Genome-wide Snapshot of Chromatin Regulators and States in Xenopus Embryos by ChIP-Seq

The goal of this procedure, commonly known as ChIP-seq, short for chromatin immunoprecipitation, followed by next generation sequencing, is to determine the genome-wide location of chromatin regulators and chromatin states in the opus embryo. This is accomplished by first fixing zap embryos and thereby covalently linking the DNA associated proteins to the genome. Next, the nuclei are extracted and their chromatin is solubilized and shared by sonication.

At this point, the DNA linked protein of interest is purified by immunoprecipitation and extensive washing. The final step is to create an indexed ChIP-seq library from the purified DNA fragments. Ultimately, millions of five prime mens of these DNA fragments, so-called res, are sequenced in parallel, aligned to the genome and extended to average fragment length.

Local enrichment of res so-called peaks are determined to identify all the site-specific DNA occupancies of the protein of interest, and thereby expanding the study of its genome-wide characteristics. So this protocol can provide detailed insights into the genome-wide chromatin architecture of emus embryos. It can also potentially be applied to other organisms with sequenced genomes.

Begin with the deed embryos. Details up to this point are provided in the text protocol. Transfer them in an eight milliliter glass vial and wash them with 0.01 XMMR.

After the wash, fix the embryos with 1%para formaldehyde and 0.01 XMMR. Allow the fix to go for at least 15 to not more than 40 minutes a room temperature. End the fix by washing the embryos three times with cold 0.01 XMMR.

Prevent the embryos from touching the surface of the solution as surface tension will lead to rupture. Once the fixative is washed away, make aliquots of 250 embryos in micro refuse tubes. Then hypo weight as much of the 0.01 XMMR as possible, and proceed with the chromatin extraction to pause.

Here equate the embryos in 250 microliters of cold HEG buffer. Once settled in the buffer, the embryos can be snap frozen in liquid nitrogen and stored at minus 80 degrees Celsius. Begin by homogenizing the fixed embryos in E one buffer.

Details on upscaling and buffer preparation are provided in the text protocol. Next centrifuge. The homogenates at four degrees Celsius aspirate and discard the sate and re suspend the pellets in E one.

Again, keep the sample on ice for 10 minutes. Repeat the centrifugation and this time Reese, suspend the palette in E two. Wait 10 minutes while the homogenate chills on ice.

Then repeat the centrifugation again, and Reese suspend the pellet in E three. This time, after chilling for another 10 minutes, the suspension should appear fairly transparent because by this point, the onic detergent renders most of the remaining yolk platelets soluble. Now, repeat the centrifugation.Andre.

Suspend the pellets in one to three milliliters of E three. If necessary, use the last centrifugation step to pull all the pellets apart from the desired cross-linked nuclei. This suspension also contains pigment granules and some residual yolk platelets.

These granules and yolk platelets will be separated from the chromatin after sonication by centrifugation. Now keep the sample on ice and proceed with chromatin fragmentation. Alternately snap, freeze the sample for temporary storage.

Begin by transferring the sample in E three to a custom built polystyrene tube. For the sonicate, attach the tube to an 800 milliliter beaker with ice water using a short thermometer clamp so it stays called during sonication. Place the beaker on a jack and adjust the jack so that the sonic's tip immerses about two thirds of the way into the sample.

The sonicate tip should not touch the tube wall. Optimize the sonication, starting with the manufacturer's recommended parameters from my Sonic Sonicate 3000 equipped with a one 16th inch tapered micro tip sonicate seven minutes in total. 30 seconds at a time between sonication.

Let the sample rest for a minute. Start each sonication at a power of one and increase it gradually to between two and four. If the sample begins to froth, reposition the tube and let the froth dissipate before continuing After the sonication, the chromatin is solubilized and sheared.

Transfer it to pre chill 1.5 milliliter to micro refuse tubes and centrifuge at full speed. For five minutes of four degrees Celsius, collect the SNA and transfer it to pre chill tubes. Discard the pellet.

Use 50 microliters of SUP natant to visually assess the fragmentation and save the remainder for immunoprecipitation. Begin by transferring 10 to 30 microliters of she chromatin SUP to a new tube to serve as an input sample. Then add chip grade antibody at about one microgram per million cells to the remaining chromatin.

Incubate the chromatin antibody sample overnight, also at four degrees Celsius, but with 10 RPM of rotation. The next day, wash the antibody compatible magnetic beads in E three for five minutes of four degrees Celsius. Using the manufacturer's suggested bead concentration at the washed beads to antibody pre incubated chromatin Incubate at four degrees Celsius with rotation for four more hours.

Then using chilled ripper buffer, wash the beads 10 times. Use the magnet for 20 to 30 seconds to separate out the beads between washes. The solution should be clear.

Follow the ripper buffer washes with one wash using chilled 10 buffer. Then transfer the beads in a small volume of 10 buffer to a new tube. Separate out the beads and discard residual buffer.

To detach the immuno precipitated chromatin. Reese has bend the beads in 50 to 100 microliters of SDS solution buffer and vortex the tube with a thermo mixer. Then centrifuge the tube at full speed for 30 seconds and collect the snat containing the immuno precipitated chromatin eluate.

Repeat the SDS solution, step once and combine all the eluate. Then proceed with the DNA extraction, ChIP-seq, library preparation, and next generation sequencing as described in the text protocol following this protocol, shared chromatin shows an asymmetric distribution of DNA fragments, mainly ranging from 100 to 1000 base pairs and peaking between 300 and 500 base pairs. A minimal 50 picograms of immuno precipitated DNA is required to successfully make an index paired N ChIP-seq library with similarly sized DNA inserts.

The library should be largely devoid of adapter dimers, which can be seen on the electropherogram at approximately 120 base pairs. Sequencing of the ChIP-seq library reduces millions of short DNA sequences, so-called reads. These get mapped to the genome while input reads align uniformly along the genome.

The chip reads show strand specific enrichments that flank the chromatin feature of interest. Extending the alignment in the reading direction to an average fragment size reduces accurate profiles for single chromatin features such as transcription factor binding events. These appear as peaks in a genome browser as shown here for veg tea at the gastro list stage of Zeno's tropics embryos.

ChIP-seq experiments allow exploring genome-wide characteristics of chromatin features such as enriched DNA sequence motifs underlying the peaks, or gene ontology analysis of gene targets, as shown here, the mapped bench TDNA interactions After its development. This method paves the way for researchers to explore the embryonic chromatin landscape, both at a genome wide scale, under a very high resolution.