Meiotic Chromosome Behavior Research Articles

Integrated cytological and transcriptomic analyses provide new insights into restoration of pollen viability in synthetic allotetraploid Brassica carinata.

Upregulation of genes involved in DNA damage repair and sperm cell differentiation leads to restoration of pollen viability in synthetic allotetraploid B. carinata after chromosome doubling. Apart from the well-known contribution of polyploidy to crop improvement, polyploids can also be induced for other purposes, such as to restore the viability of sterile hybrids. The mechanism related to viability transition between the sterile allodiploid and the fertile allotetraploid after chromosome doubling are not well understood. Here, we synthesised allodiploid B. carinata (2n = 2x = 17) and allotetraploid B. carinata (2n = 4x = 34) as models to investigate the cytological and transcriptomic differences during pollen development. The results showed that after chromosome doubling, the recovery of pollen viability in allotetraploid was mainly reflected in the stabilisation of microtubule spindle morphology, normal meiotic chromosome behaviour, and normal microspore development. Interestingly, the deposition and degradation of synthetic anther tapetum were not affected by polyploidy. Transcription analysis showed that the expression of genes related to DNA repair (DMC1, RAD51, RAD17, SPO11-2), cell cycle differentiation (CYCA1;2, CYCA2;3) and ubiquitination proteasome pathway (UBC4, PIRH2, CDC53) were positively up-regulated during pollen development of synthetic allotetraploid B. carinata. In summary, these results provide some refreshing updates about the ploidy-related restoration of pollen viability in newly synthesised allotetraploid B. carinata.

Kinesin-1-like protein PSS1 is essential for full-length homologous pairing and synapsis in rice meiosis.

The pairing and synapsis of homologous chromosomes are crucial for their correct segregation during meiosis. The LINC (Linker of Nucleoskeleton and Cytoskeleton) complex can recruit kinesin protein at the nuclear envelope, affecting telomere bouquet formation and homologous pairing. Kinesin-1-like protein Pollen Semi-Sterility1 (PSS1) plays a pivotal role in male meiotic chromosomal behavior and is essential for fertility in rice. However, its exact role in meiosis, especially as kinesin involved in homologous pairing and synapsis, has not been fully elucidated. Here, we generated three pss1 mutants by genome editing technology to dissect PSS1 biological functions in meiosis. The pss1 mutants exhibit alterations in the radial microtubule organization at pachytene and manifest a deficiency in telomere clustering, which is critical for full-length homologous pairing. We reveal that PSS1 serves as a key mediator between chromosomes and cytoskeleton, thereby regulating microtubule organization and transmitting the force to nuclei to facilitate homologous chromosome pairing and synapsis in meiosis.

Cytogenetic analysis of meiotic behaviour and stability in a trigeneric hybrid (triticale x trigopiro).

Trigeneric hybrids in Triticeae may help to establish evolutionary relationships among different genomes present in the same cellular genetic background and to transfer different alien characters into cultivated wheat. In the present study, a trigeneric hybrid involving species of Triticum, Secale, and Thinopyrum was synthesized by crossing hexaploid triticale with hexaploid trigopiro. The meiotic behaviour of chromosomes belonging to different genomes was analyzed, using routine and in situ hybridization techniques in F1, F2, and F3 generations of the trigeneric hybrid. The purpose of this study was to determine the chromosome number and genomic constitution and to discuss the mechanisms involved in the stabilization of the artificial tricepiro hybrids. The chromosome number of the trigeneric F1 hybrid was 2n = 42. Between 12 and 16 bivalents were observed in the central zone of the equatorial meiotic plate and between 9 and 18 univalents were found in the periphery of the MI equatorial plate. Seven of these univalents showed hybridization signals with rye DNA. Lagging rye and non-rye chromosomes and separation of sister chromatids were found in anaphase I. Tetrads with a maximum of six micronuclei, with and without hybridization signals of rye DNA, were observed. After three generations, meiotic cells revealed the presence of 42 chromosomes and 21 bivalents in diakinesis cells. The presence of 14 rye (Secale cereale) chromosomes and the complete pairing of chromosomes in F3 hybrids suggest that rye chromosomes would be preferentially transmitted to the progeny and that an elimination mechanism would act on chromosomes of Thinopyrum and wheat D genome.

Meiotic chromosome behaviour of a newly recorded ant-like spider, Myrmarachne melanocephala MacLeay, 1839 from Manipur, India

Cytological and chromosomal studies of ant-like spiders Myrmarachne melanocephala MacLeay, 1839, were undertaken with 12 males captured alive in the months of January to July 2023 from three habitats. The haploid count of male specimens was observed to be 13: 4 acrocentric (including X chromosome), 6 subtelocentric, 2 submetacentric, and 1 metacentric and showed X0 sex determination mechanisms, so the diploid count of the species was 25 (13+12). The single sex chromosome occupied roughly 4-6 per cent of the nuclear volume prominently in the Interphase – Prophase I stage. The structure of X chromosome in interphase stage was circular-rectangular block. The peculiar shape of rod-shaped X chromosome was maintained from early pre-leptotene stage till the end of the division particularly the Prophase I. The synapsis started early from late leptotene and duration of zygotene was long enough to visualize the perfect ones in late zygotene. There were nine diplotene bivalents with interstitial chiasma.

The chromatin-associated 53BP1 ortholog, HSR-9, regulates recombinational repair and X chromosome segregation in the Caenorhabditis elegans germ line.

53BP1 plays a crucial role in regulating DNA damage repair pathway choice and checkpoint signaling in somatic cells; however, its role in meiosis has remained enigmatic. In this study, we demonstrate that the Caenorhabditis elegans ortholog of 53BP1, HSR-9, associates with chromatin in both proliferating and meiotic germ cells. Notably, HSR-9 is enriched on the X chromosome pair in pachytene oogenic germ cells. HSR-9 is also present at kinetochores during both mitotic and meiotic divisions but does not appear to be essential for monitoring microtubule-kinetochore attachments or tension. Using cytological markers of different steps in recombinational repair, we found that HSR-9 influences the processing of a subset of meiotic double-stranded breaks into COSA-1-marked crossovers. Additionally, HSR-9 plays a role in meiotic X chromosome segregation under conditions where X chromosomes fail to pair, synapse, and recombine. Together, these results highlight that chromatin-associated HSR-9 has both conserved and unique functions in the regulation of meiotic chromosome behavior.

Meiotic chromosomal behaviour of Artemisia amygdalina Decne: A critically endangered medicinal plant, endemic to the North-western Himalaya

The limited geographic distribution of endemic species renders them more susceptible to extinction risks stemming from a myriad of factors. One such factor could be meiotic constraints, which may directly or indirectly impact the reproductive success of the endemic plant species. Thus, comprehensive research on meiotic behaviour is essential for implementing species conservation measures. This study represents the first report on the male meiotic behaviour of Artemisia amygdalina Decne., a critically endangered endemic medicinal plant species of the Kashmir Himalaya. We procured the plant material from three different locations in the Kashmir Himalaya, and the chromosome number of the species from all sites was found to be 2n=18 (x = 9, n = 9), indicating its diploid nature. Various types of chromosomal abnormalities were found in these populations, including stickiness, univalents, out-of-plate bivalents, laggards, bridges, disturbed telophase, micronuclei, abnormal pollen grains formation and seed set formation. The overall percentage of chromosomal abnormalities varied among the populations, from 8.58 % to 25.16 %. Pollen sterility also varied among different populations, with maximum pollen sterility of 23.21 % and a minimum of 5.96 % across populations. The present findings will not only help in updating the chromosome atlas with the addition of a new report on chromosome number but also contribute to the understanding of the reproductive success of A. amygdalina. Further ecological and reproductive studies can facilitate the creation of effective management and conservation strategies for this species.

The scaffold nucleoporins SAR1 and SAR3 are essential for proper meiotic progression in Arabidopsis thaliana.

Nuclear Pore Complexes (NPCs) are embedded in the nuclear envelope (NE), regulating macromolecule transport and physically interacting with chromatin. The NE undergoes dramatic breakdown and reformation during plant cell division. In addition, this structure has a specific meiotic function, anchoring and positioning telomeres to facilitate the pairing of homologous chromosomes. To elucidate a possible function of the structural components of the NPCs in meiosis, we have characterized several Arabidopsis lines with mutations in genes encoding nucleoporins belonging to the outer ring complex. Plants defective for either SUPPRESSOR OF AUXIN RESISTANCE1 (SAR1, also called NUP160) or SAR3 (NUP96) present condensation abnormalities and SPO11-dependent chromosome fragmentation in a fraction of meiocytes, which is increased in the double mutant sar1 sar3. We also observed these meiotic defects in mutants deficient in the outer ring complex protein HOS1, but not in mutants affected in other components of this complex. Furthermore, our findings may suggest defects in the structure of NPCs in sar1 and a potential link between the meiotic role of this nucleoporin and a component of the RUBylation pathway. These results provide the first insights in plants into the role of nucleoporins in meiotic chromosome behavior.

Bridging the cytogenetic gap in Trichoptera (Insecta): first karyotypic data on Neotropical species and insights into chromosomal evolution in caddisflies

Abstract Trichoptera are a diverse group of insects with aerial adults and aquatic immature stages. Despite their importance in freshwater environments, fundamental aspects of their biology are unknown, and no chromosomal studies have been performed in Neotropical species. The aim of this study was to provide the first cytogenetic analysis of four Trichoptera species from the Neotropics. We analysed the meiotic development and chromosome behaviour in Smicridea (Rhyacophylax) pampeana Flint (Annulipalpia: Hydropsychidae), Marilia flexuosa Ulmer (Integripalpia: Odontoceridae), Triplectides misionensis Holzenthal (Integripalpia: Leptoceridae), and Grumicha grumicha (Vallot) (Integripalpia: Sericostomatidae) by conventional cytogenetic procedures. The chromosome numbers are 2n = 31/32 (female/male) in S. (R.) pampeana, 2n = 57 (female) in M. flexuosa, 2n = 47 (female) in T. misionensis, and 2n = 35 (female) in G. grumicha. All four species have a simple sex chromosome system Z/ZZ (female/male). Females are the heterogametic sex, and their meiosis is achiasmatic. Our results together with available cytogenetic data provide more information on the karyology of Trichoptera and contribute to the current scientific knowledge of the possible mechanisms involved in chromosomal evolution. Based on all the evidence, we propose the existence of possible positive relationships between biological traits, ecological strategies, and cytogenetic features in Trichoptera.

Meiotic abnormalities in sugarcane (Saccharum spp.) and parental species: Evidence for peri‐ and paracentric inversions

AbstractThe modern cultivars of sugarcane (Saccharum spp.) are highly polyploid and accumulate aneuploidies due to their history of domestication, genetic improvement and interspecific hybrid origin involving the domesticated sweet species Saccharum officinarum (‘noble cane’) and the wild Saccharum spontaneum, both with an evolutionary history of polyploidy. The first hybrids were backcrossed with S. officinarum, and selection from progenies in subsequent generations established the genetic basis of modern cultivars. Saccharum genome complexity has inspired several molecular studies that have elucidated aspects of sugarcane genome constitution, architecture and cytogenetics. Herein, we conducted a comparative analysis of the meiotic behaviour of representatives of the parentals S. officinarum and S. spontaneum, and the commercial variety, SP80‐3280. S. officinarum, an octoploid species, exhibited regular meiotic behaviour. In contrast, S. spontaneum and SP80‐3280 exhibited several abnormalities from metaphase I to the end of division. We reported and typified, for the first time, the occurrence of peri‐ and paracentric inversions. Using in‐situ hybridisation techniques, we were able to determine how pairing association occurred at diakinesis, the origin of lagging chromosomes and, in particular, the mitotic chromosome composition of SP80‐3280. Interestingly, S. spontaneum and recombinant chromosomes showed the most marked tendency to produce laggards in both divisions. Future attempts to advance knowledge on sugarcane genetics and genomics should take meiotic chromosome behaviour information into account.

Cytogenetic Study and Pollen Viability of Phalaenopsis Queen Beer 'Mantefon'.

Intergeneric and interspecific hybridization has been employed for the breeding of Phalaenopsis to transfer desirable traits between species, producing novel phenotypes with improved size, color, form, and flower-bearing ability. These characteristics are often enhanced; however, many of these hybrids are triploids and have reduced or complete sterility, for example, Phalaenopsis Queen Beer 'Mantefon', an important novelty-type cultivar in Asia, particularly in China, Japan, and Republic of Korea. Despite the increasing demand for the crop for ornamental purposes, little is known about its cytogenetics, which is essential for breeding and, consequently, crop improvement. In this study, karyotyping using fluorescence in situ hybridization, meiotic chromosome behavior analysis, pollen staining, and in vitro viability germination tests were performed to understand the cause of hybrid sterility and pollen abnormality in Phalaenopsis Queen Beer 'Mantefon' from a cytogenetic perspective. Viability tests revealed pollen infertility at all flower developmental stages, confirmed by the absence of pollen tube growth. Aberrant chromosomal behavior was observed in pollen mother cells (PMCs), frequently forming univalents, chromosomal bridges, and laggards during the entire meiotic process. PMCs were also divided irregularly into sporads with varying numbers of micronuclei, which may be responsible for pollen sterility in this cultivar. Altogether, the cytogenetic analyses provided insights into the pollen development of Phalaenopsis Queen Beer 'Mantefon' and the conceivable causes of its infertility.

Influence of Hormonal Stimulation on the Oocyte Chromosome Apparatus of the Common Frog

Late vitellogenic oocytes of the common frog, Rana temporaria, represent a promising model for studying the behavior of meiotic chromosomes, since at the diplotene stage, they unite into a karyosphere, which in R. temporaria is believed to have an extrachromosomal capsule – unlike in Xenopus laevis, a classic model object of cell biology and developmental biology. However, in comparison with Xenopus, the strict breeding seasonality of R. temporaria significantly limits the possibility of using its oocytes as an experimental model. By adapting classical hormonal stimulation protocols proposed for anurans including Xenopus, we were able to obtain R. temporaria oocytes with a fully developed karyosphere outside the breeding season, namely in December–January. We observed pronounced changes in the chromosomal apparatus of oocytes with a double injection of human chorionic gonadotropin (hCG) at a dose of 500 IU. In this case, chromosomes undergo compaction and aggregation, leading to the formation of a characteristic chromosomal “knot” (karyosphere), the morphological features of which corresponded to those in R. temporaria oocytes at the beginning of the natural breeding season. Based on the proposed protocol for the use of hCG for out-of-season stimulation of oogenesis in R. temporaria, it can be further refined to obtain more stable results and improve the quality of oocytes.

Chromosome Asynapsis Is the Main Cause of Male Sterility in the Interspecies Hybrids of East Asian Voles (Alexandromys, Rodentia, Arvicolinae).

Closely related mammalian species often have differences in chromosome number and morphology, but there is still a debate about how these differences relate to reproductive isolation. To study the role of chromosome rearrangements in speciation, we used the gray voles in the Alexandromys genus as a model. These voles have a high level of chromosome polymorphism and substantial karyotypic divergence. We investigated testis histology and meiotic chromosome behavior in the captive-bred colonies of Alexandromys maximowiczii, Alexandromys mujanensis, two chromosome races of Alexandromys evoronensis, and their interracial and interspecies hybrids, to explore the relationship between karyotypic differences and male hybrid sterility. We found that the seminiferous tubules of the males of the parental species and the interracial hybrids, which were simple heterozygotes for one or more chromosome rearrangements, contained germ cells at all stages of spermatogenesis, indicating their potential fertility. Their meiotic cells displayed orderly chromosome synapsis and recombination. In contrast, all interspecies male hybrids, which were complex heterozygotes for a series of chromosome rearrangements, showed signs of complete sterility. Their spermatogenesis was mainly arrested at the zygotene- or pachytene-like stages due to the formation of complex multivalent chains, which caused extended chromosome asynapsis. The asynapsis led to the silencing of unsynapsed chromatin. We suggest that chromosome asynapsis is the main cause of meiotic arrest and male sterility in the interspecies hybrids of East Asian voles.

Karyological studies of Iranian Allium (Amaryllidaceae) species with a focus on sect. Acanthoprason. 2. Meiotic chromosomes

Meiosis in pollen mother cells (PMCs) was studied of 23 Iranian Allium species (33 accessions, 105 individuals) that belong to two subgenera and six sections. Materials of 13 species were sampled from (near) type locations. Gametic chromosome numbers, chromosome configurations at metaphase I, chiasma frequency, as well as type and percentages of abnormalities were recognized. The basic chromosome number for all taxa investigated was x = 8. Most taxa were diploid and showed eight bivalents or in rare cases two or four pairs of univalents, but in A. subakaka, A. ubipetrense and A. zagricum tetravalents also occurred. Meiosis in less than 10% of PMCs of diploid accessions was disturbed displaying lagging chromosomes, chromatid bridges, micronuclei, or unbalanced chromosome segregations, but very rarely more than one kind of irregularities were found within one dividing cell. One to three B chromosomes were found in 11 accessions, and were recognized for the first time in A. alamutense, A. elburzense and A. iranshahrii. Our data showed no correlation between the occurrence of B chromosomes and the chiasma frequency, and also no noticeable effect of habitat factors on meiotic chromosome behavior. The studied accessions of A. atroviolaceum and A. sabalense were tetraploid (n = 16) showing irregular meiosis in 20–69% of the PMCs which is regarded as sign of autopolyploidy. Since only two out of 31 investigated accessions belonging to subg. Melanocrommyum were tetraploid, we may suggest a trivial role of polyploidy in the evolution of this subgenus.

Characterization of meiotic chromosome behavior in the autopolyploid Saccharum spontaneum reveals preferential chromosome pairing without distinct DNA sequence variation

Autopolyploidy and allopolyploidy may represent an evolutionary advantage and are more common in plants than assumed. However, less attention has been paid to autopolyploidy than to allopolyploidy, and its evolutionary consequences are largely unclear, especially for plants with high ploidy levels. In this study, we developed oligonucleotide (oligo)-based chromosome painting probes to identify individual chromosomes in S. spontaneum. Using fluorescence in situ hybridization (FISH), we investigated chromosome behavior during pachytene, metaphase, anaphase, and telophase of meiosis I (MI) in autotetraploid, autooctoploid, and autodecaploid S. spontaneum clones. All autopolyploid clones showed stable diploidized chromosome behavior; so that homologous chromosomes formed almost exclusively bivalents during MI. Two copies of homologous chromosome 8 with similar sizes in the autotetraploid clone showed preferential pairing with each other with respect to the other copies. However, sequence variation analysis showed no apparent differences among homologs of chromosome 8 and all other chromosomes. We suggest that either the stable diploidized pairing or the preferential pairing between homologous copies of chromosome 8 in the studied autopolyploid sugarcane are accounted for by unknown mechanisms other than DNA sequence similarity. Our results reveal evolutionary consequences of stable meiotic behavior in autopolyploid plants.

Effects of sexual polyploidization on reproductive development in a full-sib poplar family

Populus is an important source of woody biomass in the Northern Hemisphere. Sexual polyploidization plays a valuable role in the genetic improvement of Populus, resulting in tremendous variation in phenotypic traits. Most studies have focused on the variations in the vegetative growth of allopolyploid Populus; however, variations in the reproductive development of different polyploid genotypes of the progeny remain unclear. In this study, catkin traits, pollen size and viability, meiotic development, and reproductive ability were analyzed based on a full-sib family including diploid and triploid hybrids of (Populus pseudo-simonii × P. nigra ‘Zheyin3#’) × (P. × beijingensis) to understand the effects of sexual polyploidization on reproductive development in Populus hybrids. Catkin traits varied among the genotypes in the full-sib family. A ploidy change resulted in significant variation in male catkin length and male flower number per catkin but not in female catkin traits, suggesting that Populus catkin development may be more sensitive to respond to a change in ploidy level in male plants than in female plants. The male diploid hybrids had significantly smaller pollen grains, but higher pollen germination rates than the triploid hybrids. Giant pollen grains with large diameters were recorded in all-male diploid and triploid hybrids, which were speculated to be unreduced gametes. Premature cytokinesis, misorientation of the spindles, and aberrant cytokinesis were observed in a cytological analysis, which explained the production of unreduced pollen. Premature cytokinesis was only detected in triploid hybrids, which might be attributed to a ploidy change. The frequencies of meiotic abnormalities, such as precocious chromosomal migration, chromosome bridges, and micronuclei in the triploid hybrids were higher than those in diploid hybrids, suggesting that the unbalanced chromosomes in the triploid hybrids caused more complex meiotic chromosome behaviors. Backcrosses with the triploid hybrids resulted in low seed sets and seed germination rates, suggesting that polyploidization reduced pollen viability. Our findings provide new insight into the effect of sexual polyploidization on reproductive development in Populus and could be used to guide a Populus polyploid breeding program.

CROMOSOMAS DE DOS ESPECIES DE OLYRA L. DE MISIONES, ARGENTINA (POACEAE, BAMBUSOIDEAE, OLYREAE)

The subfamily Bambusoideae comprises three monophyletic tribes, Arundinarieae, Bambuseae and Olyreae. Here we report the gametic number and the chromosomal meiotic behavior of two species belonging to the herbaceous tribe Olyreae, Olyra latifolia and Olyra humilis. Accessions were collected in Misiones, at Northeastern Argentina. We report a new gametic number for O. humilis, n=18, and we confirmed n=11 for O. latifolia. Chromosomal features, like the basic and gametic chromosome number, are important in understanding the evolution of the Poaceae family, especially in delimiting clades and elucidate inter and intra-clades relationships, and therefore it is necessary to continue producing this type of data. Key words: bamboos, cytogenetics, meiosis, ploidy, Poaceae

Phosphorylation of HORMA-domain protein HTP-3 at Serine 285 is dispensable for crossover formation.

Generation of functional gametes is accomplished through a multilayered and finely orchestrated succession of events during meiotic progression. In the Caenorhabditis elegans germline, the HORMA-domain-containing protein HTP-3 plays pivotal roles for the establishment of chromosome axes and the efficient induction of programmed DNA double-strand breaks, both of which are crucial for crossover formation. Double-strand breaks allow for accurate chromosome segregation during the first meiotic division and therefore are an essential requirement for the production of healthy gametes. Phosphorylation-dependent regulation of HORMAD protein plays important roles in controlling meiotic chromosome behavior. Here, we document a phospho-site in HTP-3 at Serine 285 that is constitutively phosphorylated during meiotic prophase I. pHTP-3S285 localization overlaps with panHTP-3 except in nuclei undergoing physiological apoptosis, in which pHTP-3 is absent. Surprisingly, we observed that phosphorylation of HTP-3 at S285 is independent of the canonical kinases that control meiotic progression in nematodes. During meiosis, the htp-3(S285A) mutant displays accelerated RAD-51 turnover, but no other meiotic abnormalities. Altogether, these data indicate that the Ser285 phosphorylation is independent of canonical meiotic protein kinases and does not regulate HTP-3-dependent meiotic processes. We propose a model wherein phosphorylation of HTP-3 occurs through noncanonical or redundant meiotic kinases and/or is likely redundant with additional phospho-sites for function in vivo.

Molecular Cytogenetic and Y Copy Number Analysis of a Reciprocal ECAY-ECA13 Translocation in a Stallion with Complete Meiotic Arrest.

Simple SummaryWe present a detailed molecular cytogenetic analysis of a translocation between horse (ECA) chromosomes Y and 13 in a Friesian stallion with complete meiotic arrest and azoospermia. We use two-color fluorescence in situ hybridization with select ECAY and ECA13 markers and show the location of translocation breakpoints in ECAY and in ECA13. The translocation generates two abnormal chromosomes: one comprised of the short arm of ECA13 and the proximal gene-poor 2/3 of ECAY and another, the long arm of ECA13 and the distal 1/3 of ECAY containing most of the single copy and ancestral genes. A copy number (CN) analysis of select ECAY multicopy genes shows that the Friesian stallion has significantly reduced CNs of TSPY, ETSTY1, and ETSTY5, suggesting some genetic loss due to the translocation. We discuss likely meiotic behavior of abnormal chromosomes and theorize about the possible effect of the aberration on Y regulation and the progression of meiosis. The study adds a unique case to equine clinical cytogenetics and contributes to understanding the role of the Y chromosome in male meiosis.We present a detailed molecular cytogenetic analysis of a reciprocal translocation between horse (ECA) chromosomes Y and 13 in a Friesian stallion with complete meiotic arrest and azoospermia. We use dual-color fluorescence in situ hybridization with select ECAY and ECA13 markers and show that the translocation breakpoint in ECAY is in the multicopy region and in ECA13, at the centromere. One resulting derivative chromosome, Y;13p, comprises of ECAY heterochromatin (ETSTY7 array), a small single copy and partial Y multicopy region, and ECA13p. Another derivative chromosome 13q;Y comprises of ECA13q and most of the single copy ECAY, the pseudoautosomal region and a small part of the Y multicopy region. A copy number (CN) analysis of select ECAY multicopy genes shows that the Friesian stallion has significantly (p < 0.05) reduced CNs of TSPY, ETSTY1, and ETSTY5, suggesting that the translocation may not be completely balanced, and genetic material is lost. We discuss likely meiotic behavior of abnormal chromosomes and theorize about the possible effect of the aberration on Y regulation and the progression of meiosis. The study adds a unique case to equine clinical cytogenetics and contributes to understanding the role of the Y chromosome in male meiosis.

Control of Chromatin Organization and Chromosome Behavior during the Cell Cycle through Phase Separation.

Phase-separated condensates participate in various biological activities. Liquid–liquid phase separation (LLPS) can be driven by collective interactions between multivalent and intrinsically disordered proteins. The manner in which chromatin—with various morphologies and activities—is organized in a complex and small nucleus still remains to be fully determined. Recent findings support the claim that phase separation is involved in the regulation of chromatin organization and chromosome behavior. Moreover, phase separation also influences key events during mitosis and meiosis. This review elaborately dissects how phase separation regulates chromatin and chromosome organization and controls mitotic and meiotic chromosome behavior.

Chromosome karyotype and stability of new synthetic hexaploid wheat.

Synthetic hexaploid wheat offers breeders ready access to potentially novel genetic variation in wild ancestral species. In this study, we crossed MY3478 (2n = 4x = 28, AABB) as the maternal parent with the stripe rust-resistant SY41 (2n = 2x = 14, DD) as the paternal parent to construct the new hexaploid wheat line NA0928 through natural allopolyploidization. Agronomic traits and the cytology of the S8-S9 generations of NA0928 were analyzed. Abundant variation in agronomic traits was observed among each strain of NA0928 in the S8 generation. Agronomic traits were superior in strains resistant to stripe rust compared with those of highly susceptible strains. The rank order of the coefficients of variation were tiller number (55.3%) > spike length (15.3%) > number of spikelets (13.9%) > plant height (8.7). Number of tillers and spike length are important traits in wheat breeding to improve yield. Cytological observation and fluorescence in situ hybridization showed that the chromosome number and configuration showed rich variation among NA0928 strains in the S9 generation. Chromosome number ranged from 36 to 44. Variation in chromosome karyotype was detected in the A and B subgenomes. Meiotic chromosome behavior in pollen mother cells and multicolor genomic in situ hybridization revealed that two new synthetic hexaploid wheat strains showed genetic stability; one strain was resistant to stripe rust and developed multiple tillers, and the other strain was susceptible to stripe rust, but both showed improved thousand-kernel weight (TKW) weight and produced multiple tillers. The two strains will be valuable germplasm resources for use in wheat breeding.