BackgroundRecent advances in clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) genome editing have led to the use of long single-stranded DNA (lssDNA) molecules for generating conditional mutations. However, there is still limited available data on the efficiency and reliability of this method.ResultsWe generated conditional mouse alleles using lssDNA donor templates and performed extensive characterization of the resulting mutations. We observed that the use of lssDNA molecules as donors efficiently yielded founders bearing the conditional allele, with seven out of nine projects giving rise to modified alleles. However, rearranged alleles including nucleotide changes, indels, local rearrangements and additional integrations were also frequently generated by this method. Specifically, we found that alleles containing unexpected point mutations were found in three of the nine projects analyzed. Alleles originating from illegitimate repairs or partial integration of the donor were detected in eight projects. Furthermore, additional integrations of donor molecules were identified in four out of the seven projects analyzed by copy counting. This highlighted the requirement for a thorough allele validation by polymerase chain reaction, sequencing and copy counting of the mice generated through this method. We also demonstrated the feasibility of using lssDNA donors to generate thus far problematic point mutations distant from active CRISPR cutting sites by targeting two distinct genes (Gckr and Rims1). We propose a strategy to perform extensive quality control and validation of both types of mouse models generated using lssDNA donors.ConclusionlssDNA donors reproducibly generate conditional alleles and can be used to introduce point mutations away from CRISPR/Cas9 cutting sites in mice. However, our work demonstrates that thorough quality control of new models is essential prior to reliably experimenting with mice generated by this method. These advances in genome editing techniques shift the challenge of mutagenesis from generation to the validation of new mutant models.Electronic supplementary materialThe online version of this article (10.1186/s12915-018-0530-7) contains supplementary material, which is available to authorized users.

The results of a cytogenetic and molecular reinvestigation of a series of 52 patients with Turner's syndrome are reported. No evidence of Y chromosome material was found among the patients with a 45,X constitution but two patients were found to have a cell line with a r(Y) chromosome which was previously thought to be a r(X). The parental origin of the single X in the 45,X patients was maternal in 69% and paternal in 31%, a similar ratio to that seen among spontaneously aborted 45,X conceptuses. This suggests that X-chromosome imprinting is not responsible for the two grossly different phenotypes associated with a 45,X chromosome constitution. Approximately half of the structurally abnormal X chromosomes were maternal in origin and half paternal. This observation is consistent with either a meiotic or post-zygotic mitotic origin and at variance with the predominantly paternal origin reported for autosome structural abnormalities.

The parental origin of the single X chromosome in 10 45,X fetuses was studied using DNA restriction fragment length polymorphisms. In six the single X was maternal in origin, in one it was paternal, and in one the results were consistent with a paternal origin. Therefore the parental origin of the X in 45,X fetuses that survive to the second or third trimester of pregnancy is similar to that of spontaneous abortions and live births with a 45,X constitution. X.4 Thus, in these two groups it is clear that the parental origin of the single X is not responsible for the widely differing phenotypes. However, there is evidence from the 45,X spontaneous abortions that the parental origin of the X may affect the phenotype as those with a paternally derived X were more likely to have a small gestational sac with or without an embryo than those with a maternally derived X.4To date there is no information on the origin of the single X chromosome in late fetal deaths or stillbirths with a 45,X constitution. The purpose of this communication is to report our observations on 10 45,X fetuses ascertained during the second trimester of pregnancy.Material and methods During the past two years 10 fetuses have been referred to us for routine cytogenetic examination and found to have a 45,X constitution (table 1). One of these was a second trimester missed abortion and the remaining nine were diagnosed as being grossly abnormal on ultrasound examination and the pregnancy subsequently terminated. It has been shown that such fetuses are very unlikely to survive to birth5 and therefore it is reasonable to consider them representative of late fetal deaths. Wherever possible, we obtained tissue for karyotyping and for DNA extraction from the fetus and a blood sample from both parents from which we set up cultures for cytogenetic analysis and also extracted DNA.

SummaryHaemorrhage remains an important cause of maternal mortality worldwide. Cell salvage carries a theoretical risk of amniotic fluid embolus syndrome and is too expensive for use in many parts of the world. To explore cheaper options, we investigated whether a leucocyte depletion filter alone removes components of pure amniotic fluid. Amniotic fluid was collected from 10 women during elective caesarean section and passed through a LeukoGuard Ò RS filter. Pre-and post-filtration samples were compared in the laboratory. Lamellar bodies and fetal squames were almost completely removed (filtration efficacy 96.6% and 99.9%, respectively; p < 0.0001 and <0.0004), and hair was completely removed (p = 0.002). Filtration had no effect on concentrations of a-fetoprotein, tissue factor or endothelin-1, or on the presence of meconium or vernix. Additional work is required to evaluate whether cell salvage using filtration alone may be useful in maternal haemorrhage in the developing world.