Paternal DNA Research Articles

Inheritance patterns of male asexuality in hybrid males of a water frog Pelophylax esculentus.

Gametogenesis produces gametes as a piece of genetic information transmitted to the offspring. While during sexual reproduction, progeny inherits a mix of genetic material from both parents, asexually reproducing organisms transfer a copy of maternal or paternal DNA to the progeny clonally. Parthenogenetic, gynogenetic and hybridogenetic animals have developed various mechanisms of gametogenesis, however, their inheritance is not fully understood. Here, we focused on the inheritance of asexual gametogenesis in hybrid Pelophylax esculentus (RL), emerging after crosses of P. lessonae (LL) and P. ridibundus (RR). To understand the mechanisms of gametogenesis in hybrids, we performed three-generation experiments of sexual P. ridibundus females and hybrids from all-male hybrid populations. Using fluorescent in situ hybridization, micronuclei analysis, flow cytometry and genotyping, we found that most adult hybrid males simultaneously produced two types of clonal sperm. Also, most male tadpole progeny in two successive backcrossed generations simultaneously eliminated L and R parental genomes, while some progeny produced only one type of sperm. We hypothesize that the reproductive variability of males producing two kinds of sperm is an adaptive mechanism to reproduce in mixed populations with P. ridibundus and may explain the extensive distribution of the all-male lineage across the European River Basin.

Sperm-carried IGF2: towards the discovery of a spark contributing to embryo growth and development.

Spermatozoa have been shown to carry key RNAs which, according to animal evidence, seem to play a role in early embryo development. In this context, a potential key growth regulator is insulin-like growth factor 2 (IGF2), a highly conserved paternally expressed imprinted gene involved in cell growth and proliferation which, recent observations indicate, is expressed in human spermatozoa. We herein hypothesized that sperm IGF2 gene expression and transmission at fertilization is required to support early embryo development. To test this hypothesis, we analyzed sperm IGF2 mRNA levels in the same semen aliquot used for homologous assisted reproductive technique (ART) in infertile couples and correlated these levels with embryo morphokinetics. To find a mechanistic explanation for the observed results, the transcriptomes of blastocysts obtained after injection of Igf2 mRNA in mouse parthenotes were analyzed. Sperm IGF2 mRNA negatively correlated with time of 2-cell stage (t2), t3, t4, t5, and time of expanded blastocyst (tEB), independently of maternal age, body mass index, anti-Müllerian hormone levels, and oocyte quality. An IGF2 mRNA index >4.9 predicted the ability of the embryos to reach the blastocyst stage on Day 5, with a sensitivity of 100% and a specificity of 71.6% (AUC 0.845; P < 0.001). In the animal study, transcriptome analysis demonstrated that 65 and 36 genes were, respectively, up- and down-regulated in the experimental group compared to the control group. These genes belong to pathways that regulate early embryo development, thus supporting the findings found in humans. This study has the potential to challenge the longstanding tenet that spermatozoa are simply vehicles carrying paternal DNA. Instead, it suggests that IGF2 mRNA in healthy spermatozoa provides critical support for early embryo development. Pre-ART sperm-carried IGF2 mRNA levels may be used as a marker to predict the chances of obtaining blastocysts to be transferred for infertile couples undergoing ART.

Characterization of blood bank and transfusion medicine practices for pregnant individuals with fetuses at risk of hemolytic disease in the United States.

Hemolytic disease of the fetus and newborn (HDFN) is caused by maternal alloantibody-mediated destruction of fetal/neonatal red blood cells (RBCs). While the pathophysiology has been well-characterized, the clinical and laboratory monitoring practices are inconsistent. We surveyed 103 US institutions to characterize laboratory testing practices for individuals with fetuses at risk of HDFN. Questions included antibody testing and titration methodologies, the use of critical titers, paternal and cell-free fetal DNA testing, and result reporting and documentation practices. The response rate was 44% (45/103). Most respondents (96%, 43/45) assess maternal antibody titers, primarily using conventional tube-based methods only (79%, 34/43). Among respondents, 51% (23/45) rescreen all individuals for antibodies in the third trimester, and 60% (27/45) perform paternal RBC antigen testing. A minority (27%, 12/45) utilize cell-free fetal DNA (cffDNA) testing to predict fetal antigen status. Maternal antibody titers are performed even when the fetus is not considered to be at risk of HDFN based on cffDNA or paternal RBC antigen testing at 23% (10/43) of sites that assess titers. There is heterogeneity across US institutions regarding the testing, monitoring, and reporting practices for pregnant individuals with fetuses at risk of HDFN, including the use of antibody titers in screening and monitoring programs, the use of paternal RBC antigen testing and cffDNA, and documentation of fetal antigen results. Standardization of laboratory testing protocols and closer collaboration between the blood bank and transfusion medicine service and the obstetric/maternal-fetal medicine service are needed.

Paternal Mitochondrial DNA Leakage in Natural Populations of Large-Scale Loach, Paramisgurnus dabryanus.

Animal mitochondrial DNA is usually considered to comply with strict maternal inheritance, and only one mitochondrial DNA haplotype exists in an individual. However, mitochondrial heteroplasmy, the occurrence of more than one mitochondrial haplotype, has recently been reported in some animals, such as mice, mussels, and birds. This study conducted extensive field surveys to obtain representative samples to investigate the existence of paternal inheritance of mitochondrial DNA (mtDNA) in natural fish populations. Evidence of paternal mitochondrial DNA leakage of P. dabryanus was discovered using high-throughput sequencing and bioinformatics methods. Two distinct mitochondrial haplotypes (16,569 bp for haplotype I and 16,646 bp for haplotype II) were observed, differing by 18.83% in nucleotide sequence. Phylogenetic analysis suggests divergence between these haplotypes and potential interspecific hybridization with M. anguillicaudatus, leading to paternal leakage. In natural populations of P. dabryanus along the Yangtze River, both haplotypes are present, with Type I being dominant (75% copy number). Expression analysis shows that Type I has higher expression levels of ND3 and ND6 genes compared to Type II, suggesting Type I's primary role. This discovery of a species with two mitochondrial types provides a model for studying paternal leakage heterogeneity and insights into mitochondrial genome evolution and inheritance.

Katanin, kinesin-13, and ataxin-2 inhibit premature interaction between maternal and paternal genomes in C. elegans zygotes

Fertilization occurs before the completion of oocyte meiosis in the majority of animal species and sperm contents move long distances within the zygotes of mouse and C. elegans. If incorporated into the meiotic spindle, paternal chromosomes could be expelled into a polar body resulting in lethal monosomy. Through live imaging of fertilization in C. elegans, we found that the microtubule disassembling enzymes, katanin and kinesin-13 limit long-range movement of sperm contents and that maternal ataxin-2 maintains paternal DNA and paternal mitochondria as a cohesive unit that moves together. Depletion of katanin or double depletion of kinesin-13 and ataxin-2 resulted in the capture of the sperm contents by the meiotic spindle. Thus limiting movement of sperm contents and maintaining cohesion of sperm contents within the zygote both contribute to preventing premature interaction between maternal and paternal genomes.

Katanin, kinesin-13, and ataxin-2 inhibit premature interaction between maternal and paternal genomes in C. elegans zygotes.

Fertilization occurs before the completion of oocyte meiosis in the majority of animal species and sperm contents move long distances within the zygotes of mouse and C. elegans. If incorporated into the meiotic spindle, paternal chromosomes could be expelled into a polar body resulting in lethal monosomy. Through live imaging of fertilization in C. elegans, we found that the microtubule disassembling enzymes, katanin and kinesin-13 limit long-range movement of sperm contents and that maternal ataxin-2 maintains paternal DNA and paternal mitochondria as a cohesive unit that moves together. Depletion of katanin or double depletion of kinesin-13 and ataxin-2 resulted in the capture of the sperm contents by the meiotic spindle. Thus limiting movement of sperm contents and maintaining cohesion of sperm contents within the zygote both contribute to preventing premature interaction between maternal and paternal genomes.

P-439 Analysis of Products of Conception (POC) using Whole Genome Next Generation Sequencing (NGS) in pregnancy loss after euploid or mosaic embryo transfer

Abstract Study question What is the outcome of genetic assessment for fetal chromosomal aberrations in miscarriages after euploid/mosaic embryo transfers (ET)? Summary answer POC testing should be recommended in patients with E/M-ET to screen for chromosomal aberrations occurring post-implantation or beyond the detection limit of PGT-A testing What is known already Spontaneous abortion is the most common complication of pregnancy, affecting approximately 15% of clinically recognized pregnancies. Although the etiology is diverse, fetal chromosomal aberrations account for 50-70% of first trimester miscarriages. Assessment of the fetal chromosomal composition is recommended by ACOG guidelines and aids in counselling and management of patients’ reproductive options. The value of this assessment in patients with miscarriage after euploid/mosaic ET has not evaluated. At the same time there is generally a lack of follow-up studies to examine the accuracy of PGT-A testing and investigate the rates of post-implantation errors causing miscarriage. Study design, size, duration This retrospective study had REB approval. This study was performed at the CReATe Fertility Centre and its Reproductive Genetics Laboratory in Toronto, Canada, between January 2019-December 2023.We evaluated the molecular karyotype of POC samples from first trimester &amp;lt;12GW miscarriages after ART: IVF-PGT-group euploid (E) and mosaic (M) embryo transfers (ET) and IVF-group; IUI and natural conception-NC groups; while controlling for maternal cell contamination (MCC) by high-resolution whole genome NGS. Participants/materials, setting, methods 549 POC samples from early miscarriages after fertility treatment were obtained by suction-dilatation-and curettage. Selection of fetal tissue/chorionic villi (4 representative samples for each case) was performed under a dissecting microscope. Maternal and paternal DNA was obtained to test for MCC. MCC was determined by testing maternal/gestational carrier and fetal DNA (fDNA) with highly informative STRs (AmpFLSTR Identifiler kit). Whole genome low-pass NGS (0.1xcoverage) was performed using the Illumina platform and analyzed with NxClinical Software. Main results and the role of chance Fetal tissue was obtained from 90.7% (498/549) of tested samples and the rest had MCC (9.3%, 51/549): IVF-PGT-A(n = 183), IVF(n = 92), IUI(n = 46) and NC(n = 173). The overall mean maternal age was 37±3.2years. The average gestational age at D&amp;C was 8w4d (range 5w-12w6d). Overall, NGS analysis of fDNA showed 44.6% male and 55.3% female fetuses, 57.6% (287/498) were euploid, 39.5% (197/498) were aneuploid and 1.8% (9/498) were mosaic. In IVF-PGT-A group there were 169 POC from euploid ET and 14 from mosaic ET. 98.2% (n = 166/169) of POCs from IVF-PGT-A euploid-ETs were confirmed as euploid, and 3 had confined placental mosaicism (CPM) (trisomy-11, trisomy-4, monosomy-X). POC from mosaic-ET (n = 14), showed CPM in 3/14(21.4%): TE mosaicism was confirmed in 1/14(7.1%), 2/14(14.3%) had CPM differing from the PGT-A result, 11/14(78.6%) were euploid. POC euploidy rate in IVF (no PGT-A) group was 59.8%(55/92), in IUI 34.8%(16/46) and in NC 24.3%(42/173). In NC group CPM was detected in 1.7%(3/173). The frequency of aberrations detected in POC(n = 197) were: T22, 16.5%; T16,12.9%; T15, 11.3%; T20, 5.2%; T8, 3.6%; T7, T9 and T13, 3.1%; T10 and T14, 2.6%; T18 and T21, 2.1%; T12, 1.5%; 1% of each T2, T4 and T11; monosomy-X,6.7% and 11.3% triploid (69,XXY or 69,XXX). Limitations, reasons for caution MCC is relatively high in POC samples from early pregnancies (9.3%) and controlling for it is warranted. Although 4 representative samples of placental tissue were tested, the true extent and existence of CPM may not be captured correctly. Wider implications of the findings NGS analysis of POC from first trimester miscarriages after fertility treatment would improve diagnostic accuracy, and could aid in patient counselling and management. We observed high PGT-A accuracy (100% for gender) and 98.2% for fetal ploidy with CPM rate of 1.8% (which is lower than observed after CVS (4%)). Trial registration number not applicable

P-406 Late paternal effect rooted in sperm DNA double-strand breaks (DSBs) correlates with the likelihood of miscarriage in patients with poor ovarian response

Abstract Study question Can paternal risk factors be minimized and prevented in ICSI procedure? Summary answer The influence of DSBs can be prevented in ICSI cases with normal ovarian response, whereas DSB is exclusively associated with miscarriage in poor ovarian reserve. What is known already Sperm DNA fragmentation (SDF) is intricately linked to male fertility capacity, with a high prevalence affecting 20% of men with unexplained infertility and up to 50% of those with idiopathic infertility. Despite these statistics, the association between paternal DNA damages and clinical outcomes is controversial. Variations in SDF effects may be influenced by female factors associated with maternal DNA repair activity. To elucidate this interrelationship, we assessed SDF effects on diverse ovarian responses using POSEIDON stratification. The goal was to identify potential paternal risk factors for ART as a preventative solution and devising preventative strategies. Study design, size, duration This retrospective study included 323 couples who underwent ICSI cycles at Lee Women’s Hospital. Normal responders (n = 89) were identified based on female age (&amp;lt;35 years) and AMH levels (≥1.2 ng/mL). Patients (n = 234) fulfilling POSEIDON group 1–4 criteria were categorized as poor ovarian response (POR). Clinical outcomes assessed included clinical pregnancy, miscarriage, and live birth rates. Participants/materials, setting, methods Paternal risk factors include male age, semen parameters (CEROS II CASA, Hamilton-Thorne), and two types of SDF evaluation. LensHooke® R10 kit (Bonraybio, Taiwan) was used to detect total SDF (tSDF), which includes single-strand breaks and double-strand breaks (DSBs). LensHooke® R11 kit was specifically used for DSB detection. Kruskal-Wallis test was conducted to compare controls and cases of ART failure. Univariate and multivariate logistic regression analyses were employed to identify potential factors. Main results and the role of chance We sought to evaluate paternal effects during the early gestation stage by comparing parental characteristics in groups with clinical pregnancy and those without pregnancy. No significant differences in paternal indications were observed between the groups. Notably, significantly lower AMH levels and advanced maternal age were prevalent in pregnancy failures across both normal responders and POR cases, highlighting maternal factors’ dominance in these outcomes. When dissecting paternal effects during the later gestation stage, male factors did not show a significant difference between the group with live birth and the group with miscarriage among normal responders. Nevertheless, several paternal pathogenic indications were identified between the groups in POR. Miscarriages were associated with compromised sperm total motility (68% vs. 54.5%, p = 0.01), reduced normal morphology rate (5.5% vs. 2.5%, p = 0.03), and elevated DSB levels (7.5% vs. 18.8%, p = 0.01). Furthermore, multivariate regression analysis identified high DSBs as an exclusive paternal factor in miscarriage risk (Odds ratio: 1.19, 95% confidence interval 1.04–1.36, p = 0.01). In the ROC curve, a DSBs threshold of 19%, based on the R11 technique, offers significant value in predicting miscarriage with an accuracy of 81%. Limitations, reasons for caution The limitations of the current study are single-center trial, and relatively small sample size. Further clinical trials are needed to robustly establish the relationship between DSB and miscarriage. Wider implications of the findings The impact of DSBs is overlooked in normal responders but not in POR due to different levels of maternal DNA repair activity. These results advocates for (1) the necessity of DSBs (R11) assessment for POR, and (2) egg donation as a potential strategy for couples facing high DSBs and POR. Trial registration number CS2-20012

Research progress on the effect of sperm chromatin integrity on function and its detection methods.

Sperm chromatin not only carries genetic information such as paternal DNA, but also carries structural proteins, epigenetic information, and higher-order chromatin structures (such as matrix attachment regions and telomeres), etc. These information play an important role in embryonic development. This article mainly reviews the effects of these different information carried by sperm chromatin on sperm function and embryonic development and the research progress of related detection methods, in order to provide a theoretical basis and scientific diagnosis and treatment strategies for the etiology screening of clinical infertility, embryo arrest and recurrent miscarriage, so as to improve the pregnancy outcomes of natural conception and assisted reproduction. Keywords: sperm chromatin; epigenetics; sperm DNA damage; sperm function; higher-order chromatin structures.

Katanin, kinesin-13 and ataxin-2 inhibit premature interaction between maternal and paternal genomes in C. elegans zygotes.

Fertilization occurs before completion of oocyte meiosis in the majority of animal species and sperm contents move long distances within zygotes of mouse and C. elegans. If incorporated into the meiotic spindle, paternal chromosomes could be expelled into a polar body resulting in lethal monosomy. Through live imaging of fertilization in C. elegans, we found that the microtubule disassembling enzymes, katanin and kinesin-13 limit long range movement of sperm contents and that maternal ataxin-2 maintains paternal DNA and paternal mitochondria as a cohesive unit that moves together. Depletion of katanin or double depletion of kinesin-13 and ataxin-2 resulted in capture of the sperm contents by the meiotic spindle. Thus limiting movement of sperm contents and maintaining cohesion of sperm contents within the zygote both contribute to preventing premature interaction between maternal and paternal genomes.

The bisexual natural gynogenetic blunt snout bream lineage derived from the distant hybridization of female blunt snout bream and male Bleeker's yellow tail

Distant hybridization often results in the generation of naturally gynogenic offspring. However, there are currently few reports about fertile natural gynogenetic bream. In this study, we established a natural gynogenetic blunt snout bream (NGBSB-YT, F1) through distant hybridization from female blunt snout bream (Megalobrama amblycephala, BSB) × male Bleeker's yellow tail (Xenocypris davidi Bleeker, YT), and further obtained NGBSB1-YT (F2) by self-cross. Except for the morphological characteristics, the DNA content, chromosome numbers, and 5 S rDNA sequences of NGBSB1-YT had no significant difference compared to those of BSB. The results of gonad sections showed that NGBSB1-YT was bisexual. The NGBSB2-YT (F3) obtained by self-cross further proved the fertility of NGBSB1-YT. Interestingly, the results of microsatellite (prime XD007) analysis and sox9 sequence analysis confirmed that paternal DNA fragments were inserted in NGBSB1-YT. This study has established a lineage of natural gynogenetic bream(F1-F3), that provides a reference for improvement of the theory of natural gynogenesis in fish. The NGBSB-YT lineage can be used as a new type of germplasm resource of bream.

Phylogenetic insights into the genetic legacies of Hungarian-speaking communities in the Carpathian Basin

This study focuses on exploring the uniparental genetic lineages of Hungarian-speaking minorities residing in rural villages of Baranja (Croatia) and the Zobor region (Slovakia). We aimed to identify ancestral lineages by examining genetic markers distributed across the entire mitogenome and on the Y-chromosome. This allowed us to discern disparities in regional genetic structures within these communities. By integrating our newly acquired genetic data from a total of 168 participants with pre-existing Eurasian and ancient DNA datasets, our goal was to enrich the understanding of the genetic history trajectories of Carpathian Basin populations. Our findings suggest that while population-based analyses may not be sufficiently robust to detect fine-scale uniparental genetic patterns with the sample sizes at hand, phylogenetic analysis of well-characterized Y-chromosomal Short Tandem Repeat (STR) data and entire mitogenome sequences did uncover multiple lineage ties to far-flung regions and eras. While the predominant portions of both paternal and maternal DNA align with the East-Central European spectrum, rarer subhaplogroups and lineages have unveiled ancient ties to both prehistoric and historic populations spanning Europe and Eastern Eurasia. This research augments the expansive field of phylogenetics, offering critical perspectives on the genetic constitution and heritage of the communities in East-Central Europe.

Investigating the role of mitochondrial membrane potential in paternal inheritance of mitochondria

Abstract The process of oxidative phosphorylation (OXPHOS) in mitochondria depends on an electrochemical gradient known as the mitochondrial membrane potential (Δψm). Reflecting high functionality, elevated Δψm usually depicts healthy mitochondria and contributes to organelle selection. This study investigates whether mitochondrial properties linked with bioenergetics, such as Δψm, play a role in paternal inheritance of mitochondria. More specifically, the study looks at how sperm Δψm responds to egg chemoattractants in bivalves characterized by distinct mitochondrial inheritance patterns: strict maternal inheritance (SMI) and doubly uniparental inheritance (DUI), the latter displaying sex-specific transmission of paternal mitochondrial DNA. Sperm Δψm was examined in four bivalve species: the blue mussel (Mytilus edulis) and the Manila clam (Ruditapes philippinarum) (DUI), plus the hard clam (Mercenaria mercenaria) and the soft-shell clam (Mya arenaria) (SMI). In the absence of egg chemoattractants, sperm Δψm did not vary between the two groups. However, there was a trend of increase in Δψm following egg detection only in sperm bearing paternally derived mitochondria (DUI). This suggests, along with bioenergetic changes, that Δψm modulation might be a specific property of at least some DUI species, possibly implicated in their unique ability to transmit their mitochondria in a sex-specific fashion.

Reciprocal restriction fragment length polymorphism (RFLP) analysis reveals mitochondrial heteroplasmy in Caenorhabditis briggsae hybrids.

Although mitochondria are typically inherited maternally, exceptions exist. We previously demonstrated that within-species crosses of Caenorhabditis briggsae result in paternal mitochondrial transmission, and it would be useful to know whether hybrids have only paternal mitochondria (homoplasmy) or paternal and maternal mitochondria (heteroplasmy). We developed a reciprocal restriction fragment length polymorphism analysis to separately detect paternal and maternal mitochondrial DNA. Using new hybrid lines, this approach revealed that some hybrids are heteroplasmous and others have become homoplasmous for the paternal mitotype. These results motivate additional investigation of how paternal mitochondrial transmission is apparently facile in C. briggsae .

Guardians of quality: advancing Castanea sativa traceability using DNA analysis from seed to processed food

Castanea sativa is one of the most appreciated species in Italy, due to timber and fruit quality; nuts are usually intended for fresh consumption, but also for the production of industrial foods. The demand for an efficient traceability system to identify Castanea species and cultivars along the supply chain, from the chestnut orchard to the processed product, is crucial to protect consumers and producers from frauds. Here we present a traceability protocol to identify the species of the Castanea genus and trace the cultivars of Castanea sativa, based on DNA markers (SSRs and SNPs) analyses. Microsatellites were applied to identify the cultivar in plant material (leaves, seed, and episperm) and processed food (creams, beverages, flour, and cookies). Although SSRs made it possible to trace cultivar starting from somatic tissues (e.g.: leaves), the presence of foreign paternal DNA from pollenizer plants in seed and processed food, interferes with the identification of the maternal one. To overcome this issue, we Illumina sequenced six C. sativa cultivars to highlight maternal-inherited markers. A set of SNP/INDEL markers in two chloroplastic regions were identified, able to effectively distinguish and trace C. sativa from C. mollissima and C. crenata. The High Resolution Melting (HRM) analysis was performed as a practical and efficient method for SNP/INDELvalidation and to develop a fast, reliable, and reproducible protocol for chestnut traceability in food.

Mutations in the germline: How the mother repairs the father’s damaged genome

Germline mutations can have a severe impact on genetic diseases, genome evolution and the fate of a species. The vast majority of inheritable mutations are passed on by the paternal genome. We discovered how paternal DNA damage is repaired by maternal repair leading to the inheritance of structural variants.

Elevated Sperm DNA Damage in IVF-ICSI Treatments Is Not Related to Pregnancy Complications and Adverse Neonatal Outcomes.

This multicenter retrospective cohort study assesses the effect of high paternal DNA fragmentation on the well-being of the woman during pregnancy and the health of the newborn delivered. It was performed with clinical data from 488 couples who had a delivery of at least one newborn between January 2000 and March 2019 (243 used autologous oocytes and 245 utilized donated oocytes). Couples were categorized according to sperm DNA fragmentation (SDF) level as ≤15% or >15%, measured by TUNEL assay. Pregnancy, delivery, and neonatal outcomes were assessed. In singleton pregnancies from autologous cycles, a higher but non-significant incidence of pre-eclampsia, threatened preterm labor, and premature rupture of membranes was found in pregnant women from the >15%SDF group. Additionally, a higher proportion of children were born with low birth weight, although the difference was not statistically significant. After adjusting for potential confounders, these couples had lower odds of having a female neonate (AOR = 0.35 (0.1-0.9), p = 0.04). Regarding couples using donor's oocytes, pregnancy and neonatal outcomes were comparable between groups, although the incidence of induced vaginal labor was significantly higher in the >15% SDF group (OR = 7.4 (1.2-46.7), p = 0.02). Adjusted analysis revealed no significant association of elevated SDF with adverse events. In multiple deliveries from cycles using both types of oocytes, the obstetric and neonatal outcomes were found to be similar between groups. In conclusion, the presence of an elevated SDF does not contribute to the occurrence of clinically relevant adverse maternal events during pregnancies, nor does it increase the risk of worse neonatal outcomes in newborns. Nevertheless, a higher SDF seems to be related to a higher ratio of male livebirths.

Paternal DNA methylation is remodeled to maternal levels in rice zygote

Epigenetic reprogramming occurs during reproduction to reset the genome for early development. In flowering plants, mechanistic details of parental methylation remodeling in zygote remain elusive. Here we analyze allele-specific DNA methylation in rice hybrid zygotes and during early embryo development and show that paternal DNA methylation is predominantly remodeled to match maternal allelic levels upon fertilization, which persists after the first zygotic division. The DNA methylation remodeling pattern supports the predominantly maternal-biased gene expression during zygotic genome activation (ZGA) in rice. However, parental allelic-specific methylations are reestablished at the globular embryo stage and associate with allelic-specific histone modification patterns in hybrids. These results reveal that paternal DNA methylation is remodeled to match the maternal pattern during zygotic genome reprogramming and suggest existence of a chromatin memory allowing parental allelic-specific methylation to be maintained in the hybrid.

Mitochondrial uniparental inheritance achieved after fertilization challenges the nuclear-cytoplasmic conflict hypothesis for anisogamy evolution.

In eukaryotes, a fundamental phenomenon underlying sexual selection is the evolution of gamete size dimorphism between the sexes (anisogamy) from an ancestral gametic system with gametes of the same size in both mating types (isogamy). The nuclear-cytoplasmic conflict hypothesis has been one of the major theoretical hypotheses for the evolution of anisogamy. It proposes that anisogamy evolved as an adaptation for preventing nuclear-cytoplasmic conflict by minimizing male gamete size to inherit organelles uniparentally. In ulvophycean green algae, biparental inheritance of organelles is observed in isogamous species, as the hypothesis assumes. So we tested the hypothesis by examining whether cytoplasmic inheritance is biparental in Monostroma angicava, a slightly anisogamous ulvophycean that produces large male gametes. We tracked the fates of mitochondria in intraspecific crosses with PCR-RFLP markers. We confirmed that mitochondria are maternally inherited. However, paternal mitochondria enter the zygote, where their DNA can be detected for over 14 days. This indicates that uniparental inheritance is enforced by eliminating paternal mitochondrial DNA in the zygote, rather than by decreasing male gamete size to the minimum. Thus, uniparental cytoplasmic inheritance is achieved by an entirely different mechanism, and is unlikely to drive the evolution of anisogamy in ulvophyceans.

Five nucleotides found in RCTG motifs are essential for post-fertilization methylation imprinting of the H19 ICR in YAC transgenic mice.

Genomic imprinting at the mouse Igf2/H19 locus is controlled by the H19 ICR, within which paternal allele-specific DNA methylation originating in sperm is maintained throughout development in offspring. We previously found that a 2.9 kb transgenic H19 ICR fragment in mice can be methylated de novo after fertilization only when paternally inherited, despite its unmethylated state in sperm. When the 118 bp sequence responsible for this methylation in transgenic mice was deleted from the endogenous H19 ICR, the methylation level of its paternal allele was significantly reduced after fertilization, suggesting the activity involving this 118 bp sequence is required for methylation maintenance at the endogenous locus. Here, we determined protein binding to the 118 bp sequence using an in vitro binding assay and inferred the binding motif to be RCTG by using a series of mutant competitors. Furthermore, we generated H19 ICR transgenic mice with a 5-bp substitution mutation that disrupts the RCTG motifs within the 118 bp sequence, and observed loss of methylation from the paternally inherited transgene. These results indicate that imprinted methylation of the H19 ICR established de novo during the post-fertilization period involves binding of specific factors to distinct sequence motifs within the 118 bp sequence.