Feed-back regulation of successive meiotic cytokinesis

The paper considers a number of abnormal phenotypes with impaired temporal regulation of cytokinesis during the meiotic division of pollen mother cells. The phenomenon of “non-stop” cytokinesis with blocked arrest of the phragmoplast centrifugal motion and cell plate growth as well as incomplete and premature cytokinesis are described. The obtained data suggested a model for regulation of the processes involved in the arrest of the main cytokinesis processes during its completion in the plant meiosis.     

Dynamics of microtubular cytoskeleton in higher plant meiosis. IX. The cycle accomplishment. Transition from phragmoplast to radial microtubule system

In this study we analysed the terminal step of cytoskeleton cycle in higher plant meiosis: transition from phragmoplast to radial interphase configuration. Wild type meiosis in a range of mono- and dicotyledonous species was studied. A number of cytoskeleton abnormalities on this stage was described in meiotic mutants, haploids and wide hybrids of various species. We described processes of cytoskeleton rearrangements on this stage: disjunction of phragmoplast MTs, their shortening and the role of daughter cell membranes. The independence of the interphase radial MT system formation from the previous steps of cytoskeleton cycle and from nuclear envelope cycle is proposed.     

A new type of microtubular cytoskeleton in microsporogenesis of Lavatera thuringiaca L.

Summary. In Lavatera thuringiaca, kariokinesis and simultaneous cytokinesis during the meiotic division of microsporogenesis follow a procedure similar to that which takes place in the majority of members of the class Angiospermae. However, chondriokinesis occurs in a unique way found only in species from the family Malvaceae. Chondriokinesis in such species is well documented, but the relationship between the tubulin cytoskeleton and rearrangement of cell organelles during meiosis in L. thuringiaca has not been precisely defined so far. In this study, the microtubular cytoskeleton was investigated in dividing microsporocytes of L. thuringiaca by immunofluorescence. The meiotic stages and positions of cell organelles were identified by staining with 4′,6-diamidino-2-phenylindole. We observed that, during prophase I and II, changes in microtubular cytoskeleton configurations have unique features, which have not been described for other plant species. At the end of prophase I, organelles (mostly plastids and mitochondria) form a compact envelope around the nucleus, and the subsequent phases of kariokinesis take place within this arrangement. At this point of cell division, microtubules surround the organelle envelope and separate it from the peripheral cytoplasm, which is devoid of plastids and mitochondria. In telophase I, two newly formed nuclei are tightly surrounded by the cell organelle envelopes, and these are separated by the phragmoplast. Later, when the phragmoplast disappears, cell organelles still surround the nuclei but also move a little, starting to occupy the place of the disappearing phragmoplast. After the breakup of tetrads, the radial microtubule system is well developed, and cell organelles can still be observed as a dense envelope around the nuclei. At a very late stage of sporoderm development, the radial microtubule system disappears, and cell organelles become gradually scattered in the cytoplasm of the microspores. Using colchicines, specific inhibitors of microtubule formation, we investigated the relationship between the tubulin cytoskeleton and the distribution of cell organelles. Our analysis demonstrates that impairment of microtubule organization, which constitutes only a single component of the cytoskeleton, is enough to disturb typical chondriokinesis in L. thuringiaca. This indicates that microtubules (independent of microfilaments) are responsible for the reorganization of cell organelles during meiotic division. Correspondence: D. Tchórzewska, Department of Plant Anatomy and Cytology, Maria Curie-Skłodowska University, Akademicka 19, 20-033 Lublin, Poland.     

Processes providing the phragmoplast centrifugal movement in cereal meiosis

A group of new abnormalities in meiotic division in the mother cells of cereal pollen that affect the processes of the centrifugal movement of a phragmoplast in successive cytokinesis is presented for the first time. These phenotypes represent new information on the formation and operation of motile phragmoplast and confirm our model of centrifugal movement as B-anaphase modification.     

Porcine oocytes are most vulnerable to the mycotoxin deoxynivalenol during formation of the meiotic spindle

Deoxynivalenol (DON, vomitoxin) is a secondary metabolite and mycotoxin produced by Fusarium species that occurs with a high prevalence in cereals and grains intended for human and animal consumption. Pigs are considered to be the most sensitive animal species and exposure to DON results in reduced feed intake, reduced performance and cause alterations in the expression of markers of inflammation and cell cycle regulation. The objective of this study was to determine how DON possibly affects the oocyte developmental potential in vitro at concentrations which correspond to those observed in practice. To evaluate DON toxicity during specific stages of oocyte meiosis, cumulus-oocyte complexes were exposed to 0.02, 0.2, or 2 μM DON. Exposure to the highest DON concentration inhibited cumulus expansion and induced cumulus cell death. After exposure for 42 h, DON at all concentrations reduced Metaphase II formation and led to malformations of the meiotic spindle. Despite spindle malformations, exposure to different concentrations of DON did not lead to increased percentages of blastomeres with abnormal ploidy in embryos. Spindle malformation occurred by DON exposure during formation of meiotic spindles at Metaphase I and II, but embryo development was also reduced when oocytes were exposed to DON during Prophase I. Together, these results indicate that exposure to DON via contaminated food or feed can affect oocyte developmental competence by interfering directly with microtubule dynamics during meiosis, and by disturbing oocyte cytoplasmic maturation through other as yet undetermined mechanisms.     

Processes of phragmoplast centrifugal movement in cereal meiosis

A group of new meiotic division abnormalities affecting processes of phragmoplast centrifugal movement in successive cytokinesis in cereal pollen mother cells is described. These phenotypes present new information about motile phragmoplast formation and operation and confirm our model of centrifugal movements as B-ana-phase modification.     

Microfilament Distribution in Maize Meiotic Mutants Correlates with Microtubule Organization

Microtubules and microfilaments often codistribute in plants; their presumed interaction can be tested with drugs although it is not always clear that these are without side effects. In this study, we exploited mutants defective in meiotic cell division to investigate in a noninvasive way the relationship between the two cytoskeletal elements. By staining unfixed, permeabilized cells with rhodamine-phalloidin, spatial and temporal changes in microfilament distribution during maize meiosis were examined. In wild-type microsporocytes, a microtubule array that radiates from the nucleus disappeared during spindle formation and returned at late telophase. This result differed from the complex cytoplasmic microfilament array that is present at all stages, including karyokinesis and cytokinesis. During division, a second class of microfilaments also was observed in the spindle and phragmoplast. To analyze this apparent association of microtubules and microfilaments, we examined several meiotic mutants known to have stage-specific disruptions in their microtubule arrays. Two mutations that altered the number or form of meiotic spindles also led to a dramatic reorganization of F-actin. In contrast, rearrangement of nonspindle, cytoplasmic microtubules did not lead to concomitant changes in F-actin distribution. These results suggested that microtubules and microfilaments interact in a cell cycle-specific and site-specific fashion during higher plant meiosis.     

Synaptonemal complex spreading in plants: Technical aspects and preliminary observations on the synaptonemal complex inPaeonia andOrnithogalum

A modified method for obtaining surface spread synaptonemal complexes (SCs) from pollen mother cells has been developed. Silver-stained SC-preparation of one monocotyledonous species,Ornithogalum flavovirens, and one dicotyledonous plant,Paeonia tenuifolia, were analysed by light and electron microscopy. The SCs in both species frequently broke into roughly equally sized SC pieces with staggered or blunt breakpoints. The telomeric ends of the SCs normally were lacking attachment organelles and, therefore, were hardly distinguishable from blunt breakpoints. Interstitially, shorter stretches of SCs often exhibited unpaired lateral elements. This phenomenon is discussed with regard to segmental incomplete homology and as it relates to the normal sequence of SC morphological changes during the course of meiotic prophase.     

八种纤毛虫减数分裂基因的分子进化研究

减数分裂是真核生物适应性进化的重要机制,以8种纤毛虫作为实验对象,通过生物信息学方法对其14个减数分裂基因进行了鉴定及分子进化研究。结果表明:(1)不同的纤毛虫种类存在一些特异性的减数分裂基因的丢失与复制现象;(2)减数分裂相关基因在纤毛虫中很保守;(3)纤毛虫减数分裂重要的同源重组过程是在真核生物中不常见的Ⅱ型。本研究表明,纤毛虫减数分裂可能代表了真核生物较原始的减数分裂方式,在进化的过程中很保守,为研究真核生物减数分裂起源与进化提供了重要线索。     

2n gametes in the potato: essential ingredients for breeding and germplasm transfer

2n gametes are the result of meiotic mutations occurring during micro – and mega-sporogenesis. They have been identified in several plant species of different taxa. The potato is probably the crop plant where they have been most intensively studied and also more appropriately used for the genetic improvement of cultivated genotypes. This paper reviews how 2n gametes allow potato breeders to broaden the genetic basis of the cultivated Solanum tuberosum, introducing both new genes for the improvement of traits of interest and allelic diversity to maximize heterozygosity. We provide molecular and breeding evidence that, in the potato, 2n gametes represent a unique tool to transfer target genes from wild forms to the cultivated tetraploid gene pool. In fact, species directly crossable to S. tuberosum haploids can be exploited through sexual polyploidization crossing schemes. For those which have developed crossability barriers, specific crossing schemes based on ploidy bridges can be designed. In this paper we also give possible hypotheses to explain conflicting results on the genetic control and meiotic mutations responsible for 2n-gamete formation in the potato. Received: 22 February 2000 / Accepted: 29 February 2000     

AtMAC stabilizes the phragmoplast by crosslinking microtubules and actin filaments during cytokinesis

The phragmoplast, a structure crucial for the completion of cytokinesis in plant cells, is composed of antiparallel microtubules (MTs) and actin filaments (AFs). However, how the parallel structure of phragmoplast MTs and AFs is maintained, especially during centrifugal phragmoplast expansion, remains elusive. Here, we analyzed a new Arabidopsis thaliana MT and AF crosslinking protein (AtMAC). When AtMAC was deleted, the phragmoplast showed disintegrity during centrifugal expansion, and the resulting phragmoplast fragmentation led to incomplete cell plates. Overexpression of AtMAC increased the resistance of phragmoplasts to depolymerization and caused the formation of additional phragmoplasts during cytokinesis. Biochemical experiments showed that AtMAC crosslinked MTs and AFs in vitro, and the truncated AtMAC protein, N-CC1, was the key domain controlling the ability of AtMAC. Further analysis showed that N-CC1(51–154) is the key domain for binding MTs, and N-CC1(51–125) for binding AFs. In conclusion, AtMAC is the novel MT and AF crosslinking protein found to be involved in regulation of phragmoplast organization during centrifugal phragmoplast expansion, which is required for complete cytokinesis.     

Arabidopsis Fused kinase TWO-IN-ONE dominantly inhibits male meiotic cytokinesis

Arabidopsis Fused kinase TWO-IN-ONE (TIO) controls phragmoplast expansion through its interaction with the Kinesin-12 subfamily proteins that anchor the plus ends of interdigitating microtubules in the phragmoplast midzone. Previous analyses of loss-of-function mutants and RNA interference lines revealed that TIO positively controls both somatic and gametophytic cell cytokinesis; however, knowledge of the full spectrum of TIO functions during plant development remains incomplete. To characterize TIO functions further, we expressed TIO and a range of TIO variants under control of the TIO promoter in wild-type Arabidopsis plants. We discovered that TIO-overexpressing transgenic lines produce enlarged pollen grains, arising from incomplete cytokinesis during male meiosis, and show sporophytic abnormalities indicative of polyploidy. These phenotypes arose independently in TIO variants in which either gametophytic function or the ability of TIO to interact with Kinesin-12 subfamily proteins was abolished. Interaction assays in yeast showed TIO to bind to the AtNACK2/TETRASPORE, and plants doubly homozygous for kinesin-12a and kinesin-12b knockout mutations to produce enlarged pollen grains. Our results show TIO to dominantly inhibit male meiotic cytokinesis in a dosage-dependent manner that may involve direct binding to a component of the canonical NACK-PQR cytokinesis signaling pathway.     

丝状真菌中的RNA干扰及其应用技术

RNA干扰是真核生物中相对保守的一种基因特录后表达调控机制,它通过双链RNA介导细胞内mRNA发生特异性降解或翻译抑制,从而调控靶基因的表达.对丝状真菌中RNA压制和减数分裂沉默等现象的研究表明,与动、植物一样,丝状真菌中也存在RNA干扰现象.通过对RNA压制缺失突变株和减教分裂沉默缺失突变株的一系列分子生物学研究,获得了与之密切相关的一系列蛋白,而这些蛋白在结构和功能上与动、植物RNA干扰途径的蛋白高度相似,这些结果证明了丝状真菌中的RNA存在干扰现象.RNA干扰技术作为丝状真菌分子生物学研究或遗传改造的工具具有特殊的意义,因为丝状真菌具有多核和发生非同源重组频率高的特点,难以用基因敲除手段进行改造.系统地介绍丝状真菌中的RNA干扰途径以及使用RNA干扰对真菌进行遗传改造的方法.     

Loading of the centromeric histone H3 variant during meiosis–how does it differ from mitosis?

In eukaryotic phyla studied so far, the essential centromeric histone H3 variant (CENH3) is loaded to centromeric nucleosomes after S-phase (except for yeast) but before mitotic segregation (except for metazoan). While the C-terminal part of CENH3 seems to be sufficient for mitotic centromere function in plants, meiotic centromeres neither load nor tolerate impaired CENH3 molecules. However, details about CENH3 deposition in meiocytes are unknown (except for Drosophila). Therefore, we quantified fluorescence signals after the immunostaining of CENH3 along meiotic and mitotic nuclear division cycles of rye, a monocotyledonous plant. One peak of fluorescence intensity appeared in the early meiotic prophase of pollen mother cells and a second one during interkinesis, both followed by a decrease of CENH3. Then, the next loading occurred in the male gametophyte before its first mitotic division. These data indicate that CENH3 loading differs between mitotic and meiotic nuclei. Contrary to the situation in mitotic cycles, CENH3 deposition is biphasic during meiosis and apparently linked with a quality check, a removal of impaired CENH3 molecules, and a general loss of CENH3 after each loading phase. These steps ensure an endowment of centromeres with a sufficient amount of correct CENH3 molecules as a prerequisite for centromere maintenance during mitotic cycles of the microgametophyte and the progeny. From a comparison with data available for Drosophila, we hypothesise that the post-divisional mitotic CENH3 loading in metazoans is evolutionarily derived from the post-divisional meiotic loading phase, while the pre-divisional first meiotic loading has been conserved among eukaryotes.     

Unravelling the mystery of female meiotic drive: where we are

Female meiotic drive is the phenomenon where a selfish genetic element alters chromosome segregation during female meiosis to segregate to the egg and transmit to the next generation more frequently than Mendelian expectation. While several examples of female meiotic drive have been known for many decades, a molecular understanding of the underlying mechanisms has been elusive. Recent advances in this area in several model species prompts a comparative re-examination of these drive systems. In this review, we compare female meiotic drive of several animal and plant species, highlighting pertinent similarities.     

Interaction of antiparallel microtubules in the phragmoplast is mediated by the microtubule-associated protein MAP65-3 in Arabidopsis

In plant cells, microtubules (MTs) in the cytokinetic apparatus phragmoplast exhibit an antiparallel array and transport Golgi-derived vesicles toward MT plus ends located at or near the division site. By transmission electron microscopy, we observed that certain antiparallel phragmoplast MTs overlapped and were bridged by electron-dense materials in Arabidopsis thaliana. Robust MT polymerization, reported by fluorescently tagged End Binding1c (EB1c), took place in the phragmoplast midline. The engagement of antiparallel MTs in the central spindle and phragmoplast was largely abolished in mutant cells lacking the MT-associated protein, MAP65-3. We found that endogenous MAP65-3 was selectively detected on the middle segments of the central spindle MTs at late anaphase. When MTs exhibited a bipolar appearance with their plus ends placed in the middle, MAP65-3 exclusively decorated the phragmoplast midline. A bacterially expressed MAP65-3 protein was able to establish the interdigitation of MTs in vitro. MAP65-3 interacted with antiparallel microtubules before motor Kinesin-12 did during the establishment of the phragmoplast MT array. Thus, MAP65-3 selectively cross-linked interdigitating MTs (IMTs) to allow antiparallel MTs to be closely engaged in the phragmoplast. Although the presence of IMTs was not essential for vesicle trafficking, they were required for the phragmoplast-specific motors Kinesin-12 and Phragmoplast-Associated Kinesin-Related Protein2 to interact with MT plus ends. In conclusion, we suggest that the phragmoplast contains IMTs and highly dynamic noninterdigitating MTs, which work in concert to bring about cytokinesis in plant cells.     

Fertilization and early embryonic development in the blue fox (Alopex lagopus)

A total of 15 blue fox vixens aged 1–6 years were mated, 12 once on the first day of estrus and three a second time 48 hr after the first mating, and were killed 4 hr to 8 days following mating. Ova were collected from the oviducts, evaluated by stereomicroscopy, and studied by transmission (TEM; N = 49, 12 vixens) or scanning (SEM, N = 11, three vixens) electron microscopy. At 0–3 days after ovulation, the ova had not cleaved and were at different stages of meiotic maturation. In about one-half of these ova, representing all stages of meiotic maturation, a decondensing sperm head without nuclear envelope or a small pronucleus with partial nuclear envelope was observed. No clear relationship was found between maternal meiotic stage and the stage of paternal pronucleus formation. Sperm tails were never identified in the ooplasm. Cortical granules were released after sperm penetration at early stages of meiotic maturation. Thus the block against polyspermic penetration was activated during maturation of the oocyte. The first two-cell stage appeared 4 days after ovulation (3 days after mating), the first four-cell stage the following day (day 5), and the first eight-cell stage 6 days after ovulation (5 days after mating). In a single vixen mated late (7 days postovulation) two- to four-cell stages appeared the following day (day 8). This indicates that the time required for the first cleavage division decreases with increasing interval from ovulation to mating. The development of a functional nucleolus with fibrillar centers and fibrillar and granular components at the eight-cell stage indicates activation of embryonic RNA synthesis in fox embryos at the six- to eight-cell stage, suggesting that the embryonic genome is activated at this stage. © 1993 Wiley-Liss, Inc.     

鸭跖草科杜若(Pollia japonica Thunb.)的减数分裂研究

首次对鸭跖草科杜若(Pollia japonicaThunb.)进行了花粉母细胞减数分裂观察,并重新报道了该种的染色体数目为2n=32。结果显示,减数分裂中期I构型为16Ⅱ,并且观察到次级联会现象。减数分裂后期I和后期Ⅱ存在落后染色体、染色体断片、二次分裂不同步等异常现象,统计各时期畸形率都低于10%。随机统计花粉粒活性,成熟率达到90%以上。这说明杜若的减数分裂过程基本正常,也证明了2n=32的体细胞染色体数目是可信的。     

Feeding ecology of mandrills (Mandrillus sphinx) in campo animal reserve,Cameroon

A field study on the ecology of mandrills (Mandrillus sphinx) was carried out for 28 months in Cameroon. Fresh food remnants and large quantities of fresh feces were collected by following the groups. Analyses of these products indicated that fruit (including seeds), monocotyledonous plant leaves and insects (especially ants and termites), were frequently eaten. Mandrills mostly ate the plant and animal foods in the lower forest stratum and on the ground. Fallen seeds and monocotyledonous plant leaves were eaten more frequently in the minor fruiting season than in the major fruiting season presumably to compensate for the shortage of fresh fruit during the former. Daily travel distances were shorter during the minor fruiting season than during the major fruiting season, because in the minor fruiting season mandrills forage for small food items, such as the new leaves and piths of monocotyledons and fallen seeds which are sparsely distributed on the ground, while in the major fruiting season they search for widely distributed food such as fruit. The daily pattern of group movement and a food intake experiment suggest that mandrills move and feed continuously throughout the day. Use of fallen seeds and monocotyledonous plant leaves appears to enable mandrills to maintain a terrestrial life in the tropical rain forest. The feeding and ranging characteristics of mandrills are basically similar to those of other baboon species in open land, though their environments differ extremely.