The utility of human two plus one small pronucleated zygotes (2.1PN) based on clinical outcomes and the focused ploidy analysis.

PURPOSE: Are human embryos arising from two plus one small pronucleated zygotes, called 2.1 pronuclei (PN), clinically useful? METHODS: In a retrospective embryo cohort study and prospective experimental study, a total of 287 cycles in which at least one 2.1PN was identified in the fertilization check were included. Embryonic development and clinical outcome were compared for the 1395 2PN zygotes and 304 2.1PN zygotes that were siblings. All embryos were individually cultured in time-lapse systems. Twenty-five 2.1PN-derived blastocysts, donated for research, were used in focused single-nucleotide variant ploidy analysis to identify the distribution pattern of heterozygosity. RESULTS: The average diameter of PN was 24.9 ± 2.4 µm for large PN and 10.2 ± 2.4 µm for small PN; 79.9% of small PN was derived from female pronuclei. Blastocyst formation rate and good-quality blastocyst rate were significantly lower with 2.1PN embryos than with 2PN embryos (40.0% vs. 57.7%, 21.4% vs. 33.5%, respectively). A total of 13 embryos derived from 2.1PN were transferred, and three healthy babies were born. In ploidy constitutions of trophectoderm (TE), 2.1PN-derived blastocyst TE was shown to be mostly diploid (95.8%, 23/24), and only one blastocyst showed triploid. CONCLUSIONS: It was suggested that 2.1PN embryos have lower embryonic developmental potential than 2PN embryos, but most of the 2.1PN were diploid, indicating that they are likely to be clinically usable. It is recommended to perform embryo transfer following a combination of PGT-A and ploidy analysis.

Multi-drug-resistant chronic endometritis in infertile women with repeated implantation failure: trend over the decade and pilot study for third-line oral antibiotic treatment.

PURPOSE: To evaluate the yearly prevalence and annual transition of multi-drug-resistant-chronic endometritis (MDR-CE) in infertile women with a history of repeated implantation failure (RIF) and to establish the third-line antibiotic treatment regimen against MDR-CE. METHODS: This retrospective/prospective cohort and pilot study included 3473 RIF women between April 2010 and September 2021. The endometrial stromal plasmacyte density index (ESPDI) was calculated in 3449 CD138-immunostained endometrial sections to evaluate CE. The microbiota in the vaginal secretions and endometrial fluid was compared between 17 patients with MDR-CE and 16 patients with antibiotics-sensitive CE. In a pilot study, oral moxifloxacin (400 mg/day, 10 days, n = 24) or azithromycin (500 mg/day, 3 days, n = 24) was administered to eligible patients with MDR-CE. RESULTS: From April 2010 to March 2020, CE was detected in 31.4% of RIF women and MDR was detected in 7.8% of CE. While the prevalence of CE was stable for a decade, MDR in CE increased steadily (OR 8.27, 95% CI 2.58-26.43, p trend < 0.001). The bacterial species/communities unique to MDR-CE were not found. The histopathologic cure rate of MDR-CE was similar between the moxifloxacin and azithromycin groups (79.2% vs 75.0%, OR 1.27, 95% CI 0.32-4.89, p value 0.73), as well as reproductive outcomes in subsequent embryo transfer cycles. CONCLUSION: In RIF women, MDR in CE increased over the decade. As a third-line treatment for MDR-CE, azithromycin may have a clinical advantage due to its shorter time administration periods. CLINICAL TRIAL NUMBER: ClinicalTrials.gov Identifier: UMIN-CTR 000029449/000031909.

Microbiome analysis in women with endometriosis: Does a microbiome exist in peritoneal fluid and ovarian cystic fluid?

Purpose: To investigate the relationship between the microbiome of the female genital tract and endometriosis. Methods: This prospective cohort study included 36 women who underwent laparoscopic surgery for ovarian tumor from July 2019 to April 2020. Of them, 18 had endometriosis, and 18 did not have endometriosis. Vaginal secretions, endometrial fluid, peritoneal fluid, and ovarian cystic fluid were collected during surgery. Next-generation sequencing of bacterial 16S rRNA was performed to characterize the microbiome. Results: Specific microbiomes were not detected in either peritoneal fluid or ovarian cystic fluid regardless of the presence or absence of endometriosis and the type of cyst. When the cutoff value of infectious bacterial abundance in the vagina was set as 64.3%, there were many cases more than a cutoff value in the endometriosis group significantly (p = 0.01). When the cutoff value of infectious bacterial abundance in the endometrium was set as 18.6%, there were many cases more than a cutoff level in the endometriosis cases significantly (p = 0.02). Conclusion: Peritoneal fluid and ovarian cystic fluid are almost sterile, although dysbiosis may occur in the vaginal and endometrial microbiome in women with endometriosis.

Abnormal cleavage is involved in the self-correction of bovine preimplantation embryos.

Chromosome instability leading to aneuploidy during early cleavage is well known in humans and cattle. Partial compaction (PC), which occurs only in some blastomeres, is suggested as a self-correction mechanism through which human embryos avoid aneuploid mosaicism. Partially compacted embryos show abnormal cleavages more frequently during early development; however, the mechanism by which blastomeres are excluded has not been elucidated. Here, we confirmed PC in approximately half of the tested bovine embryos, similar to that in human embryos. DNA sequencing of single-cell and intact embryos revealed that the morulae that excluded some blastomeres had euploidy, but many of the excluded blastomeres had aneuploidy. Time-lapse imaging of zygotes without the zona pellucida revealed that the excluded blastomeres underwent reverse and direct cleavages, which are abnormal cleavages, more frequently than the blastomeres involved in compaction. These results suggest the potential role of abnormal cleavage in the self-correction mechanism during the development of mammalian preimplantation embryos.

Involvement of Rev1 in alkylating agent-induced loss of heterozygosity in Oryzias latipes.

Translesion synthesis (TLS) polymerases mediate DNA damage bypass during replication. The TLS polymerase Rev1 has two important functions in the TLS pathway, including dCMP transferase activity and acting as a scaffolding protein for other TLS polymerases at the C-terminus. Because of the former activity, Rev1 bypasses apurinic/apyrimidinic sites by incorporating dCMP, whereas the latter activity mediates assembly of multipolymerase complexes at the DNA lesions. We generated rev1 mutants lacking each of these two activities in Oryzias latipes (medaka) fish and analyzed cytotoxicity and mutagenicity in response to the alkylating agent diethylnitrosamine (DENA). Mutant lacking the C-terminus was highly sensitive to DENA cytotoxicity, whereas mutant with reduced dCMP transferase activity was slightly sensitive to DENA cytotoxicity, but exhibited a higher tumorigenic rate than wild-type fish. There was no significant difference in the frequency of DENA-induced mutations between mutant with reduced dCMP transferase activity and wild-type cultured cell. However, loss of heterozygosity (LOH) occurred frequently in cells with reduced dCMP transferase activity. LOH is a common genetic event in many cancer types and plays an important role on carcinogenesis. To our knowledge, this is the first report to identify the involvement of the catalytic activity of Rev1 in suppression of LOH.

Next-generation sequencing of 16S rRNA for identification of invasive bacterial pathogens in a formalin-fixed paraffin-embedded placental specimen: a case report of perinatal fulminant Streptococcus pyogenes infection.

Intrauterine infection is one of the most important causes of maternal death. In perinatal emergency, we often miss an opportunity to obtain culture specimens. In this study, we tried to examine whether we investigated whether bacteria causing infection can be detected from a formalin-fixed paraffin-embedded (FFPE) placental specimen. We examined the placenta from a maternal invasive infection that resulted in infectious abortion at 18 weeks of gestation. The case was diagnosed by acute fever and abdominal pain, and the patient was cured after 3 weeks of intensive antimicrobial treatment. Four Streptococcus pyogenes strains were isolated from vaginal fluid and blood cultures of the patient. All of the strain types were emm1/ST28. We amplified the V1-V2 region of 16S rRNA from an FFPE placental specimen and sequencing was performed using a next-generation sequencer (NGS). Taxonomic analysis was then performed for sequenced data. We succeeded in detecting causative pathogens from the FFPE placenta: 69.1% of the predominantly identified bacteria were S. pyogenes and other small populations of bacteria were detected. Our results revealed the utility of NGS for 16S rRNA analysis of an FFPE placenta. This method may reveal previous perinatal invasive infections of unknown origin retrospectively.

Analysis of vaginal and endometrial microbiota communities in infertile women with a history of repeated implantation failure.

PURPOSE: To identify specific bacterial communities in vaginal and endometrial microbiotas as biomarkers of implantation failure by comprehensively analyzing their microbiotas using next-generation sequencing. METHODS: We investigated α- and ß-diversities of vaginal and endometrial microbiotas using 16S rRNA gene sequencing and compared their profiles between 145 women with repeated implantation failure (RIF) and 21 controls who lacked the factors responsible for implantation failure with a high probability of being healthy and fertile to identify specific bacteria that induce implantation failure. RESULTS: The endometrial microbiotas had higher α-diversities than did the vaginal microbiotas (P < .001). The microbiota profiles showed that vaginal and endometrial samples in RIF patients had significantly higher levels of 5 and 14 bacterial genera, respectively, than those in controls. Vaginal Lactobacillus rates in RIF patients were significantly lower at 76.4 ± 38.9% compared with those of the controls at 91.8 ± 22.7% (P = .018), but endometrial Lactobacillus rates did not significantly differ between the RIF patients and controls (56.2 ± 36.4% and 58.8 ± 37.0%, respectively, P = .79). CONCLUSIONS: Impaired microbiota communities containing specific bacteria in both the endometrium and vagina were associated with implantation failure. The vaginal Lactobacillus rates, but not the endometrial, may be a biomarker for RIF.

Characterization of Microbiota in Endometrial Fluid and Vaginal Secretions in Infertile Women with Repeated Implantation Failure.

Studies suggest that persisting intrauterine bacterial infectious conditions such as chronic endometritis potentially impair the embryo implantation process. The microbial environment in the female reproductive tract, however, remains largely undetermined in infertile patients with a history of repeated implantation failure (RIF). Using next-generation sequencing, we aimed to characterize the microbiota in the endometrial fluid (EF) and vaginal secretions (VS) in women with RIF. Twenty-eight infertile women with a history of RIF and eighteen infertile women undergoing the first in vitro fertilization-embryo transfer attempt (the control group) were enrolled in the study. On days 6-8 in the luteal phase of the natural, oocyte-pickup, or hormone replacement cycle, the paired EF and VS samples were obtained separately. Extracted genomic DNA was pyrosequenced for the V4 region of 16S ribosomal RNA using a next-generation sequencer. The EF microbiota had higher α-diversity and broader bacterial species than the VS microbiota both in the RIF and control groups. The analysis of the UniFrac distance matrices between EF and VS also revealed significantly different clustering. Additionally, the EF microbiota, but not the VS microbiota, showed significant variation in community composition between the RIF group and the control group. Burkholderia species were not detected in the EF microbiota of any samples in the control group but were detectable in a quarter of the RIF group. To our best knowledge, this is the first study investigating the microbiota in the paired EF and VS samples in infertile women with RIF.

A pilot study and case reports on endometrial microbiota and pregnancy outcome: An analysis using 16S rRNA gene sequencing among IVF patients, and trial therapeutic intervention for dysbiotic endometrium.

PURPOSE: The present study aimed to analyze the pregnancy outcomes of IVF patients presenting Lactobacillus-dominated microbiota (LDM) or non-Lactobacillus-dominated microbiota (NLDM) of their endometrium and to report cases who were treated for NLDM concurrently with antibiotics and prebiotic/probiotic supplements in a Japanese infertile population. METHODS: Ninety-two IVF patients were recruited from August 2017 to March 2018. Endometrial fluid samples for sequencing were collected using an IUI catheter. The bacterial status of the endometrium and the pregnancy outcomes were analyzed. For cases with NLDM, antibiotics and prebiotics/probiotics were administered according to their individual microbial conditions. RESULTS: Forty-seven cases (51.1%) presented LDM and 45 cases (48.9%) presented NLDM at initial analysis. Nine Patients with NLDM were treated by antibiotics and prebiotics/probiotics, and successfully became Lactobacillus-dominant. Pregnancy rates by single vitrified-warmed blastocyst transfers were higher in the LDM group (58.9% per patient and 36.3% per FBT) than in the NLDM group (47.2% per patient and 34.7% per FBT) but not significantly different. CONCLUSION: The results of this study could not necessarily prove the clear benefit of establishing Lactobacillus-dominated endometrium in terms of pregnancy outcome, but there is significance in searching for endometrial microbial status of infertile patients and recovering Lactobacillus-dominated endometrium might benefit implantation.

Analysis of endometrial microbiota by 16S ribosomal RNA gene sequencing among infertile patients: a single-center pilot study.

PURPOSE: The present study aimed to analyze the endometrial and vaginal microbiome among a Japanese infertile population by sequencing and the impact of the endometrial and vaginal environment on implantation. METHODS: In total, 102 infertile (79 in vitro fertilization [IVF] and 23 non-IVF) patients and seven healthy volunteers were recruited from August to December, 2017. Endometrial fluid and vaginal discharge samples for sequencing were collected by using an intrauterine insemination catheter. The bacterial status of the endometrium and vagina were analyzed. RESULTS: The Lactobacillus-dominated microbiota (>90% Lactobacillus spp.) in the endometrium vs vagina was 38% (30/79) vs 44.3% (44/79) in the IVF patients, 73.9% (17/23) vs 73.9% (17/23) in the non-IVF patients, and 85.7% (6/7) vs 85.7% (6/7) in the healthy volunteers. The percentage of endometrial Lactobacillus in the healthy volunteers was highly stable within the same menstrual cycle and even in the following cycle. The major taxonomies were Gardnerella, Streptococcus, Atopobium, Bifidobacterium, Sneathia, Prevotella, and Staphylococcus. Fifteen patients achieved pregnancy by a single vitrified-warmed blastocyst transfer during this study; the median percentage of Lactobacillus in the pregnant women was 96.45 ± 33.61%. CONCLUSION: A considerable percentage of non-Lactobacillus-dominated (NLD) microbiota was found in the endometrium of Japanese infertile women. Increasing the endometrial level of the Lactobacilli to >90% might favor the implantation outcome of NLD infertile patients.

Degradation of Stop Codon Read-through Mutant Proteins via the Ubiquitin-Proteasome System Causes Hereditary Disorders.

During translation, stop codon read-through occasionally happens when the stop codon is misread, skipped, or mutated, resulting in the production of aberrant proteins with C-terminal extension. These extended proteins are potentially deleterious, but their regulation is poorly understood. Here we show in vitro and in vivo evidence that mouse cFLIP-L with a 46-amino acid extension encoded by a read-through mutant gene is rapidly degraded by the ubiquitin-proteasome system, causing hepatocyte apoptosis during embryogenesis. The extended peptide interacts with an E3 ubiquitin ligase, TRIM21, to induce ubiquitylation of the mutant protein. In humans, 20 read-through mutations are related to hereditary disorders, and extended peptides found in human PNPO and HSD3B2 similarly destabilize these proteins, involving TRIM21 for PNPO degradation. Our findings indicate that degradation of aberrant proteins with C-terminal extension encoded by read-through mutant genes is a mechanism for loss of function resulting in hereditary disorders.

Novel allelic mutations in murine Serca2 induce differential development of squamous cell tumors.

Dominant mutations in the Serca2 gene, which encodes sarco(endo)plasmic reticulum calcium-ATPase, predispose mice to gastrointestinal epithelial carcinoma [1-4] and humans to Darier disease (DD) [14-17]. In this study, we generated mice harboring N-ethyl-N-nitrosourea (ENU)-induced allelic mutations in Serca2: three missense mutations and one nonsense mutation. Mice harboring these Serca2 mutations developed tumors that were categorized as either early onset squamous cell tumors (SCT), with development similar to null-type knockout mice [2,4] (aggressive form; M682, M814), or late onset tumors (mild form; M1049, M1162). Molecular analysis showed no aberration in Serca2 mRNA or protein expression levels in normal esophageal cells of any of the four mutant heterozygotes. There was no loss of heterozygosity at the Serca2 locus in the squamous cell carcinomas in any of the four lines. The effect of each mutation on Ca(2+)-ATPase activity was predicted using atomic-structure models and accumulated mutated protein studies, suggesting that putative complete loss of Serca2 enzymatic activity may lead to early tumor onset, whereas mutations in which Serca2 retains residual enzymatic activity result in late onset. We propose that impaired Serca2 gene product activity has a long-term effect on squamous cell carcinogenesis from onset to the final carcinoma stage through an as-yet unrecognized but common regulatory pathway.

Bcl11b prevents the intrathymic development of innate CD8 T cells in a cell intrinsic manner.

If Bcl11b activity is compromised, CD4(+)CD8(+) double-positive (DP) thymocytes produce a greatly increased fraction of innate CD8(+) single-positive (SP) cells highly producing IFN-γ, which are also increased in mice deficient of genes such as Itk, Id3 and NF-κB1 that affect TCR signaling. Of interest, the increase in the former two is due to the bystander effect of IL-4 that is secreted by promyelocytic leukemia zinc finger-expressing NKT and γδT cells whereas the increase in the latter is cell intrinsic. Bcl11b zinc-finger proteins play key roles in T cell development and T cell-mediated immune response likely through TCR signaling. We examined thymocytes at and after the DP stage in Bcl11b (F/S826G) CD4cre, Bcl11b (F/+) CD4cre and Bcl11b (+/S826G) mice, carrying the allele that substituted serine for glycine at the position of 826. Here we show that Bcl11b impairment leads to an increase in the population of TCRαß(high)CD44(high)CD122(high) innate CD8SP thymocytes, together with two different developmental abnormalities: impaired positive and negative selection accompanying a reduction in the number of CD8SP cells, and developmental arrest of NKT cells at multiple steps. The innate CD8SP thymocytes express Eomes and secrete IFN-γ after stimulation with PMA and ionomycin, and in this case their increase is not due to a bystander effect of IL-4 but cell intrinsic. Those results indicate that Bcl11b regulates development of different thymocyte subsets at multiple stages and prevents an excess of innate CD8SP thymocytes.

Bcl11b SWI/SNF-complex subunit modulates intestinal adenoma and regeneration after γ-irradiation through Wnt/ß-catenin pathway.

SWI/SNF chromatin remodeling complexes constitute a highly related family of multi-subunit complexes to modulate transcription, and SWI/SNF subunit genes are collectively mutated in 20% of all human cancers. Bcl11b is a SWI/SNF subunit and acts as a haploinsufficient tumor suppressor in leukemia/lymphomas. Here, we show expression of Bcl11b in intestinal crypt cells and promotion of intestinal tumorigenesis by Bcl11b attenuation in Apc (min/+) mice. Of importance, mutations or allelic loss of BCL11B was detected in one-third of human colon cancers. We also show that attenuated Bcl11b activity in the crypt base columnar (CBC) cells expressing the Lgr5 stem cell marker enhanced regeneration of intestinal epithelial cells after the radiation-induced injury. Interestingly, BCL11B introduction in human cell lines downregulated transcription of ß-catenin target genes, whereas Bcl11b attenuation in Lgr5(+) CBCs increased expression of ß-catenin targets including c-Myc and cyclin D1. Together, our results argue that Bcl11b impairment promotes tumor development in mouse and human intestine at least in part through deregulation of ß-catenin pathway.

Endometrial and vaginal microbiomes influence assisted reproductive technology outcomes.

OBJECTIVE: The role of Lactobacillus-dominant microbiota in the endometrium in reproductive function is unclear. We therefore aimed to explore the impact of the balance of Lactobacillus and pathological bacteria in the endometrial and vaginal microbiomes on the pregnancy outcomes of women treated with assisted reproductive technology (ART). METHODS: This study included 35 women with infertility submitted to good-quality embryo transfers. The cutoff values for abundance of Lactobacillus species (spp.) and pathological bacteria in the endometrium and vagina were calculated. Women with Lactobacillus spp. and pathological bacteria abundance above the cutoff values were categorized in the high-abundance group, whereas those with abundance below cutoff values were categorized in the low abundance group. We divided the patients into four groups based on the combination of high/low abundance of Lactobacillus spp. and pathological bacteria. RESULTS: The 35 cases of good-quality embryo transfer resulted in 21 pregnancies. Pregnant women were present in significantly higher proportions in the high Lactobacillus spp. abundance and low pathological bacteria abundance group, whereas the opposite combination (i.e., low Lactobacillus spp. abundance and high pathological bacteria abundance) saw a significantly higher proportion of nonpregnant women (p=0.022). CONCLUSIONS: The balance between Lactobacillus and pathological bacterial abundance in the endometrial and vaginal microbiomes is associated with pregnancy from ART.

Vaginal Microbiota and Pregnancy Outcomes of Patients with Conization Histories.

Background: One of the major risks of preterm birth is a history of conization. However, the risk of infection due to this procedure is still not well known. Using next-generation sequencing, we aimed to reveal the influence of conization on vaginal microbiota in the following pregnancy, and their relationship between spontaneous preterm birth (sPTB). Methods: We conducted a prospective cohort study including 133 pregnant patients, of whom 25 had conization histories and 108 did not. Vaginal microbiome samples were collected using swabs by an obstetrician upon inclusion in the first trimester and during delivery. V1-V2 of the 16S rRNA gene were amplified and analyzed to identify the bacteria. Results: The conization group had a significantly lower delivery week (34 weeks vs. 36 weeks, p = 0.003) and higher sPTB rate (64% vs. 8.3%, p ≤ 0.001) than the control group. In the conization group, alpha (Chao 1, p = 0.02; phylogenetic diversity whole tree, p = 0.04) and beta diversity (permutational multivariate analysis of variance test, p = 0.04) of the vaginal microbiota was significantly higher during delivery in patients who delivered preterm than in those who delivered term. Community-state type IV in the first trimester was significantly associated with sPTB (overall odds ratio 3.80, 95% confidence interval 1.33-10.8, p = 0.01). Conclusions: Conization is a risk factor for sPTB. Increased risk of sPTB in patients after conization may belong to the vulnerable defense mechanism, due to the shortened cervix and decreased cervical mucus.

Differential Vaginal Microbiota Profiling in Lactic-Acid-Producing Bacteria between Infertile Women with and without Chronic Endometritis.

PURPOSE: Chronic endometritis (CE) is an infectious and inflammatory disorder associated with infertility of unknown etiology, repeated implantation failure, and recurrent pregnancy loss. In the current clinical practice, intrauterine interventions such as endometrial biopsy/histopathologic examinations and/or hysteroscopy are required for the diagnosis of CE. In this study, we analyzed the microbiota in vaginal secretions (VS) as a potential prediction tool for CE in infertile women. METHODS: Using next-generation sequencing analysis, we compared the VS and endometrial fluid (EF) microbiota in infertile women with (n = 20) or without CE (n = 103). RESULTS: The detection rate of Streptococcus and Enterococcus as well as the bacterial abundance of Atopobium and Bifidobacterium in the VS microbiota was significantly lower in the CE group than in the non-CE group. Meanwhile, the detection rate and bacterial abundance of Lactobacillus in the EF and VS microbiota were at similar levels between the two groups. CONCLUSION: These findings suggest that VS microbiota in infertile women with CE is characterized by the reduction in Bifidobacterium and lactic-acid-producing bacteria other than Lactobacillus. Our results hold promise for the prediction of CE, not by somewhat interventional intrauterine procedures, but by less invasive VS sampling. TRIAL REGISTRATION NUMBER: UMIN000029449 (registration date 6 October 2017).

Behavioral phenotypes of Disc1 missense mutations in mice.

To support the role of DISC1 in human psychiatric disorders, we identified and analyzed two independently derived ENU-induced mutations in Exon 2 of mouse Disc1. Mice with mutation Q31L showed depressive-like behavior with deficits in the forced swim test and other measures that were reversed by the antidepressant bupropion, but not by rolipram, a phosphodiesterase-4 (PDE4) inhibitor. In contrast, L100P mutant mice exhibited schizophrenic-like behavior, with profound deficits in prepulse inhibition and latent inhibition that were reversed by antipsychotic treatment. Both mutant DISC1 proteins exhibited reduced binding to the known DISC1 binding partner PDE4B. Q31L mutants had lower PDE4B activity, consistent with their resistance to rolipram, suggesting decreased PDE4 activity as a contributory factor in depression. This study demonstrates that Disc1 missense mutations in mice give rise to phenotypes related to depression and schizophrenia, thus supporting the role of DISC1 in major mental illness.

Mutational pattern and frequency of induced nucleotide changes in mouse ENU mutagenesis.

BACKGROUND: With the advent of sequence-based approaches in the mutagenesis studies, it is now possible to directly evaluate the genome-wide pattern of experimentally induced DNA sequence changes for a diverse array of organisms. To gain a more comprehensive understanding of the mutational bias inherent in mouse ENU mutagenesis, this study describes a detailed evaluation of the induced mutational pattern obtained from a sequence-based screen of ENU-mutagenized mice. RESULTS: Based on a large-scale screening data, we derive the sequence-based estimates of the nucleotide-specific pattern and frequency of ENU-induced base replacement mutation in the mouse germline, which are then combined with the pattern of codon usage in the mouse coding sequences to infer the spectrum of amino acid changes obtained by ENU mutagenesis. We detect a statistically significant difference between the mutational patterns in phenotype- versus sequence-based screens, which presumably reflects differential phenotypic effects caused by different amino acid replacements. We also demonstrate that the mutations exhibit strong strand asymmetry, and that this imbalance is generated by transcription, most likely as a by-product of transcription-coupled DNA repair in the germline. CONCLUSION: The results clearly illustrate the biased nature of ENU-induced mutations. We expect that a precise understanding of the mutational pattern and frequency of induced nucleotide changes would be of practical importance when designing sequence-based screening strategies to generate mutant mouse strains harboring amino acid variants at specific loci. More generally, by enhancing the collection of experimentally induced mutations in unambiguously defined genomic regions, sequence-based mutagenesis studies will further illuminate the molecular basis of mutagenic and repair mechanisms that preferentially produce a certain class of mutational changes over others.

Srs2 and RecQ homologs cooperate in mei-3-mediated homologous recombination repair of Neurospora crassa.

Homologous recombination and post-replication repair facilitate restart of stalled or collapsed replication forks. The SRS2 gene of Saccharomyces cerevisiae encodes a 3'-5' DNA helicase that functions both in homologous recombination repair and in post-replication repair. This study identifies and characterizes the SRS2 homolog in Neurospora crassa, which we call mus-50. A knockout mutant of N.crassa, mus-50, is sensitive to several DNA-damaging agents and genetic analyses indicate that it is epistatic with mei-3 (RAD51 homolog), mus-11 (RAD52 homolog), mus-48 (RAD55 homolog) and mus-49 (RAD57 homolog), suggesting a role for mus-50 in homologous recombination repair. However, epistasis evidence has presented that MUS50 does not participate in post-replication repair in N.crassa. Also, the N.crassa mus-25 (RAD54 homolog) mus-50 double mutant is viable, which is in contrast to the lethal phenotype of the equivalent rad54 srs2 mutant in S.cerevisiae. Tetrad analysis revealed that mus-50 in combination with mutations in two RecQ homologs, qde-3 and recQ2, is lethal, and this lethality is suppressed by mutation in mei-3, mus-11 or mus-25. Evidence is also presented for the two independent pathways for recovery from camptothecin-induced replication fork arrest: one pathway is dependent on QDE3 and MUS50 and the other pathway is dependent on MUS25 and RECQ2.