a chromosomal comparison.

Lemons, limes and citron constitute a group of closely related Citrus species, whose species delimitations and taxonomic relationships are unclear. In order to identify karyotypic similarities and species relationships within this group, the CMA+/DAPI- banding pattern and the distribution of the 5S and 45S rDNA sites of 10 accessions of lime, lemon, and citron were investigated. The four cultivars of C. limon analyzed showed the same pattern of CMA+ bands and rDNA sites, suggesting that they originated from a single germplasm, later differentiated by distinct somatic mutations. The lemons C. jambhiri, C. limonia and C. volkameriana displayed karyotypes very similar to each other, but they differed from C. limon by the absence of a single chromosome with one band in each telomere. The limes, C. aurantifolia and C. limettioides, seemed less related to each other and exhibited different heteromorphic chromosome pairs. In C. aurantifolia, the presence of a chromosome type unknown in all other Citrus species cytologically known so far supports the assumption that this accession may be derived from a hybrid with a species from the subgenus Papeda or from another genus. Citrus medica was the only homozygous accession of this group and all of its chromosome types were clearly represented in limes and lemons, some of them forming heteromorphic pairs. The analysis of the distribution of rDNA sites allowed a further refinement of the comparison among accessions. The lemons and limes were heterozygous for all rDNA sites, whereas C. medica was entirely homozygous. These data support the hypothesis that C. medica is a true species while the other nine accessions are hybrids.

Natural killer cell-endothelial cell interactions in xenotransplantation.

Interest in xenotransplantation derives from the documented need for more organs and tissues than can be expected from living or cadaveric donors. Although the barriers to xenotransplantation are formidable, the scientific rewards in addressing these problems have been significant. The first and most potent barrier to xenotransplantation is hyperacute rejection mediated by xenoreactive natural antibodies and serum complement. The majority of the xenoreactive antibodies appear to be directed at terminal galactose epitopes, especially gal alpha1-3 gal. Significant progress has been made in surmounting hyperacute rejection, and this has led to an examination of underlying mechanisms of delayed xenograft rejection. One of these delayed mechanisms concerns the potential role of graft recipient, natural killer (NK) cells. NK cells can cause variable, low-level cytotoxicity of xenogeneic endothelial cells in vitro that may be enhanced in the presence of xenoreactive IgG. The specificity of NK cell-mediated cytotoxicity appears to overlap with a major subset of xenoreactive natural antibodies. These cytotoxic interactions can be regulated by "humanizing" the endothelial cells through expression of the appropriate human MHC class I genes. More important, NK cells induce endothelial cell activation, which results in changing the nature of the endothelial cell surface from an anticoagulant surface to a procoagulant surface. These findings parallel those observed in allogeneic NK cell-endothelial cell interactions and suggest these important observations may be extended to NK cell-endothelial cell interactions in general.

Ultrastructure of Psammobatis extenta (Rajidae) electrolytes and cytochemical localization of acetylcholinesterase, acetylcholine receptor and F-actin.

1. The electrocytes from the electric organ of the Patagonian ray P. extenta are very unusual cells: semicircular in shape, multinucleated and highly polarized. They have an anterior, concave, innervated face, which exhibits positive histochemical reactions for acetylcholinesterase and for the nicotinic acetylcholine receptor. Multiple nerve-endings are covered with Schwann cell projections, similar to those present in skeletal muscle. Their posterior face is convex, non-innervated and is in contact with collagen fibres. 2. The cytoplasm of these electrocytes possesses abundant filamentous actin (F-actin), orderly distributed in the cell and exhibiting intense fluorescence with NBD-phallacidin. The F-actin is in contact with Z-lines as in muscle, and in contrast with Torpedo (Kordeli et al., 1986, 1987) and Discopyge (Vidal et al., 1986, 1989a) electrocytes, where it is confined to the non-innervated face. 3. Electrocytes of this Rajidae are an ideal model for the study of F-actin because of the similar embryological origin with skeletal muscle tissue and also because of the peculiar characteristics of their cytoplasm, packed full with F-actin. In addition, electric organs could constitute an alternative biological source for the study of the cholinergic synapse.

Ultrastructure of Psammobatis extenta (Rajidae) electrolytes and cytochemical localization of acetylcholinesterase, acetylcholine receptor and F-actin.

1. The electrocytes from the electric organ of the Patagonian ray P. extenta are very unusual cells: semicircular in shape, multinucleated and highly polarized. They have an anterior, concave, innervated face, which exhibits positive histochemical reactions for acetylcholinesterase and for the nicotinic acetylcholine receptor. Multiple nerve-endings are covered with Schwann cell projections, similar to those present in skeletal muscle. Their posterior face is convex, non-innervated and is in contact with collagen fibres. 2. The cytoplasm of these electrocytes possesses abundant filamentous actin (F-actin), orderly distributed in the cell and exhibiting intense fluorescence with NBD-phallacidin. The F-actin is in contact with Z-lines as in muscle, and in contrast with Torpedo (Kordeli et al., 1986, 1987) and Discopyge (Vidal et al., 1986, 1989a) electrocytes, where it is confined to the non-innervated face. 3. Electrocytes of this Rajidae are an ideal model for the study of F-actin because of the similar embryological origin with skeletal muscle tissue and also because of the peculiar characteristics of their cytoplasm, packed full with F-actin. In addition, electric organs could constitute an alternative biological source for the study of the cholinergic synapse.

Gangliosides in acetylcholine receptor-rich membranes from Torpedo marmorata and Discopyge tschudii.

The ganglioside composition of membranes enriched in nicotinic acetylcholine receptor (AChR) from the electric rays Discopyge tschudii and Torpedo marmorata has been determined, and compared to that of total electric organ. A ganglioside having the chromatographic mobility of GM2 constitutes the major ganglioside (approximately 60%) in total D. tschudii electric organ, followed by a component with the mobility of GD3 (approximately 10%), and a component running just below GD1a (about 12%). Minor constituents running as GM3 (2%) and as polysialogangliosides (comprising 8-15%) were also observed. Purified native membranes of D. tschudii and T. marmorata displayed a similar profile, except that they were richer in a GM1-like component, and the proportion of GM2-like gangliosides was lower than that in total electric organ. Using a 125I-cholera toxin overlay assay on neuraminidase-treated high-performance thin layer chromatograms, the presence of GM1, GD1a and trace amounts of GD1b and GT1 (or GQ) were detected in D. Tschudii total membranes. Immunocytochemical trechniques showed the co-localization of gangliosides GQ1c/GT1c/GP1c, recognized by the monoclonal antibody Q211, and the AChR at the ventral, innervated face of the electrocyte.