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YA is needed for proper nuclear organization to transition between meiosis and mitosis in Drosophila
Katharine L Sackton, Jacqueline M Lopez, Cindy L Berman, Mariana F Wolfner
BMC Developmental Biology , 2009, DOI: 10.1186/1471-213x-9-43
Abstract: We find that meiosis is completed normally in the absence of YA function. The first defects in embryos and eggs from mutant mothers first appear just after the completion of meiosis, and are seen as abnormal associations among the resultant haploid nuclei. These defects are associated with asynchronies in the cell cycle-dependent chromatin condensation state of the haploid nuclei. However, we find evidence of DNA replication in the absence of YA function.Our data suggest YA function is needed at a control point, following meiosis II and the initiation of the first postmeiotic S phase, which is sensitive to the chromatin condensation state of the haploid meiotic products.Mature Drosophila oocytes are arrested in metaphase of meiosis I. To begin development, oocytes must undergo a number of changes that are collectively called egg activation [1-5]. The egg is hydrated, proteins in its vitelline membrane undergo cross-linking, certain maternal RNAs are polyadenylated and translated while others are degraded [6], the phosphorylation state of many proteins changes [7-9], the cortical actin cytoskeleton is reorganized [10], and meiosis resumes. Egg activation in Drosophila [1] and other insects [11-13], is independent of fertilization (in contrast to the situation in other animals) [14]; it is triggered instead by passage through the female's reproductive tract. Despite differences in trigger, the initial cause of egg activation in essentially all animals appears to be an increase in intracellular calcium [4,5,15]. Upon activation, Drosophila oocytes complete meiosis rapidly without cytokinesis, resulting in four haploid nuclei located near the membrane and aligned perpendicular to the long axis of the egg [16,17]. The chromosomes of all four meiotic products decondense and appear morphologically to be in a state similar to interphase [18]. In unfertilized, activated eggs, all four meiotic products synchronously replicate their DNA once, and then condense their chromosome
Caracterización cariotípica en mitosis y meiosis del robalo blanco Centropomus undecimalis (Pisces: Centropomidae)
Arias-Rodriguez,Lenin; Indy,Jeane R.; Ahumada-Hernández,Rosa I.; Barragán-Cupido,Helen; ávalos-Lázaro,Antonieta A.; Páramo-Delgadillo,Salomón;
Revista de Biología Tropical , 2011,
Abstract: karyotypic characterization in mitosis and meiosis of the common snook centropomus undecimalis (pisces: centropomidae). the common snook centropomus undecimalis inhabits marine, brackish and freshwater habitats in the western central atlantic ocean, including the gulf of mexico. common snook is an economically important fish in many localities, nevertheless the number of studies on its biology and genetics are still few. the present study attempts to establish the cytogenetic profiles of the specimens collected in paraiso municipality tabasco, mexico. tissue of five females and eight male organisms were processed by conventional cytological techniques to obtain chromosome slides of high quality in order to assemble the karyotype. the results from the kidney tissue analysis showed that 85.1% of 288 mitosis had a 2n=48 chromosomes, and 52.8% of 104 meiosis exhibited the haploid number 1n=24. the diploid karyotype showed 48 monoarmed chromosomes of the telocentric (t) type. there was no chromosome heteromorphism between females and males. the diploid karyotype was very similar to that observed in the majority of marine fishes. rev. biol. trop. 59 (2): 683-692. epub 2011 june 01.
Understanding of Mitosis and Meiosis in Higher Secondary Students of Northeast India and the Implications for Genetics Education
Education , 2012, DOI: 10.5923/j.edu.20120203.04
Abstract: Cell division, perhaps the most important is among the most difficult topics in biology to teach. With respect to the observation of the previous study on understanding of ‘genetic information’ in higher secondary (junior college level) students, the present study was carried out to examine the same students’ understanding of mitosis and meiosis. A total of 289 students from three undergraduate colleges were given written questionnaire having both fixed and free answer-type questions. It was found that students had a wide range of misconceptions in the process of cell division. The types of alternative concepts were identified in this study. The study revealed that a significant number of students did not understand the primary differences between the two cell division processes, the importance of the maintenance of chromosome numbers in mitosis, the significance of the formation of germ cells with haploid number of chromosomes and the recombination events taking place during meiosis and their implications. This results corroborates the earlier study among middle school children, conducted by the “Learning in Science Research Group” of Leeds University in UK. The probable reasons for the confusions surfaced in this study and the possible approaches to overcome the difficulties in classroom teaching of cell division processes, particularly in countries like India are discussed in this paper.
The Cell Cycle Timing of Centromeric Chromatin Assembly in Drosophila Meiosis Is Distinct from Mitosis Yet Requires CAL1 and CENP-C  [PDF]
Elaine M. Dunleavy equal contributor,Nicole L. Beier equal contributor,Walter Gorgescu,Jonathan Tang,Sylvain V. Costes,Gary H. Karpen
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1001460
Abstract: CENP-A (CID in flies) is the histone H3 variant essential for centromere specification, kinetochore formation, and chromosome segregation during cell division. Recent studies have elucidated major cell cycle mechanisms and factors critical for CENP-A incorporation in mitosis, predominantly in cultured cells. However, we do not understand the roles, regulation, and cell cycle timing of CENP-A assembly in somatic tissues in multicellular organisms and in meiosis, the specialized cell division cycle that gives rise to haploid gametes. Here we investigate the timing and requirements for CID assembly in mitotic tissues and male and female meiosis in Drosophila melanogaster, using fixed and live imaging combined with genetic approaches. We find that CID assembly initiates at late telophase and continues during G1 phase in somatic tissues in the organism, later than the metaphase assembly observed in cultured cells. Furthermore, CID assembly occurs at two distinct cell cycle phases during male meiosis: prophase of meiosis I and after exit from meiosis II, in spermatids. CID assembly in prophase I is also conserved in female meiosis. Interestingly, we observe a novel decrease in CID levels after the end of meiosis I and before meiosis II, which correlates temporally with changes in kinetochore organization and orientation. We also demonstrate that CID is retained on mature sperm despite the gross chromatin remodeling that occurs during protamine exchange. Finally, we show that the centromere proteins CAL1 and CENP-C are both required for CID assembly in meiosis and normal progression through spermatogenesis. We conclude that the cell cycle timing of CID assembly in meiosis is different from mitosis and that the efficient propagation of CID through meiotic divisions and on sperm is likely to be important for centromere specification in the developing zygote.
Mutations in Drosophila Greatwall/Scant Reveal Its Roles in Mitosis and Meiosis and Interdependence with Polo Kinase  [PDF]
Vincent Archambault equal contributor,Xinbei Zhao equal contributor
PLOS Genetics , 2007, DOI: 10.1371/journal.pgen.0030200
Abstract: Polo is a conserved kinase that coordinates many events of mitosis and meiosis, but how it is regulated remains unclear. Drosophila females having only one wild-type allele of the polo kinase gene and the dominant Scant mutation produce embryos in which one of the centrosomes detaches from the nuclear envelope in late prophase. We show that Scant creates a hyperactive form of Greatwall (Gwl) with altered specificity in vitro, another protein kinase recently implicated in mitotic entry in Drosophila and Xenopus. Excess Gwl activity in embryos causes developmental failure that can be rescued by increasing maternal Polo dosage, indicating that coordination between the two mitotic kinases is crucial for mitotic progression. Revertant alleles of Scant that restore fertility to polo–Scant heterozygous females are recessive alleles or deficiencies of gwl; they show chromatin condensation defects and anaphase bridges in larval neuroblasts. One recessive mutant allele specifically disrupts a Gwl isoform strongly expressed during vitellogenesis. Females hemizygous for this allele are sterile, and their oocytes fail to arrest in metaphase I of meiosis; both homologues and sister chromatids separate on elongated meiotic spindles with little or no segregation. This allelic series of gwl mutants highlights the multiple roles of Gwl in both mitotic and meiotic progression. Our results indicate that Gwl activity antagonizes Polo and thus identify an important regulatory interaction of the cell cycle.
Caracterización cariotípica en mitosis y meiosis del robalo blanco Centropomus undecimalis (Pisces: Centropomidae)  [cached]
Lenin Arias-Rodriguez,Jeane R. Indy,Rosa I. Ahumada-Hernández,Helen Barragán-Cupido
Revista de Biología Tropical , 2011,
Abstract: El robalo blanco Centropomus undecimalis, vive en hábitats marinos, salobres y dulceacuícolas en el océano Atlántico occidental, incluyendo el golfo de México. La especie, es económicamente importante en varias localidades, no obstante los estudios sobre su biología y genética son hasta el momento pocos. El presente estudio tiene como propósito, la caracterización citogenética de especímenes recolectados en el municipio de Paraíso, Tabasco, México. Cinco hembras y ocho machos fueron procesados por técnicas citológicas convencionales para la obtención de preparaciones cromosómicas de buena calidad para elaborar el cariotipo. Los resultados del análisis del tejido del ri ón, mostraron que 85.1% de 288 mitosis tienen 2n=48 cromosomas y 52.8% de 104 meiosis exhiben el número haploide de 1n=24. El cariotipo diploide mostro 48 cromosomas monorrámeos de tipo telocéntrico (T). No se observó heteromorfismo cromosómico entre hembras y machos. El cariotipo diploide fue similar a los observados en la mayoría de peces marinos. Karyotypic characterization in mitosis and meiosis of the common snook Centropomus undecimalis (Pisces: Centropomidae). The common snook Centropomus undecimalis inhabits marine, brackish and freshwater habitats in the Western Central Atlantic Ocean, including the Gulf of Mexico. Common snook is an economically important fish in many localities, nevertheless the number of studies on its biology and genetics are still few. The present study attempts to establish the cytogenetic profiles of the specimens collected in Paraiso Municipality Tabasco, Mexico. Tissue of five females and eight male organisms were processed by conventional cytological techniques to obtain chromosome slides of high quality in order to assemble the karyotype. The results from the kidney tissue analysis showed that 85.1% of 288 mitosis had a 2n=48 chromosomes, and 52.8% of 104 meiosis exhibited the haploid number 1n=24. The diploid karyotype showed 48 monoarmed chromosomes of the telocentric (T) type. There was no chromosome heteromorphism between females and males. The diploid karyotype was very similar to that observed in the majority of marine fishes. Rev. Biol. Trop. 59 (2): 683-692. Epub 2011 June 01.
Haploid Meiosis in Arabidopsis: Double-Strand Breaks Are Formed and Repaired but Without Synapsis and Crossovers  [PDF]
Marta Cifuentes, Maud Rivard, Lucie Pereira, Liudmila Chelysheva, Raphael Mercier
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0072431
Abstract: Two hallmark features of meiosis are i) the formation of crossovers (COs) between homologs and ii) the production of genetically-unique haploid spores that will fuse to restore the somatic ploidy level upon fertilization. In this study we analysed meiosis in haploid Arabidopsis thaliana plants and a range of haploid mutants to understand how meiosis progresses without a homolog. Extremely low chiasma frequency and very limited synapsis occurred in wild-type haploids. The resulting univalents segregated in two uneven groups at the first division, and sister chromatids segregated to opposite poles at the second division, leading to the production of unbalanced spores. DNA double-strand breaks that initiate meiotic recombination were formed, but in half the number compared to diploid meiosis. They were repaired in a RAD51- and REC8-dependent manner, but independently of DMC1, presumably using the sister chromatid as a template. Additionally, turning meiosis into mitosis (MiMe genotype) in haploids resulted in the production of balanced haploid gametes and restoration of fertility. The variability of the effect on meiosis of the absence of homologous chromosomes in different organisms is then discussed.
Cyclin E and Cdk2 Control GLD-1, the Mitosis/Meiosis Decision, and Germline Stem Cells in Caenorhabditis elegans  [PDF]
Johan Jeong,Jamie M. Verheyden,Judith Kimble
PLOS Genetics , 2011, DOI: 10.1371/journal.pgen.1001348
Abstract: Coordination of the cell cycle with developmental events is crucial for generation of tissues during development and their maintenance in adults. Defects in that coordination can shift the balance of cell fates with devastating clinical effects. Yet our understanding of the molecular mechanisms integrating core cell cycle regulators with developmental regulators remains in its infancy. This work focuses on the interplay between cell cycle and developmental regulators in the Caenorhabditis elegans germline. Key developmental regulators control germline stem cells (GSCs) to self-renew or begin differentiation: FBF RNA–binding proteins promote self-renewal, while GLD RNA regulatory proteins promote meiotic entry. We first discovered that many but not all germ cells switch from the mitotic into the meiotic cell cycle after RNAi depletion of CYE-1 (C. elegans cyclin E) or CDK-2 (C. elegans Cdk2) in wild-type adults. Therefore, CYE-1/CDK-2 influences the mitosis/meiosis balance. We next found that GLD-1 is expressed ectopically in GSCs after CYE-1 or CDK-2 depletion and that GLD-1 removal can rescue cye-1/cdk-2 defects. Therefore, GLD-1 is crucial for the CYE-1/CDK-2 mitosis/meiosis control. Indeed, GLD-1 appears to be a direct substrate of CYE-1/CDK-2: GLD-1 is a phosphoprotein; CYE-1/CDK-2 regulates its phosphorylation in vivo; and human cyclin E/Cdk2 phosphorylates GLD-1 in vitro. Transgenic GLD-1(AAA) harbors alanine substitutions at three consensus CDK phosphorylation sites. GLD-1(AAA) is expressed ectopically in GSCs, and GLD-1(AAA) transgenic germlines have a smaller than normal mitotic zone. Together these findings forge a regulatory link between CYE-1/CDK-2 and GLD-1. Finally, we find that CYE-1/CDK-2 works with FBF-1 to maintain GSCs and prevent their meiotic entry, at least in part, by lowering GLD-1 abundance. Therefore, CYE-1/CDK-2 emerges as a critical regulator of stem cell maintenance. We suggest that cyclin E and Cdk-2 may be used broadly to control developmental regulators.
Advances in the Research on Plant Meiosis
植物减数分裂研究进展

LI Ya-Xuan,
李雅轩

植物学报 , 1999,
Abstract: The work on regulation of gene expression in the process of plant meiosis has been paid attention to by researchers. Advances in important issues in the studies of plant meiosis, including eremitic mitosis, premises, synopsizing of tetrad, and spindle formation, are summarized in this paper.
Reconstruction of the kinetochore: a prelude to meiosis
Haruhiko Asakawa, Tokuko Haraguchi, Yasushi Hiraoka
Cell Division , 2007, DOI: 10.1186/1747-1028-2-17
Abstract: Eukaryotic chromosomes are spatially organized within the nucleus. While such nuclear architecture provides a physical framework for the genetic activities of chromosomes, this framework however is dynamic, able to change its functional organization during the cell cycle or developmental stages. Local chromatin structures change as chromosomes undergo processes such as replication, transcription, recombination and repair. During chromosome segregation, a specialized structure called kinetochore is formed on the centromeric DNA. Global organization of chromosomes within the nucleus can also change in association with their activities. A prominent example of reconstruction of the nuclear and chromosomal frameworks is observed during the transition from mitosis to meiosis.Meiosis is a process that produces haploid gametes from parental diploid germ cells in sexually reproducing organisms. In this process, a single round of chromosome replication is followed by two rounds of chromosome segregation. A characteristic feature of meiosis is the behavior of sister chromatids in the first division (meiosis I). In meiosis I, homologous chromosomes segregate while sister chromatids remain held together. Sister chromatids then segregate in the second division (meiosis II). Reductional segregation of homologous chromosomes in meiosis I requires a recombination-mediated physical link between a pair of homologous chromosomes. This regulated segregation of homologous chromosomes and sister chromatids is achieved by selective use of monopolar and bipolar structures of the kinetochore, which provide a structural basis for monopolar and bipolar attachment of the spindle, respectively. Monopolar attachment of the spindle to sister kinetochores leads to movement of sister chromatids to the same pole in meiosis I. Bipolar attachment of the spindle to sister kinetochores causes segregation to the opposite poles in meiosis II (as well as in mitosis).Meiotic reorganization of the chromosome
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