Hybrid Sterility Research Articles

Development Features of Ixodes ricinus × I. persulcatus Hybrids under Laboratory Conditions.

Widely distributed Ixodes ricinus and Ixodes persulcatus ticks transmit many pathogens of both medical and veterinary significance. The ranges of these tick species overlap and form large sympatric areas in the East European Plain and Baltic countries. It has previously been shown that crossing I. ricinus and I. persulcatus is possible, resulting in the appearance of sterile hybrids. In the present study, we analyzed the features of this hybrid's life cycle under laboratory conditions. For this purpose, virgin females of I. ricinus and I. persulcatus ticks were obtained in the laboratory, and hybrid generations of ticks were bred from the reciprocal crossings of these two tick species. According to our data, mating the females of I. ricinus and I. persulcatus with the males of another species leads to a decrease in the engorgement success of the females, a decrease in the number of hatched larvae, and the appearance of a hybrid generation in which both females and males are sterile. Under laboratory conditions at a constant room temperature and under natural daylight, the morphogenetic diapause of the engorged I. persulcatus larvae began in September. For I. persulcatus nymphs, it occurred earlier than for I. ricinus, in October and November, respectively. The hybrids generally repeated the features of the life cycle of the mother species.

Genomic mechanisms and consequences of diverse postzygotic barriers between monkeyflower species.

The evolution of genomic incompatibilities causing postzygotic barriers to hybridization is a key step in species divergence. Incompatibilities take two general forms - structural divergence between chromosomes leading to severe hybrid sterility in F1 hybrids and epistatic interactions between genes causing reduced fitness of hybrid gametes or zygotes (Dobzhansky-Muller incompatibilities). Despite substantial recent progress in understanding the molecular mechanisms and evolutionary origins of both types of incompatibility, how each behaves across multiple generations of hybridization remains relatively unexplored. Here, we use genetic mapping in F2 and RIL hybrid populations between the phenotypically divergent but naturally hybridizing monkeyflowers Mimulus cardinalis and M. parishii to characterize the genetic basis of hybrid incompatibility and examine its changing effects over multiple generations of experimental hybridization. In F2s, we found severe hybrid pollen inviability (< 50% reduction vs. parental genotypes) and pseudolinkage caused by a reciprocal translocation between Chromosomes 6 and 7 in the parental species. RILs retained excess heterozygosity around the translocation breakpoints, which caused substantial pollen inviability when interstitial crossovers had not created compatible heterokaryotypic configurations. Strong transmission ratio distortion and inter-chromosomal linkage disequilibrium in both F2s and RILs identified a novel two-locus genic incompatibility causing sex-independent gametophytic (haploid) lethality. The latter interaction eliminated three of the expected nine F2 genotypic classes via F1 gamete loss without detectable effects on the pollen number or viability of F2 double heterozygotes. Along with the mapping of numerous milder incompatibilities, these key findings illuminate the complex genetics of plant hybrid breakdown and are an important step toward understanding the genomic consequences of natural hybridization in this model system.

Potential Involvement of DNA Methylation in Hybrid Sterility in Hermaphroditic Argopecten Scallops.

DNA methylation is an important epigenetic modification factor in regulating fertility. Corresponding process remains poorly investigated in hermaphroditic scallops. The interspecific F1 hybrids between the hermaphroditic bay scallops (Argopecten irradians) and Peruvian scallops (Argopecten purpuratus) exhibited significant heterosis in yield, but sterility in hybrids obstructs the utilization of the genetic resources. However, the determination mechanism of hybrid sterility in the hermaphroditic Argopecten scallops is still unclear. In this study, the effect of DNA methylation in the hybrid sterility of hermaphroditic Argopecten scallops was explored. The results showed that the mean methylation level was higher in sterile hybrids than fertile hybrids, especially on chromosome 11 of the paternal parent. A total of 61,062 differentially methylated regions (DMRs) were identified, containing 3619 differentially methylated genes (DMGs) and 1165 differentially methylated promoters that are located in the DMRs of CG sequence context. The hyper-methylated genes were enriched into five KEGG pathways, including ubiquitin-mediated proteolysis, ECM-receptor interaction, non-homologous end-joining, notch signaling, and the mismatch repair pathways. The DMGs might induce hybrid sterility by inhibition of oogenesis and egg maturation, induction of apoptosis, increased ROS, and insufficient ATP supply. Our results would enrich the determination mechanism of hybrid sterility and provide new insights into the utilization of the genetic resources of the interspecific hybrids.

Hybrid sterility genes with driving force for speciation in rice

Hybrid sterility genes with driving force for speciation in rice

Comparative studies on ovary and serum hormone levels in silver and blue foxes and their hybrids

The silver and blue fox appear closely related despite their belonging to different genera, and the male and female fox hybrids are completely sterile in mating inter se or back to either of the parental groups. In the present study, we compared ovarian morphology and serum hormone concentrations among silver foxes, blue foxes, HSBs (silver fox male × blue fox female hybrids) and HBSs (blue fox male × silver fox female hybrids) during the pre-breeding and the breeding period. We found that either the fertile blue and silver foxes or the infertile hybrid foxes showed typical characteristics of ovary, with primordial, primary, secondary, antral and Graafian follicles. The diameters and quantities of different follicle classes in fertile foxes were greater than that in hybrids during the two period, while the thickness of zona pellucida (ZP) represented an opposite trend (P < 0.05). The relative weight of bilateral ovaries in fertile foxes was greater than that in hybrids during the pre-breeding period, while mean serum FSH represented an opposite trend during the breeding period (P < 0.05). The mean serum estradiol in fertile foxes was greater than that in HBS foxes during the pre-breeding period, and greater than hybrids during the breeding period (P < 0.05). These findings indicated that in the infertile hybrid foxes, lower estradiol levels produced by lesser and smaller antral follicles, thicker ZP during the two period, higher FSH levels during the breeding period, could be the basis of interpretations in cases of female fox hybrid infertility.

Ornamental Invasive Plants in Florida with Research-founded Alternatives

The ornamental horticulture industry has long been significant in its vast economic contributions to the US agricultural sector, with Florida ranking second in nursery and greenhouse plant sales. A small proportion of introduced plants eventually escape cultivation and become invasive, leaving fragile ecosystems at risk. In response, a series of propagation and production research studies have been conducted over the years to 1) evaluate the female sterility and landscape performance of cultivars and/or hybrids of ornamental invasives, and 2) develop reliable propagation systems of novel or underused natives having ornamental and ecological value. Attractive, fruitless selections of popular species such as butterfly bush (Buddleja sp.), heavenly bamboo (Nandina domestica), Mexican petunia (Ruellia simplex), lantana (Lantana strigocamara), trailing lantana (Lantana montevidensis), privet (Ligustrum sp.), maiden silvergrass (Miscanthus sp.), and fountain grass (Pennisetum sp.) have been identified as suitable non-native alternatives to the invasive or potentially invasive resident species (wild type). Simultaneously, researchers have taken a closer look at native plant alternatives that may offer similar aesthetic traits as invasive plants, while bringing added biodiversity and function for more ecologically friendly landscapes and gardens. As such, successful multisite trialing and/or propagation systems have been developed for a number of species native to Florida, such as squareflower (Paronychia erecta), coastalplain honeycombhead (Balduina angustifolia), wireweeds (Polygonella sp.), blue porterweed (Stachytarpheta jamaicensis), wild coffees (Psychotria sp.), sweet acacia (Vachellia farnesiana), and wild lime (Zanthoxylum fagara). With pronounced marketing and consumer education, it is hopeful that together sterile cultivars and native species will ultimately replace wild-type forms of commercially available ornamental invasives. This paper summarizes the current status of ornamental invasives in Florida and the role of native species and sterile non-native cultivars.

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.

Two complementary genes in a presence-absence variation contribute to indica-japonica reproductive isolation in rice

Understanding the evolutionary forces in speciation is a central goal in evolutionary biology. Asian cultivated rice has two subspecies, indica and japonica, but the underlying mechanism of the partial reproductive isolation between them remains obscure. Here we show a presence-absence variation (PAV) at the Se locus functions as an indica-japonica reproductive barrier by causing hybrid sterility (HS) in indica-japonica crosses. The locus comprises two adjacent genes: ORF3 encodes a sporophytic pollen killer, whereas ORF4 protects pollen in a gametophytic manner. In F1 of indica-japonica crosses, pollen with the japonica haplotype, which lacks the sequence containing the protective ORF4, is aborted due to the pollen-killing effect of ORF3 from indica. Evolutionary analysis suggests ORF3 is a gene associated with the Asian cultivated rice species complex, and the PAV has contributed to the reproductive isolation between the two subspecies of Asian cultivated rice. Our analyses provide perspectives on rice inter-subspecies post-zygotic isolation, and will promote efforts to overcome reproductive barriers in indica-japonica hybrid rice breeding.

A natural gene drive system confers reproductive isolation in rice

Hybrid sterility restricts the utilization of superior heterosis of indica-japonica inter-subspecific hybrids. In this study, we report the identification of RHS12, a major locus controlling male gamete sterility in indica-japonica hybrid rice. We show that RHS12 consists of two genes (iORF3/DUYAO and iORF4/JIEYAO) that confer preferential transmission of the RHS12-i type male gamete into the progeny, thereby forming a natural gene drive. DUYAO encodes a mitochondrion-targeted protein that interacts with OsCOX11 to trigger cytotoxicity and cell death, whereas JIEYAO encodes a protein that reroutes DUYAO to the autophagosome for degradation via direct physical interaction, thereby detoxifying DUYAO. Evolutionary trajectory analysis reveals that this system likely formed de novo in the AA genome Oryza clade and contributed to reproductive isolation (RI) between different lineages of rice. Our combined results provide mechanistic insights into the genetic basis of RI as well as insights for strategic designs of hybrid rice breeding.

Neo-octaploids of Asplenium prolongatum Hook. (Aspleniaceae) occurred in Korea

Asplenium L. is a sub-cosmopolitan genus of ferns comprising approximately 700 species. It includes various ploidy-leveled taxa, and, in particular, polyploid species occupy a higher proportion than diploid species within the genus. In addition, it is regarded as an essential process to confirm the cytotype of taxa because the ploidy level is sometimes used to identify a particular taxon in Asplenium. In the case of A. prolongatum, two cytotypes, tetraploid and hexaploid, have been reported in Japanese and Chinese populations. However, to date, there have been no attempts to confirm the ploidy of the Korean species. In the present study, we investigated the cytotype of Korean A. prolongatum using chromosome counting and genome size measurements, and we found that two cytotypes, hexaploid (2n = 6x = 216) and octaploid (2n = 8x = 288), were distributed in Jeju Island, Korea. To the best of our knowledge, this is the first report of a neo-cytotype of A. prolongatum. The hexaploids mostly had empty, shrunken sporangia, which is one of the traits observed in sterile hybrid ferns. From these results, it was concluded that A. prolongatum has three cytotypes: tetraploid, hexaploid, and octaploid.

Hybridization in heliothine moths: impacts on reproduction, pheromone communication, and pest management

Heliothine moths (Family Noctuidae : Subfamily Heliothinae) are ubiquitous crop pests with three documented species combinations known to hybridize: Helicoverpa zea x Helicoverpa armigera, H. armigera x Helicoverpa assulta, and Heliothis virescens x Heliothis subflexa. Hybrids can have advantageous traits, such as increased host range, resistance to insecticides, and increased mating success, posing serious threats to agriculture. However, deleterious traits of hybrids, such as developmental abnormalities or sterility, can be exploited for pest management. In this review, the characteristics of F1 hybrids and backcrosses are examined through a historical lens. Topics reviewed include developmental characteristics, sex pheromone synthesis and perception, mating and calling behavior, sperm morphology, gene expression, electrophysiological responses, structures of the central and peripheral nervous systems, hybrid sterility, and applications in pest control. Recommendations for future studies based on existing gaps of knowledge are given, as are proposed pest management strategies.

Hybrid sterility in hermaphroditic Argopecten scallops: Mutated mitochondrial genes and abnormal expression of nuclear genes

Bay scallops (Argopecten irradians) are a commercially important bivalve species for fisheries and aquaculture in China, the USA, Peru and Chile, but their small size and serious inbreeding depression restrict the sustainable development of their aquaculture. We successfully hybridized bay scallops with Peruvian scallops (Argopecten purpuratus), and the F1 hybrids showed significant heterosis in growth, but the majority of them were sterile. Nevertheless, Argopecten scallops are typical hermaphroditic animals, resulting in a low proportion of interspecific hybrids. Hybrid sterility restricts the utilization of Argopecten scallop resources and causes reproductive isolation in speciation. However, the underlying mechanism of hybrid sterility remains unexplored in hermaphroditic scallops. In this study, we investigated the mechanism of hybrid sterility in hermaphroditic Argopecten scallops by examining mutations in mitochondrial genes and the expression of nuclear genes. Our results showed that the ATP content in the gonads of F1 hybrid scallops was significantly lower than that in their parents, indicating that energy deficiency may be an immediate cause of sterility in F1 hybrid scallops. Thirteen SNPs were detected in five mitochondrial genes of F1 hybrids, and 92.3% of which were transitions that could change the hydrophobicity of amino acids and protein structures, and the allele frequencies of the SNP loci were significantly different between sterile hybrids and fertile scallops. Abnormal interaction between the mitochondrial and nuclear genes might contribute to hybrid sterility through the following pathways: (1) inhibition of oocyte maturation by enhanced expression of Mfn2; (2) cell cycle arrest in G1 phase of oocytes by inhibited expression of CDK2; (3) cell apoptosis induced by mitochondrial apoptosis; (4) insufficient energy supply from abnormal mitochondria, and (5) mitochondrial dysfunction resulting from abnormal expression of other nuclear genes. The present results provide more information for understanding the mechanism of hybrid sterility in hermaphroditic animals and benefit extensive hybrid breeding.

Dynamic hybridization between two spleenworts, Asplenium incisum and Asplenium ruprechtii in Korea.

Natural hybridization between Asplenium incisum and A. ruprechtii has been observed in Northeast Asia and its allotetraploid species, A. castaneoviride, was reported. However, the hybridization process between the parental species and the origin of the allotetraploid taxon remains obscure. Additionally, the systematic affinities of the recently described hybrid A. bimixtum, considered to have originated from the hybridization of A. ruprechtii, A. trichomanes, and A. incisum, is unresolved owing to its similarity to A. castaneoviride. The goals of this study were to (1) investigate the hybridization between A. ruprechtii and A. incisum; (2) verify the origin of A. castaneoviride occurring in Korea, whether it independently arose from 2x sterile hybrids; and (3) elucidate the reliability of identifying A. bimixtum. Three genotypes, A. incisum, A. ruprechtii, and their hybrid, were identified based on the nuclear gene pgiC sequence and finally divided them into six types by ploidy levels: diploid A. incisum, A. ruprechtii, and four hybrid types (diploid A. × castaneoviride, triploid A. × castaneoviride, allotetraploid A. castaneoviride, and A. bimixtum). In the analyses of plastid DNA, all hybrids had an A. ruprechtii-type rbcL gene. In addition, the four plastomes of A. ruprechtii and the hybrids had high pairwise sequence identities greater than 98.48%. They increased up to 99.88% when a large deletion of A. x castaneoriviride (2x) collected from Buramsan populations was ignored. Notably, this large deletion was also found in triploid A. × castaneoviride and allotetraploid A. castaneoviride in the same populations. Sequence data of the nuclear and plastid genes showed that hybridization is unidirectional, and A. ruprechtii is the maternal parent. The large deletion of rpoC2-rps2 commonly found in the different ploidy hybrids of the Buramsan population suggests that the allotetraploid A. castaneoviride can be created independently from sterile hybrids. We assume that both polyploidization driving allopolyploidy and minority cytotype exclusion took place independently in the population, since A castaenoviride co-occurs with A. ruprechtii in small populations. Furthermore, it was also observed that an enlarged noncoding region in fern organelle (ENRIFO) of the plastome was found in the genus Asplenium.

Speciation and development.

Understanding general principles about the origin of species remains one of the foundational challenges in evolutionary biology. The genomic divergence between groups of individuals can spawn hybrid inviability and hybrid sterility, which presents a tantalizing developmental problem. Divergent developmental programs may yield either conserved or divergent phenotypes relative to ancestral traits, both of which can be responsible for reproductive isolation during the speciation process. The genetic mechanisms of developmental evolution involve cis- and trans-acting gene regulatory change, protein-protein interactions, genetic network structures, dosage, and epigenetic regulation, all of which also have roots in population genetic and molecular evolutionary processes. Toward the goal of demystifying Darwin's "mystery of mysteries," this review integrates microevolutionary concepts of genetic change with principles of organismal development, establishing explicit links between population genetic process and developmental mechanisms in the production of macroevolutionary pattern. This integration aims to establish a more unified view of speciation that binds process and mechanism.

A CRISPR-Cas9-Derived Male Sterility System for Tomato Breeding

Male sterility can reduce cost and enable high seed purity during hybrid seed production. However, the commercial application of male sterility in hybrid seed production has not been widely used in tomatoes. CRISPR/Cas9-mediated gene editing can facilitate acceleration for the practical application of male sterility in hybrid seed production. Here, by using the CRISPR-Cas9 system, two genes DYSFUNCTIONAL TAPETUM1 (SlDYT1) and Glutathione S-transferase (SlGSTAA), which underly the two closely linked loci Male sterile 10 (Ms10) and Anthocyanin absent (AA), were knocked out simultaneously in two tomato parental lines. The generated dyt1gstaa double mutants developed green hypocotyl owing to anthocyanin deficiency and exhibited stable male sterility. Up to 92% effectiveness in selecting male sterility was achieved using green hypocotyl as a morphological marker, and thereafter an efficient and stable propagation strategy of male sterility with the aid of the morphological marker selection was developed. Furthermore, dyt1gstaa-derived hybrid seeds were produced and found to have comparable yield, weight, and germination rate with the corresponding WT-derived F1 seeds. The dyt1gstaa system not only increased hybrid seed purity to 100% but also facilitated its rapid and cost-effective determination. Moreover, this system was discovered to have no evident side effects on important agronomic traits. This study suggested that our CRISPR/Cas9-created dyt1gstaa system can be deployed in tomato hybrid seed production.

Inheritance regularities of economic and valuable traits in selection of sugar beet simple cytoplasmic male sterile hybrids

Aim. To study the influence of parental components of the crossing on the manifestation of the traits “yield of root crops” and “sugar content” in the hybrid progeny for the production of simple CМS hybrids. To create high-yielding simple CМS hybrids as a parent component for the formation of experimental sugar beet hybrids on а CМS basіs. Methods. Field (experiments, phenological observations), laboratory (to determine sugar content), measuring and weighing (to determine the crop structure), statistical (mathematical processing of research results). Results. The nature of the inheritance of productivity traits for the formation of simple CМS sugar beet hybrids has been established. For different combinations of crossings, the value of the inheritance coefficients (h2) of the trait “yield of root crops” from the parent form (O-type line) to the hybrid varied within 0.11–0.71 and 0.52–0.63 from the maternal form (CМS line). The inheritance coefficients of the trait “sugar content” from the parental form were in the range of 0.46–0.53 and 0.42–0.55 from the maternal form. An intermediate type of inheritance was observed for the sugar content in root crops. The best CМS lines and O-type lines have been identified as sources of economic and valuable traits. Seven combining-capable simple CМS hybrids with a high level of basic productivity were created for further use as a maternal component in the selection of sugar beet hybrids on а CМS basіs. Conclusions. A significant influence of the maternal component genotype on the level of yield of root crops of simple CМS hybrids has been established. A regularity has been revealed that the higher the total combining ability of CМS lines, the lower the degree of transfer of the trait “yield of root crops” from the parental form (O-type line) to the hybrid. There is no “mother plant” effect on sugar content in root crops, and an intermediate type of inheritance was observed in hybrids. The use of simple CМS hybrids with an increased level of basic productivity as a maternal component will significantly increase the efficiency of the breeding process for creating competitive sugar beet hybrids on а CМS basіs.

A Test of Haldane's Rule in Neodiprion Sawflies and Implications for the Evolution of Postzygotic Isolation in Haplodiploids.

AbstractHaldane's rule-a pattern in which hybrid sterility or inviability is observed in the heterogametic sex of an interspecific cross-is one of the most widely obeyed rules in nature. Because inheritance patterns are similar for sex chromosomes and haplodiploid genomes, Haldane's rule may apply to haplodiploid taxa, predicting that haploid male hybrids will evolve sterility or inviability before diploid female hybrids. However, there are several genetic and evolutionary mechanisms that may reduce the tendency of haplodiploids to obey Haldane's rule. Currently, there are insufficient data from haplodiploids to determine how frequently they adhere to Haldane's rule. To help fill this gap, we crossed a pair of haplodiploid hymenopteran species (Neodiprion lecontei and Neodiprion pinetum) and evaluated the viability and fertility of female and male hybrids. Despite considerable divergence, we found no evidence of reduced fertility in hybrids of either sex, consistent with the hypothesis that hybrid sterility evolves slowly in haplodiploids. For viability, we found a pattern opposite to that of Haldane's rule: hybrid females, but not males, had reduced viability. This reduction was most pronounced in one direction of the cross, possibly due to a cytoplasmic-nuclear incompatibility. We also found evidence of extrinsic postzygotic isolation in hybrids of both sexes, raising the possibility that this form or reproductive isolation tends to emerge early in speciation in host-specialized insects. Our work emphasizes the need for more studies on reproductive isolation in haplodiploids, which are abundant in nature but underrepresented in the speciation literature.

Genomic Architecture of Hybrid Male Sterility in a Species Without Sex Chromosomes (Tigriopus californicus, Copepoda: Harpacticoida).

Sterility among hybrids is one of the most prevalent forms of reproductive isolation delineating species boundaries and is expressed disproportionately in heterogametic XY males. While hybrid male sterility (HMS) due to the "large X effect" is a well-recognized mechanism of reproductive isolation, it is less clear how HMS manifests in species that lack heteromorphic sex chromosomes. We evaluated differences in allele frequencies at approximately 460,000 SNPs between fertile and sterile F2 interpopulation male hybrids to characterize the genomic architecture of HMS in a species without sex chromosomes (Tigriopus californicus). We tested associations between HMS and mitochondrial-nuclear and/or nuclear-nuclear signatures of incompatibility. Genomic regions associated with HMS were concentrated on a single chromosome with the same primary 2-Mbp regions identified in one pair of reciprocal crosses. Gene Ontology analysis revealed that annotations associated with spermatogenesis were the most overrepresented within the implicated region, with nine protein-coding genes connected with this process found in the quantitative trait locus of chromosome 2. Our results indicate that a narrow genomic region was associated with the sterility of male hybrids in T. californicus and suggest that incompatibilities among select nuclear loci may replace the large X effect when sex chromosomes are absent.

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.

Comparative proteomic analysis identifies differentially expressed proteins associated with meiotic arrest in cattle-yak hybrids.

Cattle-yak, the interspecific hybrid between yak and taurine cattle, exhibits male-specific sterility. Massive loss of spermatogenic cells, especially spermatocytes, results in azoospermia in these animals. Currently, the mechanisms underlying meiosis block and defects in spermatocyte development remain elusive. The present study was designed to investigate the differences in the protein composition of spermatocytes isolated from 12-month-old yak and cattle-yak testes. Histological analysis confirmed that spermatocytes were the most advanced germ cells in the testes of yak and cattle-yak at this developmental stage. Comparative proteomic analysis identified a total of 452 differentially abundant proteins (DAPs) in the fluorescence-activated cell sorting (FACS) isolated spermatocytes from cattle-yak and yak. A total of 291 proteins were only present in yak spermatocytes. Gene Ontology analysis revealed that the downregulated DAPs were mostly enriched in the cellular response to DNA damage stimulus and double-strand break (DSB) repair via break-induced replication, while the proteins specific for yak were related to cell division and cycle, spermatogenesis, and negative regulation of the extrinsic apoptotic signaling pathway. Ultimately, these DAPs were related to the critical process for spermatocyte meiotic events, including DSBs, homologous recombination, synapsis, crossover formation, and germ cell apoptosis. The database composed of proteins associated with spermatogenesis, including KPNA2, HTATSF1, TRIP12, STIP1, LZTFL1, LARP7, MTCH2, STK31, ROMO1, CDK5AP2, DNMT1, RBM44 and CHRAC1 is the focus of further research on male hybrid sterility. In total, these results provide insight into the molecular mechanisms underlying failed meiotic processes and male infertility in cattle-yak. This article is protected by copyright. All rights reserved.