Dirk van den Boom

OCT4-INDUCED PLURIPOTENCY IN ADULT NEURAL STEM CELLS

The four transcription factors Oct4, Sox2, Klf4, and c-Myc can induce pluripotency in mouse and human fibroblasts. We previously described direct reprogramming of adult mouse neural stem cells (NSCs) by Oct4 and either Klf4 or c-Myc. NSCs endogenously express Sox2, c-Myc, and Klf4 as well as several intermediate reprogramming markers. Here we report that exogenous expression of the germline-specific transcription factor Oct4 is sufficient to generate pluripotent stem cells from adult mouse NSCs. These one-factor induced pluripotent stem cells (1F iPS) are similar to embryonic stem cells in vitro and in vivo. Not only can these cells can be efficiently differentiated into NSCs, cardiomyocytes, and germ cells in vitro, but they are also capable of teratoma formation and germline transmission in vivo. Our results demonstrate that Oct4 is required and sufficient to directly reprogram NSCs to pluripotency.

DNA sequencing of maternal plasma to detect Down syndrome: An international clinical validation study

Purpose: Prenatal screening for Down syndrome has improved, but the number of resulting invasive diagnostic procedures remains problematic. Measurement of circulating cell-free DNA in maternal plasma might offer improvement.Methods: A blinded, nested case-control study was designed within a cohort of 4664 pregnancies at high risk for Down syndrome. Fetal karyotyping was compared with an internally validated, laboratory-developed test based on next-generation sequencing in 212 Down syndrome and 1484 matched euploid pregnancies. None had been previously tested. Primary testing occurred at a CLIA-certified commercial laboratory, with cross validation by a CLIA-certified university laboratory.Results: Down syndrome detection rate was 98.6% (209/212), the false-positive rate was 0.20% (3/1471), and the testing failed in 13 pregnancies (0.8%); all were euploid. Before unblinding, the primary testing laboratory also reported multiple alternative interpretations. Adjusting chromosome 21 counts for guanine cytosine base content had the largest impact on improving performance.Conclusion: When applied to high-risk pregnancies, measuring maternal plasma DNA detects nearly all cases of Down syndrome at a very low false-positive rate. This method can substantially reduce the need for invasive diagnostic procedures and attendant procedure-related fetal losses. Although implementation issues need to be addressed, the evidence supports introducing this testing on a clinical basis.

Noninvasive detection of fetal trisomy 21 by sequencing of DNA in maternal blood: a study in a clinical setting

OBJECTIVE We sought to evaluate a multiplexed massively parallel shotgun sequencing assay for noninvasive trisomy 21 detection using circulating cell-free fetal DNA. STUDY DESIGN Sample multiplexing and cost-optimized reagents were evaluated as improvements to a noninvasive fetal trisomy 21 detection assay. A total of 480 plasma samples from high-risk pregnant women were employed. RESULTS In all, 480 prospectively collected samples were obtained from our third-party storage site; 13 of these were removed due to insufficient quantity or quality. Eighteen samples failed prespecified assay quality control parameters. In all, 449 samples remained: 39 trisomy 21 samples were correctly classified; 1 sample was misclassified as trisomy 21. The overall classification showed 100% sensitivity (95% confidence interval, 89-100%) and 99.7% specificity (95% confidence interval, 98.5-99.9%). CONCLUSION Extending the scope of previous reports, this study demonstrates that plasma DNA sequencing is a viable method for noninvasive detection of fetal trisomy 21 and warrants clinical validation in a larger multicenter study.

DNA sequencing of maternal plasma reliably identifies trisomy 18 and trisomy 13 as well as Down syndrome: an international collaborative study.

Purpose:To determine whether maternal plasma cell–free DNA sequencing can effectively identify trisomy 18 and 13.Methods:Sixty-two pregnancies with trisomy 18 and 12 with trisomy 13 were selected from a cohort of 4,664 pregnancies along with matched euploid controls (including 212 additional Down syndrome and matched controls already reported), and their samples tested using a laboratory-developed, next-generation sequencing test. Interpretation of the results for chromosome 18 and 13 included adjustment for CG content bias.Results:Among the 99.1% of samples interpreted (1,971/1,988), observed trisomy 18 and 13 detection rates were 100% (59/59) and 91.7% (11/12) at false-positive rates of 0.28% and 0.97%, respectively. Among the 17 samples without an interpretation, three were trisomy 18. If z-score cutoffs for trisomy 18 and 13 were raised slightly, the overall false-positive rates for the three aneuploidies could be as low as 0.1% (2/1,688) at an overall detection rate of 98.9% (280/283) for common aneuploidies. An independent academic laboratory confirmed performance in a subset.Conclusion:Among high-risk pregnancies, sequencing circulating cell–free DNA detects nearly all cases of Down syndrome, trisomy 18, and trisomy 13, at a low false-positive rate. This can potentially reduce invasive diagnostic procedures and related fetal losses by 95%. Evidence supports clinical testing for these aneuploidies.Genet Med 2012:14(3):296–305

Comparative genome sequencing of Escherichia coli allows observation of bacterial evolution on a laboratory timescale

We applied whole-genome resequencing of Escherichia coli to monitor the acquisition and fixation of mutations that conveyed a selective growth advantage during adaptation to a glycerol-based growth medium. We identified 13 different de novo mutations in five different E. coli strains and monitored their fixation over a 44-d period of adaptation. We obtained proof that the observed spontaneous mutations were responsible for improved fitness by creating single, double and triple site-directed mutants that had growth rates matching those of the evolved strains. The success of this new genome-scale approach indicates that real-time evolution studies will now be practical in a wide variety of contexts.

MALDI-TOF mass spectrometry : A versatile tool for high-performance DNA analysis

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) has developed during the past decade into a versatile tool for biopolymer analysis. The aim of this review is to summarize this development and outline the applications, which have been enabled for routine use in the field of nucleic acid analysis. These include the anlaysis of mutations, the resequencing of amplicons with a known reference sequence, and the quantitative analysis of gene expression and allelic frequencies in complex DNA mixtures.

The use of MassARRAY technology for high throughput genotyping.

This chapter will explore the role of mass spectrometry (MS) as a detection method for genotyping applications and will illustrate how MS evolved from an expert-user-technology to a routine laboratory method in biological sciences. The main focus will be time-of-flight (TOF) based devices and their use for analyzing single-nucleotide-polymorphisms (SNPs, pronounced snips). The first section will describe the evolution of the use of MS in the field of bioanalytical sciences and the protocols used during the early days of bioanalytical MALDI TOF mass spectrometry. The second section will provide an overview on intraspecies sequence diversity and the nature and importance of SNPs for the genomic sciences. This is followed by an exploration of the special and advantageous features of mass spectrometry as the key technology in modern bioanalytical sciences in the third chapter. Finally, the fourth section will describe the MassARRAY technology as an advanced system for automated high-throughput analysis of SNPs.

Association testing by DNA pooling: An effective initial screen

With an ever-increasing resource of validated single-nucleotide polymorphisms (SNPs), the limiting factors in genome-wide association analysis have become genotyping capacity and the availability of DNA. We provide a proof of concept of the use of pooled DNA as a means of efficiently screening SNPs and prioritizing them for further study. This approach reduces the final number of SNPs that undergo full, sample-by-sample genotyping as well as the quantity of DNA used overall. We have examined 15 SNPs in the cholesteryl ester transfer protein (CETP) gene, a gene previously demonstrated to be associated with serum high-density lipoprotein cholesterol levels. The SNPs were amplified in two pools of DNA derived from groups of individuals with extremely high and extremely low serum high-density lipoprotein cholesterol levels, respectively. P values <0.05 were obtained for 14 SNPs, supporting the described association. Genotyping of the individual samples showed that the average margin of error in frequency estimate was ≈4% when pools were used. These findings clearly demonstrate the potential of pooling techniques and their associated technologies as an initial screen in the search for genetic associations.

Cytosine methylation profiling of cancer cell lines

DNA-methylation changes in human cancer are complex and vary between the different types of cancer. Capturing this epigenetic variability in an atlas of DNA-methylation changes will be beneficial for basic research as well as translational medicine. Hypothesis-free approaches that interrogate methylation patterns genome-wide have already generated promising results. However, these methods are still limited by their quantitative accuracy and the number of CpG sites that can be assessed individually. Here, we use a unique approach to measure quantitative methylation patterns in a set of >400 candidate genes. In this high-resolution study, we employed a cell-line model consisting of 59 cancer cell lines provided by the National Cancer Institute and six healthy control tissues for discovery of methylation differences in cancer-related genes. To assess the effect of cell culturing, we validated the results from colon cancer cell lines by using clinical colon cancer specimens. Our results show that a large proportion of genes (78 of 400 genes) are epigenetically altered in cancer. Although most genes show methylation changes in only one tumor type (35 genes), we also found a set of genes that changed in many different forms of cancer (seven genes). This dataset can easily be expanded to develop a more comprehensive and ultimately complete map of quantitative methylation changes. Our methylation data also provide an ideal starting point for further translational research where the results can be combined with existing large-scale datasets to develop an approach that integrates epigenetic, transcriptional, and mutational findings.

DNA sequencing of maternal plasma to identify Down syndrome and other trisomies in multiple gestations

Studies on prenatal testing for Down syndrome (trisomy 21), trisomy 18, and trisomy 13 by massively parallel shotgun sequencing (MPSS) of circulating cell free DNA have been, for the most part, limited to singleton pregnancies. If MPSS testing is offered clinically, it is important to know if these trisomies will also be identified in multiple pregnancies.