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Biomedical subjects

M Ponsà

Publications and source records attributed to M Ponsà.

23 records · Page 2Linked to original sources
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↗