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L Santella

Publications and source records attributed to L Santella.

27 records · Page 2Linked to original sources
PubMed1992

Fertilization envelope in diapause eggs of Pontella mediterranea (Crustacea, Copepoda).

The sequence and timing of morphological changes during envelope formation was followed in diapause eggs of Pontella mediterranea (Crustacea, Copepoda). The multilayer coat enveloping these eggs resulted from the exocytosis of 4 types of cortical vesicles that sequentially released their contents in the perivitelline space. These included small high-density vesicles (hDV) with electron-dense material, vesicles (V) with dense ring granules and a uniform matrix contained within the same compartment, large high-density (HDV) vesicles, and large moderately dense (MDV) vesicles. All of these cortical vesicles were present in newly spawned, fertilized eggs. Their exocytosis resulted from egg activation. One of these cortical vesicles (V) was similar in morphology to the intracisternal granules precursors of endogenous yolk. Intracisternal granules, characteristic of previtellogenic oocytes of many crustaceans, were present in previtellogenic oocytes of P. mediterranea but disappeared in later stages of oocyte development once yolk formation was completed. We discuss the role of cortical vesicles in the formation of the complex extracellular coat enveloping copepod diapause eggs.

Adaptation, Physiological↗
PubMed1992

Is the human oocyte plasma membrane polarized?

Using scanning electron microscopy, we have shown that the plasma membrane of the human metaphase II oocyte is organized in evenly spaced, short microvilli of 1-3 microns in length. In contrast to other mammals studied to date, there is no microvillus-free area overlying the metaphase spindle and there were no other indications of polarization at this level of organization. Functional polarity of the plasma membrane, studied using localized microsurgery of the zona pellucida followed by insemination, suggests that sperm fusion and entry in the human may occur anywhere over the oocyte surface. Aged oocytes and those exposed to acidic Tyrode's solution had surfaces which were not homogeneously covered by microvilli. Oocytes exposed to a sucrose solution and subzonally injected with spermatozoa showed evidence of partial cortical granule exocytosis.

Cell Membrane↗
PubMed1991

Intercellular communication in the early human embryo.

A preliminary study on intercellular communicative devices in the early human embryo has been made using dye-coupling techniques and electron microscopy (EM). Lucifer yellow injected into single blastomeres of embryos at the 4-cell stage up to the late morula stage did not spread to neighbouring cells, indicating that gap junctions and cytoplasmic bridges are not significant pathways for information transfer. Dye spread was first observed in the blastocyst stage, where trophectoderm cells and inner mass cells were shown to be in communication through gap junctions. Studies at the EM level confirmed this finding. Tight junctions and desmosome-like structures, apparent from the 6-cell stage onward, were located both peripherally and centrally and were initially nonzonular. The role of intercellular devices in the primary differentiation of the human embryo is discussed.

Blastocyst↗
PubMed1991

Gap-junctional permeability in early and cleavage-arrested ascidian embryos.

Using the whole-cell voltage clamp technique, we have studied junctional conductance (Gj), and Lucifer Yellow (LY) coupling in 2-cell and 32-cell ascidian embryos. Gj ranges from 17.5 to 35.3 nS in the 2-cell embryo where there is no passage of LY, and from 3.5 to 12.2 nS in the later embryo where LY dye spread is extensive. In both cases, Gj is independent of the transjunctional potential (Vj). Manually apposed 2-cell or 32-cell embryos established a junctional conductance of up to 10 nS within 30 min of contact. Furthermore, since we did not observe any significant number of cytoplasmic bridges at the EM and Gj is sensitive to octanol, it is probable that blastomeres in the 2-cell and 32-cell embryos are in communication by gap junctions. In order to compare Gj in the two stages and to circumvent problems of cell size, movement and spatial location, we used cytochalasin B to arrest cleavage. Gj in cleavage-arrested 2-cell embryos ranged from 25.0 to 38.0 nS and remained constant over a period of 2.5 h. LY injected into a blastomere of these arrested embryos did not spread to the neighbour cell until they attained the developmental age of a 32- to 64-cell control embryo. Our experiments indicate a change in selectivity of gap junctions at the 32-cell stage that is not reflected by a macroscopic change in ionic permeability.

Animals↗
PubMed1989

Cold shock induces actin reorganization and polyspermy in sea urchin eggs.

The effect of low temperature on the cortical actin system and polyspermy in sea urchin eggs was studied. Eggs cold-shocked at 3 degrees C for 1 hour formed a cortical system of polymerized actin and were polyspermic when fertilized. These effects were completely reversible following a 7-20 minute recovery period at room temperature. The present data raises the possibility that actin, or components of the egg cytoskeleton, regulate sperm entry in sea urchin eggs.

Actins↗
PubMed1985

Sperm-oocyte interaction in the sea-urchin.

A study was made of the electrical and morphological changes in the sea-urchin oocyte during interaction with spermatozoa. The first event, a small step depolarization accompanied by a 20-40% decay in input resistance occurs within seconds of attachment. The evidence suggests that this electrical event is the result of sperm-oocyte fusion, and that the ion channels that lower the resistance across the oocyte-sperm complex are located in the sperm plasma membrane. This primary electrical event does not necessarily lead to sperm incorporation. A second, determinative, event occurs at 50 s, which leads to sperm entry and the formation of a cytoplasmic protrusion at the site of sperm entry. This second event probably results from the transfer of a soluble component from the spermatozoon into the oocyte cytoplasm, which leads to sperm incorporation and formation of the protrusion. The changes in the oocyte following insemination are compared with the events of egg activation.

Action Potentials↗
PubMed1983

Studies on the differentiation of egg envelopes. I. The starfish, Astropecten aurantiacus.

We have studied the differentiation of the oocyte vitelline coat (VC) and jelly coat (JC) of the starfish, Astropecten aurantiacus. The precursor material of both envelopes is secreted by the oocyte while the follicle cells do not appear to participate in the secretory process. The first indication of differentiation of the VC is the deposition of a fine fibrillar material between the microvilli which emerge from the oocyte surface. External to this, a more loosely organized material becomes the precursor of the JC. At this time both layers are periodic acid-Schiff (PAS)-positive. In a later stage, the material between the microvilli acquires a more compact organization, looses its PAS-positivity while acquiring fucose binding protein (FBP) affinity. On the contrary, the JC remains PAS-positive and FBP-negative. In the full grown oocytes the VC is made up of densely packed fibrils oriented tangentially to the oocyte surface and is tightly bound to the microvilli. The observations are discussed in connection with the problem of the role of the egg envelopes in sperm-egg recognition and in the induction of the acrosome reaction.

Animals↗
PubMedDate not supplied

Calcium, protease action, and the regulation of the cell cycle.

Proteolysis is a key event in the control of the cell cycle. Most of the proteins which are degraded at specific cycle points, e.g. cyclins A, B, and E, are substrates of the ubiquitin/proteasome pathway. The Ca2+ dependent neutral protease calpain also cleaves cell cycle proteins, among them cyclin D1 and the c-mos proto-oncogene product which is a component of the CSF. The proteasome itself, however, may be under Ca2+ control through the binding of Ca2+ to its 29 kDa regulatory subunit. Calpain undergoes relocation among cell compartments during the various steps of the mitotic and meitotic cycles. It promotes the initiation and the progression of mitosis when injected into the perinuclear space of synchronized PtK1 cells, and the resumption of meiosis when directly injected into the nuclei of prophase-arrested starfish oocytes. Apart from the proteins mentioned above, most of the substrates of calpain which become cleaved during mitosis and meiosis are still unknown. Microtubule-associated proteins are likely candidates.

Animals↗