End Of Meiosis Research Articles

Cloning and differential expression during the sexual cycle of a meiotic endonuclease-encoding gene from the basidiomycete Coprinus cinereus

The naturally synchronous meiosis of the fungus, Coprinus cinereus provides an ideal system for the investigation of differential gene expression in relation to meiosis and fruiting body development. We have cloned a cDNA from the fruiting body of C. cinereus encoding the 12-kDa subunit of a meiotic endonuclease (mENase). The identification of the 12-kDa subunit cDNA clone was achieved by the mENase antiserum against a τ17 cDNA expression library. It was confirmed by a direct match of the amino acid (aa) sequence obtained from purified 12-kDa polypeptide with the nucleotide sequence. Northern blot analysis using the cDNA clone as a probe showed that the mENase-encoding gene ( MenA) for the 12-kDa subunit was expressed mainly in fruiting bodies and at a very low level in the asexual vegetative mycelium. In addition, it was differentially expressed in the early meiotic stages. The MenA transcript was most abundant in fruiting body primordia prior to the premeiotic S-phase; it remained high from karyogamy to early pachytene, declined drastically by late pachytene and diplotene, and was undetectable by sterigma stage. Western blot analysis showed that the mENase protein was produced at a very low level in mycelium; it was produced in great quantity during the early meiotic stages and decreased to a low level at the end of meiosis.

Activation of p42 MAP kinase and the release of oocytes from cell cycle arrest.

Clam oocytes are arrested naturally at the G2/M border in meiosis and contain an inactive 42 kDa ERK/MAP kinase, p42MAPK. Following fertilization, p42MAPK is rapidly phosphorylated on tyrosine residues and concomitantly activated. Both tyrosine phosphorylation and activation of p42MAPK begin within 2-3 min of fertilization, peak at approximately 15 min, then rapidly decline and disappear around the end of meiosis I. Neither the tyrosine phosphorylated form of p42MAPK nor p42MAPK activity reappears during meiosis II or the succeeding mitotic cell cycles. High doses of molybdate, a potent PTPase inhibitor, block the phosphorylation of p42MAPK and entry into the cell cycle. Lower doses of molybdate delay both p42MAPK phosphorylation and the release from cell cycle arrest, but once cells have re-entered the cell cycle, they continue with near-normal timing. These results argue that the transient activation of p42MAPK at fertilization is a one-time event linked to release from cell cycle arrest. In trying to reconcile this one-time activation of p42MAPK in clam embryos with the recurring, M-phase specific activation of MBP/MAP kinases reported in other systems, we show that cdc2 kinase contributes a major portion of the MBP kinase activity in mitotic extracts. Furthermore, a small fraction of p42MAPK and other related kinases are present in p13suc1-bound material, cautioning against the use of p13suc1 beads for experiments where, in addition to cdc2, the unaccounted presence of other kinase activities could be misleading.

Species-specific characteristics of spermatogenesis in Drosophila mojavensis (Patterson) (Diptera : Drosophilidae)

Spermatogenesis in Drosophila mojavensis (Diptera : Drosophilidae) begins with the proliferation of a primary gonial cell, leading to the formation of a cyst with 16 primary spermatocytes that subsequently enter a growth phase towards the end of meiosis. As their development proceeds, primary spermatocytes assume a characteristic species-specific appearance regarding the morphology of their nucleus. Meiosis produces a syncytium of 64 spermatids, each one of which bears one nucleus and one compact mass (nebenkern), composed of mitochondria. During spermiogenesis, the newly formed spermatids undergo a structural transformation that leads to the formation of the mature sperm: the spherical nucleus is reduced to a 0.1 × 75 μm cylinder and the nebenkern separates into 2 mitochondrial derivatives, which elongate to 2400 μm, while associated with the axoneme. Both mitochondrial derivatives of the mature sperm, although disparate in size, are relatively large and have paracrystalline bodies that occupy a great part of their mass.

CYCLIC INVASION OF TAPETAL CELLS INTO LOCULI DURING MICROSPORE DEVELOPMENT IN NYMPHAEA COLORATA (NYMPHACEAE)

In work with Nymphaea colorata Peter three distinct intervals were recorded during which tapetal cells (protoplasts) protruded into anther locules either as bridges and partitions or as invasive cells between or around tetrads of microspores. Before these intervals and between and after them, tapetal cells, while variable in shape, were noninvasive. Observations were based on sections of over 60 fixed and epoxy‐embedded anthers covering the relatively brief interval from the end of meiosis through the vacuolate microspore stage. The progression of development, from early microspore stages through the microspore vacuolate period, is illustrated by transmission electron micrographs showing change in proexine and exine size and complexity. Our results indicate cycles of tapetal cell differentiation and dedifferentiation in this species.

Cyclic Invasion of Tapetal Cells into Loculi During Microspore Development in Nymphaea colorata (Nymphaceae)

In work with Nymphaea colorata Peter three distinct intervals were recorded during which tapetal cells (protoplasts) protruded into anther locules either as bridges and partitions or as invasive cells between or around tetrads of microspores. Before these intervals and between and after them, tapetal cells, while variable in shape, were noninvasive. Observations were based on sections of over 60 fixed and epoxy-embedded anthers covering the relatively brief interval from the end of meiosis through the vacuolate microspore stage. The progression of development, from early microspore stages through the microspore vacuolate period, is illustrated by transmission electron micrographs showing change in proexine and exine size and complexity. Our results indicate cycles of tapetal cell differentiation and dedifferentiation in this species.

Expression of ogu cytoplasmic male sterility in cybrids of Brassica napus

A light and electron microscopic investigation revealed that ogu cytoplasmic male sterility (CMS) in cybrids of Brassica napus is primarily a deficiency of the tapetum and clearly time and site specific. Three patterns of ogu CMS were found, and specific conclusions drawn. First, the partially male fertile cybrid 23 was highly variable. It sometimes produced heterogeneous stamens with an endothecium formed exclusively around the fertile locules, thus delineating each microsporangium as a functional unit. The second type, including cybrids 27, 58 and 85, on the contrary, was stable and completely male sterile. In the four locules of normal length, microspores were observed to die at the vacuolate polarized stage while the tapetum disappeared prematurely through excessive vacuolization by the end of meiosis followed by a rapid autolysis during the tetrad or early free microspore stage. The subepidermal layer of the locule wall failed to form characteristic thickenings. The male-sterile stamens were completely indehiscent. At the time of anthesis they contained only collapsed empty exines adhering to each other. These cybrids, 27, 58 and 85, were closest to the ogu CMS trait of radish and seemed to be the best suited for further use in plant breeding. The third pattern was found in cybrids 77 and 118, which besides showing abortion of the microsporangia also showed a feminization of the stamens. We suggest that this feminization might be due to an alloplasmic situation associating Brassica napus nuclear genes with the mitochondrial DNA of radish.

Cytological Analysis of Macro‐ and Microsporogenesis of a Diploid Alfalfa Clone Producing Male and Female 2n Gametes

Gametes with the somatic chromosome number (2n gametes) are important in germplasm transfer and in the evolution of polyploidy. In this work a stain‐clearing methodology was applied to the cytological study of both macrosporogenesis and microsporogenesis in the diploid (2n = 2x = 16) clone H33 of alfalfa (Medicago sativa L.), which produces both male and female 2n gametes. Normal diploid and tetraploid plants were analyzed as controls. The analysis of macrosporogenesis indicated that done H33 produced ≈19% 2n macrospores of the second division restitution (SDR) type as a consequence of the absence of cytokinesis in the chalazal dyad. The analysis of microsporogenesis showed clone H33 produced a high frequency of dyads with two 2n microspores. About 64% of these dyads were of the first division restitution (FDR) type, as a consequence of parallel or nearly parallel spindles at metaphase II; the other dyads originated by abnormal cytokinesis at the end of meiosis and therefore they could be either FDR or SDR type. Abnormal cytokinesis was also responsible for the production of dyads with one n and one 3n microspore; moreover some rare 4n microspores originated by the total lack of cytokinesis. Clearing methodology proved very effective in alfalfa for the study of both macro‐ and microsporogenesis. It can therefore be efficiently used for the analysis of meiotic mutants that produce male and/or female 2n gametes at high frequency.

The relationship between nuclear envelope-derived annulate lamellae and the asymmetric division of primary spermatocytes in aphids

The structure of dividing primary spermatocytes of Amphorophora tuberculata (Aphididae, Hemiptera) as determined by electron microscopy and serial sectioning is described. The developmental stages examined extend from late prophase I to late telophase I. We looked for any asymmetric organization that could be causally linked to the differences in chromatin behaviour between the two daughter nuclei towards the end of meiosis I of this species. In late prophase I, evaginations of the nuclear envelope in the vicinity of two neigh-bouring centrosomes develop into closed cytoplasmic compartments with a dense content. The compartments open in prometaphase I and come to lie together with fragments of the nuclear envelope within the spindle area. Since nuclear pores are preserved in the membranes, intraspindle annulate lamellae have formed. These and material of presumed nuclear origin associated with them are asymmetrically distributed within the cell. Although dispersed at stages beyond prometaphase I, the material may be largely incorporated into one of the two daughter cells and thus be decisive for further development. Some annulate lamellae form a cap at the chromosome surface opposite to the neighbouring centrosomes in prometaphase I. These membranes may prevent interaction between spindle microtubules and chromosomes until a bipolar spindle forms in metaphase I. At this stage, both the banana-shaped autosomal bivalent and the X univalent occupy the equatorial plane. This is strange, because the X univalent has microtubular connections with one spindle pole and would be expected to migrate towards that pole. Possibly, the kinetochore of the X chromosome is inactive, and remains so in anaphase I, when the X univalent remains located between the two autosomal half-bivalents.

Absence of Callose and Tetrad in the Microsporogenesis of Pandanus odoratissimus with Well-formed Pollen Exine

In the microsporocytes of Pandanus odoratissimus, cytokinesis is succesive with centrifugal cleavage in both the meiotic divisions. The dyads move apart from each other after the first division, and the microspores likewise after the second division, so that only monads are formed at the end of meiosis. Although no trace of callose wall is found any stage around the microsporocyte or microspore, fertile, monocolpate pollen with well-developed, spinescent exine develops, and is shed at the two-celled stage

Evolution de la Paroi Spéciale au Cours de la Microsporogénèse duSoja Hispida(Papilionaceae)

Abstract At the beginning of the prophase of the first division, the first deposits of the special wall are visible at the angles of each mother cell. They are highly contrasted and finely fibrillar. At the end of the telophase I, the special wall fills the whole space between the primary wall and the plasmalemma. During this time, accumulation of vesicles arise from the fragmentation of the endoplasmic reticulum, and is observed on the surface of the mother cell. Lipidic globules, in relation with the reticulum, are expelled through the plasma-lemma. At the end of meiosis, the special wall surrounds the tetrads. Simultaneously, plasmalemma invaginations isolate the four daughter cells. The intersporal septa are continuous and have the same contrast as the special wall. Cytochemical tests show that the special wall is likely formed of callose associated with lipids and acid polysaccharides. L'origine de la paroi speciale (activite du reticulum endoplasmique, secretion lipidique), sa mise en place des la p...

Ultrastructure and development of the gametophyte vaginula-sporophyte foot complex in the liverwort Targionia hypophylla L.

The development of the placental complex including the gametophyte vaginula and the bulbous foot of the sporophyte in the liverwort Targionia hypophylla L. (Marchantiales) was studied by transmission electron microscopy. The vaginula and foot are separated by an intervening space and each consist of parenchymatous cells without intercellular spaces. Transfer cells begin to differentiate at the gametophyte-sporophyte interface just prior the onset of meiosis. While a single epidermal transfer-cell layer has developed in the foot by the end of meiosis, a multilayered pattern of transfer cells is formed in the vaginula. Gametophyte transfer cells have wall labyrinths which decrease in complexity with distance from the foot, lack plasmodesmata, and show signs of degeneration in the proximity of the foot. During meiosis, amyloplasts of both vaginula and foot lack starch and develop some thylakoid grana. In the subsequent stage of spore maturation, obliteration of the wall labyrinth occurs in both gametophyte and sporophyte transfer cells. The developmental pattern of the placental complex in Targionia is discussed in relation to that of mosses.

Transcriptional and translational control of the message for transition protein 1, a major chromosomal protein of mammalian spermatids.

The spermatid transition proteins comprise a set of basic chromosomal proteins that appear during the period when spermatids are undergoing nuclear elongation and condensation, about midway between the end of meiosis and the release of spermatozoa from the seminiferous tubule. The transition proteins replace the histones but are themselves subsequently replaced by protamines, and they are not found in sperm nuclei. We have used a cDNA clone for the smallest transition protein (TP1, 54 amino acids) to show that its message first appears postmeiotically in late round spermatids. Thus production of TP1 is an example of haploid gene expression. The message remains translationally inactive for some 3-4 days before translation occurs in early elongating spermatids. While translationally repressed, TP1 message is nonpolysomal and has a discrete size of about 590 bases, including a 140 residue poly(A) tail. In contrast, polysome-associated message is of heterogeneous size due to variability of poly(A) lengths.

Cytoskeleton, cell surface and the development of invasive plasmodial tapetum inTradescantia virginiana L.

The anther tapetum inTradescantia virginiana L. is of the invasive plasmodial type: the cells lose their walls during early spore meiosis and develop long invasion processes which invade the loculus to penetrate spaces between the sporogenous cells. Fusion to form a syncytium is delayed and conventional ultra-thin sections and the Thiery reaction reveal the presence of a loose fibrillar extracellular cell coat on the free surfaces of tapetal cells and their invasion processes. Cell fusion involves formation of apposition areas characterized by an absence of cell coat and the local appearance of microtubular arrays. Conspicuous membrane sacs, associated closely with microtubules, were found to migrate to and accumulate at the plasma membranes near the fusion sites and sporogenous cells. Microtubules are always present in the cortical regions of the tapetal cells and their invasion processes. It is surmised that microtubules are not responsible either for initiating or guiding tapetal invasion of the loculus; instead they may help to sustain the form of the invasion processes, help in the migration of membrane sacs, and participate in cell fusion. The cell coat disappears with syncytium formation towards the end of meiosis, and the developing spore cells become surrounded by a “perispore membrane”, which, derived from the original plasma membranes and augmented by membrane sacs, forms labyrinthine membrane reservoirs that are described further in the accompanying paper.

Microtubules and macrotubules in fish meiosis

During meiosis in the male of a cyprinodontid fish, Aphyosemion splendopleure, and during the organization of the spindle of division, the spindle is made of two types of tubules: microtubules (20–25 nm) and macrotubules (30–50 nm). The macrotubules are associated only with the polar region of the meiotic apparatus and are located outside the spindle of microtubules. At the end of meiosis, the spindle microtubules depolymerize whereas the macrotubules remain. One can find them throughout the entire process of spermiogenesis; later, they disappear only at the end of spermatid maturation. We have studied four populations from Cameroon, three of them with macrotubules.

Microsporogenesis in genic male-sterile lines of barley (Hordeum vulgare)

Pollen development has been studied by various microscopical techniques in five genic male-sterile lines and in male-fertile lines of barley (Hordeum vulgare L.). Two of the male-sterile lines (msg,,ho and msg,,fz) exhibited apparently identical abnormalities: defective cytokinesis at the end of meiosis 1. Another male-sterile gene (msg,,fg) also appeared to cause defects at this stage; in this case nuclear restitution was incomplete. In the male-sterile line msg,,gf a failure of the periclinal division of the inner secondary parietal layer occurred, so that a tapetal layer was not formed. Development was normal through meiosis in anthers from msg,,fp plants until the early vacuolated microspore stage when normal sporopollenin production was inhibited.

Zygospore germination and meiosis in Closterium ehrenbergii Meneghini (Conjugatophyceae)

Abstract The processes of zygospore germination and meiosis in Closterium ehrenbergii Meneghini are reported, utilizing several clones of the same mating group. The first sign of zygospore germination is the greening of the zygospore. Thereafter the germination vesicle is released through the ruptured zygospore wall into the surrounding medium; this occurs in the dark as well as in the light period. The two plastids, visible on one side of the vesicle just released, first move apart and then come closer to each other again, probably accompanied by cytoplasmic movement. As the vesicular volume reduces, a cytoplasmic cleavage progresses to produce a pair of gones, each containing one plastid. Meiosis begins in the greening zygospore and is completed in the germination vesicle. At the end of meiosis two non-sister nuclei abort. One surviving nucleus and one aborting one are incorporated in each gone with one plastid. Closterium ehrenbergii has a great number of rod-like chromosomes and at least two long acro...

Ultrastructure of meiosis in the hollyhock rust fungus,Puccinia malvacearum I. Prophase I — Prometaphase I

A thoroughly documented account of the ultrastructure of the meiotic spindle pole body (SPB) cycle in a rust (Basidiomycota, Uredinales) is presented for the first time. The three-dimensional structure of the SPB and spindle during meiosis in the hollyhock rust fungusPuccinia malvacearum is analyzed from serial sections of preselected stages. This paper covers prophase I to prometaphase I. At late prophase I, the nucleolus disperses and does not reappear until the end of meiosis. The SPB at late prophase I consists of two, 4-layered discs, 0.8–1.0 μm in diameter, connected by a middle piece (MP). The SPB is associated with a differentiated region of the nuclear envelope and nucleoplasm. At late diplotene to diakinesis, each disc generates a half spindle as it inserts into an otherwise intact nuclear envelope. The MP connecting the interdigitating half spindles elongates and eventually splits transversely during subsequent spindle elongation. Each half MP, which is attached to a SPB disc, becomes inserted in a sheath-like extension of the nuclear envelope. The intranuclear late prometaphase I spindle always becomes oriented perpendicularly to the longitudinal axis and sagittal plane of the metabasidium. There are 200–290 spindle microtubules (MTs) at each SPB at late prometaphase. The nonkinetochore MTs form a coherent central spindle around which the kinetochore MTs and bivalents are spread. A metaphase plate is absent. The results are compared with SPB behavior and spindle structure in early meiosis of other basidiomycetes and ascomycetes.

Studies on microspore development in liliaceous plants

In microspores of angiosperm plants, the period from the end of meiosis in microsporocytes unitl the first cell division may be considered as one cell cycle, and the division is polarized, resulting in the formation of two functionally different nuclei. InLilium longiflorum, the duration of the cell cycle was measured in some detail. Identification of individual stages was based on the correlation between bud length and developmental stage. The results showed that the process begins at a bud length of 24 mm and is completed about 15 days later, at a bud length of 58 mm. By autoradiography of cells cultured in the presence of3H-thymidine, approximate durations of the G1, S, and G2 plus M phases were estimated to be about 12, 2, and 1 days, respectively. A detailed cytological analysis of the transitions between the various microspore stages has revealed some convenient parameters which point to ghe progression of change during the interval.

Meiosis and sporogenesis in a haploid plant of Pellaea glabella var. occidentalis

In spore mother cells of a sporophyte of Pellaea glabella var. occidentalis (E. Nelson) Butters resulting from induced apogamy, the chromosomes did not pair during prophase I and separated randomly, usually into two groups. Meiosis II generally produced tetrads with nuclei of unequal sizes. Spore walls began to form around these nuclei, but most of the spores eventually aborted. One apparently normal spore, which later germinated, is assumed to have resulted from the formation of a restitution nucleus at the end of meiosis I.The total lack of pairing among the 29 chromosomes of this plant is evidence that this number represents the basic haploid complement of the species.

HISTOLOGICAL AND CYTOCHEMICAL STUDIES ON FIVE GENETIC MALE-STERILE LINES OF BARLEY (HORDEUM VULGARE)

The action of the genes msg5, msg9, msg10, msg14, and msg18 in barley (Hordeum vulgare L.) is almost entirely restricted to the sporogenous and tapetal tissues of the anther. No histological effects are found before the completion of meiosis except in msg18. Subsequently their behavior becomes distinctly deviant. In msg5, 9, 14 and 18 soon after a normal meiosis the microspores begin to deteriorate and are almost completely deformed at a period corresponding to that just before microspore division in normal anthers. In msg10 deleterious effects on microspores first appear midway between the end of meiosis and the beginning of microspore karyokinesis.The tapetum remains nondegenerate and persistent in msg5, 10 and 14 but suddenly collapses after the free microspore stage in msg9. In msg18 it shows an early effect during the meiotic period, when failure in the last tapetal nuclear division (karyokinesis) results in an early collapse of this tissue.Nuclear DNA and histone in male-sterile sporogenous and tapetal tissues as measured by microspectrophotometry increase at the normal rate during the premeiotic S phase. However, in the sporogenous tissues, the subsequent DNA and histone syntheses that normally culminate in microspore mitosis are distinctly lacking. Thus in all male-steriles except msg10, the microspore nuclei show an actual loss in these two macromolecules and in msg10 there is an initial rise only for a short period, followed by a dramatic drop.Nuclear DNA and histone in tapetal tissues subsequently show variable behavior, which seems to be specific for each male-sterile line.The behavior of sporogenous and tapetal tissues thus lends support to the hypothesis that there is transport of substances, critical to development, between the porogenous tissue and tapetum. The effects on DNA-histone turnover, first in the sporogenous tissue and then in the tapetum, suggest that the action of msg5 and 9 is initiated within the microspores when they are still invested in a callose wall. On the other hand, in msg10 and 14 a reverse sequence indicates that the action is initiated in tapetal tissues. The effect in msg18 is a direct consequence of defective tapetal functioning.All male-steriles at the free microspore stage show drastic reductions in nucleolar volume (and hence in rRNA synthesis) accompanied by a high frequency of binucleolate microspore nuclei.