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Biomedical subjects

A J Solari

Publications and source records attributed to A J Solari.

At least 19 recordsLinked to original sources
PubMed1992

Polyamines and cell wall organization in Saccharomyces cerevisiae.

Cells of Saccharomyces cerevisiae 179-5, an ornithine decarboxylase mutant (spe-1), showed several ultrastructural abnormalities when cultivated in the absence of polyamines. Besides the appearance of microvacuole-like spaces in the cytoplasm and of deformed nuclei, the most important alterations seemed to be located in the cell wall, which was thicker and of heterogeneous texture, and in the cell membrane, of irregular contour. These modifications could not be evoked by general stress conditions elicited by lack of nutrients. The relative levels of cell wall polysaccharides were altered in polyamine-deprived organisms, giving an envelope with increased mannan and decreased glucan content; this cell wall was incompletely attacked by the lytic enzyme zymolyase. Polyamine depletion led also to some abnormalities in the budding pattern. The above observations suggest the involvement of polyamines in the correct structure and organization of the yeast cell.

Cell Wall↗
PubMed1992

Equalization of Z and W axes in chicken and quail oocytes.

The different morphological types of ZW pairs have been classified in three main types according to the relative extension of the free segment of the Z axis: 1, "long asynaptic segment;" 2, "medium asynaptic segment;" and 3, "equalized." Pre- and post-pairing types have also been defined. Frequencies of each type were determined at day 20 and day 21 of incubation, and one and three days after hatching. The changing frequencies and the morphological transitions observed show a definite sequence of ZW types that can be used as a timetable for pachytene substaging. Measurements made on each ZW type show that the Z axis of the chicken shortens from 20.6 microns to 13.1 microns. This shortening occurs both in the free segment (at a higher rate) and in the paired segment (at a lower rate). The synaptonemal complex becomes elongated while adjustment occurs. The equalized Z axis makes many twists around the W axis. However, a segment 1 micron long from the synaptic terminus is free from twists and is assumed to be the homologously paired region. The ZW pair of the quail shows a similar behavior but equalization of the Z and W axes ends earlier and forms a straighter synaptonemal complex as compared with the chicken. In both species a recombination nodule is strictly localized near the synaptic terminus. In the ZW pair of the quail the average location of this nodule is 0.14 microns from the synaptic terminus. The meiotic behavior of ZW pairs in birds may be conserved.

Animals↗
PubMed1991

An 'axis-like' material in the centromeric region of metaphase-I chromosomes from mouse spermatocytes.

This study reports the persistence of axis-like structures in the centromeric region of both homologues during the metaphase-I and anaphase-I stages of meiotic division of mouse spermatocytes. A novel type of silver 'argentaffin' technique (NH4-Ag) is employed. This technique includes the treatment of glutaraldehyde-fixed tissues with dilute ammonium hydroxide followed by a reduction of aldehyde groups with sodium borohydride. Staining is accomplished with ammoniacal silver nitrate in darkness followed by sulfite washing. The lateral elements of synaptonemal complexes and the single chromosomal axes of diplotene spermatocytes show a prominent reactivity with this technique. The pattern of very small grains over condensed chromatin is uniform and gives only a light opacity to the electron beam. The presence of an axis-like structure is seen in every centromeric end of meiotic chromosomes at metaphase I and anaphase I. The chromatin (heterochromatin) that surrounds the centromeric filament and some material distributed in irregular linear arrays along some of the homologues also showed a higher electron opacity than the bulk of deoxyribonucleoprotein. While the former is related to C+ heterochromatin, the latter could represent dispersed material of diplotene axes. It is suggested that the disposal of axial material is differentially delayed at the centromeric regions. The present evidence supports the hypothesis that axial fragments or lateral-element segments persisting at these regions contribute to the cohesiveness of centromeres of sister chromatids during normal disjunction.

Animals↗
PubMed1991

Presence of a centromeric filament during meiosis.

Spermatocytes at meiotic metaphase I and anaphase I have a characteristic centromeric filament in a variety of vertebrate organisms. This centromeric filament was first demonstrated on mouse spermatocytes and its presence is now extended to spermatocytes from the human, rat, golden hamster, bull, and chicken. The visualization of this filament was possible through the use of a novel silver-staining technique, which allows a high contrast between the filament and the centromeric chromatin. In the species cited, the centromeric filament shares an intense staining, a short (0.2-0.6 micron) length, a curved and branched shape, and location inside the centromeric chromatin of seemingly every homologue of the complement. The similarity of staining reactivity and the observation of transitional structures during first meiotic prophase strongly suggest that the centromeric filament is a remnant of a lateral element of the synaptonemal complex, which stays specifically at both centromeric regions of each bivalent. This filament is not found at the second meiotic division or at the centromeres of mitotic chromosomes. It is assumed that this centromeric filament joins the two sister chromatids of each homologue at the centromere and thus ensures the proper coorientation of sister kinetochores at metaphase I. Further testable assumptions on the functions of this filament are presented.

Animals↗
PubMed1991

Synaptonemal complex karyotyping in an oligospermic patient with heterochromatin duplication in chromosome n. 9.

Synaptonemal complex karyotyping has been performed in an oligospermia of unknown etiology in a patient carrying a 9qh+ chromosomal polymorphism. The testicular histology showed hypospermatogenesis at the spermatid level and an abnormal pattern of chromatin condensation. Spermatocytes at early pachytene showed a large, asymmetric loop in SC #9, which disappeared at late pachytene, probably because of synaptic adjustment. The loop was formed by a lateral element 7.02% longer than the average normal one. The loop exceeded the centromere towards the short arm, and it is interpreted as a tandem duplication of about 50% of the paracentromeric heterochromatin. The present observation and the previously reported asynaptic loops in carriers of pericentric inversions and showing severe oligospermia suggest that chromosomal variants producing asynaptic loops may be associated with germ cell loss. Further meiotic studies in infertile carriers of such variants are indicated.

Adult↗
PubMed1989

Meiotic behavior of gonosomically variant females of Akodon azarae (Rodentia, Cricetidae).

The meiotic behavior of sex chromosomes has been investigated in variant females of Akodon azarae, both in pachytene oocytes and metaphase I. In somatic cells, these females have a heteromorphic sex pair, in which the minor chromosome has been previously interpreted as a major deletion of the long arm of the X chromosome (dX). After microspreading for synaptonemal complex analysis, pachytene oocytes show two axes of very different lengths (100:17.1), which correspond to the sex chromosomes X and dX. True synapsis is abnormally restricted (43.3%) between these sex chromosomes; on the other hand, self-synapsis of both the X and dX chromosomes is frequent (60%). Single, nonsynapsed axes or axial segments are thickened. Strong chromatin condensation occurs around nonsynapsed axes or axial segments, giving many of these sex pairs an appearance similar to an XY body ("sex vesicle"). The minor gonosome axis differs from that of the Y chromosome of male meiosis, as the former is shorter (relative to the X) and has a different synaptic behavior. In 17 metaphases I from XdX variant females, only heteromorphic, end-to-end joined sex pairs were observed. These variant females differ from the variant females of the wood lemming Myopus schisticolor in several respects, but a similar mechanism seems to be prevalent in other species of the genus Akodon. Self-synapsis of unequal gonosomes in oocytes is assumed as an escape from functional deterioration, following the hypothesis put forward by others.

Animals↗
PubMed1988

Synaptic behaviour and recombination nodules in the human XY pair.

A sample of 90 XY pairs from men with normal karyotypes has been analyzed by measuring their morphological features in electron micrographs of microspread spermatocytes. The classification of human XY types (Solari, 1980) has been given stricter definitions. Stepwise splitting of the axes is seen in types 1 and 2. The development of axial branches and lengthening of the X axis is seen in type 3. In the two subtypes a and b of type 4 the net-like filamentous array grows in length to a maximum (average = 59.7 microns) in subtype b. The location of the putative Y kinetochore defines a short arm that measures 22.34% of Y axis length, and the kinetochore of the X axis defines a short arm of 38.15% of the axial length. The average number of excrescences in the X axis is 19.9 and in the Y is 4.3. The frequency of a non-homologous, distal end-joining grows steadily from type 0 to type 3. The average length of the synaptonemal complex (SC) in 51 XY pairs of types 1 and 2 is 1.33 microns (SD = 0.65) and it corresponds to 25.54% of the Y axis length. Thus, the average SC covers the short arm of the Y and the pericentromeric region. Maximum lengths of this SC may reach up to 81.8% of the Y axis. 30 recombination nodules (RNs) were located in 26 XY pairs, and 90% of the nodules are located in the distal half of the short arm of the Y axis. Thus, RNs are restricted to a segment much shorter than the length of the average SC. A gradient of decreasing probability of recombination may reach up to the centromeric region of the Y chromosome. Some possible consequences of these facts are discussed.

Humans↗
PubMed1988

Quadrivalent formation in a tetraploid chicken oocyte.

Synaptonemal complex analysis of an exceptional tetraploid oocyte from a diploid chicken heterozygous for the MN t (Z;1) rearrangement was performed by electron microscopy of a spread preparation. Ten separate quadrivalents (26% of the chromosomal axes) were analyzed, as well as 50 autosomal bivalents. All the axes less than 2.5 microns in length formed bivalents (38) only, while axes in the 2.5-4.2 micron range formed 5 quadrivalents and 12 bivalents. The longer, separate axes formed quadrivalents only. Partner switches in excess of one were documented. The two identical W chromosomes paired only at the ends of their short arms. Quadrivalent formation may require a threshold length (2.5 microns), at least in this species. The tip of the short arm of the W chromosome may be a pairing initiation point, and it corresponds to the region associated with a localized recombination nodule previously described in diploid oocytes.

Animals↗
PubMed1988

Pairing of ZW gonosomes and the localized recombination nodule in two Z-autosome translocations in Gallus domesticus.

Electron microscopic observations of synaptonemal complexes of oocytes from chickens heterozygous for two Z-autosome translocations have been used to identify and study the pairing region of the Z and W chromosomes. The two translocations, MN t(Z;1) and t(OH 10), have breakpoints in opposite arms of the Z, and the arm having the breakpoint of MN t(Z;1) is marked by the terminal C+ band. In both translocations the short arm of the W was specifically paired with the euchromatic short arm of the Z. In MN t(Z;1) only open quadrivalents (74%) and trivalents plus W univalents (26%) were observed, whereas t(OH 10) exhibited, in addition to the prevalent quadrivalents (62%), III + I (19%) and II + II (19%) configurations. The extent of W pairing was slightly decreased in MN t(Z;1) (68.4% of the W chromosomes paired) and considerably decreased in t(OH 10) (25.3% of the W chromosomes paired). Nonhomologous synapsis occurred regularly at the quadrivalent crosspoint in MN t(Z;1) and also in bivalents from t(OH 10). The recombination nodule normally located in the terminus of the pairing region in normal ZW pairs is present in both translocations without any alteration of its frequency or its strict terminal position. Based on these data and previous observations (Rahn and Solari, 1986), it is proposed that an obligatory recombination event occurs at a locus between 0.7 microns and 0.15 microns of the paired ZW telomeres, establishing a recombinational region and a pseudoautosomal region which determine partial sex-linkage and no sex-linkage, respectively. Most of the pairing region of the ZW pair is nonhomologously paired.

Animals↗
PubMed1986

Recombination nodules in the oocytes of the chicken, Gallus domesticus.

Chicken oocytes at pachytene were processed with the microspreading technique (Moses, 1977), and their synaptonemal complex (SC) complements were analyzed by electron microscopy. Ellipsoidal nodules, 140 X 120 nm in diameter, were associated with the central space of synaptonemal complexes. The average number of nodules per pachytene oocyte was 57.5. The number of nodules per bivalent showed a clear linear relationship with SC length, except for the microchromosomes, which showed a single obligatory nodule. The distribution of nodules along the 10 longest SCs was nonrandom, with low frequencies in the vicinity of kinetochores and high frequencies near the telomeres. The microchromosomes showed a single nodule whose average location was 1.21 micron from the kinetochore. In the ZW pair there was a single nodule whose average location was 0.31 micron from the paired telomeres and not more than 0.65 micron from them. The total number of nodules per cell and the number of nodules in each of the five major bivalents showed good agreement with the total number of chiasmata and the number of chiasmata of the major bivalents of roosters. Thus, these nodules share the characteristics of recombination nodules described in other organisms. The single, obligatory, strictly localized recombination nodule found in the pairing end of the ZW pair strongly suggests that recombination between the Z and W chromosomes in the female chicken is a regular process that may be similar to the obligatory recombination between the pairing ends of the human X and Y chromosomes that was recently described in studies using DNA probes.

Animals↗
PubMed1985

Fine structure and cytochemistry of the mitotic plaques of Trypanosoma cruzi and Crithidia fasciculata.

The mitotic plaques are double, electron-dense structures which are located at the equator of the nucleus during the equatorial (metaphase) stage of mitosis in Trypanosoma cruzi, Crithidia fasciculata and other trypanosomatids. Each part of the equatorial plaques separates from the other and becomes an hemiplaque at the beginning of nuclear elongation. Variations of size of the plaques in different species of Trypanosomatidae are restricted to a limited range (less than 30% of the average thickness). At least two different components are found in the plaques with cytochemical methods: a) a basic protein with a high affinity for ethanolic-phosphotungstic acid, which is located in a narrow band towards the cleavage plane in each hemiplaque; and b) an osmiophilic component (possibly a protein) with a low affinity for uranyl acetate and which is located throughout the body of the plaque. The affinity for uranyl acetate can be abolished by methylation and acetylation, but remains after extraction with cold perchloric acid. No cytochemical evidence for the presence of DNA in the plaques is found. However, electron microscopy and cytochemical observations show that the PTA-affine band of the plaques is associated at its sides with chromatin fibers. Thus plaques, as the outer layer of kinetochores in higher eukaryots, have a component with high affinity for phosphotungstic acid, strengthening the hypothesis that these structures are phylogenetically related.

Acetylation↗
PubMed1978

Multiple complexes in human spermatocytes.

Multiple complexes develop during metaphase I in normal human spermatocytes. Usually they form two separate bodies about 1 micron in diameter, composed of tripartite units and a denser matrix. The tripartite units are structurally identical to the components of the central space of synaptonemal complexes (SCs). Formation of the multiple complexes occurs by shedding of SC fragments from a few chromosomal regions at prometaphase I. The combined total length of central elements in each multiple complex is 1 to 3 micron. Multiple complexes remain as cytoplasmic, perinuclear bodies during telophase I and interphase of spermatocytes II, but they were not observed during or after the second meiotic division. Although multiple complexes are initially located in the spindle, they do not show microtubular attachments and seem to be passively moved towards the periphery.

Chromosomes, Human↗
PubMed1977

Synaptonemal complex karyotyping in Melanoplus differentialis.

The chromosomal axes of the spermatocytes of the grasshopper Melanoplus differentialis have been studied with a modification of the microspreading procedure used previously. The whole complement of synaptonemal complexes (SCs) and the axis of the X chromosome have been described and measured. The relative length of each SC is characteristic and constant and permits the construction of an idiogram. Relative lengths of SCs are almost equal to the relative lengths of mitotic chromosomes of spermatogonia (with the exception of the X chromosome), thus extending to an invertebrate the relationship between SCs and mitotic chromosomes that has been demonstrated in mammals. All the SCs except the 3 smallest (which are apparently telocentric) show a small short arm beyond the kinetochore. The progression of changes in the chromosomal axes during meiotic prophase has been staged by centriolar behaviour. During leptotene, axes are first formed near the nuclear envelope at a special (polar) region. SCs also begin to appear in the polar region and extend towards the nuclear interior. The beginning and completion of synapsis is not synchronous among bivalents. The X-axis is formed in midzygotene and shows a characteristic sequence of changes in shape during pachytene. Cells in post-synaptic stages show whole chromosome complements with characteristic chiasmatic configurations. Kinetochores are prominent and bipartite during diplotene-diakinesis.

Animals↗