First Metaphase Of Meiosis Research Articles

Interspecies hybridization is not the end: the lesson from asexual fishes from European spined loaches complex (Cobitis)

Interspecies hybridization is not the end: the lesson from asexual fishes from European spined loaches complex (Cobitis)

Transmission of the Aegilops ovata chromosomes carrying gametocidal factors in hexaploid triticale (×Triticosecale Wittm.) hybrids.

The main aim of this work was to induce the chromosome rearrangements between Aegilops ovata (UUMM) and hexaploid triticale (AABBRR) by expression of the gametocidal factor located on the chromosome 4M. The Aegilops ovata × Secale cereale (UUMMRR) amphiploids and triticale ‘Moreno’ were used to produce hybrids by reciprocal crosses. Chromosome dynamics was observed in subsequent generations of hybrids during mitotic metaphase of root meristems and first metaphase of meiosis of pollen mother cells. Chromosomes were identified by genomic in situ hybridisation (GISH) and fluorescence in situ hybridisation (FISH) using pTa71, pTa791, pSc119.2 and pAs1 DNA probes. It has been shown that the origin of the genetic background had an influence on Aegilops chromosome transmission. Moreover, it has been reported that the preferential transmission of chromosome 4M appeared during both androgenesis and gynogenesis. It is also hypothesised that the expression of the triticale Gc gene suppressor had an influence on the semi-fertility of hybrids but did not inhibit the chromosome rearrangements. This paper also describes the double haploid production, which enabled to obtain plants with two identical copies of triticale chromosomes with translocations of Aegilops chromatin segments.

Allocation of the S-genome chromosomes of Aegilops variabilis Eig. carrying powdery mildew resistance in triticale (× Triticosecale Wittmack).

It has been hypothesized that the powdery mildew adult plant resistance (APR) controlled by the Pm13 gene in Aegilops longissima Schweinf. & Muschl. (SlSl) has been evolutionary transferred to Aegilops variabilis Eig. (UUSS). The molecular marker analysis and the visual evaluation of powdery mildew symptoms in Ae. variabilis and the Ae. variabilis × Secale cereale amphiploid forms (2n = 6x = 42, UUSSRR) showed the presence of product that corresponded to Pm13 marker and the lower infection level compared to susceptible model, respectively. This study also describes the transfer of Ae. variabilis Eig. (2n = 4x = 28, UvUvSvSv) chromosomes, carrying powdery mildew resistance, into triticale (× Triticosecale Wittm., 2n = 6x = 42, AABBRR) using Ae. variabilis × S. cereale amphiploid forms. The individual chromosomes of Ae. variabilis, triticale ‘Lamberto’ and hybrids were characterized by genomic and fluorescence in situ hybridization (GISH/FISH). The chromosome configurations of obtained hybrid forms were studied at first metaphase of meiosis of pollen mother cells (PMCs) using GISH. The statistical analysis showed that the way of S-genome chromosome pairing and transmission to subsequent hybrid generations was diploid-like and had no influence on chromosome pairing of triticale chromosomes. The cytogenetic study of hybrid forms were supported by the marker-assisted selection using Pm13 marker and visual evaluation of natural infection by Blumeria graminis, that allowed to select the addition or substitution lines of hybrids carrying chromosome 3Sv which were tolerant to the powdery mildew infection.

MAPK-Activated Protein Kinase 2 Is Required for Mouse Meiotic Spindle Assembly and Kinetochore-Microtubule Attachment

MAPK-activated protein kinase 2 (MK2), a direct substrate of p38 MAPK, plays key roles in multiple physiological functions in mitosis. Here, we show for the first time the unique distribution pattern of MK2 in meiosis. Phospho-MK2 was localized on bipolar spindle minus ends and along the interstitial axes of homologous chromosomes extending over centromere regions and arm regions at metaphase of first meiosis (MI stage) in mouse oocytes. At metaphase of second meiosis (MII stage), p-MK2 was localized on the bipolar spindle minus ends and at the inner centromere region of sister chromatids as dots. Knockdown or inhibition of MK2 resulted in spindle defects. Spindles were surrounded by irregular nondisjunction chromosomes, which were arranged in an amphitelic or syntelic/monotelic manner, or chromosomes detached from the spindles. Kinetochore–microtubule attachments were impaired in MK2-deficient oocytes because spindle microtubules became unstable in response to cold treatment. In addition, homologous chromosome segregation and meiosis progression were inhibited in these oocytes. Our data suggest that MK2 may be essential for functional meiotic bipolar spindle formation, chromosome segregation and proper kinetochore–microtubule attachments.

Unusual arrangement and behaviour of the sex chromosomes of Aphodius (Agolius) abdominalis Bonelli, 1812, and comparison with A. (A.) bonvouloiri Harold, 1860 (Coleoptera: Aphodiidae)

Aphodius abdominalis Bonelli, 1812 is shown to have a karyotype comprising nine pairs of autosomes and sex chromosomes which are X0 (male), XX (female). At fi rst metaphase of meiosis the X chromosome is linked to an au- tosomal bivalent by a darkly staining area of the cytoplasm, resembling the Xy p arrangement typical of Aphodius species, but giving nine, rather than 10, ele- ments in the nucleus. C-banding, which shows the centromeres, confi rms this unusual arrangement. A. bonvouloiri, the only other known species of subge- nus Agolius Mulsant et Rey, 1869, has a male karyotype with nine pairs of auto- somes and Xy sex chromosomes. No preparations of its meiosis are available.

Condensation of rye chromatin in somatic interphase nuclei of Ph1 and ph1b wheat

The Ph1 locus in hexaploid wheat (Triticum aestivum L.) enforces diploid-like behavior in the first metaphase of meiosis. To test the hypothesis that this chromosome pairing control is exercised by affecting the degree of chromatin condensation, the dispersion of rye chromatin in interphase nuclei in somatic tissues of wheat-rye chromosome translocations 1RS.1BL, 2RS.2BL, 2BS.2RL, 3RS.3DL and 5RS.5BL was compared in Ph1 and ph1b isogenic backgrounds. No significant differences in rye chromatin condensation that could be attributed to the Ph1 locus were detected. Regardless of the Ph1 status, each rye chromosome arm tested conformed to the general Rabl’s orientation and occupied portions of the nuclei proportional to their length. Earlier observations that indicated the involvement of Ph1 locus in rye chromatin condensation in wheat could have been due either to specific loci on the studied 5RL rye arm that control the chromosome condensation process or to damage to the genetic system controlling chromatin condensation in the existing ph1b stocks of wheat. That damage might have been caused by homoeologous recombination and uneven disjunction of chromosomes from multivalents.

Genome relationships in the genus Dasypyrum (Gramineae).

To elucidate the genome relationships in the genus Dasypyrum and the ancestry of tetraploid D. breviaristatum, two cytotypes of D. breviaristatum and D. villosum were reciprocally crossed with one another. Chromosome pairing at the first metaphase of meiosis and fertility were examined in the F1 hybrids and the parental plants. The mean pairing configuration and mean arm pairing frequency in D. villosum-D. breviaristatum (2x) hybrids were 11.12I + 1.44II per cell and 0.107, respectively, and they were almost completely sterile. In D. breviaristatum (4x)-D. breviaristatum (2x) hybrid, up to seven trivalents were formed, and the mean pairing configuration was 3.38I + 3.20II + 3.74III + 0.005IV per cell. The mean arm pairing frequency and relative affinity calculated in that F1 hybrid were 0.915 and 0.641, respectively. Seven bivalents and seven univalents were characteristically formed in D. villosum-D. breviaristatum (4x) hybrids. Based on the present results, we clearly concluded that the genome of diploid D. breviaristatum is distantly related to the genome V of D. villosum, and that these two species have different basic genomes. We, therefore, proposed the symbol Vb for the haploid genome of diploid cytotype of D. breviaristatum. Moreover, we concluded that tetraploid D. breviaristatum is an autotetraploid with doubled sets of the genomes homologous with that of diploid D. breviaristatum, and we proposed the genome constitution VbVb for the haploid genome set of tetraploid cytotype of D. breviaristatum. Furthermore, from the chromosome pairing in the F1 hybrids involving Moroccan and Greek accessions, it was suggested that complicated rearrangements of chromosome structure have occurred in tetraploid D. breviaristatum in its natural populations across the entire distribution area.

Meiotic chromosome interactions in inbred autotetraploid rye (Secale cereale)

Electron microscopy of whole-mount surface-spread synaptonemal complex complements and conventional light microscopy of chromosomes at first metaphase of meiosis were used to compare the relative frequencies of pairing configurations at the two stages in inbred autotetraploid rye (Secale cereale L.). Statistical tests showed significantly fewer multivalents at first metaphase than expectations based on random initiation of synapsis at each telomeric site within each group of four homologues. Direct observations of synaptic behaviour of chromosomes showed that this deviation is due primarily to a preponderance of bivalents during zygotene and pachytene. It is also the result of a significant drop in multivalent frequency from meiotic prophase to metaphase I, which is attributable both to a lack of chiasmata with which to consolidate multivalents and inhibition of chiasma formation in synaptonemal complex segments of multivalents that are nonhomologous.

Image analysis of C-banded chromosomes and pairing regionalization in wheat

C-banding and image analysis are used to characterize nine somatic chromosomes of wheat and to quantify a series of physical parameters (arm length, heterochromatic band intensity and position) in tetraploid Triticum turgidum and hexaploid T. aestivum wheat. The arm-by-arm meiotic association of the chromosomes at first meiotic metaphase is evaluated with respect to these parameters and genetic pairing regulators. The effect of the genetic factors is analyzed comparatively in homozygous lines or both normal and mutant lines (Ph1/Ph1, ph1a/ph1a, ph1b/ph1b, and ph1c/ph1c) and in aneuploids (ditelo-5BL and nulli-5B–tetra-5D). The pairing values were progressively reduced as follows: 'Chinese Spring' Ph1/Ph1 > 'Chinese Spring' dt-5BL > 'Chinese Spring' ph1a/ph1a > 'Chinese Spring' nulli-5B–tetra-5D > 'Chinese Spring' ph1b/ph1b > 'Cappelli' ph1c/ph1c. The results indicate that although a different contribution to overall pairing exists for each specific chromosome region, the differences in the genetic systems regulating pairing from line to line indiscriminately affected chiasma levels and did not lead to specific deviations in any line. The results seem to show that maintenance of chiasmata at first metaphase of meiosis depends on chromosome length and correlation is strong for the chance of double chiasmata. Moreover, there are indications that some C-bands, particularly in intercalary positions in chromosome arms 4AL, 2BL, 5BS, and 7BL, increase the frequency of chiasma at first metaphase. The pairing intensity in each specific chromosomal segment may be the product of an integrated action of chromosome length, the presence or absence of heterochromatin, and genetic factors.Key words: image analysis, heterochromatin, Triticum, C-banding, meiotic pairing.

Strategies of bivalent formation in allopolyploid plants

Allopolyploids constitute a large proportion of flowering plant species. They are the product of natural or synthetic hybridization between related diploid species or genera, and therefore contain three or more sets of chromosomes which are structurally and genetically different. Many allopolyploids are highly fertile and show disomic inheritance, because chiasma formation at first metaphase of meiosis is restricted to homologous chromosomes only. Observations of synaptonemal complexes during meiotic prophase have shown that the diploidization of these species can be achieved in several ways depending upon the synaptic behaviour of chromosomes and the strict localization of chiasmata. These strategies of bivalent formation are described and compared in several allopolyploid species, with particular emphasis upon the relative importance of structural and genotypic components of the process.

Meiosis and fertilization of the Japanese pearl oyster eggs at different temperature observed with a fluorescence microscope.

The events of meiosis and fertilization in Japanese pearl oyster eggs allowed to develop at dif-ferent temperatures (18°C, 23°C, and 28°C) were investigated with fluorescence microscope. Change of matemal and paternal chromatin of eggs at 23°C were as follows. Spawned eggs were at metaphase of first meiosis. Subsequent to sperm penetration most eggs completed first and second meiosis by 15 and 24 min after insemination, respectively. Female and male pronuclei were formed by 30 min after insemination. The chromatin of male and female pronuclei con-densed gradually and were finally observed as two groups of chromosomes. The two groups of chromosomes combined and formed on the metaphas plate for first cleavage. By 62 min most eggs completed first cleavage. It was observed at the higher temperature, that the eggs developed faster. Percentages of eggs which showed abnormal chromosome behavior were higher at 18°C and 28°C than at 23°C. Asynchronous development of eggs was observed in all temperature groups. Asynchrony of eggs development was more apparend at 18°C.

Elimination of multivalents during meiotic prophase in Scilla autumnalis. II. Tetraploid

The pairing behaviour of chromosomes during meiotic prophase in two Scilla autumnalis tetraploids was investigated by observing synaptonemal complexes from serial sections and whole-mount surface spreads. In one of the tetraploids with the genomic constitution AAB7B7 pairing at first metaphase of meiosis is restricted to homologous chromosomes and only bivalents appear. In the second tetraploid, AB7B7B7, some multivalents are found at first metaphase, but most of the configurations are bivalent. The bivalents, however, result from chiasma formation between homoeologous as well as homologous chromosomes. Both tetraploids show extensive multivalent formation at zygotene. The transformation of these multivalents to bivalents is described and interpreted in the two tetraploid forms.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination, polyploids.

Segregation of isoenzyme markers and meiotic pairing control genes in Lolium

The genetic basis of the control system responsible for suppressing the association of homoeologous chromosomes at first metaphase of meiosis in interspecific hybrids of Lolium was investigated by means of cytological and genetical analyses of a test cross between L. temulentum and L. perenne. It is concluded that more than one gene is involved. Linkage to a gene which codes for an Esterase enzyme of low electrophoretic mobility is clearly identified with the possibility that a second gene is associated with another Esterase locus. The phenotypic effect of individual pairing genes in relation to the distance between them and linked markers is discussed.

The genetics of meiotic chromosome pairing in Lolium temulentum x Lolium perenne tetraploids

The degree of preferential pairing of homologous chromosomes was estimated in a series of tetraploid hybrids of Lolium temulentum x Lolium perenne by means of cytological and genetic analyses. The correlations between the frequency of bivalents at first metaphase of meiosis in the hybrid tetraploids and the degree of preferential pairing calculated from the segregation pattern of isozyme alleles in a test cross was extremely high. The results showed clearly that suppression of heterogenetic pairing in these Lolium tetraploids is achieved by a genetic system involving the A chromosomes as well as the B chromosome system which has been known for some time. Certain similarities with the genetic system controlling pairing in polyploid wheats are discussed.

Identification of a diploidizing genotype of Lolium multiflorum

Thirty diploid populations of Lolium multiflorum were screened for genes that were capable of modifying meiosis in species hybrids. A standard genotype of L. temulentum was used as the tester species. Modified pairing at first metaphase of meiosis was identified in some of the hybrid progeny of a single plant from a population from Uruguay and also in one from Portugal. Evidence is presented to show that the high incidence of univalents in diploid hybrids of L. temulentum × L. multiflorum from Uruguay was due to the suppression of homoeologous chromosome association only. A proportion of equivalent triploid and tetraploid hybrids had an excess of bivalents at first metaphase of meiosis. This was confirmed by comparison of the observed meiotic data with that expected from three separate mathematical models. It is concluded that this single plant from the Uruguayan population was heterozygous for genes that suppress chiasmate association of homoeologous chromosomes.Key words: interspecific hybrid, Lolium, chromosome pairing.

The potential for diploidizing Lolium multiflorum × L. perenne tetraploids

The possibility of diploidizing meiosis in tetraploid hybrids of the two closely related Lolium species, L. multiflorum and L. perenne, was investigated using specific genotypes of both parents. Both these parental genotypes had previously been shown to reduce homoeologous pairing in a separate but wider cross with the inbreeder L. temulentum. A preponderance of bivalents was recorded at first metaphase of meiosis in several of the hybrid progeny with the frequency of multivalents being reduced to 0.6/pollen mother cell in one plant. Although it is not unambiguously established that the bivalents so formed are solely between homologous chromosomes, it is highly likely that this is so. It is concluded that it is feasible to genetically modify the pattern of meiosis even in tetraploid hybrids of species of similar karyotypes.Key words: chromosome pairing, Lolium, interspecific hybrid.

Hierarchical control of multivalent formation in natural populations of a hexaploid perennial grass ( Koeleria vallesiana )

Observations on variation in multivalent frequency in Koeleria vallesiana are reported. The species is self-incompatible and has a standard karyotype divided into six haploid genomes each of four metacentric and three submetacentric euchromatic chromosomes (2.6–3.6 μm), one of the submetacentrics being a nucleolar–organizer with a minute satellite on the short arm. Of the 83 plants examined, 67 had the hexaploid number 2 n = 6 x = 42,12 were aneuploids (2 n = 41-45) and four had a single B-chromosome. At first metaphase of meiosis 92% of chromosomes form bivalents. Quadrivalents are the most common multivalents (5.5%) and sexivalents (1.1 %), the largest. Each chromosome of the standard complement is equally likely to be incorporated in a multivalent. There is extensive variation in chiasma number per pollen mother cell between cells (21–43) and plants (22.6–38.8) but not between populations (27.6–31.5) or countries (29.1–30.1). Variation in multivalent frequency is partly chiasma-dependent and partly synaptic in origin. It is not associated with the variation in chromosome number. Phenotypic variation at synapsis influences the frequency of pairing partner exchange and is found both between plants and between populations. Some populations are more variable in synaptic behaviour than others. The mechanisms determining such synaptic variation are unknown but their investigation should provide a useful insight into the general nature of chromosome homology as well as shedding light on evolutionary processes in polyploids.

Chromosome structural variation in Aegilops ovata L.

Seventy three strains of Aegilops ovata L. collected in Jordan, Lebanon Syria, Turkey, Greece and Italy by The Botanical Mission of University of Kyoto to Eastern Mediterranean Countries were crossed with one common pollen parent and chromosome pairing at first metaphase of meiosis and pollen fertility of their F1 plants were observed.Based on chromosome pairing, 73 strains were classified into four chromosome types, that is, (I) pollen parent type (one strain), (II) one reciprocal translocation type (55), (III) type with two independent reciprocal translocations (14) and (IV) type with two translocations involving three chromosomes (3).From the frequency of quadrivalents, it is suggested that there are some kinds of reciprocal translocations in Ae. Ovata. It is revealed that no complicated chromosomal differentiation has occured in this species.

THE EFFECT OF COLCHICINE ON CHROMOSOME PAIRING

Beginning at 120 hours prior to first metaphase of meiosis (MI) a 0.03% aqueous solution of colchicine was injected into the boot of pentaploid (hexaploid triticale × tetraploid wheat) hybrids developing at 20 °C ± 1° under continuous illumination. Colchicine applied 40 h or less prior to MI had no effect on chromosome pairing, while its application 40 h or more prior to MI induced a steady decline, culminating in a 40% reduction in chromosome pairing at about 80 h from MI. Between 48 and 35 h before MI (late premeiotic interphase to early zygotene) meiocytes underwent a period of active nucleolar fusion. The time, therefore, at which the colchicine sensitive aspects of chromosome pairing were completed coincided with the completion of nucleolar fusion. From comparison with other findings it was concluded that there is a colchicine sensitive bouquet stage which appears in leptotene and early zygotene; this bouquet is responsible for active nucleolar fusion and final close association between homologous chromosomes.

THE EFFECT OF GENES CONTROLLING DIFFERENT DEGREES OF HOMOEOLOGOUS PAIRING ON QUADRIVALENT FREQUENCY IN INDUCED AUTOTETRAPLOID LINES OF TRITICUM LONGISSIMUM

Different genotypes of Triticum longissimum are known to either promote or suppress chromosome pairing in crosses with polyploid wheats. Lines that promote homoeologous pairing are here designated as intermediate pairing lines, while those which have no such effect or suppress pairing are known as low pairing lines. To determine a possible effect of these genotypes on homologous pairing, tetraploidy was induced in both lines and chromosomal pairing was studied at first metaphase of meiosis. While the two induced autotetraploids did not differ in chiasma frequency or in the number of paired chromosomal arms, they differed significantly in multivalent frequency; the intermediate-pairing autotetraploid exhibited the same multivalent frequency as that expected on the basis of two telomeric initiation sites, while the low pairing autotetraploid exhibited a significantly lower frequency. It is assumed that in the autotetraploid the low pairing genotype does not affect meiotic pairing per se, but modifies the pattern of homologous association in a similar manner to that known in polyploids and caused by diploidization genes. It is speculated that the tendency for bivalent pairing in the low pairing autotetraploid is due to spatial separation of the four homologous chromosomes in somatic and premeiotic cells into two groups of two.