Chromatin Immunoprecipitation (ChIP) Protocol for Low-abundance Embryonic Samples.

Chromatin immunoprecipitation (ChIP) is a widely-used technique for mapping the localization of post-translationally modified histones, histone variants, transcription factors, or chromatin-modifying enzymes at a given locus or on a genome-wide scale. The combination of ChIP assays with next-generation sequencing (i.e., ChIP-Seq) is a powerful approach to globally uncover gene regulatory networks and to improve the functional annotation of genomes, especially of non-coding regulatory sequences. ChIP protocols normally require large amounts of cellular material, thus precluding the applicability of this method to investigating rare cell types or small tissue biopsies. In order to make the ChIP assay compatible with the amount of biological material that can typically be obtained in vivo during early vertebrate embryogenesis, we describe here a simplified ChIP protocol in which the number of steps required to complete the assay were reduced to minimize sample loss. This ChIP protocol has been successfully used to investigate different histone modifications in various embryonic chicken and adult mouse tissues using low to medium cell numbers (5 x 104 - 5 x 105 cells). Importantly, this protocol is compatible with ChIP-seq technology using standard library preparation methods, thus providing global epigenomic maps in highly relevant embryonic tissues.

Design and use of mouse control DNA for DNA biomarker extraction and PCR detection from urine: Application for transrenal Mycobacterium tuberculosis DNA detection.

Urine samples are increasingly used for diagnosing infections including Escherichia coli, Ebola virus, and Zika virus. However, extraction and concentration of nucleic acid biomarkers from urine is necessary for many molecular detection strategies such as polymerase chain reaction (PCR). Since urine samples typically have large volumes with dilute biomarker concentrations making them prone to false negatives, another impediment for urine-based diagnostics is the establishment of appropriate controls particularly to rule out false negatives. In this study, a mouse glyceraldehyde 3-phosphate dehydrogenase (GAPDH) DNA target was added to retrospectively collected urine samples from tuberculosis (TB)-infected and TB-uninfected patients to indicate extraction of intact DNA and removal of PCR inhibitors from urine samples. We tested this design on surrogate urine samples, retrospective 1milliliter (mL) urine samples from patients in Lima, Peru and retrospective 5mL urine samples from patients in Cape Town, South Africa. Extraction/PCR control DNA was detectable in 97% of clinical samples with no statistically significant differences among groups. Despite the inclusion of this control, there was no difference in the amount of TB IS6110 Tr-DNA detected between TB-infected and TB-uninfected groups except for samples from known HIV-infected patients. We found an increase in TB IS6110 Tr-DNA between TB/HIV co-infected patients compared to TB-uninfected/HIV-infected patients (N=18, p=0.037). The inclusion of an extraction/PCR control DNA to indicate successful DNA extraction and removal of PCR inhibitors should be easily adaptable as a sample preparation control for other acellular sample types.

A Prototype Biomarker Detector Combining Biomarker Extraction and Fixed Temperature PCR.

PCR is the most sensitive molecular diagnostic available for infectious diseases. The goal for low-resource settings is a simple, inexpensive instrument. Toward this goal, we previously published a self-contained sample preparation instrument that uses magnetics and prearrayed reagents in thin tubing to extract nucleic acids and perform isothermal amplification and detection of extracted biomarkers. To incorporate PCR thermal cycling, after biomarker is magnetically extracted from a patient sample, the section of tubing containing the extracted biomarker and PCR reagents is alternately positioned within two constant temperature blocks. This instrument was evaluated initially by extracting and amplifying a 140 bp fragment of the IS6110 sequence of tuberculosis from TE buffer. The mean cycle threshold for 5 × 10(6) copies of IS6110 was 25.5 ± 1.5 cycles (n = 4), which was significantly different from negative control samples (34.0 ± 2.6 cycles; n = 3). Using a more clinically relevant sample, we extracted and amplified Plasmodium falciparum DNA from malaria-infected human blood cultures. The average cycle threshold for 1% parasitemia samples was 24.7 ± 1.5 cycles (n = 3) and significantly different from negatives (31.5 ± 2.1 cycles; n = 3). This approach integrates biomarker extraction, PCR amplification, and detection in a simple, linear tubing design with potential for use as a low-resource instrument.

Tuberculosis Biomarker Extraction and Isothermal Amplification in an Integrated Diagnostic Device.

In this study, we integrated magnetic bead-based sample preparation and isothermal loop mediated amplification (LAMP) of TB in a single tube. Surrogate sputum samples produced by the Program for Appropriate Technology in Health containing inactivated TB bacteria were used to test the diagnostic. In order to test the sample preparation method, samples were lysed, and DNA was manually extracted and eluted into water in the tube. In a thermal cycler, LAMP amplified TB DNA from 103 TB cells/mL of sputum at 53.5 ± 3.3 minutes, 104 cells/mL at 46.3 ± 2.2 minutes, and 105 cells/mL at 41.6 ± 1.9 minutes. Negative control samples did not amplify. Next, sample preparation was combined with in-tubing isothermal LAMP amplification by replacing the water elution chamber with a LAMP reaction chamber. In this intermediate configuration, LAMP amplified 103 cells/mL at 74 ± 10 minutes, 104 cells/mL at 60 ± 9 minutes, and 105 TB cells/mL of sputum at 54 ± 9 minutes. Two of three negative controls did not amplify; one amplified at 100 minutes. In the semi-automated system, DNA was eluted directly into an isothermal reaction solution containing the faster OptiGene DNA polymerase. The low surrogate sputum concentration, 103 TB cells/mL, amplified at 52.8 ± 3.3 minutes, 104 cells/mL at 45.4 ± 11.3 minutes, and 105 cells/mL at 31.8 ± 2.9 minutes. TB negative samples amplified at 66.4 ± 7.4 minutes. This study demonstrated the feasibility of a single tube design for integrating sample preparation and isothermal amplification, which with further development could be useful for point-of-care applications, particularly in a low-resource setting.