Absence Of Chiasmata Research Articles

Asynapsis and meiotic restitution in tomato male meiosis induced by heat stress.

Susceptibility of the reproductive system to temperature fluctuations is a recurrent problem for crop production under a changing climate. The damage is complex as multiple processes in male and female gamete formation are affected, but in general, particularly pollen production is impaired. Here, the impact of short periods of elevated temperature on male meiosis of tomato (Solanum lycopersicon L.) is reported. Meiocytes in early stage flower buds exposed to heat stress (>35°C) exhibit impaired homolog synapsis resulting in partial to complete omission of chiasmata formation. In the absence of chiasmata, univalents segregate randomly developing unbalanced tetrads and polyads resulting in aneuploid spores. However, most heat-stressed meiotic buds primarily contain balanced dyads, indicating a propensity to execute meiotic restitution. With most meiocytes exhibiting a complete loss of chiasma formation and concomitantly showing a mitotic-like division, heat stress triggers first division restitution resulting in clonal spores. These findings corroborate with the plasticity of male meiosis under heat and establish a natural route for the induction of sexual polyploidization in plants and the engineering of clonal seed.

Achiasmate male meiosis in two Cymatia species (Hemiptera, Heteroptera, Corixidae).

The karyotype and male meiosis, with a particular focus on the presence or absence of chiasmata between the homologs, were studied in the water boatman species Cymatia rogenhoferi (Fieber) and Cymatia coleoptrata (Fabricius) (Corixidae, Cymatiainae). It is shown that the species have 2n = 33 (28A+2m+X1X2Y) and 2n = 24 (20A+2m+XY) respectively, post-reduction of sex chromosomes, and achiasmate meiosis of an alignment type in males. Cytogenetic and some morphological diagnostic characters separating Cymatia Flor from the rest of Corixidae are discussed.

The Role of Rice HEI10 in the Formation of Meiotic Crossovers

HEI10 was first described in human as a RING domain-containing protein that regulates cell cycle and cell invasion. Mice HEI10mei4 mutant displays no obvious defect other than meiotic failure from an absence of chiasmata. In this study, we characterize rice HEI10 by map-based cloning and explore its function during meiotic recombination. In the rice hei10 mutant, chiasma frequency is markedly reduced, and those remaining chiasmata exhibit a random distribution among cells, suggesting possible involvement of HEI10 in the formation of interference-sensitive crossovers (COs). However, mutation of HEI10 does not affect early recombination events and synaptonemal complex (SC) formation. HEI10 protein displays a highly dynamic localization on the meiotic chromosomes. It initially appears as distinct foci and co-localizes with MER3. Thereafter, HEI10 signals elongate along the chromosomes and finally restrict to prominent foci that specially localize to chiasma sites. The linear HEI10 signals always localize on ZEP1 signals, indicating that HEI10 extends along the chromosome in the wake of synapsis. Together our results suggest that HEI10 is the homolog of budding yeast Zip3 and Caenorhabditis elegans ZHP-3, and may specifically promote class I CO formation through modification of various meiotic components.

Repositioning of Aurora B Promoted by Chiasmata Ensures Sister Chromatid Mono-Orientation in Meiosis I

During meiosis I, kinetochores of sister chromatids are juxtaposed or fused and mono-orient, while homologous chromosomes that are paired by chiasmata (bivalents) have to biorient. In the absence of chiasmata, biorientation of sister chromatids (univalents), which carries a risk of aneuploidy, has been occasionally detected in several species, including humans. We show in fission yeast that biorientation of fused sister kinetochores predominates during early prometaphase I. Without chiasmata, this undesirable biorientation of univalents persists and eventually evades the spindle assembly checkpoint, provoking abnormal anaphase. When univalents are connected by chiasmata or by an artificial tether, this erroneous attachment is converted to monopolar attachment and stabilized. This stabilization is apparently achieved by a chromosome configuration that brings kinetochores to the outer edge of the bivalent, while bringing Aurora B, a destabilizer of kinetochore-microtubule attachment, inward. Our results elucidate how chiasmata favor biorientation of bivalents over that of univalents at meiosis I.

Sgo1 is required for co-segregation of sister chromatids during achiasmate meiosis I

The reduction of chromosome number during meiosis is achieved by two successive rounds of chromosome segregation, called meiosis I and meiosis II. While meiosis II is similar to mitosis in that sister kinetochores are bi-oriented and segregate to opposite poles, recombined homologous chromosomes segregate during the first meiotic division. Formation of chiasmata, mono-orientation of sister kinetochores and protection of centromeric cohesion are three major features of meiosis I chromosomes which ensure the reductional nature of chromosome segregation. Here we show that sister chromatids frequently segregate to opposite poles during meiosis I in fission yeast cells that lack both chiasmata and the protector of centromeric cohesion Sgo1. Our data are consistent with the notion that sister kinetochores are frequently bi-oriented in the absence of chiasmata and that Sgo1 prevents equational segregation of sister chromatids during achiasmate meiosis I.

Evidence Implicating CCNB1IP1, a RING Domain-Containing Protein Required for Meiotic Crossing Over in Mice, as an E3 SUMO Ligase

The RING domain-containing protein CCNB1IP1 (Cyclin B1 Interacting Protein 1) is a putative ubiquitin E3 ligase that is essential for chiasmata formation, and hence fertility, in mice. Previous studies in cultured cells indicated that CCNB1IP1 targets Cyclin B for degradation, thus playing a role in cell cycle regulation. Mice homozygous for a mutant allele (mei4) of Ccnb1ip1 display no detectable phenotype other than meiotic failure from an absence of chiasmata. CCNB1IP1 is not conserved in key model organisms such as yeast and Drosophila, and there are no features of the protein that implicate clear mechanisms for a role in recombination. To gain insight into CCNB1IP1’s function in meiotic cells, we raised a specific antibody and determined that the protein appears in pachynema. This indicates that CCNB1IP1 is involved with crossover intermediate maturation, rather than early (leptotene) specification of a subset of SPO11-induced double strand breaks towards the crossover pathway. Additionally, a yeast 2-hybrid (Y2H) screen revealed that CCNB1IP1 interacts with SUMO2 and a set of proteins enriched for consensus sumoylation sites. The Y2H studies, combined with scrutiny of CCNB1IP1 domains, implicate this protein as an E3 ligase of the sumoylation cascade. We hypothesize CCNB1IP1 represents a novel meiosis-specific SUMO E3 ligase critical to resolution of recombination intermediates into mature chiasmata.

Chiasma redistribution in the presence of different sized supernumerary segments in a grasshopper: dependence on nonhomologous synapsis

Eight different sized supernumerary segments located at distal ends of the long arms of chromosomes M4, M5, M6, and S8 of the grasshopper Stenobothrus festivus were studied in males with regard to the synaptic process and chiasma distribution in the bivalents that carry them. The M4, M5, and M6 bivalents heterozygous for extra segments were always monochiasmate, in contrast to their bichiasmate condition observed in basic homozygotes. Furthermore, the presence of any of these extra segments led to chiasma redistribution in the carrier bivalents, so that such chiasmata were formed preferentially further away from the extra segment. The intensity of this effect is dependent on the size of the segment. Not all heteromorphic bivalents exhibited synaptonemal complexes with equalized axes at pachytene, but there was always a variable proportion of heterosynapsis around the distal ends of the long arms that was dependent on both the size of the segment and the size of the carrier chromosome. It is proposed that the absence of chiasmata in nonhomologous synapsed regions is responsible for the results obtained. Length measurements of the different extra segments and their carrier chromosomes between pachytene and diplotene indicated that synaptonemal complex is underrepresented in supernumerary heterochromatin.

Direct Evidence of a Role for Heterochromatin in Meiotic Chromosome Segregation

We have investigated the mechanism that enables achiasmate chromosomes to segregate from each other at meiosis I in D. melanogaster oocytes. Using novel cytological methods, we asked whether nonexchange chromosomes are paired prior to disjunction. Our results show that the heterochromatin of homologous chromosomes remains associated throughout prophase until metaphase I regardless of whether they undergo exchange, suggesting that homologous recognition can lead to segregation even in the absence of chiasmata. However, partner chromosomes lacking homology do not pair prior to disjunction. Furthermore, euchromatic synapsis is not maintained throughout prophase. These observations provide a physical demonstration that homologous and heterologous achiasmate segregations occur by different mechanisms and establish a role for heterochromatin in maintaining the alignment of chromosomes during meiosis.

The relationship between synapsis and chiasma distribution in grasshopper bivalents heterozygous for supernumerary segments

The relationship between chiasma distributions and pairing behaviour of grasshopper bivalent heterozygous for supernumerary segments has been analysed. The extra segments were located at the telomeric end of the long arm in chromosome S8 of Chorthippus jacobsi and at interstitial position in chromosomes S8 and M7 of Euchorthippus pulvinatus. In all cases these heteromorphic bivalents exhibited fully paired synaptonemal complexes with equalized axial lengths either at late zygotene or early pachytene, that is, heterosynapsis in regions near the extra segments is achieved at these meiotic stages. It is proposed that the absence of chiasmata in those regions in which nonhomologous pairing took place, would lead to chiasma redistributions observed in these bivalents when compared with those observed in bivalents in which extra segments are lacking.

Chiasma distribution and centromere orientation in a spontaneous interchange in the grasshopper Chorthippus vagans

One of 18 Chorthippus vagans males from a natural population was heterozygous for an interchange between the L1 and M4 chromosomes when examined cytologically. Chiasma distribution within multiple chromosome configurations and the relation between chiasma formation in the interstitial segments and centromere orientation were investigated. Our results confirm previous observations that adjacent-2 is the most common orientation in absence of chiasmata on the interstitial segments.Key words: Chorthippus, interchange, interstitial segments, chiasma distribution, orientation.

Hybrids between Agropyron trachycaulum and A. intermedium

Interspecific hybrids between Agropyron trachycaulum (Link) Malte (2n=28 and 56) as female and A. intermedium (Host) Beauv. (2n=42) were obtained by controlled pollination and embryo culture. Five pentaploid hybrids (2n=35 or aneuploid) were closest to A. intermedium in morphology, whereas a septaploid hybrid (2n=49), containing the tetraploid A. trachycaulum chromosome complement, was more like A. trachycaulum. Pentaploid hybrids showed achiasmatic and chiasmatic all types at meiosis, and in one of such hybrids the latter cells provided an average metaphase I configuration of 19.57I, 6.86II, 0.43II and 0.10IV. An aneuploid hybrid (2n=37) displayed extensive chromosome fragmentation at anaphase I, and other hybrids displayed absence of chiasmata in about half of meiotic cells. Pollen was usually shrivelled and non-staining. The septaploid hybrid had an average metaphase I configuration of 8.08I, 20.31II and 0.05III, and had 40% stainable pollen. Chromosome behaviour in parent genotypes was in accordance with genome formulae of SSHH for tetraploid A. trachycaulum and NNN1N1X4X4 for A. intermedium. Bivalent formation in the hybrids was attributed to pairing within H,S (septaploid hybrids) and N genomes and between H and S genomes (pentaploid hybrid). Multivalent formation was attributed to translocations and/or to segmental homologies within the N and X genomes.

Absence of chiasmata from the heteromorphic region of chromosome I during spermatogenesis in Triturus cristatus carnifex

Analysis of squash preparations of spermatocytes from crested newts, Triturus cristatus carnifex, has shown that in most cells at least one large bivalent regularly fails to form chiasmata in one arm-pair. Feulgen microphotometry of diplotene and metaphase bivalents has shown that it is the largest bivalent in each cell which shows chiasma failure in one arm-pair. A C-banding technique which identifies chromosome I by virtue of a long, darkly stained region in its long arm, was used to confirm the absence of chiasmata from one arm-pair of the longest bivalent, and specifically from the darkly stained region. The achiasmate region which chromosome I exhibits during spermatogenesis, corresponds to the “heteromorphic region” of oocyte lampbrush bivalent I in which chiasmata never form. A possible correlation between the complete absence of crossing-over from the heteromorphic region and unusual cytological and molecular features which it exhibits, are discussed.

Absence of Chiasmata and Formation of a Complex Chromosomal Body in the Spermatogenesis of the ScorpionPalamnaeus Longimanus

SUMMARYThe behaviour of chromosomes during the spermatogenesis of the scorpion Palamnaeus longimanus has been studied. The following facts have been noticed: 1. The spermatogonial metaphase shows 64 chromosomes, and so does the oogonial metaphase.2. The male is the heterogametic sex, possessing X- and Y- chromosome.3. All the specimens of this species examined have been found to be reciprocal translocation heterozygotes for two pairs of chromosomes, which may, for example, be designated as AB, BC, CD, DA. The behaviour of these chromosomes is subject to variation. Mostly they pair to produce, at the first metaphase, two bivalents, or a single quadrivalent; sometimes pairing fails altogether or partly, resulting in the appearance of four univalents or one bivalent and two univalents. Hence the total number of chromosomal bodies at the first metaphase fluctuates between 31 and 34. This fluctuation is due at times to the dissociation of other bivalents.4. The bivalents lack chiasmata.5. The first anaphase poleward movement of chromosomes is markedly asynchronous.6. The chromosomes are monocentric.

The chromosomes of mantids (Orthoptera; Manteidae) in relation to taxonomy.

The distinguishing cytological characters, including chromosome number and sex chromosome mechanism, have been tabulated for all mantids thus far studied cytologically—including 16 species (starred in Table 1) not hitherto examined. Data on 46 species in 17 subfamilies are reviewed. The XO♂—XX ♀ sex chromosome mechanism represents the ancestral condition for the family and has been retained in 14 of the subfamilies sampled. The distribution of the X1X2Y♂—X1X1X2X2♀ mechanism, previously known in the subfamilies Manteinae and Choeradodinae, is extended to include Mellierinae, Acromantinae and Vatinae. Cytological evidence indicates a monophyletic origin of the compound sex chromosomes and necessitates a reconsideration of the taxonomic association of XO and X1X2Y forms in the same subfamily, specifically of Miomantis and Callimantis with the other Manteinae, and Aethalocroa with Vates and Phyllovates in the Vatinae. The pre-metaphase stretch is established as a regular stage in male meiosis in 14—and is absent in 3—of the species checked for this character. It should prove of taxonomic value when a wider sampling of the lower categories is available. The prolongation of parallel pairing of homologous chromosomes in male meiosis appears to be characteristic of the Manteidae as a whole. No correlation is apparent between the degree of its expression and taxonomic category. Since it provides a mechanism, additional or alternative to chiasmata, for the post-pachytene association of homologues, its establishment permits the evolution of non-chiasmate meiosis in the group. Two structural types of bivalents—one with, one without chiasmata—are found. Present evidence favors the multiple origin of the non-chiasmate type within the family, and since both types may coexist in the karyotype of the same sex of a single species, presence or absence of chiasmata cannot be considered a valid taxonomic criterion.

Crossing-over in the Males of Drosophila subobscura

MEIOSIS in the males of the higher Diptera is characterized by absence of chiasmata. This means that as a rule genetical crossing-over occurs only in females. There are, however, a few exceptional families in Drosophila melanogaster1,2 and virilis3, the constitution of which can only be explained as due to crossing-over in the father. In these cases the exceptional offspring occurred in batches rather than singly. It was therefore supposed that crossing-over had taken place in one of the early spermatogonial divisions, though there is no cytological basis for this assumption.