Aneuploid Progeny Research Articles

The novel expression of clonality following whole-genome multiplication compensates for reduced fertility in natural autopolyploids.

Exploring the fitness consequences of whole-genome multiplication (WGM) is essential for understanding the establishment of autopolyploids in diploid parental populations, but suitable model systems are rare. We examined the impact of WGM on reproductive traits in three major cytotypes (2x, 3x, 4x) of Pilosella rhodopea, a species with recurrent formation of neo-autopolyploids in mixed-ploidy populations. We found that diploids had normal female sporogenesis and gametogenesis, high fertility, and produced predominantly euploid seed progeny. By contrast, autopolyploids had highly disturbed developmental programs that resulted in significantly lower seed set and a high frequency of aneuploid progeny. All cytotypes, but particularly triploids, produced gametes of varying ploidy, including unreduced ones, that participated in frequent intercytotype mating. Noteworthy, the reduced investment in sexual reproduction in autopolyploids was compensated by increased production of axillary rosettes and the novel expression of two clonal traits: adventitious rosettes on roots (root-sprouting), and aposporous initial cells in ovules which, however, do not result in functional apomixis. The combination of increased vegetative clonal growth in autopolyploids and frequent intercytotype mating are key mechanisms involved in the formation and maintenance of the largest diploid-autopolyploid primary contact zone ever recorded in angiosperms.

A female fertile triploid loquat line produces fruits with less seed and aneuploid germplasm

Most loquat cultivars are diploid (2n=2x=34) and produce numerous large seeds, affecting their edibility rate and processing. Therefore, breeding less seed triploid cultivars has always been a primary goal of loquat breeding. However, most triploid plants have low fertility and cannot meet commercial needs. Here, we identified a triploid line, Q24, that can set seeds normally under natural conditions. We statistically analyzed the fruit setting rate, seed number, and external quality of Q24. The fruit setting rate of Q24 was similar to that of diploid Q14. The number of seeds in Q24 was 79.40% less than that in Q14. Pollen viability analysis and hybridization experiments revealed that Q24 male gametes were sterile. Further cytological observations showed that male gamete sterility was caused by abnormal chromosome pairing during meiosis. Hybridization experiments also confirmed that Q24 female gametes were fertile. Finally, chromosome counts showed that the progeny of Q24 could produce aneuploids at a frequency of 92.52%. In conclusion, the triploid Q24 loquat is a valuable breeding resource, not only because it has less seed and fertile female gametes but also because most of its offspring are aneuploids. This study provides an optimal material for breeding the less seed loquat, and its large number of aneuploid progenies enrich the germplasm resources of loquat.

Microsporogenesis in the triploid hybrid ‘Beilinxiongzhu 1#’ and detection of primary trisomy in 2x × 3 × Populus hybrids

BackgroundPrimary trisomy is a powerful genetic tool in plants. However, trisomy has not been detected in Populus as a model system for tree and woody perennial plant biology.ResultsIn the present study, a backcross between Populus alba × Populus glandulosa ‘YXY 7#’ (2n = 2x = 38) and the triploid hybrid ‘Beilinxiongzhu 1#’ (2n = 3x = 57) based on the observation of microsporogenesis and an evaluation of the variations in pollen was conducted to create primary trisomy. Many abnormalities, such as premature migration of chromosomes, lagging of chromosomes, chromosome bridges, asymmetric separation, micronuclei, and premature cytokinesis, have been detected during meiosis of the triploid hybrid clone ‘Beilinxiongzhu 1#’. However, these abnormal behaviors did not result in completely aborted pollen. The pollen diameter of the triploid hybrid clone ‘Beilinxiongzhu 1#’ is bimodally distributed, which was similar to the chromosomal number of the backcross progeny. A total of 393 progeny were generated. We provide a protocol for determining the number of chromosomes in aneuploid progeny, and 19 distinct simple sequence repeat (SSR) primer pairs covering the entire Populus genome were developed. Primary trisomy 11 and trisomy 17 were detected in the 2x × 3 x hybrid using the SSR molecular markers and counting of somatic chromosomes.ConclusionsNineteen distinct SSR primer pairs for determining chromosomal number in aneuploid individuals were developed, and two Populus trisomies were detected from 2x × 3 x hybrids by SSR markers and somatic chromosome counting. Our findings provide a powerful genetic tool to reveal the function of genes in Populus.

Caenorhabditis elegans spermatocytes can segregate achiasmate homologous chromosomes apart at higher than random frequency during meiosis I.

Chromosome segregation errors during meiosis are the leading cause of aneuploidy. Faithful chromosome segregation during meiosis in most eukaryotes requires a crossover which provides a physical attachment holding homologs together in a "bivalent." Crossovers are critical for homologs to be properly aligned and partitioned in the first meiotic division. Without a crossover, individual homologs (univalents) might segregate randomly, resulting in aneuploid progeny. However, Caenorhabditis elegans zim-2 mutants, which have crossover defects on chromosome V, have fewer dead embryos than that expected from random segregation. This deviation from random segregation is more pronounced in zim-2 males than that in females. We found three phenomena that can explain this apparent discrepancy. First, we detected crossovers on chromosome V in both zim-2(tm574) oocytes and spermatocytes, suggesting a redundant mechanism to make up for the ZIM-2 loss. Second, after accounting for the background crossover frequency, spermatocytes produced significantly more euploid gametes than what would be expected from random segregation. Lastly, trisomy of chromosome V is viable and fertile. Together, these three phenomena allow zim-2(tm574) mutants with reduced crossovers on chromosome V to have more viable progeny. Furthermore, live imaging of meiosis in spo-11(me44) oocytes and spermatocytes, which exhibit crossover failure on all 6 chromosomes, showed 12 univalents segregating apart in roughly equal masses in a homology-independent manner, supporting the existence of a mechanism that segregates any 2 chromosomes apart.

Heat stress promotes haploid formation during CENH3-mediated genome elimination in Arabidopsis.

Impaired activity of centromeric histone CENH3 causes inaccurate chromosome segregation and in crosses between the Arabidopsis recombinant CENH3 mutant GFP-tailswap and CENH3G83E with wild-type pollen it results in chromosome loss with the formation of haploids. This genome elimination in the zygote and embryo is not absolute as also aneuploid and diploid progeny is formed. Here, we report that a temporal and moderate heat stress during fertilization and early embryogenesis shifts the ratio in favour of haploid progeny in CENH3 mutant lines. Micronuclei formation, a proxy for genome elimination, was similar in control and heat-treated flowers, indicating that heat-induced seed abortion occurred at a late stage during the development of the seed. In the seeds derived from heat-treated crosses, the endosperm did not cellularize and many seeds aborted. Haploid seeds were formed, however, resulting in increased frequencies of haploids in CENH3-mediated genome elimination crosses performed under heat stress. Therefore, heat stress application is a selective force during genome elimination that promotes haploid formation and may be used to improve the development and efficacy of in vivo haploid induction systems.

Empirical single-cell tracking and cell-fate simulation reveal dual roles of p53 in tumor suppression.

The tumor suppressor p53 regulates various stress responses via increasing its cellular levels. The lowest p53 levels occur in unstressed cells; however, the functions of these low levels remain unclear. To investigate the functions, we used empirical single-cell tracking of p53-expressing (Control) cells and cells in which p53 expression was silenced by RNA interference (p53 RNAi). Here, we show that p53 RNAi cells underwent more frequent cell death and cell fusion, which further induced multipolar cell division to generate aneuploid progeny. Those results suggest that the low levels of p53 in unstressed cells indeed have a role in suppressing the induction of cell death and the formation of aneuploid cells. We further investigated the impact of p53 silencing by developing an algorithm to simulate the fates of individual cells. Simulation of the fate of aneuploid cells revealed that these cells could propagate to create an aneuploid cell population. In addition, the simulation also revealed that more frequent induction of cell death in p53 RNAi cells under unstressed conditions conferred a disadvantage in terms of population expansion compared with Control cells, resulting in faster expansion of Control cells compared with p53 RNAi cells, leading to Control cells predominating in mixed cell populations. In contrast, the expansion of Control cells, but not p53 RNAi cells, was suppressed when the damage response was induced, allowing p53 RNAi cells to expand their population compared with the Control cells. These results suggest that, although p53 could suppress the formation of aneuploid cells, which could have a role in tumorigenesis, it could also allow the expansion of cells lacking p53 expression when the damage response is induced. p53 may thus play a role in both the suppression and the promotion of malignant cell formation during tumorigenesis.

Production and cytology of Brassica autoallohexaploids with two and four copies of two subgenomes.

Different digenomic Brassica autoallohexaploids were produced from the crosses of three allotetraploids and ancestral diploids and characterized for the cytological behavior of two subgenomes with two and four copies. Interspecific hybridization and allopolyploidization present an important pathway for plant evolution and breeding. In this study, different types of digenomic autoallohexaploids with two or four copies of two subgenomes (AAAACC, AACCCC, AAAABB, BBBBCC, BBCCCC) were synthesized by the crosses between three Brassica allotetraploids and their diploid progenitors and the chromosome doubling, and their meiotic behaviors were analyzed by fluorescence in situ hybridization (FISH). These autoallohexaploids showed some variations in pollen fertility and seed-sets and produced both euploid and aneuploid progenies with some chromosomes lost. Two subgenomes in these autoallohexaploids showed some aberrant pairings and segregations, and the degrees of meiotic regularity were negatively associated with the genome affinities. The chromosomes of the subgenome with four copies formed few quadrivalents with the average number < 2, and mainly paired as bivalents, and majority of the chromosomes from the subgenome with two copies gave the expected bivalents. The different extents of the equal and unequal segregations corresponded to the chromosome pairings. The development and cytological investigation of these autoallohexaploids provide not only the new germplasm for genetic research and breeding but also the new clues for the genome behavior and interplay between these subgenomes with different copies.

Abstract SY39-02: Accessing evolutionary programs to enable therapeutic resistance

Abstract Twenty million people around the world are diagnosed with cancer every year and over ten million people die because their cancer has metastasized and is incurable using current systemic therapies. Metastatic disease remains incurable because tumors evade all forms of programmed cell death. How is this possible? Unicellular and multicellular organisms have evolved multiple strategies to avoid death from internal and external stresses. While the nature of these catastrophes may be varied, their common property is to doom the organism unless it can access a survival mechanism and/or evolve a resistance mechanism rapidly. One such stress survival mechanism that is present across the tree of life in both unicellular and multicellular organisms is the utilization of a program that enables whole genome doubling (polyploidization) and cell cycle arrest. This evolutionary program allows the organism to avoid environmental stresses and protect the integrity of its genomic material by adopting a quiescent phenotype. In addition, by doubling DNA and increasing RNA and protein material, organisms have increased capacity to evolve further resistance mechanisms to stressors. To date, no common genomic signature has been defined that can explain or identify which patients will develop therapeutically resistant and lethal metastatic cancer. In all these incurable patients, therefore, lethal cancer independently evolves capacities for metastasis, avoidance of all cellular death pathways, and resistance. This convergent outcome across all patients demands an explanation beyond the accrual of stochastic mutations. Since the tumor ecosystem is exposed to constantly changing chemical and biologic conditions, it is generally assumed that cancer cell populations must have the ability to evolve rapidly to acquire mutations to adapt and survive. An alternative and complementary theory to explain cancer cell fitness is that a subset of cancer cells access evolutionary stress survival programs that are inherited as development programs. These development programs enable whole genome doubling (polyploidization) and cell cycle arrest and are seen in multiple cell types, including regenerating liver cells, myocytes under physical strain, and megakaryocytes under metabolic stress. In cancer, access to these stress programs result in cancer cell survival though a state of cell cycle arrest that is simultaneously polyploid and aneuploid. Entering the polyaneuploid cancer cell (PACC) state, cancer cells pause their cell cycle and protect the integrity of their DNA from tumor microenvironmental stresses as well as have increased potential to develop further resistance mechanisms to environmental stressors and toxic therapies. After stress is removed, cells in the PACC state undergo depolyploidization and generate resistant progeny. This enables the generation of heritable variation that can be dispensed to their 2N+ aneuploid progeny, providing population rescue in response to therapeutic stress. Targeting cells in the PACC state opens a new avenue for cancer therapy. Citation Format: Kenneth J. Pienta. Accessing evolutionary programs to enable therapeutic resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr SY39-02.

Near-Hexaploid and Near-Tetraploid Aneuploid Progenies Derived from Backcrossing Tetraploid Parents Hibiscus syriacus × (H. syriacus × H. paramutabilis).

Hibiscus syriacus, azalea, is an important woody ornamental shrub planted throughout many temperate and subtropical regions of the world. However, flower size is smaller in this species than some of its relatives. To increase flower size, interspecific hybridization has been used, and such hybrid cultivars are usually characterized by larger flowers, increased vigor, diverse leaf shapes, and reduced fertility. Our earlier studies have shown that these hybrid cultivars could backcross with H. syriacus when used as male parents. To understand the breeding potential of these hybrid cultivars, two popular tetraploid hybrid cultivars, ‘Lohengrin’ and ‘Resi’, were used as pollen parents to backcross several tetraploid H. syriacus cultivars. As a result, 28.76% and 64.4% of ‘Lohengrin’ and ‘Resi’ progenies exhibited larger flowers than both of their parents. Interestingly, 14 of 18 progenies of ‘Resi’ were putative hexaploids, whereas 19 tested ‘Lohengrin’ progenies were tetraploid. Because putative hexaploid progenies were only observed among progenies of ‘Resi’, this hybrid cultivar appears to produce unreduced gametes. In addition, among the 14 putative hexaploids derived from ‘Resi’, 11 had larger flowers than both of their parents and their tetraploid siblings (p < 0.05). The 45S rDNA and 5S rDNA locus segregation among those BC1F1 progenies was tested by fluorescent in situ hybridization (FISH), and the wide range of 45S rDNA signal numbers among siblings indicated that these aneuploids resulted from unequal segregation or chromosome rearrangement. Chromosome counting confirmed aneuploidy among BC1F1 progenies. Ploidy diversity and aneuploidy have been known to contribute to various elements of morphological diversity, such as larger flower size and reduced fertility, which are important in ornamental plant breeding. The present study demonstrated the breeding potential of interspecific Hibiscus cultivars for increasing ploidy level and flower size.

Abstract IA017: The polyaneuploid cancer cell state as a mediator of therapeutic resistance

Abstract More than ten million people around the world will die from metastatic cancer in 2022. To date, no common genomic signature has been defined that can explain or identify which patients will develop lethal metastatic cancer. In all of these incurable patients lethal cancer independently evolves capacities for metastasis, avoidance of all cellular death pathways, and resistance. This convergent outcome demands an explanation beyond the slow and steady accrual of stochastic mutations. Generally, it is thought that cancer cells utilize the forces of natural selection when utilizing accumulating mutations during its evolution. Their utilization of heritable variation permits the cancer cell population to respond and survive environmental hazards. The tumor ecosystem is exposed to extreme and constantly changing chemical conditions. These changes can be natural, (e.g., loss of blood supply) or imposed (therapeutic). While the nature of these catastrophes may be varied or unique, their common property may be to doom the current cancer phenotype unless it evolves rapidly. We propose a complementary theory to explain cancer cell fitness through these environmental hazards that lead to metastasis, therapeutic resistance, and lethality. The basis of this theory is that a subset of cancer cells accesses evolutionary or developmental (evo/devo) stress survival programs that enable whole genome doubling (polyploidization) and cell cycle arrest. These stress survival programs are observed across the tree of life, from unicellular both prokaryotes and eukaryotes, such as Archaea, Bacteria, and yeast, to multicellular organism including plants and animals. In cancer, environmental stress and these stress programs result in cancer cell survival though a state of cell cycle arrest that is simultaneously polyploid and aneuploid. During this polyaneuploid cancer cell (PACC) state, cancer cells pause their cell cycle and protect the integrity of their DNA. This avoids the environmental stresses associated with the tumor microenvironment and metastatic cascade as well as the toxic effects of systemic therapy. In addition, by doubling their DNA and increasing their RNA and protein material, cancer cells in the PACC state have increased potential to develop further resistance mechanism to environmental stressors and otherwise toxic therapies. We have demonstrated that upon removal of stress, e.g., chemotherapy, cells in the PACC state undergo depolyploidization and generate resistant progeny. Thus, cells in the PACC state may play a critical role in lethality by their increased capacity to endure novel and stressful environments. This enables the metastatic phenotype and the generation of heritable variation that can be dispensed to their 2N+ aneuploid progeny, providing population rescue in response to therapeutic stress. Targeting cells in the PACC state is essential to cancer therapy and patient cure. Citation Format: Kenneth J. Pienta. The polyaneuploid cancer cell state as a mediator of therapeutic resistance [abstract]. In: Proceedings of the AACR Special Conference on the Evolutionary Dynamics in Carcinogenesis and Response to Therapy; 2022 Mar 14-17. Philadelphia (PA): AACR; Cancer Res 2022;82(10 Suppl):Abstract nr IA017.

Nuclear DNA contents and ploidy levels of North American Vaccinium species and interspecific hybrids

Breeding strategies for improving blueberry (Vaccinium corymbosum and V. virgatum) cultivars often include introgressing regionally adapted species into the cultivated gene pools through interspecific hybridization. However, these approaches are complicated by variation in ploidy, triploid blocks and infertility, production of unreduced gametes, and aneuploidy. The objective of this study was to use flow cytometry, k-mer distribution analysis, and known pedigree information to evaluate genome sizes (2C nuclear and 1Cx monoploid), and ploidy of diverse accessions from Vaccinium sections and species. A total of 369 accessions, including a diversity panel (DP) of 251 inter- and intra-specific hybrid Vaccinium accessions, as well as 118 non-hybrid Vaccinium species across multiple sections, were sampled from the North Carolina State University blueberry breeding program and the National Clonal Germplasm Repository. The nuclear DNA content was analyzed via flow cytometry. The mean (range) DNA content of diploid, tetraploid, and hexaploid reference species were 1.20 pg (0.99 pg in V. crassifolium ‘Well's Delight’ to 1.41 pg in V. caesariense NC79–24), 2.37 pg (2.11 pg in V. corymbosum ‘Concord’ to 3.01 pg in V. corymbosum DE599), and 3.64 pg (3.24 in V. constablaei NC83–21–2 to 3.80 in V. virgatum ‘Premier’ and NC4790), respectively. Of the 369 unique accessions analyzed for ploidy, 259 were tetraploid, 46 were diploid, one was triploid, 51 were pentaploid or aneuploid with 2C values between tetraploid and hexaploid values, and 12 were hexaploid. Tetraploid hybrid pedigrees, which involved hexaploid crosses within three prior generations, had a 2C value range between 2.22 pg and 2.59 pg. Interspecific pentaploid and aneuploid progeny 2C DNA content ranged from 2.61 pg to 3.15 pg. We speculate some of these progeny to be near tetraploids with extra chromosomes from hexaploid progenitors. Further karyotyping of these individuals is necessary to ascertain aneuploidy anomalies. This research provides an expanded knowledge base of genome sizes, ploidy, and reproductive pathways for diverse species and hybrids to enhance future breeding, improvement, and the genomic study of blueberry.

Structural Maintenance of Chromosomes 5/6 Complex Is Necessary for Tetraploid Genome Stability in Arabidopsis thaliana.

Polyploidization is a common phenomenon in the evolution of flowering plants. However, only a few genes controlling polyploid genome stability, fitness, and reproductive success are known. Here, we studied the effects of loss-of-function mutations in NSE2 and NSE4A subunits of the Structural Maintenance of Chromosomes 5/6 (SMC5/6) complex in autotetraploid Arabidopsis thaliana plants. The diploid nse2 and nse4a plants show partially reduced fertility and produce about 10% triploid offspring with two paternal and one maternal genome copies. In contrast, the autotetraploid nse2 and nse4a plants were almost sterile and produced hexaploid and aneuploid progeny with the extra genome copies or chromosomes coming from both parents. In addition, tetraploid mutants had more severe meiotic defects, possibly due to the presence of four homologous chromosomes instead of two. Overall, our study suggests that the SMC5/6 complex is an important player in the maintenance of tetraploid genome stability and that autotetraploid Arabidopsis plants have a generally higher frequency of but also higher tolerance for aneuploidy compared to diploids.

Untangling structural factors driving genome stabilization in nascent Brassica napus allopolyploids.

Allopolyploids have globally higher fitness than their diploid progenitors; however, by comparison, most resynthesized allopolyploids have poor fertility and highly unstable genome. Elucidating the evolutionary processes promoting genome stabilization and fertility is thus essential to comprehend allopolyploid success. Using the Brassica model, we mimicked the speciation process of a nascent allopolyploid species by resynthesizing allotetraploid Brassica napus and systematically selecting for euploid individuals over eight generations in four independent allopolyploidization events with contrasted genetic backgrounds, cytoplasmic donors, and polyploid formation type. We evaluated the evolution of meiotic behavior and fertility and identified rearrangements in S1 to S9 lineages to explore the positive consequences of euploid selection on B.napus genome stability. Recurrent selection of euploid plants for eight generations drastically reduced the percentage of aneuploid progenies as early as the fourth generation, concomitantly with a decrease in number of newly fixed homoeologous rearrangements. The consequences of homoeologous rearrangements on meiotic behavior and seed number depended strongly on the genetic background and cytoplasm donor. The combined use of both self-fertilization and recurrent euploid selection allowed identification of genomic regions associated with fertility and meiotic behavior, providing complementary evidence to explain B.napus speciation success.

Haploid Bio-Induction in Plant through Mock Sexual Reproduction.

SummaryHaploidization is invaluable for basic genetic research and crop breeding. The haploid bio-induction principle is an important topic that remains largely unexplored. In this study, both CenH3 RNAi and in vitro inhibition were used to simulate and induce haploids in allopolyploid crop. Notably, in vitro CenH3 inhibition showed that the results were much the same to that of RNAi in phenotype, chromosome behavior, microspore production, and haploid induction. Cytological analyses of RNAi and inhibitor-treated progenies revealed elimination of chromosomes, defective microspores with empty nuclei, thereby giving rise to pseudo male gametes, and haploid parthenogenesis induction. We found distinct defective empty microspores that were positively correlated with the decrease of CenH3 during RNAi manipulation. Investigation through both in vivo and in vitro studies revealed that haploidization was induced through the pseudo male gamete-mediated mock sexual reproduction. The present results provide insights for the haploid parthenogenesis induction process.

Activation of Meiotic Genes Mediates Ploidy Reduction during Cryptococcal Infection.

Cryptococcus neoformans is a global human fungal pathogen that causes fatal meningoencephalitis in mostly immunocompromised individuals. During pulmonary infection, cryptococcal cells form large polyploid cells that exhibit increased resistance to host immune attack and are proposed to contribute to the latency of cryptococcal infection. These polyploid titan cells can generate haploid and aneuploid progeny that may result in systemic infection. What triggers cryptococcal polyploidization and how ploidy reduction is achieved remain open questions. Here, we discovered that Cryptococcus cells polyploidize in response to genotoxic stresses that cause DNA double-strand breaks. Intriguingly, meiosis-specific genes are activated in C.neoformans and contribute to ploidy reduction, both invitro and during infection in mice. Cryptococcal cells that activated their meiotic genes in mice were resistant to specific genotoxic stress compared to sister cells recovered from the same host tissue but without activation of meiotic genes. Our findings support the idea that meiotic genes, in addition to their conventional roles in classic sexual reproduction, contribute to adaptation of eukaryotic cells that undergo dramatic genome changes in response to genotoxic stress. The discovery has additional implications for evolution of sexual reproduction and the paradox of the presence of meiotic machinery in asexual species. Finally, our findings inthis eukaryotic microbe mirror the revolutionary discoveries of the polyploidization and meiosis-like ploidy reduction process in cancer cells, suggesting that the reversible ploidy change itself could provide a general mechanism for rejuvenation to promote individual survival in response to stress.

Poly-aneuploid cancer cells promote evolvability, generating lethal cancer.

Cancer cells utilize the forces of natural selection to evolve evolvability allowing a constant supply of heritable variation that permits a cancer species to evolutionary track changing hazards and opportunities. Over time, the dynamic tumor ecosystem is exposed to extreme, catastrophic changes in the conditions of the tumor—natural (e.g., loss of blood supply) or imposed (therapeutic). While the nature of these catastrophes may be varied or unique, their common property may be to doom the current cancer phenotype unless it evolves rapidly. Poly‐aneuploid cancer cells (PACCs) may serve as efficient sources of heritable variation that allows cancer cells to evolve rapidly, speciate, evolutionarily track their environment, and most critically for patient outcome and survival, permit evolutionary rescue, therapy resistance, and metastasis. As a conditional evolutionary strategy, they permit the cancer cells to accelerate evolution under stress and slow down the generation of heritable variation when conditions are more favorable or when the cancer cells are closer to an evolutionary optimum. We hypothesize that they play a critical and outsized role in lethality by their increased capacity for invasion and motility, for enduring novel and stressful environments, and for generating heritable variation that can be dispensed to their 2N+ aneuploid progeny that make up the bulk of cancer cells within a tumor, providing population rescue in response to therapeutic stress. Targeting PACCs is essential to cancer therapy and patient cure—without the eradication of the resilient PACCs, cancer will recur in treated patients.

Genomic Outcomes of Haploid Induction Crosses in Potato (Solanum tuberosum L.).

The challenges of breeding autotetraploid potato (Solanum tuberosum) have motivated the development of alternative breeding strategies. A common approach is to obtain uniparental dihaploids from a tetraploid of interest through pollination with S. tuberosum Andigenum Group (formerly S. phureja) cultivars. The mechanism underlying haploid formation of these crosses is unclear, and questions regarding the frequency of paternal DNA transmission remain. Previous reports have described aneuploid and euploid progeny that, in some cases, displayed genetic markers from the haploid inducer (HI). Here, we surveyed a population of 167 presumed dihaploids for large-scale structural variation that would underlie chromosomal addition from the HI, and for small-scale introgression of genetic markers. In 19 progeny, we detected 10 of the 12 possible trisomies and, in all cases, demonstrated the noninducer parent origin of the additional chromosome. Deep sequencing indicated that occasional, short-tract signals appearing to be of HI origin were better explained as technical artifacts. Leveraging recurring copy number variation patterns, we documented subchromosomal dosage variation indicating segregation of polymorphic maternal haplotypes. Collectively, 52% of the assayed chromosomal loci were classified as dosage variable. Our findings help elucidate the genomic consequences of potato haploid induction and suggest that most potato dihaploids will be free of residual pollinator DNA.

Activation of Meiotic Genes Mediates Ploidy Reduction and Generates Phenotypic Diversity During Cryptococcal Infection

Cryptococcus neoformans is a global human fungal pathogen that causes fatal meningoencephalitis in mostly immunocompromised individuals. During pulmonary infection, cryptococcal cells form big polyploid cells that exhibit increased resistance to host immune attack and are proposed to contribute to the latency of cryptococcal infection. These polyploidy titan cells can generate haploid and aneuploid progeny that may result in systematic infection. What triggers cryptococcal polyploidization and how ploidy reduction is achieved remain open questions. Here we discovered that Cryptococcus cells polyploidize in response to genotoxic stresses that cause DNA double strand breaks. Intriguingly, meiosis-specific genes are activated in C. neoformans and contribute to ploidy reduction, both in vitro and during infection in mice. Strikingly, cryptococcal cells that activated their meiotic genes in mice showed increased phenotypic diversity and were resistant to specific genotoxic stress comparing with sister cells recovered from the same host tissue but without activation of meiotic genes. Our findings support the idea that meiotic genes, in addition to the conventional roles during classic sexual reproduction, contribute to adaptation of eukaryotic cells undergoing dramatic genome changes in response to genotoxic stress. The discovery has additional implication for evolution of sexual reproduction and the paradox of the presence of meiotic machinery in asexual species. Finally, our findings in this eukaryotic microbe mirror the revolutionary discoveries of gametogenesis (polyploidization and meiosis-like process) in cancer cells, suggesting that the gametogenesis process itself could provide a general mechanism for rejuvenation in response to stress to promote individual survival.

Gonad Development and Reproductive Ability of Aneuploid Ornamental Koi Carp Obtained by Crossing Triploid Females with Diploid Males

AbstractIt was described earlier that triploid female koi (ornamental variant of the Common Carp Cyprinus carpio) from heat‐shocked progeny developed large ovaries and produced mass aneuploid progeny when crossed with normal diploid koi males. This study presents data on gonad development and reproductive ability of aneuploid koi obtained from triploid females. Aneuploid koi had low viability when raised in indoor recirculating systems; only 12–19% of fish survived up to 25–28 months of age. The 28‐month‐old aneuploid fish with a ploidy range of 2.31–2.78n obtained in 2013 (n = 30) did not release sperm or eggs after hormonal injection. Dissection of fish showed that similar to triploid males, aneuploid males had pinkish testes that did not contain sperm; the gonadosomatic index (GSI) of aneuploid males varied from 0.3% to 3.5%, with a mean value of 1.2%. More than 50% of aneuploid females had ovaries that were severely reduced in development, with GSI values less than 2%; about 40% of females had ovaries at the maturing stage, with GSIs ranging from 2.5% to 5.6%. One aneuploid female had mature ovaries filled with fully grown oocytes (GSI = 9.6%). The aneuploid fish obtained in 2015 (n = 165) did not produce sperm at 25 months of age; all fish from this group died during subsequent overwintering in an earthen pond. Our results show that aneuploid koi males are functionally sterile, whereas some potentially fertile aneuploid females can be found. However, because aneuploid koi have very low viability, the chance of survival for fertile aneuploid females is low, especially under natural conditions. Fertile aneuploid females, even if they survive, would likely produce aneuploid eggs, and fertilization of those eggs would again result in aneuploid progeny with low viability and fertility.

Polyploidy in Liver Regeneration and Adaptation to Chronic Injury

The liver contains diploid and polyploid hepatocytes (tetraploid, octaploid, etc.), with polyploids comprising ≥90% of the hepatocyte population in adult mice. The molecular mechanisms that regulate polyploidization have been well‐characterized; however, it is unclear if diploid and polyploid hepatocytes function similarly in multiple contexts. Moreover, polyploid hepatocytes form multipolar spindles in mitosis, which lead to chromosome gains and/or losses and random aneuploidy. The effect of aneuploidy on liver function is also unknown and the degree of liver aneuploidy is debated, with reports showing aneuploidy affects 5–60% of hepatocytes. To study the function of polyploidy and aneuploidy in the liver, we used mice lacking E2f7 and E2f8 in the liver (LKO), which have a polyploidization defect. Here, we found diploid hepatocytes were enriched 20‐fold in LKO livers, and LKO hepatocytes remained predominantly diploid following extensive proliferation. Moreover, cytogenetic analysis showed that nearly all LKO hepatocytes were euploid compared to control hepatocytes, which were mostly aneuploid, suggesting polyploid hepatocytes are required for production of aneuploid progeny. Livers from LKO mice maintained normal function but became highly tumorigenic when challenged with tumor‐promoting stimuli, suggesting that tumors in LKO mice were driven, at least in part, by diploid hepatocytes capable of rapid proliferation. Indeed, hepatocytes from LKO mice were more proliferative and out‐competed control hepatocytes in competitive repopulation studies. To eliminate potentially confounding effects associated with E2f7/E2f8 deficiency, diploid and polyploid hepatocytes from wild‐type mice were examined. The wild‐type diploid cells also showed a proliferative advantage, entering and progressing through the cell cycle faster than polyploid cells, both in vitro and during liver regeneration. Finally, to investigate the role of diploids and polyploids in chronic injury we bred LKO mice, deficient in polyploidy and aneuploidy, onto a tyrosinemia background, a disease model where the liver can develop disease‐resistant, regenerative nodules. Survival was significantly reduced in tyrosinemic LKO mice, compared to controls, but they maintained the ability to form regenerative nodules. Molecular analyses revealed that the nodules in the tyrosinemic livers were generated via aneuploidy and inactivating mutations. In summary we identified diverse, context‐specific roles for diploids and polyploids in liver function, demonstrating diploid hepatocytes are the most proliferative and have the highest capacity for liver regeneration, and polyploid hepatocytes are required for the formation of aneuploid progeny and facilitate adaptation to chronic liver disease.Support or Funding InformationGrants awarded to Dr. Duncan from the NIH (R01 DK103645) and the Commonwealth of Pennsylvania.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.