New insights into vitamin D regulation: is there a role for alkaline phosphatase?

PURPOSE

The diagnosis of vitamin D deficiency is based on the determination of total plasma 25-hydroxyvitamin D (25-OHD) concentrations, but the regulation of vitamin D 25-hydroxylation is not a major consideration and very little information is available on this activity. To check what factors could interfere with the activity of vitamin D-25-hydroxylase and thus alter the 25-OHD concentrations, we looked for potential correlations between 25-OHD and results of liver function tests in healthy adults.

METHODS

This single-centre study was retrospective and consisted of evaluating the correlations between 25-OHD and the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP), and bone alkaline phosphatase (BALP) in 349 healthy subjects aged from 18 to 65 years. In particular, in Group 1 (n = 119), we looked for correlations between 25OHD and all liver function tests and in Group 2 (n = 230) the correlation between 25OHD and BALP.

RESULTS

In Group 1, we found no correlation between 25OHD and AST (r =  - 0.03; p = 0.8), ALT (r =  - 0.02; p = 0.91), GGT (r =  - 0.08; p = 0.68), direct bilirubin (r =  - 0.02; p = 0.89), indirect bilirubin (r =  - 0.24; p = 0.21), and total bilirubin (r =  - 0.24; p = 0.21) but one between 25OHD and ALP (r =  - 0.2; p = 0.007); in Group 2, we found a significant negative correlation between 25-OHD and BALP (r =  - 0.2; p = 0.0008).

CONCLUSIONS

The correlations that we found suggest that ALP and BALP might be involved in the regulation of vitamin D-25-hydroxylase activity, but further studies are mandatory to confirm our assumptions.

Cerium and erbium effects on Daphnia magna generations: A multiple endpoints approach

Cerium (Ce, CeCl₃) and Erbium (Er, ErCl₃) are increasingly used in many electronic devices facilitating the alteration of their biogeochemical cycles (e.g. e-waste). Previous surveys stated that their environmental concentrations due to natural or anthropogenic events can reach up to 161 μg/L in ore mine effluent for Ce with a mean water concentration of 0.79 μg/L, and 11.9 μg/L for Er in ore mine effluents with a mean water concentration of 0.004 μg/L. Their potential effects onto aquatic organisms are still relatively unexplored. In this study, long-term multigenerational effects on Daphnia magna were assessed using various exposure times (3, 7, 14, and 21 days) in three generations (F0, F1 and F2). Each generation was exposed to environmental concentrations of Ce and Er (0.54 and 0.43 μg/L, respectively - mean values) and effects included organisms' size, parental reproduction, and survival, determination of reactive oxygen species (ROS), enzymatic activity (superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST)), gene expression of ATP-binding cassette (ABC) transporter, and uptake. Results evidenced that chronic multi-generational exposure of daphnids to Ce and Er reduced survival, growth and reproduction, decreasing ROS, SOD and CAT from F0 to F2. Ce reduced the number of generated offsprings after each generation, while Er delayed the time of offsprings emergence, but not their number. ROS, SOD, CAT and GST evidenced that Er is slightly more toxic than Ce. Up- and downregulation of genes was limited, but Ce and Er activated the ABC transporters. Uptake of Ce and Er decreased through exposure time and generations.

Polymicrobial antibiofilm activity of the membranotropic peptide gH625 and its analogue

This work illustrates a new role for the membranotropic peptide gH625 and its derivative gH625-GCGKKK in impairing formation of polymicrobial biofilms. Mixed biofilms composed of Candida and bacterial species cause frequently infections and failure of medical silicone devices and also show a major drug resistance than single-species biofilms. Inhibition and eradication of biofilms were evaluated by complementary methods: XTT-reduction, and crystal violet staining (CV). Our results indicate that gH625-GCGKKKK, better than the native peptide, strongly inhibited formation of mixed biofilms of clinical isolates of C. tropicalis/S. marcescens and C. tropicalis/S. aureus and reduced the biofilm architecture, interfering with cell adhesion and polymeric matrix, as well as eradicated the long-term polymicrobial biofilms on silicone surface.

Evidence on the effectiveness of mosses for biomonitoring of microplastics in fresh water environment

Mosses are well known as biomonitors of fresh water for metal pollutants, but no studies were reported so far about their ability to intercept plastic particles, although this kind of pollution has become an urgent issue worldwide. In the present work, the interaction between the moss Sphagnum palustre L. cultured in vitro and polystyrene nanoparticles (NPs) was studied for the first time in a laboratory experiment, in the view of using moss transplants for detecting microplastics in fresh water environments. The ability of S. palustre to intercept and retain polystyrene, and the effects of vitality and post-exposure washing on NP retention by moss were tested. Fluorescence microscope observations showed that polystyrene NPs were retained by moss leaves in form of small (the most abundant fraction) and large aggregates. Particle count analysis highlighted that the number of particles increased while increasing the exposure time. Moreover, moss devitalization favored NP accumulation, likely because of cell membrane damages occurred in dead moss material. Post-exposure washing induced a loss of larger aggregates, suggesting that exposure time is a key point to be carefully evaluated in field conditions. These results encourage the use of S. palustre transplants for monitoring microplastics contamination of fresh water environments.

Insulin resistance is associated with impaired cardiac sympathetic innervation in patients with heart failure

AIMS

Insulin resistance (IR) represents, at the same time, cause and consequence of heart failure (HF) and affects prognosis in HF patients, but pathophysiological mechanisms remain unclear. Hyperinsulinemia, which characterizes IR, enhances sympathetic drive, and it can be hypothesized that IR is associated with impaired cardiac sympathetic innervation in HF. Yet, this hypothesis has never been investigated. Aim of the present observational study was to assess the relationship between IR and cardiac sympathetic innervation in non-diabetic HF patients.

METHODS AND RESULTS

One hundred and fifteen patients (87% males; 65 ± 11.3 years) with severe-to-moderate HF (ejection fraction 32.5 ± 9.1%) underwent iodine-123 meta-iodobenzylguanidine ((123)I-MIBG) myocardial scintigraphy to assess sympathetic innervation and Homeostasis Model Assessment Insulin Resistance (HOMA-IR) evaluation to determine the presence of IR. From (123)I-MIBG imaging, early and late heart to mediastinum (H/M) ratios and washout rate were calculated. Seventy-two (63%) patients showed IR and 43 (37%) were non-IR. Early [1.68 (IQR 1.53-1.85) vs. 1.79 (IQR 1.66-1.95); P = 0.05] and late H/M ratio [1.50 (IQR 1.35-1.69) vs. 1.65 (IQR 1.40-1.85); P = 0.020] were significantly reduced in IR compared with non-IR patients. Early and late H/M ratio showed significant inverse correlation with fasting insulinemia and HOMA-IR.

CONCLUSION

Cardiac sympathetic innervation is more impaired in patients with IR and HF compared with matched non-IR patients. These findings shed light on the relationship among IR, HF, and cardiac sympathetic nervous system. Additional studies are needed to clarify the pathogenetic relationship between IR and HF.

Lipovitellin constitutes the protein backbone of glycoproteins involved in sperm-egg interaction in the amphibian Discoglossus pictus

Our knowledge of the molecules that interact with sperm at the egg membrane is restricted to a short list. In the eggs of Discoglossus pictus, fusion with sperm is limited to a differentiated structure, the dimple, offering several advantages for detecting molecules involved in fertilization. Previous studies have identified fucosylated glycoproteins of 200, 260, and 270 kDa located at the surface of the dimple that are able to bind sperm in vitro. Here, we show that dimple glycoproteins and a protein represented by a 120-kDa band released following gel-into-gel SDS-PAGE of both glycoproteins share the same N-terminal amino acid sequence, which itself is similar to the N-termini of Xenopus liver-synthesized vitellogenin (VTG) and the lipovitellin 1. MALDI/MS mass spectrometry indicated that the 120-kDa band is part of both gps 200 and 270/260. A 117-kDa major protein of the egg lysate exhibits the same MALDI/MS spectrum, and LC-MSMS indicates that this is a lipovitellin 1 (DpLIV) that coincides with the 120-kDa band and is responsible for the formation of the 200-270-kDa dimers. Therefore, lipovitellin 1 constitutes the protein backbone of the dimple glycoconjugates. In vitro assays using polystyrene beads coated with DpLIV or with its dimers indicate that significant sperm binding occurs only with DpLIV dimers. In amphibians, VTG is taken up by the oocyte, where it releases lipovitellins destined to form yolk. In Discoglossus, our data suggest that yolk proteins are also synthesized by the oocyte. The dimple forms in the ovulated oocyte following the exocytosis of vesicles that likely expose DpLIVs at their membrane. Indeed, in whole mounts of immunostained eggs, anti-vitellogenin antibodies label only the surface of the dimple.

A transient asymmetric distribution of XNOA 36 mRNA and the associated spectrin network bisects Xenopus laevis stage I oocytes along the future A/V axis

In Xenopus oogenesis, the mechanisms governing the localisation of molecules crucial for primary axis determination have been uncovered in recent years. In stage I oocytes, the mitochondrial cloud (MC) entraps RNAs implicated in germ line specification and other RNAs, such as Xwnt-11 and Xlsirts, that are later delivered to the vegetal pole. Microfilaments and microtubules gradually develop in the cytoplasm, sustaining organelles as well as the MC. At stage III, other mRNAs migrate to the vegetal hemisphere through a microtubule-dependent mechanism. We report here the isolation of a cDNA encoding XNOA 36, a highly conserved protein, whose function is to date not fully understood. The XNOA 36 transcript is abundantly accumulated in stage I oocytes where it decorates a filamentous network. At the end of stage I the transcript gradually segregates in a sector of the oocyte surrounding the MC and opposite the ovarian hylum. Here, XNOA 36 mRNA distributes in a gradient-like pattern extending from a peripheral network towards the interior of the oocyte. This distribution is similar to that of alpha-spectrin mRNA. Both mRNAs are segregated in one half of the 250 microm oocytes, with the MC located between the XNOA 36/alpha-spectrin mRNA-labelled and unlabelled regions. XNOA 36 mRNA localisation was uncoupled from that of alpha-spectrin mRNA by cytochalasin B or ice-nocodazole treatments, suggesting that the two transcripts rely on different mechanisms for their localisation. However, immunolocalisation experiments coupled with in situ hybridisation revealed that the XNOA 36 transcript co-localises with the protein spectrin. This observation, together with the finding that XNOA 36 mRNA co-precipitates with spectrin, indicates that these two molecules interact physically. In conclusion, our data suggest that XNOA 36 mRNA is localized and/or anchored in the oocyte through a cytoskeletal network containing spectrin. The putative implications of this finding are discussed.

Phosphorylation of p27BBP/eIF6 and its association with the cytoskeleton are developmentally regulated in Xenopus oogenesis

p27BBP/eIF6 is an evolutionarily conserved regulator of ribosomal function. It is necessary for 60S biogenesis and impedes improper joining of 40S and 60S subunits, regulated by protein kinase C or Efl1p. No data on p27BBP/eIF6 during early development of Metazoa are available. We studied the distribution, post-translational changes and association with the cytoskeleton of p27BBP/ eIF6 during Xenopus oogenesis and early development. Results indicate that p27BBP/eIF6 is present throughout oogenesis, partly associated with 60S subunits, partly free and with little cytoskeleton bound. During prophase I, p27BBP/eIF6 is detected as a single band of 27-kDa. Upon maturation induced by progesterone or protein kinase C, a serine-phosphorylated 29 kDa isoform appears and is kept throughout development to the neurula stage. Confocal microscopy showed that the distribution of p27BBP/eIF6 and its association with the cytoskeleton varies according to oogenesis stages. Briefly, in stage 6 oocytes, p27BBP/eIF6 has a limited dot-like distribution, and does not co-localize with cytokeratin, whereas upon maturation it spreads throughout the cytoplasm. After fertilization, a large fraction coalesces around cytomembranes and a cytochalasin B-sensitive co-localization with cytokeratin occurs. RNAse removes p27BBP/eIF6 from the cytokeratin fibres. Developmental data suggest a role of p27BBP/eIF6 in controlling ribosomal availability or regulating cross-talk between ribosomes and the cytoskeleton.

PSpice modeling of capacitive microfabricated ultrasonic transducers

Capacitive microfabricated ultrasonic transducers (cMUTs) are the newest and potentially the most promising devices to convert electrical into acoustic signals and vice-versa. These devices are based on the capacitance modulation of a microcondenser which is obtained by microfabrication onto a silicon substrate. The aim of this paper is to describe a PSpice model of the cMUT, based on an analytical distributed model previously reported (IEEE Trans. UFFC 49 (2) (2002) 159-168), which can be used to simulate the performances of a general ultrasound system, either in frequency or time domain. The PSpice model consists of a capacitor with a parallel resistor, which represent the static capacitance and the loss and bias resistances of the transducer, respectively, plus two quadrupoles (GLAPLACE) modeling the mechanical impedance of the membranes and the radiation impedance of the medium. The usefulness of a PSpice model is the possibility to simulate and optimize the cMUT transducers in transmission and reception, along with driving and receiving electronics, in a general ultrasound system. Experimental measurements on a 5 MHz cMUT operating in pulse-echo are in good agreement with model predictions.

Confocal microscopy analysis of the activity of mitochondria contained within the 'mitochondrial cloud' during oogenesis in Xenopus laevis

We have used ratiometric confocal microscopy and three fluorescence techniques to study the distribution and activity of mitochondria in frog oocytes during the early stages of oogenesis. Mitochondria in frog oocytes during oogenesis were characterised by a high ratio in the 'mitochondrial cloud' and perinuclear region and a low ratio in mitochondria freely dispersed within the cytoplasm. We tested whether the high ratio visualised by the three techniques represented mitochondrial membrane potential by perturbing the mitochondrial membrane potential. Carbonyl cyanide p-(trifluoromethyl)phenylhydrazone (FCCP) caused the immediate destruction of the membrane potential, and consequent loss of fluorescence from the membrane-potential-sensitive confocal channel. In contrast, nigericin caused an increase in membrane potential represented by a steady increase in fluorescence ratio. These data demonstrate that mitochondrial activity can be measured during oogenesis in frog oocytes, and suggest that the mitochondrial cloud and perinuclear regions are characterised by highly active mitochondria.

Following passage through the oviduct, the coelomic envelope of Discoglossus pictus (amphibia) acquires fertilizability upon reorganization, conversion of gp 42 to gp 40, extensive glycosylation, and formation of a specific layer

This paper describes the morphological and biochemical changes in Discoglossus pictus coelomic oocyte envelope (CE) following passage through the oviduct. As in other anurans, in this species, the transformation of the envelope into vitelline envelope (VE) leads to the acquisition of fertilizability and involves the cleavage of a glycoprotein. In addition, several features, typical of Discoglossus pictus, were observed. A new layer, VE-D, forms underneath the VE region facing the site of sperm entrance, the dimple. In the VE, arrowhead-like bundles of fibrils are perpendicularly oriented toward the dimple. Ultrastructural observations and staining with UEA-I suggested that VE-D might have a role in supporting sperm penetration into the dimple by orienting VE bundles and exposing sugar residues such as fucose. In 'in vitro' tests, VE binding of sperm occurs only if sperm are exposed to A23187, in agreement with previous data (Campanella et al., 1997: Mol Reprod Dev 47:323-333). Sperm binding occurs all over the VE. Accordingly, extracts of the VE covering the animal or the vegetal hemisphere have the same affinity to lectins (DBA, DSA, GNA, MAA, SBA, SNA, UEA-I, WGA). The CE contains six main glycoproteins. Peptide mapping indicated that during CE transformation into VE, gp 42 shifts to an apparent M(r) of 40 and gp 61 is converted to an apparent M(r) of 63 kDa. Lectin blot analyses showed extensive changes in cross-reactivity of most glycoproteins during the CE-->VE transition. The fact that DBA and UEA-I stain gp 63 rather than gp 61 and that this change is related only to gp 63, suggested that O-glycosylation and terminal fucose might be acquired by gp 63 in preparation of fertilization. Gp 63 has recently been cloned (Vaccaro et al., submitted) and shown to exhibit high homology to Xenopus gp 69/64, a VE sperm ligand (Tian et al., 1997a: J. Cell Biol. 136: 1099-1108; Tian et al., 1997b: Dev Biol 187:143-153), and to ZP2 of mammals.

Characterization of piezoceramic rectangular parallelepipeds by means of a two-dimensional model

The characterization of piezoelectric resonators is a field of intense scientific work; moreover, clear and accepted IEEE and IEC Standards have been published, showing the concepts and routes to perform the complete characterization of piezoelectric resonators. All of the accepted procedures define some resonator geometries, each of them related with a set of parameters, that can be obtained following resonance measurements at the corresponding resonance frequencies. The basis of the standards is the existence, for each geometry, of well-defined modes that have been analytically solved. The development of multi-dimensional models of the waves' propagation in piezoceramic materials opens the possibility of characterizing piezoelectric resonators with geometries different from those recommended in the standards. In this paper, a two-dimensional model, which takes into account the mechanical and dielectric losses, has been used to characterize piezoceramics with the shape of a regular parallelepiped. A set of elastic, dielectric, and piezoelectric parameters, which are useful for piezoelectric transducer design, can be obtained. For a given sample, the measured input electrical impedance is used to obtain the parameters by means of a fitting process with the corresponding model output. The results obtained with low and high loss materials show that the parameters found have values similar to those obtained following the procedures and geometries recommended by the standards. This procedure permits the characterization of materials when the manufacturing procedure does not allow the fabrication of the shapes recommended by the standards, making it a useful tool for transducer manufacturers and material scientists.

A matrix model of the axle vibration of a piezoelectric motor

In this work, a matrix model of the axle vibration of a piezoelectric motor is proposed. The stator of this motor is composed of a thin piezoelectric membrane and a steel axle fitted at the center of the membrane. The rotor consists of a cylinder-shaped permanent magnet, pressed in contact with the other end of the axle by means of the magnetic forces. A travelling wave is excited in the membrane by using four electrodes and four, properly delayed, driving signals. The rotating flexural displacement of the membrane produces a wide precessional motion of the axle. In this way, a continuous slipping takes place between the axle and the rotor, and therefore, a torque is transmitted to the rotor. In this paper, the precessional motion of the axle is modeled as the composition of two transverse vibrations belonging to two perpendicular planes passing through the axle. The axle, vibrating in its transverse mode, is modeled as a two-port system: the input is the bending moment supplied by the membrane, and the output is the transverse force at the terminal end of the axle. With this model, we have computed the trasmission transfer function as a function of frequency, and the transversal displacement along the axle at its resonance frequency. The computed results are in reasonable agreement with experimental interferometric measurements carried out on a prototype.

alpha-Spectrin has a stage-specific asymmetrical localization during Xenopus oogenesis

Xenopus oocyte organization largely depends upon the cytoskeleton distribution, which is dynamically regulated during oogenesis. An actin-based cytoskeleton is present in the cortex starting from stage 1. At stages 4-6, a complex and polarized cytoskeleton network forms in the cytoplasm. In this paper, we studied the distribution of spectrin, a molecule that has binding sites for several cytoskeletal proteins and is responsible for the determination of regionalized membrane territories. The localization of alpha-spectrin mRNA was analyzed during Xenopus oogenesis by in situ hybridization on both whole mount and sections, utilizing a cDNA probe encoding a portion of Xenopus alpha-spectrin. Furthermore, an antibody against mammalian alpha-spectrin was used to localize the protein. Our results showed a stage-dependent mRNA localization and suggested that spectrin may participate in the formation of specific domains in oocytes at stages 1 and 2 and 4-6. Mol. Reprod. Dev. 55:229-239, 2000.

Two-dimensional modelling of multifrequency piezocomposites

The multifrequency composites of 2-2 connectivity modelled in this work are made with groups of piezoelectric elements of different lateral dimensions, periodically reproduced in the structure. These composites have potential to improve the performances of standard piezoelectric composites with the same materials and ceramic fraction, on account that they have different resonators coupled mechanically along the structure. A one-dimensional model was developed to study their performances in a first approximation. In order to obtain a design model, a two-dimensional model, previously used to describe multielement array transducers, has been extended to the case of 2-2 polymer-piezoceramic composites. Several composite samples, having piezoceramic strips with different width-to-thickness ratios, have been built, and their resonance behaviour compared with the model prediction. Finally, the model has been extended to the case of 2-2 multifrequency composites. For multifrequency composites having in the same composite structure two or three piezoceramic strips with different lateral dimensions, the comparison between experimental and predicted results shows good agreement. The model has been used to optimise a double composite in comparison with a standard one with the same volume fraction and constituents.

Analysis of the radial symmetrical modes of thin piezoceramic rings

In this work, the radial symmetric vibration modes of thin piezoceramic rings have been analyzed by means of a previously proposed theoretical model. Both the resonance frequencies and the effective electromechanical coupling factor (k(eff)), as a function of the aspect ratio G between the inner and outer radii of the ring, were computed. The results have shown that the disk structure (G-->0) has only one radial symmetrical mode (with its harmonics), but, for the ring structure (G-->1), two different modes are clearly distinguished: the ring mode, which has no harmonics, and a width-like mode, with its harmonics. Moreover, the results show that the ring structure can be assumed to be definitely reached for G>0.6. An analysis of the material coupling factor in the ring geometry is reported as well.

Specific glycoconjugates are present at the oolemma of the fertilization site in the egg of Discoglossus pictus (Anurans) and bind spermatozoa in an in vitro assay

In the egg of the anuran Discoglossus pictus, the site of fertilization is restricted to the central portion of an animal hemisphere indentation (the dimple). Previous studies showed that the acrosome reaction of D. pictus sperm is triggered in the jelly, and yet sperm arrive at the dimple surface with the plasma membrane at an early stage of vesiculation. Reactivity of the dimple surface with specific lectins suggests that fucose might be utilized as a marker of glycoproteins located at the dimple surface. In this paper, proteins of the egg surface were labeled with the membrane impermeable sulfo-NHS-biotin. Four main bands of 200, 230, 260, and 270 kDa labeled only at the dimple surface, although they were detected in the cortex of the whole egg. The 270-kDa band reacted with Galanthus nivalis agglutinin only in the cortex of the dimple, suggesting that this band is differently glycosylated according to its localization. The alpha-l-fucose-specific lectin Ulex europaeus agglutinin I was utilized both in lectin blotting and in affinity chromatography and cross-reacted with the 200- and 270/260-kDa bands. Furthermore, two polypeptides were obtained by exposure of intact eggs to lysylendoproteinase C. They were also reactive to Ulex europaeus agglutinin I. The 200- and 270/260-kDa bands were eluted from the acrylamide gels and adsorbed to polystyrene beads. An assay for sperm binding to 200-kDa glycoprotein-bound beads was developed. Sperm stuck to the beads before but not after Ca-ionophore treatment. When the beads were coated with the 270/260-kDa glycoproteins, binding occurred after ionophore treatment. In these assays, the 200- and 270/260-kDa glycoproteins competitively inhibited sperm binding to the beads coated with the corresponding glycoprotein. These results indicate that the assayed glycoproteins, located either in the glycocalyx or in the plasma membrane of the fertilization site, are involved in sperm binding.

A novel protein cross-reacting with antibodies against spectrin is localised in the nucleoli of amphibian oocytes

Cytoskeletal proteins such as actin and myosin are important constituents of the nucleoplasm. Spectrin is an actin binding protein typically related to plasma membrane; recently, it has been found that it is widespread and forms distinct membrane protein domains in such organelles as the Golgi. In this paper, the large germinal vesicle of amphibian oocytes was chosen as a particularly suitable system to investigate the presence and location of spectrin in the nucleus. We manually isolated the germinal vesicles of both Discoglossus pictus and Xenopus laevis oocytes, and processed them for SDS-PAGE, immunoblotting and immunoprecipitation. By the use of an antibody against the general form of brain beta spectrin (betaIIsigma1) and of an anti-alpha brain spectrin (alphaIIsigma*), a band of 230 kDa was identified as a nuclear spectrin-like molecule. Moreover the 230 kDa protein was extracted from the nuclei by 1 M KCl, similarly to spectrin in other systems. In oocyte sections and nuclear spreads incubated with anti-alphaIIsigma* and/or anti-betaIIsigma1 antibodies, the immunostain was localised in the nucleoplasm and in the outer shell of the round bodies abundantly present in the germinal vesicle. Sections of the same oocytes, stained with a monoclonal antibody against nucleolar fibrillarin and anti-alphaIIsigma*, showed co-localisation of the two antibodies. It was concluded that, in the germinal vesicle of amphibian oocytes, a spectrin-like molecule is a part of the outer shell of nucleoli. It is hypothesised that spectrin, together with actin, might be instrumental in keeping nucleoli attached to the inner nuclear membrane, as nucleoli migrate during oogenesis to the inner aspect of the nuclear envelope, where they are stably kept until the end of their growth. Furthermore, these results strongly suggest that the 230 kDa band might comprise both an alpha and a beta chain of the same apparent molecular mass, thus constituting a novel form of a spectrin-like molecule.

Sperm-egg interaction in the painted frog (Discoglossus pictus): an ultrastructural study

The ultrastructure of sperm changes and penetration in the egg was studied in the anuran Discoglossus pictus, whose sperm have an acrosome cap with a typical tip, the apical rod. The first stage of the sperm apical rod and acrosome reaction (AR) consists in vesiculation between the plasma membrane and the outer acrosome membrane. The two components of the acrosome cap are released in sequence. The innermost component (component B) is dispersed first. The next acrosome change is the dispersal of the outermost acrosome content (component A). At 30 sec postinsemination, when the loss of component B is first observed, holes are seen in the innermost jelly coat (J1), surrounding the penetrating sperm. Therefore, this acrosome constituent might be related to penetration through the innermost egg investments. At 1 min postinsemination, during sperm penetration into the egg, a halo of finely granular material is observed around the inner acrosome membrane of the spermatozoon, suggesting a role for component A at this stage of penetration. Gamete-binding and fusion take place between D1 (the egg-specific site for sperm interaction) and the perpendicularly oriented sperm. Spermatozoa visualized at their initial interaction (15 sec postinsemination) with the oolemma are undergoing vesiculation. The first interaction is likely to occur between the D1 glycocalyx and the plasma membrane of the hybrid vesicles surrounding the apical rod. As fusion is observed between the internal acrosome membrane and the oolemma, it can be postulated that gametic interaction might be followed by fusion of the latter with the apical rod internal membrane that extends posteriorly into the inner acrosome membrane. Insemination of the outermost jelly layer (J3) dissected out of the egg, and observations of the ultrastructural changes of spermatozoa in this coat, indicate that J3 rather than the vitelline coat (VC) induces the AR. Interestingly, at the late postinsemination stage, VC fibrils are seen crosslinking the inner acrosome membrane. The role of this binding is here discussed.

Antispectrin antibodies stain the oocyte nucleus and the site of fertilization channels in the egg of Discoglossus pictus (Anura)

In Discoglossus pictus eggs, only the dimple contains ionic channels active at fertilization; in particular, chloride channels are found in the central portion of the dimple, which is also the site of sperm penetration. Moreover the dimple hosts an imposing cytoskeleton, consisting of a cortical network and bundles of microfilaments extending from the microvilli. Since spectrin cross links actin and is connected through ankyrin to anion transporters in the plasma membrane of erythrocytes as well as to anion channels in other cells, we studied, in D. pictus egg, the relationship between the localization of spectrin and the high polarization of ionic channels and cytoskeletal organization. By means of immunocytochemistry, we localized spectrin exclusively in the egg dimple. In an attempt to trace back the source of spectrin localization, we immunostained sections of D. pictus ovary and localized spectrin in the nuclei of previtellogenic oocytes, where actin is also present. Antispectrin staining remained until germinal vesicle breakdown. By contrast, a cortical localization was found only when the oocytes divided into two hemispheres and into the germinative area (GA), which, after germinal vesicle breakdown, gives rise to the dimple. At this stage the antispectrin signal was particularly strong in the GA. Using Rho-pialloidin, we also established that spectrin is generally present where F-actin is found. However, spectrin and F-actin do not have the same pattern of fluorescence. In conclusion, our data suggest that spectrin may play a role in oocyte and egg polarity. In eggs, it could be instrumental in anchoring to the cytoskeleton membrane proteins such as receptors and ionic channels, including chloride-permeable channels.