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Biomedical subjects

A Monroy

Publications and source records attributed to A Monroy.

At least 19 recordsLinked to original sources
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↗
PubMed1986

Sperm-egg interactions preparatory to fertilization.

In 1902, Boveri introduced the important concept that for the success of fertilization the gametes must activate one another. Based primarily on studies on the sea urchin and ascidian fertilization the suggestion is presented here that "activation" of the spermatozoon actually involves a switching off of its metabolic machinery as a result of its interaction with the sperm receptors of the egg envelopes and prior to its fusion with the egg. Concerning the activation of the egg, there is a fairly large body of old and new experimental evidence that activation per se does not require sperm incorporation. Indeed, the chain of reactions culminating in the activation of the egg is initiated upon attachment of the spermatozoon to the egg plasma membrane.

Animals↗
PubMed1985

Processes controlling sperm-egg fusion.

Sperm interaction with the egg envelopes triggers the acrosome reaction. Indeed, sperm-egg fusion is accomplished by the fusion of the acrosomal process (or of the exposed inner acrosomal membrane in mammals) with the egg plasma membrane. Fusion must be preceded by the establishment of molecular contact between the two membranes. It is suggested that, as in the case of artificial phospholipid membranes, the two major obstacles to the establishment of molecular contact are electrostatic repulsion and the hydration barrier. It is argued that morphology of the acrosome is such as to favour the overcoming of such barriers. By analogy with the conditions governing fusion of artificial phospholipid membranes and cell fusion, it is proposed that the following processes play a role in sperm-egg fusion. The large calcium uptake accompanying the acrosome reaction may help fusion either through the known effect of calcium on fusion of phospholipid membranes or by shielding the surface charges of the acrosomal process. Fusogenic proteins at the surface of the acrosomal process are likely to play a role in the fusion of the acrosomal process with the egg plasma membrane. The activation of phospholipases in conjunction with the acrosome reaction may also be instrumental in sperm-egg fusion through the transient production of lysophosphatides. Clearance or translocation of intramembraneous proteins in the egg plasma membrane at the site of contact with the acrosomal process may also be required for fusion. Lastly it is suggested that a translocation or a conformational change of some proteins of the egg plasma membrane, which is required for fusion, may be induced by the depolarization of the egg plasma membrane that follows molecular contact with the acrosomal process.

Acrosome↗
PubMed1983

A fucosyl glycoprotein component with sperm receptor and sperm-activating activities from the vitelline coat of Ciona intestinalis eggs.

In this paper we describe a mild procedure which results in the extraction of a glycoprotein fraction from the vitelline coat (VC) of Ciona intestinalis while leaving behind the bulk of the VC components. When acting upon the spermatozoa this fraction inhibits sperm binding to the VC and fertilization and elicits sperm activation including the acrosome reaction. SDS-PAGE shows that it contains the same (fucosyl) glycoprotein components previously recognized in the total extracts of VC. It is suggested that this material contains the sperm receptors or those components of the receptors that are essential for their Chinese function.

Animals↗
PubMed1983

A thermodynamic study of sperm-egg interaction.

We have studied the binding of spermatozoa to the receptor sites on the vitelline coat (VC) of glycerol-treated eggs (ghost eggs) of the Ascidian, Ciona intestinalis (Protochordate). Glycerol treatment cytolyses the egg without affecting the ability of the VC to bind spermatozoa in a species-specific manner; however, in this system binding is not followed by the acrosome reaction. The ghost eggs are metabolically inert. As a base line for our analysis, we have studied the concentration-dependent heat evolved and oxygen consumption of spermatozoa when diluted in sea water. The process has been analyzed on the basis of equations derived by Liquori and Tripiciano to describe cell growth. Upon binding to the ghost eggs, the spermatozoa produce an explosive heat evolution (excess heat) which is not accompanied by oxygen consumption. The excess heat produced plotted against sperm concentration (at constant egg concentrations) gives an asymmetric bell-shaped curve. This is interpreted as being due to the competitive effect of sperm agglutination at a high sperm concentration. It is concluded that only spermatozoa that attach singly (monomeric spermatozoa) to the egg undergo metabolic activation.

Animals↗
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↗
PubMed1983

On the segregation of the germ and somatic cell lines in the embryo.

In this paper we argue that the mechanisms underlying the segregation of the somatic and germ cell lines are basically similar. The interaction of the genome with specific cytoplasmic factors is responsible for the restriction of their developmental potencies in the somatic cell lines, and for the prevention of such a restriction in the germ cell line. In particular, it is suggested that meiosis is part of the differentiation program of the germ cells.

Animals↗
PubMed1982

Synthesis of fucosyl-containing glycoproteins of the vitelline coat in oocytes of Ciona intestinalis (Ascidia).

The sperm receptors of the ascidian oocyte are located at the outer surface of the vitelline coat (formerly called the chorion). The fucose residues are the receptor's most important components for sperm recognition and binding. We asked whether the fucosyl-containing glycoproteins of the vitelline coat are a product of the oocyte, the follicle cells, or the test cells. Ovaries of Ciona intestinalis were injected with L-[3H]fucose and the progress of its incorporation was followed by using autoradiography and sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the injected gonads and of the isolated vitelline coats. We found that incorporation of fucose begins within the vitellogenic oocytes, and fucose slowly accumulates in the differentiating vitelline coat. At no time could fucose incorporation be detected in the follicle cells or in the test cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of vitelline coats prepared from the injected ovaries showed fucose incorporation into the same three glycoproteins present in vitelline coats from mature oocytes and identified by their affinity for 125I-labeled fucose-binding protein [Pinto, M. R., De Santis, R., D'Alessio, G. & Rosati, F. (1981) Exp. Cell Res. 132, 289-295]. A radioactive band not found in the mature oocyte was also present.

Animals↗
PubMed1981

A theoretical equation for diauxic growth and its application to the kinetics of the early development of the sea urchin embryo.

The equation for diauxic growth is derived as a linear combination of two functions describing a slow and a fast rate of cell multiplication. The growth curve displays the typical biphasic shape, containing two sigmoidal branches. The curve fits very satisfactorily experimental data describing the increase of cell number in developing sea urchin embryos as a function of time, thus suggesting the presence of diauxia in this system. The hypothesis is formulated that diauxia in sea urchin embryos is the expression of two distinct metabolic pathways that result in a slow and a fast division process.

Animals↗
PubMed1980

Cell-cell recognition.

The earlier step of morphogenesis is the segregation of cell lines which are homogeneous cell populations each endowed with its own specific developmental program. In order for the program to unfold in each line cells must be endowed with specific surface properties whereby the cells belonging to the same line can recognize each other as such in addition to recognizing those belonging to other cell lines as different. Experiments supporting this view are described. The hypothesis is presented that the cell-cell recognition system is phylogenetically linked with the invention of sexuality.

Animals↗
PubMed1980

Histological studies of the elimination of Leishmania enriettii from skin lesions in the guinea-pig.

Nineteen guinea-pigs were each inoculated intradermally with 10(6) amastigotes of Leishmania enriettii, and the development of the lesions was followed from Weeks 4 to 10 with a view to elucidating the histological mechanisms involved with the elimination of parasites. Electron microscopic observations were made in 1 animal. Extensive necrosis of the parasite-laden macrophages was observed in 7 out of 7 animals at 4 and 5 weeks. In the ulcerated core of the lesion at 4 weeks no intact macrophages could be identified. Very many amastigotes were extracellular. Others were present in the cytoplasm of residual macrophages the cell walls of which had disintegrated. Necrosis was less marked at 8 weeks and absent in the resolving lesions at 10 weeks. Signs of stimulation or maturation of macrophages were only apparent when parasites were few. At 4 weeks macrophages were almost all of the non-stimulated form, but cytological evidence of activation became progressively more definite and widespread from 5 to 8 weeks, starting at the periphery of the lesion. Ultrastructural observations of amastigotes suggested that there might be more than one mechanism of degradation. It appeared that the majority of parasites were released through necrosis and discharged through the ulcer, and that intracellular degradation of the remaining parasites was important mainly in the later phase before resolution. The first phase was associated mainly with plasma-cell production, the second mainly with lymphocytes.

Animals↗