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L Santella

Publications and source records attributed to L Santella.

At least 19 recordsLinked to original sources
PubMed2005

The cell cycle: a new entry in the field of Ca2+ signaling.

Ca2+ signaling plays a crucial role in virtually all cellular processes, from the origin of new life at fertilization to the end of life when cells die. Both the influx of external Ca2+ through Ca2+-permeable channels and its release from intracellular stores are essential to the signaling function. Intracellular Ca2+ is influenced by mitogenic factors which control the entry and progression of the cell cycle; this is a strong indication for a role of Ca2+ in the control of the cycle, but surprisingly, the possibility of such a role has only been paid scant attention in the literature. Substantial progress has nevertheless been made in recent years in relating Ca2+ and the principal decoder of its information, calmodulin, to the modulation of various cycle steps. The aim of this review is to critically discuss the evidence for a role of Ca2+ in the cell cycle and to discuss Ca2+-dependent pathways regulating cell growth and differentiation.

Animals↗
PubMed2003

Ca2+ signalling and membrane current activated by cADPr in starfish oocytes.

Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+](i)) in a variety of cell types, including immature oocytes from the starfish Astropecten auranciacus. In this study, we employed confocal laser scanning microscopy and voltage clamp techniques to investigate the source of the cADPr-elicited Ca2+ wave originating from the cortical Ca2+ patches we have described previously. The Ca2+ swing was accompanied by a membrane current with a reversal potential of approximately +20 mV. Decreasing external Na+ almost abolished the current without affecting the Ca2+ response. Removal of extracellular Ca2+ altered neither the Ca2+ transient nor the ionic current, nor did the holding potential exert any effect on the Ca2+ wave. Both the Ca2+ response and the membrane current were abolished when BAPTA, ruthenium red or 8-NH(2)-cADPr were preinjected into the oocytes, while perfusion with ADPr did not elicit any [Ca2+](i) increase or ionic current. However, elevating [Ca2+](i) by uncaging Ca2+ from nitrophenyl- (NP-EGTA) or by photoliberating inositol 1,4,5-trisphosphate (InsP(3)) induced an ionic current with biophysical properties similar to that elicited by cADPr. These results suggest that cADPr activates a Ca2+ wave by releasing Ca2+ from intracellular ryanodine receptors and that the rise in [Ca2+](i) triggers a non-selective monovalent cation current that does not seem to contribute to the global Ca2+ elevation.

Animals↗
PubMed2003

Activated M-phase-promoting factor (MPF) is exported from the nucleus of starfish oocytes to increase the sensitivity of the Ins(1,4,5)P3 receptors.

Starfish oocytes that are extracted from the ovaries are arrested at the prophase of the first meiotic division. At this stage of maturation, they are characterized by a large nucleus called the germinal vesicle. Meiosis resumption (maturation) can be induced in vitro by adding the hormone 1-methyladenine (1-MA) to the seawater in which the oocytes are suspended. Earlier work in our laboratory had detected Ca(2+) increases in both the cytoplasm and the nucleus of the oocytes approx. 2 min after the 1-MA challenge. The nuclear Ca(2+) increase was found to be essential for the continuation of the meiotic cycle, since the injection of bis-(o-aminophenoxy)ethane- N,N,N',N' -tetra-acetic acid (BAPTA) into the nuclear compartment completely blocked the re-initiation of the cell cycle. We have recently confirmed, using confocal microscopy, that the cytoplasmic and nuclear Ca(2+) pools are regulated independently and that the nuclear envelope in starfish oocytes is not freely permeated by the Ca(2+) wave that sweeps across the nuclear region. Studies by others have shown that the sensitivity of the Ins(1,4,5) P (3) (IP(3)) receptors (IP(3)Rs) to IP(3) increases during oocyte maturation, so that they release progressively more calcium in response to the injection of IP(3), as maturation proceeds. We have now shown that the increased sensitivity of the IP(3)Rs may depend on the activation of the cyclin-dependent kinase, MPF (M-phase-promoting factor) that occurs in the nucleus. MPF does not directly phosphorylate IP(3)Rs but phosphorylates instead the actin-binding protein actin depolymerization factor (ADF)/cofilin.

Actin Depolymerizing Factors↗
PubMed2001

Generation, control, and processing of cellular calcium signals.

In the course of evolution, Ca2+ has emerged as the most versatile intracellular messenger. Its concentration within cells is controlled by reversible binding to specific classes of proteins that act as Ca2+ sensors to decode its information before passing it on to targets. The decoding operation is based on specific conformational changes in the sensor proteins. Other proteins intrinsic to membranes simply control Ca2+ concentration without processing its message, by transporting it across membrane boundaries. They are located in the plasma membrane and in the membranes of the organelles (the endo(sarco)plasmic reticulum, the mitochondria, the nuclear envelope), which play distinctive roles in the cellular homeostasis of Ca2+. Ca2+ is an ambivalent signaling agent. It carries information to virtually all processes important to cell life (e.g., it couples excitation to contraction, secretion, gene transcription, and controls enzyme activity through protein phosphorylation-dephosphorylation), but also transmits signals that promote the programmed demise of cells. When escaping control, Ca2+ also precipitates toxic cell death.

Animals↗
PubMed2001

NAADP+ initiates the Ca2+ response during fertilization of starfish oocytes.

We have explored the role of the recently discovered second messenger nicotinic acid adenine nucleotide phosphate (NAADP+) in Ca2+ swings that accompany the fertilization process in starfish oocytes. The injection of NAADP+ deep into the cytoplasm of oocytes matured by the hormone 1-methyladenine (1-MA), mobilized Ca2+ exclusively in the cortical layer, showing that the NAADP+-sensitive Ca2+ pool is restricted to the subplasma membrane region of the cell. At variance with this, InsP3 initiated the liberation of Ca2+ next to the point of injection in the center of the cell. The initial cortical Ca2+ liberation induced by NAADP+ was followed by a spreading of the Ca2+ wave to the remainder of the cell and by a massive cortical granule exocytosis similar to that routinely observed on injection of InsP3. A striking difference in the responses to NAADP+ and InsP3 was revealed by the removal of the nucleus from immature oocytes, i.e., from oocytes not treated with 1-MA. Whereas the Ca2+ response and the cortical granule exocytosis induced by NAADP+ were unaffected by the removal of the nucleus, the Ca2+ response promoted by InsP3 was significantly slowed. In addition, the cortical granule exocytosis was completely abolished. When enucleated oocytes were fertilized, the spermatozoon still promoted the Ca2+ wave and normal cortical exocytosis, strongly suggesting that the Ca2+ response was mediated by NAADP+ and not by InsP3. InsP3-sensitive Ca2+ stores may mediate the propagation of the wave initiated by NAADP+ since its spreading was strongly affected by removal of the nucleus.

Animals↗
PubMed2000

Breakdown of cytoskeletal proteins during meiosis of starfish oocytes and proteolysis induced by calpain.

Meiosis reinitiation in starfish oocytes is characterized by Ca(2+) transients in the cytosol and in the nucleus and is accompanied by the disassembly of the nuclear envelope, a process which is likely to be mediated by the cleavage of selected proteins. We have used mass spectrometry analysis (mass profile fingerprinting) on 2D polyacrylamide gels of extracts of oocytes in which meiosis resumption was induced by 1-methyladenine and have identified five proteins that were specifically degraded: alpha-tubulin, lamin B, dynamin, and two kinds of actin. They are all components of the cytoskeleton or associated with it. We then investigated whether calpain, which is activated by the increase in cell Ca(2+), could cleave the same proteins that became degraded under the influence of 1-methyladenine and thus be involved in nuclear membrane breakdown. The investigation was prompted by the finding that microinjection of calpain into the nuclei of prophase arrested oocytes induced meiosis in the absence of 1-methyladenine. Incubation of prophase arrested (disrupted) oocytes with calpain produced a 2D gel protein pattern in which some of the degradation products coincided with those seen in oocytes challenged with 1-methyladenine.

Actins↗
PubMed2000

Nicotinic acid adenine dinucleotide phosphate-induced Ca(2+) release. Interactions among distinct Ca(2+) mobilizing mechanisms in starfish oocytes.

An intracellular mechanism activated by nicotinic acid adenine dinucleotide phosphate (NAADP(+)) contributes to intracellular Ca(2+) release alongside inositol 1,4,5-trisphosphate (Ins-P(3)) and ryanodine receptors. The NAADP(+)-sensitive mechanism has been shown to be operative in sea urchin eggs, ascidian eggs, and pancreatic acinar cells. Furthermore, most mammalian cell types can synthesize NAADP(+), with nicotinic acid and NADP(+) as precursors. In this contribution, NAADP(+)-induced Ca(2+) release has been investigated in starfish oocytes. Uncaging of injected NAADP(+) induced Ca(2+) mobilization in both immature oocytes and in oocytes matured by the hormone 1-methyladenine (1-MA). The role of extracellular Ca(2+) in NAADP(+)-induced Ca(2+) mobilization, which was minor in immature oocytes, was instead essential in mature oocytes. Thus, the NAADP(+)-sensitive Ca(2+) pool, which is known to be distinct from those sensitive to inositol 1,4,5-trisphosphate or cyclic ADPribose, apparently migrated closer to (or became part of) the plasma membrane during the maturation process. Inhibition of both Ins-P(3) and ryanodine receptors, but not of either alone, substantially inhibited NAADP(+)-induced Ca(2+) mobilization in both immature and mature oocytes. The data also suggest that NAADP(+)-induced Ca(2+) mobilization acted as a trigger for Ca(2+) release via Ins-P(3) and ryanodine receptors.

Adenine↗
PubMed1999

Cortical granule translocation during maturation of starfish oocytes requires cytoskeletal rearrangement triggered by InsP3-mediated Ca2+ release.

Cortical granules (secretory vesicles located under the cortex of mature oocytes) release their contents to the medium at fertilization. Their exocytosis modifies the extracellular environment, blocking the penetration of additional sperm. The granules translocate to the surface during the maturation process, and it has been suggested that they move to the cortex via cytoskeletal elements. In this paper we show that the increase in intracellular Ca2+, which the maturing hormone 1-methyladenine (1-MA) induces in starfish through the activation of inositol 1,4, 5-trisphosphate (InsP3) receptors, triggers changes in filamentous actin, which then direct the correct movement and reorientation of the cortical granules and the elevation of the fertilization envelope.

Adenine↗
PubMed1998

Separate activation of the cytoplasmic and nuclear calcium pools in maturing starfish oocytes.

The dynamics of the cytoplasmic and nuclear Ca2+ pools in starfish oocytes arrested at the prophase of the first meiotic division or after induction of meiosis by 1-methyladenine (1-MA) have been studied by confocal microscopy. A 70 kDa fluorescent Ca2+ indicator has been injected in either the cytoplasm or the nucleus, and shown to remain restricted to the compartment of injection. 1-MA induced a first Ca2+ transient in the cytosol, followed by a nuclear transient, and eventually by a second cytosolic transient. The latter failed to occur if the nuclear peak was suppressed. This required the nuclear injection of antagonists of the inositol 1,4,5-trisphosphate (InsP3) and cyclic-ADPribose (cADPr) Ca2+ channels, showing that both channel types were active in the inner envelope membrane. The nuclear injection of the Ca2+ channel antagonists affected the process of meiosis reinitiation: in about one third of the injected oocytes no breakdown of the nuclear envelope (GVBD) was observed. In the others, even if GVBD eventually occurred, the intermixing of the nucleoplasm and cytoplasm was inhibited.

Adenine↗
PubMed1998

The role of calcium in the cell cycle: facts and hypotheses.

The regulation of cell cycle progression is a complex process which involves kinase cascades, protease action, production of second messengers and other operations. Increasing evidence now compellingly suggests that changes in the intracellular Ca2+ concentration may also have a crucial role. Ca2+ transients occur at the awakening from quiescence, at the G/S transition, during S-phase, and at the exit from mitosis. They may lead to the activation of Ca2+ binding proteins like S-100, but the key decoder of the Ca2+ signals in the cycle is calmodulin. Activation of calmodulin leads to the stimulation of protein kinases, i.e., CaM-kinase II, and of the CaM-dependent protein phosphatase calcineurin. Ample evidence now indicates the G/S transition, the progression from G2 to M, and the metaphase/anaphase transition as specific points of intervention of CaM-kinase II. Another attractive possibility for the role of Ca2+ in the cycle is through the activation of the Ca(2+)-dependent protease calpain: other proteases (e.g., the proteasome) have been suggested to be responsible for the degradation of some of cyclins, which is essential to the progression of the cycle. One of the cyclins, however, (D1) is instead degraded by calpain, which has been shown to promote both mitosis and meiosis when injected into somatic cells or oocytes.

Animals↗
PubMed1997

Association of calmodulin with nuclear structures in starfish oocytes and its role in the resumption of meiosis.

The resumption of meiosis in prophase-arrested starfish oocytes is induced by the hormone 1-methyladenine, which has been shown previously to induce a calcium transient in the nucleus which at this stage is called the germinal vesicle. This transient precedes the breakdown of the germinal vesicle (GVBD). Experiments were performed to establish whether nuclear calmodulin (CaM) was involved in the progression of the meiotic cycle. CaM antagonists, antibodies, and an inhibitory peptide corresponding to the CaM-binding domain of myosin-light-chain kinase have been injected into the nucleus of prophase-arrested starfish oocytes. The antagonists failed to affect the final response to 1-methyladenine, i.e. GVBD, although two antagonists delayed it, whereas the peptide inhibitor and the antibodies completely inhibited it. The antibodies suppressed the nuclear Ca2+ spikes that were shown by previous work to be induced by the photoreleasing of caged adenosine 3',5'-(cyclic)diphosphate ribose in the germinal vesicle. Immunofluorescence staining of isolated starfish oocyte nuclei with CaM antibodies showed CaM in the envelope and in the nucleolus. Immunogold labelling of oocytes revealed aggregates of CaM and of a 36-kDa protein, of the heterogeneous ribonucleoprotein particles (hnRNP), in electron-dense hnRNP in the nuclear matrix. 1-Methyladenine induced the disappearance of these hnRNP from the nucleoplasm and the translocation of CaM and the 36-kDa protein previously associated with them to the cytoplasm, prior to the breakdown of the nuclear envelope.

Adenine↗
PubMed1997

Calcium signalling in the cell nucleus.

The First European Conference on Calcium Signalling in the Cell Nucleus took place in Baia Paraelios, Calabria, Italy, from 4-8 October 1997. It was organized by O. Bachs, E. Carafoli, P. Nicotera and L. Santella (local organizers, G. Bagetta and D. Rotiroti) and attended by about 90 specialists. The scientific content was very high and the discussions were particularly intense. Considering that the area is famous for its controversies, one could perhaps have expected aggressive overtones. Instead, in spite of the liveliness of the discussions, the atmosphere was congenial and constructive. The controversies have not disappeared, but a better understanding of some of their origins is now well under way.

Calcium↗
PubMed1997

Effects of 1-methyladenine on nuclear Ca2+ transients and meiosis resumption in starfish oocytes are mimicked by the nuclear injection of inositol 1,4,5-trisphosphate and cADP-ribose.

The treatment of prophase-arrested starfish oocytes with the hormone 1-methyladenine (1-MA) induces the elevation of Ca2+ in both the cytoplasm and the germinal vesicle (nucleus), and is followed by the resumption of meiosis. The injection of the modulators of the intracellular Ca2+ channels inositol 1,4,5-trisphosphate (InsP3) or cyclic adenosine diphosphate ribose (cADPr) into the germinal vesicle promoted meiosis resumption in the absence of 1-MA in about 50% of the oocytes. Caged InsP3 or caged cADPr were injected into the nuclei of oocytes together with the Ca2+ indicator calcium green dextran; their photoreleasing elicited nuclear calcium spikes which, in the case of cADPr, had repetitive behaviour. The spikes were abolished by the nuclear injection of antagonists or antibodies to the InsP3 or cADPr-sensitive Ca2+ channels. cADPr-modulated channels were localized on the membranes of the nuclear envelope using specific antibodies conjugated with IgG-gold complexes.

Adenine↗
PubMed1997

Calcium signaling in the cell nucleus.

Regulation of Ca2+ in the nucleus is a debated issue, essentially due to the presence in the envelope of the pores, which are large enough to permit the passive traffic of small molecules like Ca2+. Work with a number of cell systems has shown that Ca2+ diffuses freely in and out of the nucleus, whereas other studies have suggested instead that the nuclear envelope could become an efficient Ca2+ filter: electrophysiological work has shown that it could become impermeable to ions, and persistent nucleus cytoplasmic Ca2+ gradients have been documented in various cell types. The problem of the control of nuclear Ca2+ thus is still open: mechanisms for gating of the pores, based on the state of depletion of the cell Ca2+ stores, have been proposed. Irrespective of the mechanisms for possible pore gating, a final picture on the traffic of Ca2+ in and out of the nucleus must also include the Ca2+ pump as well as the InsP3 and cyclic ADP ribose-modulated Ca2+ channels in the envelope. The channels can be activated by their ligands from inside the nucleus, producing Ca2+ transients in the nucleoplasm; the machinery for producing InsP3 has been documented in the envelope. Most Ca2+-sensitive nuclear functions are jointly modulated by Ca2+ and calmodulin: calmodulin-dependent kinases and the calmodulin-dependent phosphatase calcineurin have been documented in the nucleus. An interesting case for the modulation of intranuclear processes by calmodulin-dependent kinases is that of immediate early genes, i.e., CREB. Other Ca2+-modulated nuclear processes are calmodulin independent: chief among them is the intranucleosomal cleavage of chromatin and the fragmentation of nuclear proteins during apoptosis.

Animals↗
PubMed1994

Reinitiation of meiosis in starfish oocytes requires an increase in nuclear Ca2+.

Here we report that an increase in nuclear Ca2+ is hormonally regulated and is required for reinitiation of meiosis in starfish oocytes. We have shown in Asterina pectinifera that a Ca2+ transient and a baseline increase of Ca2+ occur both in the cytoplasm and in the nucleus. These increases are in response to 1-methyladenine (1-MA), the hormone responsible for the induction of meiotic maturation. The Ca2+ transients are not necessary for the reinitiation of meiosis. However, blocking the baseline increase in nuclear Ca2+ blocks both the nuclear envelope breakdown (NEBD) and the continuation of meiosis.

Adenine↗
PubMed1994

Fertilization of sea urchin eggs in space and subsequent development under normal conditions.

Sea urchin eggs are generally considered as most suitable animal models for studying fertilization processes and embryonic development. In the present study, they are used for determining a possible role of gravity in fertilization and the establishment of egg polarity and the embryonic axis. For this purpose, eggs of the particularly well known and suitable species Paracentrotus lividus have been automatically fertilized under microgravity conditions during the Swedish sounding rocket flights MASER IV and MASER V. It turns out, that fertilization "in Space" occurs normally and that subsequent embryonic and larval development of such eggs, continued on the ground, is normal, leading to advanced pluteus stages.

Animals↗
PubMed1992

Tight junctions and cavitation in the human pre-embryo.

In the human morula, tight junctions are found between all cell pairs, at all levels of cellular apposition, associated with underlying masses of microfilaments. In cavitating morula, lanthanum tracer gained access to the intracellular spaces, except at the intersections with nascent extracellular cavities, marking the first assembly of zonulae occludentes. Presumptive trophectoderm cells contained vacuoles and larger cavities often associated with secondary lysosome-like bodies. Since the vacuoles and intracellular and extracellular cavities contain electron-dense polygranules of about 23 nm diameter, they may have common origins. In trophectoderm cells of the early blastocytes, the large intracellular vacuoles and cavities were absent, and the zonulae occludentes were located apically. Mechanisms for nascent blastocoele formation are discussed.

Blastocyst↗