Distinct geographic parthenogenesis in spite of niche conservatism and a single ploidy level: A case of Rubus ser. Glandulosi (Rosaceae).

Asexual organisms often differ in their geographic distributions from their sexual relatives. This phenomenon, termed geographic parthenogenesis, has long been known, but the underlying factors behind its diverse patterns have been under dispute. Particularly problematic is an association between asexuality and polyploidy in most taxa. Here, we present a new system of geographic parthenogenesis on the tetraploid level, promising new insights into this complex topic. We used flow cytometric seed screen and microsatellite genotyping to characterise the patterns of distribution of sexuals and apomicts and genotypic distributions in Rubus ser. Glandulosi across its range. Ecological modelling and local-scale vegetation and soil analyses were used to test for niche differentiation between the reproductive groups. Apomicts were detected only in North-western Europe, sexuals in the rest of the range in Europe and West Asia, with a sharp borderline stretched across Central Europe. Despite that, we found no significant differences in ecological niches. Genotypic richness distributions suggested independence of the reproductive groups and a secondary contact. We argue that unless a niche differentiation (resulting from polyploidy and/or hybridity) evolves, the main factors behind the patterns of geographic parthenogenesis in plants are phylogeographic history and neutral microevolutionary processes, such as clonal turnover.

Aneuploidy during development in facultative parthenogenetic Drosophila.

From concatenated chromosomes to polyploidization, large-scale genome changes are known to occur in parthenogenetic animals. Here, we report mosaic aneuploidy in larval brains of facultatively parthenogenetic Drosophila. We identified a background of aneuploidy in D. mercatorum strains and found increased levels of aneuploidy in the larval brain tissue of animals arising parthenogenetically versus those arising from sexual reproduction. There is also intra-individual variation in germline-derived aneuploidy within the same strain. To determine if this is a general feature of facultative parthenogenesis in drosophilids, we compared sexually reproduced and parthenogenetic offspring from an engineered facultative parthenogenetic strain of D. melanogaster. In addition to germline-derived aneuploidy, this revealed somatic aneuploidy that increased by up to fourfold in parthenogens compared to sexually reproduced offspring. Therefore, the genetic combination identified in D. mercatorum that causes facultative parthenogenesis in D. melanogaster results in aneuploidy, which indicates that the loss of mitotic control resulting in parthenogenesis causes subsequent genome variation within the parthenogenetic offspring. Our findings challenge the assumption that parthenogenetic offspring are near genetic replicas of their mothers.

A genetic basis for facultative parthenogenesis in Drosophila.

Facultative parthenogenesis enables sexually reproducing organisms to switch between sexual and asexual parthenogenetic reproduction. To gain insights into this phenomenon, we sequenced the genomes of sexually reproducing and parthenogenetic strains of Drosophila mercatorum and identified differences in the gene expression in their eggs. We then tested whether manipulating the expression of candidate gene homologs identified in Drosophila mercatorum could lead to facultative parthenogenesis in the non-parthenogenetic species Drosophila melanogaster. This identified a polygenic system whereby increased expression of the mitotic protein kinase polo and decreased expression of a desaturase, Desat2, caused facultative parthenogenesis in the non-parthenogenetic species that was enhanced by increased expression of Myc. The genetically induced parthenogenetic Drosophila melanogaster eggs exhibit de novo centrosome formation, fusion of the meiotic products, and the onset of development to generate predominantly triploid offspring. Thus, we demonstrate a genetic basis for sporadic facultative parthenogenesis in an animal.

Parthenogenesis in dipterans: a genetic perspective.

Parthenogenesis has been documented in almost every phylum of animals, and yet this phenomenon is largely understudied. It has particular importance in dipterans since some parthenogenetic species are also disease vectors and agricultural pests. Here, we present a catalogue of parthenogenetic dipterans, although it is likely that many more remain to be identified, and we discuss how their developmental biology and interactions with diverse environments may be linked to different types of parthenogenetic reproduction. We discuss how the advances in genetics and genomics have identified chromosomal loci associated with parthenogenesis. In particular, a polygenic cause of facultative parthenogenesis has been uncovered in Drosophila mercatorum, allowing the corresponding genetic variants to be tested for their ability to promote parthenogenesis in another species, Drosophila melanogaster. This study probably identifies just one of many routes that could be followed in the evolution of parthenogenesis. We attempt to account for why the phenomenon has evolved so many times in the dipteran order and why facultative parthenogenesis appears particularly prevalent. We also discuss the significance of coarse genomic changes, including non-disjunction, aneuploidy, and polyploidy and how, together with changes to specific genes, these might relate to both facultative and obligate parthenogenesis in dipterans and other parthenogenetic animals.

Mendelian segregation for parthenogenetic embryo development at the diploid level in the flowering plant Erigeron.

PREMISE: Parthenogenesis is the capacity of organisms to develop embryos from unfertilized eggs. When parthenogenesis is coupled with unreduced gamete formation (apomeiosis), genetically maternal progeny result. Genetic elucidation of this form of reproduction in plants, apomixis, has important agronomic implications. However, genetic characterization of apomeiosis and parthenogenesis has been problematic in part because the traits usually co-occur and are restricted to polyploids. In this work, the inheritance of parthenogenetic embryo development, by itself, was studied at the diploid level. METHODS: Progeny resulting from a cross between a diploid (2n = 18), heterozygous, parthenogenetic pollen donor, and a diploid, wildtype, sexual seed parent were evaluated. Paternity was tested with conserved orthologous sequence (COS) markers, reproductive development of F1s was evaluated with microscopy of cleared ovules, and an amplified fragment length polymorphism (AFLP) marker (Eagc × Macg.615) co-segregating with parthenogenesis was characterized at the sequence level. RESULTS: Of 102 diploid biparental progeny, 47 exhibited parthenogenetic embryo and endosperm development, and 55 lacked development of the egg and central cell. This result is consistent with Mendelian inheritance for a single locus (P = 0.43). Isolation and sequencing of the AFLP marker indicates that it is likely a portion of a Ty-Gypsy retrotransposon. Attempts to develop a sequence-characterized amplified region marker from the AFLP were unsuccessful. CONCLUSIONS: This work shows that parthenogenesis can be transmitted simply at the diploid level. This advance is key in the development of a tractable system in Erigeron aimed at the identification of the parthenogenesis locus using genetic mapping strategies.

The Origin of Asexual Brine Shrimps.

AbstractDetermining how and how often asexual lineages emerge within sexual species is central to our understanding of sex-asex transitions and the long-term maintenance of sex. Asexuality can arise "by transmission" from an existing asexual lineage to a new one through different types of crosses. The occurrence of these crosses, cryptic sex, variations in ploidy, and recombination within asexuals greatly complicates the study of sex-asex transitions, as they preclude the use of standard phylogenetic methods and genetic distance metrics. In this study we show how to overcome these challenges by developing new approaches to investigate the origin of the various asexual lineages of the brine shrimp Artemia parthenogenetica. We use a large sample of asexuals, including all known polyploids, and their sexual relatives. We combine flow cytometry with mitochondrial and nuclear DNA data. We develop new genetic distance measures and methods to compare various scenarios describing the origin of the different lineages. We find that all diploid and polyploid A. parthenogenetica likely arose within the past 80,000 years through successive and nested hybridization events that involved backcrosses with different sexual species. All A. parthenogenetica have the same common ancestor and therefore likely carry the same asexuality gene(s) and reproduce by automixis. These findings radically change our view of sex-asex transitions in this group and show the importance of considering scenarios of asexuality by transmission. The methods developed are applicable to many other asexual taxa.

Premeiotic endoreplication is essential for obligate parthenogenesis in geckos.

Obligate parthenogenesis evolved in reptiles convergently several times, mainly through interspecific hybridization. The obligate parthenogenetic complexes typically include both diploid and triploid lineages. Offspring of parthenogenetic hybrids are genetic copies of their mother; however, the cellular mechanism enabling the production of unreduced cells is largely unknown. Here, we show that oocytes go through meiosis in three widespread, or even strongly invasive, obligate parthenogenetic complexes of geckos, namely in diploid and triploid Lepidodactylus lugubris, and triploid Hemiphyllodactylus typus and Heteronotia binoei. In all four lineages, the majority of oocytes enter the pachytene at the original ploidy level, but their chromosomes cannot pair properly and instead form univalents, bivalents and multivalents. Unreduced eggs with clonally inherited genomes are formed from germ cells that had undergone premeiotic endoreplication, in which appropriate segregation is ensured by the formation of bivalents made from copies of identical chromosomes. We conclude that the induction of premeiotic endoreplication in reptiles was independently co-opted at least four times as an essential component of parthenogenetic reproduction and that this mechanism enables the emergence of fertile polyploid lineages within parthenogenetic complexes.

Derivation of Mouse Parthenogenetic Advanced Stem Cells.

Parthenogenetic embryos have been widely studied as an effective tool related to paternal and maternal imprinting genes and reproductive problems for a long time. In this study, we established a parthenogenetic epiblast-like stem cell line through culturing parthenogenetic diploid blastocysts in a chemically defined medium containing activin A and bFGF named paAFSCs. The paAFSCs expressed pluripotent marker genes and germ-layer-related genes, as well as being alkaline-phosphatase-positive, which is similar to epiblast stem cells (EpiSCs). We previously showed that advanced embryonic stem cells (ASCs) represent hypermethylated naive pluripotent embryonic stem cells (ESCs). Here, we converted paAFSCs to ASCs by replacing bFGF with bone morphogenetic protein 4 (BMP4), CHIR99021, and leukemia inhibitory factor (LIF) in a culture medium, and we obtained parthenogenetic advanced stem cells (paASCs). The paASCs showed similar morphology with ESCs and also displayed a stronger developmental potential than paAFSCs in vivo by producing chimaeras. Our study demonstrates that maternal genes could support parthenogenetic EpiSCs derived from blastocysts and also have the potential to convert primed state paAFSCs to naive state paASCs.

Moving beyond assumptions: Polyploidy and environmental effects explain a geographical parthenogenesis scenario in European plants.

Geographical parthenogenesis (GP) describes the phenomenon that apomicts tend to have larger distribution areas and/or occur at higher altitudes or latitudes compared to sexual relatives. However, the complex effects of genome-wide heterozygosity, ploidy, reproduction mode (sexual vs. apomictic), and environment shaping GP of plants are still not well understood. We ascertained ploidy and reproduction mode by flow cytometry of 221 populations, and added genomic RADseq data (maximum 33,165 loci) of 80 taxa of the Ranunculus auricomus polyploid plant complex in temperate Europe. We observed 7% mainly diploid sexual, 28% facultative apomictic (mean sexuality 7.1%), and 65% obligate apomictic populations. Sexuals occupied a more southern, smaller distribution area, whereas apomicts expanded their range to higher latitudes. Within the complex, we detected three main genetic clusters and highly reticulate relationships. A genetically-informed path analysis using GLMMs revealed several significant relationships. Sexuality of populations (percent of sexual seeds) was higher in diploids compared to polyploids, associated with more petals, and similar between forests and open habitats. In contrast to other apomictic plant complexes, sexuality was mainly positively correlated to solar radiation and isothermality, which fits the southern distribution. We found up to three times higher heterozygosity in polyploids compared to diploids, and generally more heterozygous individuals in forests compared with open habitats. Interestingly, we revealed a previously unknown positive association between heterozygosity and temperature seasonality, suggesting a higher resistance of polyploids to more extreme climatic conditions. We provide empirical evidence for intrinsic and extrinsic factors shaping the GP pattern in a polyploid plant complex.

A Single Gene Causes Thelytokous Parthenogenesis, the Defining Feature of the Cape Honeybee Apis mellifera capensis.

In honeybees, the ability of workers to produce daughters asexually, i.e., thelytokous parthenogenesis, is restricted to a single subspecies inhabiting the Cape region of South Africa, Apis mellifera capensis. Thelytoky has unleashed new selective pressures and the evolution of traits such as social parasitism, invasiveness, and social cancer. Thelytoky arises from an abnormal meiosis that results in the fusion of two maternal pronuclei, restoring diploidy in newly laid eggs. The genetic basis underlying thelytoky is disputed. To resolve this controversy, we generated a backcross between thelytokous A. m. capensis and non-thelytokous A. m. scutellata from the neighboring population and looked for evidence of genetic markers that co-segregated with thelytokous reproduction in 49 backcross females. We found that markers associated with the gene GB45239 on chromosome 11, including non-synonymous variants, showed consistent co-segregation with thelytoky, whereas no other region did so. Alleles associated with thelytoky were present in all A. m. capensis genomes examined but were absent from all other honeybees worldwide including A. m. scutellata. GB45239 is derived in A. m. capensis and has a putative role in chromosome segregation. It is expressed in ovaries and is downregulated in thelytokous bees, likely because of polymorphisms in the promoter region. Our study reveals how mutations affecting the sequence and/or expression of a single gene can change the reproductive mode of a population.

microRNA-670 modulates Igf2bp1 expression to regulate RNA methylation in parthenogenetic mouse embryonic development.

Aberrant epigenetic modification, including N6-methylation of adenosine (m6A), has been frequently reported in embryos derived from parthenogenetic activation (PA). However, the role of Igf2bp1 expression pattern in m6A modification and the mechanism through which Igf2bp1 function is regulated in PA embryos remains elusive. Therefore, in this study, using si-Igf2bp1 and betaine (N,N,N-trimethylglycine, a major methyl donor), we investigated the effect of Igf2bp1 expression in m6A modification on the development of PA embryos. The results indicated that the down-regulation of Igf2bp1 reduced the cleavage and blastula rates of PA embryos. Moreover, m6A expression level was markedly down-regulated following microinjection with si-Igf2bp1. However, the treatment with betaine could significantly restore the m6A level. Further bioinformatics analysis revealed Igf2bp1 as the putative target of microRNA 670 (miR-670). Thus, to confirm this finding, mimics and inhibitor of miR-670 were microinjected into PA embryos. The results demonstrated that miR-670 inhibitor augmented the expression of Igf2bp1 and rescued cleavage and blastula rates. In addition, the miR-670 inhibitor promoted the m6A expression level. TUNEL assay revealed a loss of expression of Igf2bp1 induced cell apoptosis in PA embryos. Taken together, these results demonstrated that miR-670-3p functions as the regulator of Igf2bp1 expression and plays a crucial role in PA development through m6A modification.

Genetic analysis of embryo in a human case of spontaneous oocyte activation: a case report.

Parthenogenesis, a unique form of reproduction, is normally inhibited in mammals and a human embryo with parthenogenetic origin is not considered capable of producing offspring. The aim of this report is to analyze a parthenogenetic oocyte retrieved from a patient so as to have a better understanding on parthenogenesis and causes of infertility. A 38-year-old woman presented at our center with a history of primary infertility for 10 years and underwent an IVF-ICSI cycle. Three MII oocytes retrieved and one of which presented with 1 pronucleus before conducting ICSI and developed into an embryo 30 h post-retrieval. Blastomere biopsy, genome amplification, copy number variation (CNV) analysis and MultiSNPs analysis was performed on the embryo. The results showed that only one blastomere contains DNA and CNV analysis indicated a genotype of 48, XX, +17, +17 and the genetic contribution of biopsied embryo was of exclusively maternal origin. Such analysis might be beneficial for patients with a history of oocyte spontaneous activation in diagnosing case-specific aberrations and providing individualized therapeutic strategies such as preimplantation genetic diagnosis to choose a genetic normal embryo to transplant.

NLRP7 is expressed in the ovine ovary and associated with in vitro pre-implantation embryo development.

NLRP (NACHT, LRR and PYD domain-containing proteins) family plays pivotal roles in mammalian reproduction. Mutation of NLRP7 is often associated with human recurrent hydatidiform moles. Few studies regarding the functions of NLRP7 have been performed in other mammalian species rather than humans. In the current study, for the first time, the function of NLRP7 has been explored in ovine ovary. NLRP7 protein was mainly located in ovarian follicles and in in vitro pre-implantation embryos. To identify its origin, 763 bp partial CDS of NLRP7 deriving from sheep cumulus oocyte complexes (COCs) was cloned, it showed a great homology with Homo sapiens. The high levels of mRNA and protein of NLRP7 were steadily expressed in oocytes, parthenogenetic embryos or IVF embryos. NLRP7 knockdown by the combination of siRNA and shRNA jeopardized both the parthenogenetic and IVF embryo development. These results strongly suggest that NLRP7 plays an important role in ovine reproduction. The potential mechanisms of NLRP7 will be fully investigated in the future.

The role of hybridisation in the origin and evolutionary persistence of vertebrate parthenogens: a case study of Darevskia lizards.

Obligate parthenogenesis is found in only 0.1% of the vertebrate species, is thought to be relatively short lived and is typically of hybrid origin. However, neither the evolutionary persistence of asexuality in vertebrates, nor the conditions that allow the generation of new parthenogenetic lineages are currently well understood. It has been proposed that vertebrate parthenogenetic lineages arise from hybridisation between two divergent taxa within a specific range of phylogenetic distances (the 'Balance Hypothesis'). Moreover, parthenogenetic species often maintain a certain level of hybridisation with their closest sexual relatives, potentially generating new polyploid hybrid lineages. Here we address the role of hybridisation in the origin and evolutionary lifespan of vertebrate parthenogens. We use a set of microsatellite markers to characterise the origins of parthenogens in the lizard genus Darevskia, to study the distinctiveness of sexual and asexual taxa currently in sympatry, and to analyse the evolutionary consequences of interspecific hybridisation between asexual females and sexual males. We find that parthenogens result from multiple past hybridisation events between species from specific lineages over a range of phylogenetic distances. This suggests that the Balance Hypothesis needs to allow for lineage-specific effects, as envisaged in the Phylogenetic Constraint Hypothesis. Our results show recurrent backcrossing between sexual and parthenogenic Darevskia but neither gene flow nor formation of new asexual lineages. We suggest that, along with their demographic advantage, parthenogens gain additional leverage to outcompete sexuals in nature when the retention of sexual reproductive machinery allows backcrossing with their sexual ancestors.

Insulin-like peptides involved in photoperiodism in the aphid Acyrthosiphon pisum.

Aphids were the first animals reported as photoperiodic as their life cycles are strongly determined by the photoperiod. During the favourable seasons (characterised by long days) aphid populations consist exclusively of viviparous parthenogenetic females (known as virginoparae). Shortening of the photoperiod in autumn is perceived by aphids as the signal that anticipates the harsh season, leading to a switch in the reproductive mode giving place to the sexual morphs (oviparae females and males) that mate and lay winter-resistant (diapause-like) eggs. The molecular and cellular basis governing the switch between the two reproductive modes are far from being understood. Classical experiments identified a group of neurosecretory cells in the pars intercerebralis of the aphid brain (the so called group I of neurosecretory cells) that were essential for the development of embryos as parthenogenetic females and were thus proposed to synthesise a parthenogenesis promoting substance that was termed "virginoparin". Since insulin-like peptides (ILPs) have been implicated in the control of diapause in other insects, we investigated their involvement in aphid photoperiodism. We compared the expression of two ILPs (ILP1 and ILP4) and an Insulin receptor coding genes in A. pisum aphids reared under long- and short-day conditions. The three genes showed higher expression in long-day reared aphids. In addition, we localised the site of expression of the two ILP genes in the aphid brain. Both genes were found to be expressed in the group I of neurosecretory cells. Altogether, our results suggest that ILP1 and ILP4 play an important role in the control of the aphid life-cycle by promoting the parthenogenetic development during long-day seasons while their repression by short days would activate the sexual development. Thus we propose these ILPs correspond to the so called "virginoparin" by early bibliography. A possible connection with the circadian system is also discussed.

Genetic Control of Facultative Parthenocarpy in Nicotiana tabacum L.

Investigation of parthenocarpy, the production of fruit without fertilization, in multiple plant species could result in development of technologies for conferring seedless fruits and increased stability of fruit formation in economically important plants. We studied parthenocarpy in the model species Nicotiana tabacum L., and observed variability for expression of the trait among diverse genetic materials. Parthenocarpy was found to be partially dominant, and a single major quantitative trait locus on linkage group 22 was found to control the trait in a doubled haploid mapping population derived from a cross between parthenocarpic cigar tobacco cultivar "Beinhart 1000" and nonparthenocarpic flue-cured tobacco cultivar, "Hicks." The same genomic region was found to be involved with control of the trait in the important flue-cured tobacco cultivar, "K326." We also investigated the potential for the production of maternal haploids due to parthenogenesis in parthenocarpic tobacco seed capsules. Maternal haploids were not observed in parthenocarpic capsules, suggesting a requirement of fertilization for maternal haploid production due to parthenogenesis in N. tabacum.

Not always young: The first vertebrate ancient origin of true parthenogenesis found in an Amazon leaf litter lizard with evidence of mitochondrial haplotypes surfing on the wave of a range expansion.

In vertebrates, true parthenogenesis is found only in squamate reptiles and (mostly) originates via interspecific hybridization after secondary contact. In many cases, parthenogenesis is followed by an increase of ploidy, resulting in triploid lineages. Phylogenetic analyses derived from nuclear and maternally inherited markers can help to clarify the mechanisms of origin and the potential parental species involved. In the Amazon region, parthenogenetic lizards of the Loxopholis percarinatum complex are widely distributed, comprising both diploid and triploid clones. Recently, putative males of L. percarinatum were reported, suggesting the existence of bisexual populations based on morphological data. Here, we used mitochondrial and nuclear data to investigate the origin of parthenogenesis in Loxopholis. Mitochondrial DNA analysis revealed three major lineages: unisexual/2n, unisexual/3n and bisexual, the last of which comprised two sub-lineages placed as the sister taxon to the unisexual/3n lineage. Genetic divergence among the lineages was ∼10% but was lower between the unisexual/3n and bisexual lineages (∼6%). Both mtDNA and nuDNA indicated that individuals from the bisexual lineages might belong to a new species. Nuclear DNA evidence indicates that crossings occasionally occur between unisexual 2n and males from the new bisexual species. Phylogenetic analysis of nuDNA showed L. ferreirai as the closest described bisexual species to the complex. Our results revealed an ancient origin of parthenogenesis in the L. percarinatum complex, in contrast to most young (Pleistocene) parthenogenetic lizards described thus far. Two hybridization events seem to have been involved: the first event occurred in late Miocene, between the ancestral lineage ("A") of the new bisexual species (as a maternal species) and the ancestral lineage of L. ferreirai, as a paternal species of L. percarinatum 2n; and the second event occurred in Pliocene-Pleistocene, in a backcross between L. percarinatum 2n and a male from the common ancestor ("B") of the new bisexual species giving rise to the lineage of L. percarinatum 3n. With these results, we showed that L. percarinatum complex also includes, at least, one undescribed bisexual species in addition to the two known parthenogenetic lineages (2n and 3n). Finally, we present evidence that diploid individuals of L. percarinatum experienced an event of wide demographic expansion over the past million years under an allele surfing model.

Ascorbic acid improves parthenogenetic embryo development through TET proteins in mice.

The TET (Ten-Eleven Translocation) proteins catalyze the oxidation of 5mC (5-methylcytosine) to 5hmC (5-hydroxymethylcytosine) and play crucial roles in embryonic development. Ascorbic acid (Vc, Vitamin C) stimulates the expression of TET proteins, whereas DMOG (dimethyloxallyl glycine) inhibits TET expression. To investigate the role of TET1, TET2, and TET3 in PA (parthenogenetic) embryonic development, Vc and DMOG treatments were administered during early embryonic development. The results showed that Vc treatment increased the blastocyst rate (20.73 ± 0.46 compared with 26.57 ± 0.53%). By contrast, DMOG reduced the blastocyst rate (20.73 ± 0.46 compared with 11.18 ± 0.13%) in PA embryos. qRT-PCR (quantitative real-time PCR) and IF (immunofluorescence) staining results revealed that TET1, TET2, and TET3 expressions were significantly lower in PA embryos compared with normal fertilized (Con) embryos. Our results revealed that Vc stimulated the expression of TET proteins in PA embryos. However, treatment with DMOG significantly inhibited the expression of TET proteins. In addition, 5hmC was increased following treatment with Vc and suppressed by DMOG in PA embryos. Taken together, these results indicate that the expression of TET proteins plays crucial roles mediated by 5hmC in PA embryonic development.

Uroplakins play conserved roles in egg fertilization and acquired additional urothelial functions during mammalian divergence.

Uroplakin (UP) tetraspanins and their associated proteins are major mammalian urothelial differentiation products that form unique two-dimensional crystals of 16-nm particles ("urothelial plaques") covering the apical urothelial surface. Although uroplakins are highly expressed only in mammalian urothelium and are often referred to as being urothelium specific, they are also expressed in several mouse nonurothelial cell types in stomach, kidney, prostate, epididymis, testis/sperms, and ovary/oocytes. In oocytes, uroplakins colocalize with CD9 on cell-surface and multivesicular body-derived exosomes, and the cytoplasmic tail of UPIIIa undergoes a conserved fertilization-dependent, Fyn-mediated tyrosine phosphorylation that also occurs in Xenopus laevis eggs. Uroplakin knockout and antibody blocking reduce mouse eggs' fertilization rate in in vitro fertilization assays, and UPII/IIIa double-knockout mice have a smaller litter size. Phylogenetic analyses showed that uroplakin sequences underwent significant mammal-specific changes. These results suggest that, by mediating signal transduction and modulating membrane stability that do not require two-dimensional-crystal formation, uroplakins can perform conserved and more ancestral fertilization functions in mouse and frog eggs. Uroplakins acquired the ability to form two-dimensional-crystalline plaques during mammalian divergence, enabling them to perform additional functions, including umbrella cell enlargement and the formation of permeability and mechanical barriers, to protect/modify the apical surface of the modern-day mammalian urothelium.

Imprinting Status in Two Human Parthenogenetic Embryonic Stem Cell Lines: Analysis of 63 Imprinted Gene Expression Levels in Undifferentiated and Early Differentiated Stages.

Human parthenogenetic embryonic stem cells (hPESCs) represent a source of histocompatible tissues for transplantation and carry two copies of the maternal genome, but lack the paternal genome. In this study, we selected 63 known human imprinted genes to investigate the imprinting status of hPESC. The expression level of these genes, including 27 maternally and 36 paternally imprinted were illustrated in hPESC and human embryonic stem cells (hESCs) derived from fertilized embryo lines. The expression activity changes of these genes were analyzed in undifferentiated and early differentiated hPESC lines. In addition, the methylation status of four differentially methylated regions (DMRs) of the imprinted genes was analyzed in undifferentiated and early differentiated hPESC and hESC lines. As a result, we found that all the maternally imprinted genes were expressed at similar levels in the undifferentiated hPESC lines and the hESC lines, except ZNF264 and ATP10A. Twenty-one analyzed paternal imprinted genes were expressed at the same level in two separated hPESC lines as well as compared with the hESC lines, whereas 15 other paternal imprinted genes were significantly downregulated or inactivated in hPESC lines as compared with the hESC line. During prolonged passage, the expression levels of the majority of imprinted genes remained stable in two hPESC lines. The four DMRs, including PEG3/ZIM2 (DMRs), SNURF/SNRPN DMRs, and KVDMR1 DMRs are highly methylated in the genes of two undifferentiated hPESCs and its embryonic bodies (EBs), whereas the genes of the undifferentiated hESCs and its EBs are half methylated. During the early differentiation stage, the imprinted genes showed the same expression trend and the expression levels of H19, IGF2, SLC22A2, SLC22A3/SLC22A18, and CPA4 were significantly upregulated in both hPESC lines. As conclusion, hPESCs show a substantial degree of epigenetic stability with respect to some imprinted genes.