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Biomedical subjects

M Ponsà

Publications and source records attributed to M Ponsà.

13 recordsLinked to original sources
PubMed1997

Characteristics of actin fibers and ultrastructure of the contact regions involved in the separation of blastomeres of two-cell mouse embryos, frozen-thawed without the zona pellucida.

Freezing of embryos deprived of the zona pellucida (ZP) decreases their survival rate immediately after thawing, and gives rise to the separation of their blastomeres in a high percentage of cases. We have studied the ultrastructure and the characteristics of actin fibers in the cell-to-cell contact region in mouse embryos frozen-thawed without the ZP at the two-cell stage. Our results indicate that most of the embryos that retain their blastomeres united after freezing and thawing show either the presence of a midbody, or a contact region with a close apposition of the plasma membranes but without an organized actin cortex in their contact region. Only a small percentage of embryos that retain their blastomeres united after freezing and thawing show a contact region with widely separated plasma membranes and an organized actin cytocortex.

Actins↗
PubMed1995

Freezing of zona-free mouse embryos: characteristics of the plasma membrane and subsequent development of the embryos.

Frozen-thawed mouse embryos with (+ZP) and without (-ZP) zona pellucida have been studied at the Scanning Electron Microscope (SEM) to determine how the process affects the plasma membrane and the subsequent embryo development. The main difference observed in -ZP embryos immediately after thawing is the abnormal morphology and distribution of microvilli. This could explain the spontaneous separation of blastomeres in -ZP embryos, and the decrease in their survival rate. If thawed -ZP embryos are allowed to recover in culture, their plasma membrane characteristics and survival rate are identical to those of control embryos.

Animals↗
PubMed1995

Cytogenetic studies of oocyte fusion products.

We describe for the first time the cytogenetic characteristics of mouse 'embryos' obtained by oocyte fusion (oocyte fusion products; OFP). Our results indicate that, after fusion, meiosis II is resumed correctly, with extrusion of two haploid polar bodies, and that metaphase synchronisation of the two haploid sets and chromosome segregation during the first cleavage are also normal.

Animals↗
PubMed1994

Ultrastructural studies of early mouse embryos obtained by oocyte fusion.

Oocyte fusion induced by inactivated Sendai virus results in the production of 'zygotes' that are able to undergo the first stages of embryonic development. The oocyte fusion products (OFP) obtained follow a morphological developmental pattern equivalent to that of control embryos, at least up to the 8-cell stage. The percentage of OFP that reach the 8-cell stage is extremely low (3%) compared with control embryos cultured in vitro (95%). On light microscopy, the OFP obtained show morphological characteristics identical to control embryos, although their cell diameters are larger. The cortical reaction, meiotic reactivation, extrusion of second polar bodies and pronucleus formation take place as observed in controls. The ultrastructural characteristics of oocyte fusion products at the 1-, 2-, 4- and 8-cell stages are analogous to those of controls, including the presence of structures related to the activation of the embryo genome. However some differences concerning cell ultrastructure, mainly in the nucleus, are observed and discussed in the text.

Animals↗
PubMed1994

A simple method for processing individual oocytes and embryos for electron microscopy.

A simple method for handling individual specimens that must be processed either for scanning or transmission electron microscopy studies is described. For scanning microscope processing, dehydration is carried out with samples enclosed in small cages made from TAAB capsules in which top and bottom are substituted by plankton nets, and for transmission electron microscopy, samples are preembedded in agarose. This procedure significantly reduces mouth pipetting, dissecting microscope observations, is less labour intensive and, most importantly, reduces sample loss.

Animals↗
PubMed1992

Zona pellucida surface of immature and in vitro matured mouse oocytes: analysis by scanning electron microscopy.

PURPOSE: The aim of this work was to determine the morphology of the zona pellucida surface of immature and in vitro matured mouse oocytes by scanning electron microscopy. For this purpose two groups of immature oocytes (germinal vesicle group and metaphase I group) were studied either before or after in vitro maturation. RESULTS: Before in vitro maturation, the germinal vesicle immature group showed mainly an unstructured zona pellucida surface with smooth cumulus cells. The metaphase I immature group showed a more structured zona pellucida with smooth or blebbing cumulus cells. After in vitro maturation, development of the zona pellucida toward a mature surface, related to the initial degree of oocyte maturity, was observed in both groups. CONCLUSIONS: These observations show a correlation between the morphology of the zona pellucida surface and the degree of oocyte maturity; the in vitro maturation process can give rise to a proper development of this endowment when immature oocytes are used.

Animals↗
PubMed1991

Scanning electron microscope (SEM) study of mouse embryos obtained from isolated blastomeres.

Preimplantation diagnosis and embryo sexing offer great possibilities in the prevention of human diseases and in the field of animal production. These techniques involve blastomere isolation. Isolated blastomeres can grow in culture and develop as whole embryos. In this paper we describe, at the scanning electron microscope level, the characteristics of the plasma membrane surface of isolated blastomeres obtained from mouse embryos at the two-cell stage and of embryos grown to the 2/4- and 4/8-cell stages and compare them to control embryos grown in vitro. According to our results the in vitro manipulation of these embryos does not affect the surface characteristics of the plasma membrane in the early cleavage stages.

Animals↗
PubMed1990

Evolution of the Simiiformes and the phylogeny of human chromosomes.

This paper is based on the results of Primate chromosome studies obtained using high resolution techniques in our and other laboratories. We discuss the origin and the evolution of the chromosomes in the human karyotype and the time in evolution of the Simiiformes when they acquired their present morphology. Our results indicate that the chromosomes that underwent a higher number of reorganizations during the evolution of the Simiiformes coincide with the chromosomes most often implicated in human chromosome pathology. We describe the main reorganizations that took place during Primate evolution. Centromere activation and inactivation and heterochromatin changes are discussed as mechanisms of chromosome evolution.

Animals↗
PubMed1989

Trivalent behavior during prophase I in male mice heterozygous for three Robertsonian translocations: an electron-microscopic study.

A synaptonemal complex (SC) analysis was carried out in male mice heterozygous (CHT/+) for three Robertsonian translocations. All pachytene preparations studied showed the presence of three trivalents. At early pachytene, the nonhomologous centromeric regions of the acrocentric chromosomes were unpaired. Heterosynapsis subsequently took place with complete pairing of the trivalents. Association between one of the three trivalents and the sex vesicle was observed in 30.4% of the nuclei. Association between the unpaired regions of two trivalents was present in 14.4% of the cells, suggesting that the relationship between unpaired regions of structural rearrangements and the X-Y bivalent may simply reflect the tendency of unpaired regions to establish end-to-end associations or heterosynapses among them, which are usually resolved during the pachytene stage of prophase I. Since the sex bivalent always has unpaired regions, these associations often affect the sex chromosomes.

Animals↗
PubMed1988

Effects of aging on the zona pellucida surface of mouse oocytes.

In a scanning microscopy study of mouse oocytes from immature, young, and aged females and of oocytes aged in vivo or in vitro, we have observed four types of zona pellucida, which we classify as types A, B, C, and D. Oocyte aging gives rise to a significant increase in predegenerative (type C) oocytes; this type of zona pellucida surface could result from a zona hardening effect and decrease the rate of fertilization of the oocytes affected.

Aging↗
PubMed1987

New data on the synaptic process of Mesocricetus auratus: connecting fibers, telomere association and heterosynapsis.

The progression of the prophase-I stage in Syrian hamster spermatocytes has been studied at different ages, from 12 to 41 days after birth. Two stages, leptotene and diplotene, were identified, which had not previously been described in the Syrian hamster using spreading techniques. The most interesting observations are the presence of heterosynapses and telomere associations in 2.5% of the cells studied, and of nucleolar filaments also in 2.5%. Connecting fibers are structures that establish different types of bridges between two or three synaptonemal complexes (SCs) or between the elements of a single SC. Heterosynapses and telomere associations consist in the partial pairing of the terminal regions of non-homologous lateral elements. These phenomena can be observed both in the autosomes and in the sex chromosomes.

Animals↗
PubMed1987

Development of the first meiotic prophase stages in human fetal oocytes observed by light and electron microscopy.

The development of the first meiotic prophase stages was studied in two series of human female embryos and fetuses aborted for social reasons. The first series (64 embryos or fetuses aborted at 6-24 weeks of gestation) was used mainly to perfect the methods applied to obtain chromosome preparations and synaptonemal complex spreads. The second series (37 embryos or fetuses aborted at 9-24 weeks of gestation) was used to establish the timing and to characterize the different stages of prophase I. Leptotene-zygotene figures were observed in some embryos at 10 weeks of gestation. Typical zygotene figures were seen at 11-22 weeks. Pachytenes were first observed at 12-13 weeks, and the proportion of these figures was usually lower than 40%. Diplotenes were seen in fetuses with a gestational age of 14 weeks or more. The duration of the process in the human female is thus about 3-4 weeks, a similar period to that described for the male.

Embryo, Mammalian↗