Name: in-nucleus hi-c in drosophila cells
Uploaded: 2021-09-15T15:00:00
Description: Watch this Scientific Journal Video about In-Nucleus Hi-C in Drosophila Cells at JoVE.com

This work was supported by UNAM Technology Innovation and Research Support Program (PAPIIT) grant number IN207319 and the Science and Technology National Council (CONACyT-FORDECyT) grant number 303068. A.E.-L. is a master&#39;s student supported by the Science and Technology National Council (CONACyT) CVU number 968128.

1. Fixation
<ol>
	<li>Start with 10 million Schneider&#39;s line 2 plus (S2R+) cells to prepare 17.5 mL of a cell suspension in Schneider medium containing 10% fetal bovine serum (FBS) at room temperature (RT).</li>
	<li>Add methanol-free formaldehyde to obtain a final concentration of 2%. Mix and incubate for 10 min at RT, taking care to mix every minute. 
	NOTE: Formaldehyde is a hazardous chemical. Follow the appropriate health and safety regulations, and work in the fume hood.</li>
	<li>Quench the reaction by ...

<ol>
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V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Active+chromatin+and+transcription+play+a+key+role+in+chromosome+partitioning+into+topologically+associating+domains.">Active chromatin and transcription play a key role in chromosome partitioning into topologically associating domains.</a> Genome Research. 26, 70-84 (2016).</li><li>Rowley, M. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolutionarily+conserved+principles+predict+3D+chromatin+organization.">Evolutionarily conserved principles predict 3D chromatin organization.</a> Molecular Cell. 67, 837-852 (2017).</li><li>Gavrilov, A. A., Golov, A. K., Razin, S. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actual+ligation+frequencies+in+the+chromosome+conformation+capture+procedure.">Actual ligation frequencies in the chromosome conformation capture procedure.</a> PLoS One. 8, 60403 (2013).</li><li>Gavrilov, A. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disclosure+of+a+structural+milieu+for+the+proximity+ligation+reveals+the+elusive+nature+of+an+active+chromatin+hub.">Disclosure of a structural milieu for the proximity ligation reveals the elusive nature of an active chromatin hub.</a> Nucleic Acids Research. 41, 3563-3575 (2013).</li><li>Nagano, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+Hi-C+reveals+cell-to-cell+variability+in+chromosome+structure.">Single-cell Hi-C reveals cell-to-cell variability in chromosome structure.</a> Nature. 502, 59-64 (2013).</li><li>Rao, S. S. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+3D+map+of+the+human+genome+at+kilobase+resolution+reveals+principles+of+chromatin+looping.">A 3D map of the human genome at kilobase resolution reveals principles of chromatin looping.</a> Cell. 159 (7), 1665-1680 (2014).</li><li>Nagano, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+Hi-C+results+using+in-solution+versus+in-nucleus+ligation.">Comparison of Hi-C results using in-solution versus in-nucleus ligation.</a> Genome Biology. 16, 175 (2015).</li><li>Arzate-Mej&#237;a, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+dissection+of+domain+boundaries+affect+genome+topology+and+gene+transcription+in+Drosophila.">In situ dissection of domain boundaries affect genome topology and gene transcription in Drosophila.</a> Nature Communications. 11, 894 (2020).</li><li>Schoenfelder, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Promoter+capture+Hi-C:+high-resolution,+genome-wide+profiling+of+promoter+interactions.">Promoter capture Hi-C: high-resolution, genome-wide profiling of promoter interactions.</a> Journal of Visualized Experiments. (136), e57320 (2018).</li><li>Servant, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HiC-Pro:+an+optimized+and+flexible+pipeline+for+Hi-C+processing.">HiC-Pro: an optimized and flexible pipeline for Hi-C processing.</a> Genome Biology. 16, 259 (2015).</li><li>Philip, E., M&#229;ns, M., Sverker, L., Max, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MultiQC:+Summarize+analysis+results+for+multiple+tools+and+samples+in+a+single+report.">MultiQC: Summarize analysis results for multiple tools and samples in a single report.</a> Bioinformatics. 10, 1093 (2016).</li><li>Wingett, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HiCUP:+pipeline+for+mapping+and+processing+Hi-C+data.">HiCUP: pipeline for mapping and processing Hi-C data.</a> F1000 Research. 4, 1310 (2015).</li><li>Imakaev, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Iterative+correction+of+Hi-C+data+reveals+hallmarks+of+chromosome+organization.">Iterative correction of Hi-C data reveals hallmarks of chromosome organization.</a> Nature Methods. 9 (10), 999-1003 (2012).</li><li>Akdemir, K. C., Chin, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HiCPlotter+integrates+genomic+data+with+interaction+matrices.">HiCPlotter integrates genomic data with interaction matrices.</a> Genome Biolog. 16, 198 (2015).</li><li>Ramirez, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+TADs+reveal+DNA+sequences+underlying+genome+organization+in+flies.">High-resolution TADs reveal DNA sequences underlying genome organization in flies.</a> Nature Communications. 9, 189 (2018).</li><li>Ando-Kuri, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+global+and+promoter-centric+3D+genome+organization+temporally+resolved+during+a+circadian+cycle.">The global and promoter-centric 3D genome organization temporally resolved during a circadian cycle.</a> bioRxiv. , (2020).</li><li>Cuellar-Partida, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epigenetic+priors+for+identifying+active+transcription+factor+binding+sites.">Epigenetic priors for identifying active transcription factor binding sites.</a> Bioinformatics. 28 (1), 56-62 (2012).</li><li>Zhang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Model-based+analysis+of+ChIP-Seq+(MACS).">Model-based analysis of ChIP-Seq (MACS).</a> Genome Biology. 9, 137 (2008).</li><li>Ong, C. -. 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The in-nucleus Hi-C method presented here has allowed detailed exploration of Drosophila genome topology at high resolution, providing a view of genomic interactions at different genomic scales, from chromatin loops between regulatory elements such as promoters and enhancers to TADs and large compartment identification25. The same technology has also been efficiently applied to mammalian tissues with some modifications33. For example, when processing a tissue instead of a s...

In eukaryotes, the genome is partitioned into chromosomes that occupy specific territories in the nuclear space during interphase1. The chromatin forming the chromosomes can be divided into two main states: one of accessible chromatin that is transcriptionally permissive, and the other of compact chromatin that is transcriptionally repressive. These chromatin states segregate and rarely mix in the nuclear space, forming two distinct compartments in the nucleus2. At the sub-megabase scale, boundaries separate domains of high-frequency chromatin interactions, called TADs, that mark chromosomal organization3,4,5. In mammals, TAD boundaries are occupied by cohesin and CCCTC-binding factor (CTCF)6,7,8. The cohesin complex extrudes chromatin and halts at CTCF-binding sites that are disposed in a convergent orientation in the genomic sequence to form stable chromatin loops9,10,13,14. Genetic disruption of the CTCF DNA-binding site at the boundaries or reduction in CTCF and cohesin protein abundance results in abnormal interactions between regulatory elements, loss of TAD formation, and gene expression deregulation9,10,11,13,14.
In Drosophila, the boundaries between TADs are occupied by several APs, including boundary element-associated factor 32 kDa (BEAF-32), Motif 1 binding protein (M1BP), centrosomal protein 190 (CP190), suppressor of hairy-wing (SuHW), and CTCF, and are enriched in active histone modifications and Polymerase II16,17,18. It has been suggested that in Drosophila, TADs appear as a consequence of transcription13,17,19, and the exact role of independent APs in boundary formation and insulation properties is still under investigation. Thus, whether domains in Drosophila are a sole consequence of the aggregation of regions of similar transcriptional states or whether APs, including CTCF, contribute to boundary formation remains to be fully characterized. Exploration of genomic contacts at high resolution has been possible through the development of chromosome conformation capture technologies coupled with next-generation sequencing. The Hi-C protocol was first described with the ligation step performed &#34;in solution&#34;2 in an attempt to avoid spurious ligation products between chromatin fragments. However, several studies pointed to the realization that the useful signal in the data came from ligation products formed at partially lysed nuclei that were not in solution20,21.
The protocol was then modified to perform the ligation inside the nucleus as part of the single-cell Hi-C experiment22. The in-nucleus Hi-C protocol was subsequently incorporated into cell population Hi-C to yield a more consistent coverage over the full range of genomic distances and produce data with less technical noise23,24. The protocol, described in detail here, is based on the population in-nucleus Hi-C protocol23,24 and was used to investigate the consequences of genetically removing DNA-binding motifs for CTCF and M1BP from a domain boundary at the Notch gene locus in Drosophila25. The results show that altering the DNA-binding motifs for APs at the boundary has drastic consequences for Notch domain formation, larger topological defects in the regions surrounding the Notch locus, and gene expression deregulation. This indicates that genetic elements at domain boundaries are important for the maintenance of genome topology and gene expression in Drosophila25.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>16% (vol/vol) paraformaldehyde solution</td>
			<td>Agar Scientific</td>
			<td>R1026</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotin-14-dATP</td>
			<td>Invitrogen</td>
			<td>CA1524-016</td>
			<td></td>
		</tr>
		<tr>
			<td>ClaI enzyme</td>
			<td>NEB</td>
			<td>R0197S</td>
			<td></td>
		</tr>
		<tr>
			<td>COVARIS Ultrasonicator</td>
			<td>Covaris</td>
			<td>LE220-M220</td>
			<td></td>
		</tr>
		<tr>
			<td>Cut Smart</td>
			<td>NEB</td>
			<td>B72002S</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle Medium (DMEM) 1x</td>
			<td>Life Technologies</td>
			<td>41965-039</td>
			<td></td>
		</tr>
		<tr>
			<td>Dynabeads MyOne Streptabidin C1</td>
			<td>Invitrogen</td>
			<td>65002</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS) sterile filtered</td>
			<td>Sigma</td>
			<td>F9665</td>
			<td></td>
		</tr>
		<tr>
			<td>Klenow Dna PolI large fragment</td>
			<td>NEB</td>
			<td>M0210L</td>
			<td></td>
		</tr>
		<tr>
			<td>Klenow exo(-)</td>
			<td>NEB</td>
			<td>M0210S</td>
			<td></td>
		</tr>
		<tr>
			<td>Ligation Buffer</td>
			<td>NEB</td>
			<td>B020S</td>
			<td></td>
		</tr>
		<tr>
			<td>MboI enzyme</td>
			<td>NEB</td>
			<td>R0147M</td>
			<td></td>
		</tr>
		<tr>
			<td>NP40-Igepal</td>
			<td>SIGMA</td>
			<td>CA-420</td>
			<td>Non-ionic surfactant for addition in lysis buffer</td>
		</tr>
		<tr>
			<td>PE adapter 1.0</td>
			<td>Illumina</td>
			<td>5&#39;-P-GATCGGAAGAGCGGTTCAGCAG 
			GAATGCCGAG-3&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>PE adapter 2.0</td>
			<td>Illumina</td>
			<td>5&#39;-ACACTCTTTCCCTACACGACGCT 
			CTTCCGATCT-3&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>PE PCR primer 1.0</td>
			<td>Illumina</td>
			<td>5&#39;-AATGATACGGCGACCACCGAGAT 
			CTACACTCTTTCCCTACACGACG 
			CTCTTCCGATCT-3&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>PE PCR primer 2.0</td>
			<td>Illumina</td>
			<td>5&#39;-CAAGCAGAAGACGGCATACGAG 
			ATCGGTCTCGGCATTCCTGCTGA 
			ACCGCTCTTCCGATCT-3&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenol: Chloroform:Isoamyl Alcohol 25:24:1</td>
			<td>SIGMA</td>
			<td>P2069</td>
			<td></td>
		</tr>
		<tr>
			<td>Primer 1 (known interaction, Figure 2A)</td>
			<td>Sigma</td>
			<td>5&#39;-TCGCGGTAATTTTGCGTTTGA-3&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>Primer 2 (known interactions, Figure 2A)</td>
			<td>Sigma</td>
			<td>5&#39;-CCTCCCTGCCAAAACGTTTT-3&#39;</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease inhibitor cocktail tablet</td>
			<td>Roche</td>
			<td>4693132001</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteinase K</td>
			<td>Roche</td>
			<td>3115879001</td>
			<td></td>
		</tr>
		<tr>
			<td>Qubit</td>
			<td>ThermoFisher</td>
			<td>Q33327</td>
			<td></td>
		</tr>
		<tr>
			<td>RNAse</td>
			<td>Roche</td>
			<td>10109142001</td>
			<td></td>
		</tr>
		<tr>
			<td>SPRI Beads</td>
			<td>Beckman</td>
			<td>B23318</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA ligase</td>
			<td>Invitrogen</td>
			<td>15224-025</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA polymerase</td>
			<td>NEB</td>
			<td>M0203S</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 polynucleotide kinase (PNK)&#160;</td>
			<td>NEB</td>
			<td>M0201L</td>
			<td></td>
		</tr>
		<tr>
			<td>TaqPhusion</td>
			<td>NEB</td>
			<td>M0530S</td>
			<td>DNA polymerase</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td></td>
			<td></td>
			<td>Non-ionic surfactant for quenching of SDS</td>
		</tr>
	</tbody>
</table>

in-nucleus hi-c in drosophila cells

The genome is organized into topologically associating domains (TADs) delimited by boundaries that isolate interactions between domains. In Drosophila, the mechanisms underlying TAD formation and boundaries are still under investigation. The application of the in-nucleus Hi-C method described here helped to dissect the function of architectural protein (AP)-binding sites at TAD boundaries isolating the Notch gene. Genetic modification of domain boundaries that cause loss of APs results in TAD fusion, transcriptional defects, and long-range topological alterations. These results provided evidence demonstrating the contribution of genetic elements to domain boundary formation and gene expression control in Drosophila. Here, the in-nucleus Hi-C method has been described in detail, which provides important checkpoints to assess the quality of the experiment along with the protocol. Also shown are the required numbers of sequencing reads and valid Hi-C pairs to analyze genomic interactions at different genomic scales. CRISPR/Cas9-mediated genetic editing of regulatory elements and high-resolution profiling of genomic interactions using this in-nucleus Hi-C protocol could be a powerful combination for the investigation of the structural function of genetic elements.

Described below are the results of a successful Hi-C protocol (see a summary of the Hi-C protocol workflow in Figure 1A). There are several quality control checkpoints during the in-nucleus Hi-C experiment. Sample aliquots were collected before (UD) and after (D) the chromatin restriction step as well as after ligation (L). Crosslinks were reversed, and DNA was purified and run on an agarose gel. A smear of 200-1000 bp was observed when restriction with Mbo I was successful (<strong class="x...

Watch this Scientific Journal Video about In-Nucleus Hi-C in Drosophila Cells at JoVE.com

In-Nucleus Hi-C in Drosophila Cells

The genome is organized in the nuclear space into different structures that can be revealed through chromosome conformation capture technologies. The in-nucleus Hi-C method provides a genome-wide collection of chromatin interactions in Drosophila cell lines, which generates contact maps that can be explored at megabase resolution at restriction fragment level.

The genome is organized into topologically associating domains (TADs) delimited by boundaries that isolate interactions between domains. In Drosophila, ...

The nucleus Hi-C protocols allow the exploration of chromosomal confirmation at different resolution for the characterization of chromatin loops, domains, and compartment organizing the genome. This protocol provides high-resolution profiling of genomic interactions at different scales, yielding a more consistent coverage over the full range of genomic distances and data with less technical noise. Combining this protocol with genetic editing is a powerful strategy for testing the structural function of genetic elements.It can also be applied to the characterization of structural variations that lead to disease. The nucleus Hi-C protocol can be applied to explore the genome organization of any eukaryotic genome. Doing SDS and Triton treatment disaggregates any nuclear clumps by pipetting as aggregates interfere with enzymatic reaction efficiency, and be sure to perform the appropriate quality controls measure prior to sequencing.Begin by adding methanol-free formaldehyde to one times 10 to the seven Schneider's Line 2 Plus Drosophila cells in 17.5 milliliters of Schneider medium supplemented with 10%FBS to a final concentration of 2%Incubate the cells for 10 minutes at room temperature with mixing every 60 seconds or on a rotating wheel, and add glycine to a final concentration of 0.125 molar with mixing. After five minutes at room temperature and 15 minutes on ice, collect the cells by centrifugation and carefully resuspend the pellet in 25 milliliters of cold PBS and collect the cells with another centrifugation. At the end of the centrifugation, resuspend the cells in one milliliter of ice cold lysis buffer for counting and adjust the cells to a one times 10 to the six cells per milliliter concentration.Incubate the cells on ice for 30 minutes, inverting the tube every two minutes to mix and collect the cells with another centrifugation. Resuspend the pellet in one milliliter of fresh ice cold lysis buffer. After centrifugation, wash the lysate with one milliliter of 1.25X restriction buffer.Centrifuge again to collect the lysate. Resuspend the pellet in 360 microliters of fresh restriction buffer and 11 microliters of 10%SDS with careful pipetting and incubate for 45 minutes at 37 degrees Celsius and 7 to 950 revolutions per minute with occasional pipetting. At the end of the incubation, stop the permeabilization with 75 microliters of non-ionic surfactant and return the tube to the incubator for an additional 45 minutes with shaking at 950 revolutions per minute with occasional pipetting.For chromatin digestion, add 200 units of Mbo1 to the tube for a four to 16-hour incubation at 37 degrees Celsius with rotation. At the end of the incubation, inactivate the enzyme with 20-minute incubation at 60 degrees Celsius. To fill in the restriction fragment overhangs and to label the DNA ends with biotin, add 1.5 microliters each of 10 millimolar dCTP, dGTP, dTTP, 20 microliters of 0.4 millimolar biotin dATP, 17.5 microliters of tris low EDTA buffer, and 10 microliters of five units per microliter of DNA polymerase one large fragment to the tube with careful mixing.Incubate the reaction for 75 minutes at 37 degrees Celsius with shaking at 700 revolutions per minute every 10 seconds for 30 seconds. At the end of the incubation, add the ligation mix to the chromatin and adjust it to one milliliter final reaction volume with thorough gentle mixing and incubate overnight at 16 degrees Celsius. To degrade the sample proteins, add 50 microliters of 10 milligram per milliliter proteinase K to the tube for a two-hour incubation at 37 degrees Celsius.At the end of the incubation, increase the temperature to 65 degrees Celsius overnight to reverse crosslink the sample. The next morning, degrade the RNA with 10 microliters of 10 milligram per milliliter RNAse A.After one hour at 37 degrees Celsius, add one volume of phenol chloroform to the tube and mix thoroughly by inversion to obtain a homogenous white phase. After precipitating the DNA according to standard protocols, quantify the DNA using a fluorogenic dye that binds selectively to DNA and a fluorometer according to the manufacturer's instructions.To purify the DNA from undigested and digested aliquots, load 100 nanograms of undigested, digested, and ligated samples onto a 1.5%agarose gel and look for a smear centered around 500 base pairs in the digested sample versus a high molecular weight band for the ligated sample. To verify the Hi-C marking and ligation efficiency by amplification and digestion of a known interaction, after PCR, digest the products with Mbo1, Cla1, or both, and run the samples on a new 1.5 to 2%gel to allow estimation of the relative number of 3C and Hi-C ligation junctions. After sonicating the sample to obtain 200 to 500 base pair DNA fragments, transfer 130 microliters with five micrograms of DNA from each sample into new microcentrifuge tubes containing 16 microliters of 10X ligation buffer, two microliters of 10 millimolar dATP, five microliters of T4 DNA polymerase, and seven microliters of double distilled water for a 30-minute incubation at 20 degrees Celsius.At the end of the incubation, add five microliters of 10 millimolar dNTPs, four microliters of 10X ligation buffer, five microliters of T4 polynucleotide kinase, one microliter of DNA polymerase one large fragment, and 25 microliters of double distilled water to the tubes for a second 30-minute incubation at 20 degrees Celsius. To select fragments mostly in the 250 to 550 base pair size range, perform sequential solid phase reversible and mobilization size selection with 0.6X, then 0.9X according to the manufacturer's instructions and elute the DNA with 100 microliters of tris low EDTA. For biotin pulldown for each library, wash 150 microliters of Streptavidin-linked magnetic beads two times with 400 microliters of 1X Tween buffer and rotate the samples for three minutes on a rotating wheel.At the end of the incubation, resuspend the beads in 300 microliters of 2X no Tween buffer and mix with 300 microliters of Hi-C material for a 30-minute rotation on a rotating wheel. At the end of the incubation, wash the beads with 400 microliters of 0.5X Tween buffer for a three-minute incubation at 55 degrees Celsius and 750 revolutions per minute, followed by two washes in 200 microliters of 1X restriction buffer per wash. After the second wash, resuspend the beads in 100 microliters of dATP tailing mix for a 30-minute incubation at 37 degrees Celsius.At the end of the incubation, resuspend the beads in 50 microliters of 1X ligation buffer and transfer the suspension to a new tube containing four microliters pre-annealed paired end adapters and two microliters of T4 ligase. After two hours at room temperature, remove the supernatant and wash the beads two times with 400 microliters of Tween buffer, then wash the beads one time with 200 microliters of no Tween buffer and one time with 100 microliters of restriction buffer before re-suspending the beads in 40 microliters of 1X restriction buffer. A smear of 200 to 1, 000 base pairs is observed when restriction with Mbo1 is successful.If the ligation is successful, a high molecular weight band is observed at the top of the gel. Digestion efficiency can also be confirmed by quantitative PCR. An acceptable digestion efficiency is 80%or higher.As illustrated, the amplification of a known medium range interaction in Hi-C ligation products can be estimated by digestion of the PCR product recovered in the amplification. A digestion efficiency of more than 70%is recommended to avoid having a large proportion of non-useful reads for the libraries after sequencing. The number of PCR cycles for the final amplification should be one cycle less than the number of cycles for which the smear is visible.The level of digestion of the library indicates the abundance of valid Hi-C pairs and reflects the proportion of useful reads that will be obtained from the library. Using the unique valid Hi-C pairs, basic analysis of the pair distribution can be performed. As observed in this representative example, the NOTCH gene locus can be seen along with the architectural proteins, domains one and two, and histone modifications along the locus.Upon deletion of the region containing both the CTCF and M1BP DNA binding sites, a dramatic change in chromatin contacts can be observed. After Hi-C experiment, a can be performed to reach a specific set of contacts, for example, from promoter regions. This is particularly useful when assessing large genomes.As demonstrated, combining the Hi-C protocol with genetic addition can be used to assess the structural and regulatory function of genomic elements.

Research

JoVE Journal

Genetics

In Situ Labeling of Mitochondrial DNA Replication in Drosophila Adult Ovaries by EdU Staining

The mitochondrial genome is inherited exclusively through the maternal line. Understanding of how the mitochondrion and its genome are proliferated and transmitted from one generation to the next through the female oocyte is of fundamental importance. Because of the genetic tractability, and the elegant, ordered simplicity by which oocyte development proceeds, Drosophila oogenesis has become an invaluable system for mitochondrial study. An EdU (5-ethynyl-2&#180;-deoxyuridine) labeling method was utilized to detect mitochondrial DNA (mtDNA) replication in Drosophila ovaries. This method is superior to the BrdU (5-bromo-2'-deoxyuridine) labeling method in that it allows for good structural preservation and efficient fluorescent dye penetration of whole-mount tissues.
Here we describe a detailed protocol for labeling replicating mitochondrial DNA in Drosophila adult ovaries with EdU. Some technical solutions are offered to improve the viability of the ovaries, maintain their health during preparation, and ensure high-quality imaging. Visualization of newly synthesized mtDNA in the ovaries not only reveals the striking temporal and spatial pattern of mtDNA replication through oogenesis, but also allows for simple quantification of mtDNA replication under various genetic and pharmacological perturbations.

In Situ Labeling of Mitochondrial DNA Replication in Drosophila Adult Ovaries by EdU Staining

Drosophila oogenesis continues to be exceptionally useful in the study of mitochondrial proliferation and inheritance. This manuscript describes a detailed protocol used to label the replicating mitochondrial DNA (mtDNA) in Drosophila adult ovaries with 5-ethynyl-2&#180;-deoxyuridine (EdU), which facilitates uncovering mechanisms associated with mitochondrial inheritance that were previously debatable.

The mitochondrial genome is inherited exclusively through the maternal line. Understanding of how the mitochondrion and its genome are proliferated and ...

Quantifying Abdominal Pigmentation in Drosophila melanogaster

Pigmentation is a morphologically simple but highly variable trait that often has adaptive significance. It has served extensively as a model for understanding the development and evolution of morphological phenotypes. Abdominal pigmentation in Drosophila melanogaster has been particularly useful, allowing researchers to identify the loci that underlie inter- and intraspecific variations in morphology. Hitherto, however, D. melanogaster abdominal pigmentation has been largely assayed qualitatively, through scoring, rather than quantitatively, which limits the forms of statistical analysis that can be applied to pigmentation data. This work describes a new methodology that allows for the quantification of various aspects of the abdominal pigmentation pattern of adult D. melanogaster. The protocol includes specimen mounting, image capture, data extraction, and analysis. All the software used for image capture and analysis feature macros written for open-source image analysis. The advantage of this approach is the ability to precisely measure pigmentation traits using a methodology that is highly reproducible across different imaging systems. While the technique has been used to measure variation in the tergal pigmentation patterns of adult D. melanogaster, the methodology is flexible and broadly applicable to pigmentation patterns in myriad different organisms.

Quantifying Abdominal Pigmentation in Drosophila melanogaster

This work presents a method to quickly and precisely quantify the abdominal pigmentation of Drosophila melanogaster using digital image analysis. This method streamlines the procedures between phenotype acquisition and data analysis and includes specimen mounting, image acquisition, pixel value extraction, and trait measurement.

Pigmentation is a morphologically simple but highly variable trait that often has adaptive significance. It has served extensively as a model for ...

Promoter Capture Hi-C: High-resolution, Genome-wide Profiling of Promoter Interactions

The three-dimensional organization of the genome is linked to its function. For example, regulatory elements such as transcriptional enhancers control the spatio-temporal expression of their target genes through physical contact, often bridging considerable (in some cases hundreds of kilobases) genomic distances and bypassing nearby genes. The human genome harbors an estimated one million enhancers, the vast majority of which have unknown gene targets. Assigning distal regulatory regions to their target genes is thus crucial to understand gene expression control. We developed Promoter Capture Hi-C (PCHi-C) to enable the genome-wide detection of distal promoter-interacting regions (PIRs), for all promoters in a single experiment. In PCHi-C, highly complex Hi-C libraries are specifically enriched for promoter sequences through in-solution hybrid selection with thousands of biotinylated RNA baits complementary to the ends of all promoter-containing restriction fragments. The aim is to then pull-down promoter sequences and their frequent interaction partners such as enhancers and other potential regulatory elements. After high-throughput paired-end sequencing, a statistical test is applied to each promoter-ligated restriction fragment to identify significant PIRs at the restriction fragment level. We have used PCHi-C to generate an atlas of long-range promoter interactions in dozens of human and mouse cell types. These promoter interactome maps have contributed to a greater understanding of mammalian gene expression control by assigning putative regulatory regions to their target genes and revealing preferential spatial promoter-promoter interaction networks. This information also has high relevance to understanding human genetic disease and the identification of potential disease genes, by linking non-coding disease-associated sequence variants in or near control sequences to their target genes.

DNA regulatory elements, such as enhancers, control gene expression by physically contacting target gene promoters, often through long-range chromosomal interactions spanning large genomic distances. Promoter Capture Hi-C (PCHi-C) identifies significant interactions between promoters and distal regions, enabling the assignment of potential regulatory sequences to their target genes.

The three-dimensional organization of the genome is linked to its function. For example, regulatory elements such as transcriptional enhancers control the ...

Purification of Low-abundant Cells in the Drosophila Visual System

Recent improvements in the sensitivity of next generation sequencing have facilitated the application of transcriptomic and genomic analyses to small numbers of cells. Utilizing this technology to study development in the Drosophila visual system, which boasts a wealth of cell type-specific genetic tools, provides a powerful approach for addressing the molecular basis of development with precise cellular resolution. For such an approach to be feasible, it is crucial to have the capacity to reliably and efficiently purify cells present at low abundance within the brain. Here, we present a method that allows efficient purification of single cell clones in genetic mosaic experiments. With this protocol, we consistently achieve a high cellular yield after purification using fluorescence activated cell sorting (FACS) (~25% of all labeled cells), and successfully performed transcriptomics analyses on single cell clones generated through mosaic analysis with a repressible cell marker (MARCM). This protocol is ideal for applying transcriptomic and genomic analyses to specific cell types in the visual system, across different stages of development and in the context of different genetic manipulations.

Here, we present a cell dissociation protocol for efficiently isolating cells present at low abundance within the Drosophila visual system through fluorescence activated cell sorting (FACS).

Recent improvements in the sensitivity of next generation sequencing have facilitated the application of transcriptomic and genomic analyses to small ...

In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

Advances in sequencing technology have made whole-genome and whole-exome datasets more accessible for both clinical diagnosis and cutting-edge human genetics research. Although a number of in silico algorithms have been developed to predict the pathogenicity of variants identified in these datasets, functional studies are critical to determining how specific genomic variants affect protein function, especially for missense variants. In the Undiagnosed Diseases Network (UDN) and other rare disease research consortia, model organisms (MO) including Drosophila, C. elegans, zebrafish, and mice are actively used to assess the function of putative human disease-causing variants. This protocol describes a method for the functional assessment of rare human variants used in the Model Organisms Screening Center Drosophila Core of the UDN. The workflow begins with gathering human and MO information from multiple public databases, using the MARRVEL web resource to assess whether the variant is likely to contribute to a patient&#39;s condition as well as design effective experiments based on available knowledge and resources. Next, genetic tools (e.g., T2A-GAL4 and UAS-human cDNA lines) are generated to assess the functions of variants of interest in Drosophila. Upon development of these reagents, two-pronged functional assays based on rescue and overexpression experiments can be performed to assess variant function. In the rescue branch, the endogenous fly genes are &#34;humanized&#34;&#160;by replacing the orthologous Drosophila gene with reference or variant human transgenes. In the overexpression branch, the reference and variant human proteins are exogenously driven in a variety of tissues. In both cases, any scorable phenotype (e.g., lethality, eye morphology, electrophysiology) can be used as a read-out, irrespective of the disease of interest. Differences observed between reference and variant alleles suggest a variant-specific effect, and thus likely pathogenicity. This protocol allows rapid, in vivo assessments of putative human disease-causing variants of genes with known and unknown functions.

In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

The goal of this protocol is to outline the design and performance of in vivo experiments in Drosophila melanogaster to assess the functional consequences of rare gene variants associated with human diseases.

Advances in sequencing technology have made whole-genome and whole-exome datasets more accessible for both clinical diagnosis and cutting-edge human ...

In Vivo Forward Genetic Screen to Identify Novel Neuroprotective Genes in Drosophila melanogaster

There is much to understand about the onset and progression of neurodegenerative diseases, including the underlying genes responsible. Forward genetic screening using chemical mutagens is a useful strategy for mapping mutant phenotypes to genes among Drosophila and other model organisms that share conserved cellular pathways with humans. If the mutated gene of interest is not lethal in early developmental stages of flies, a climbing assay can be conducted to screen for phenotypic indicators of decreased brain functioning, such as low climbing rates. Subsequently, secondary histological analysis of brain tissue can be performed in order to verify the neuroprotective function of the gene by scoring neurodegeneration phenotypes. Gene mapping strategies include meiotic and deficiency mapping that rely on these same assays can be followed by DNA sequencing to identify possible nucleotide changes in the gene of interest.

In Vivo Forward Genetic Screen to Identify Novel Neuroprotective Genes in Drosophila melanogaster

We present a protocol using a forward genetic approach to screen for mutants exhibiting neurodegeneration in Drosophila melanogaster. It incorporates a climbing assay, histology analysis, gene mapping and DNA sequencing to ultimately identify novel genes related to the process of neuroprotection.

There is much to understand about the onset and progression of neurodegenerative diseases, including the underlying genes responsible. Forward genetic ...

Use of Drosophila S2 Cells for Live Imaging of Cell Division

Drosophila S2 cells are an important tool in studying mitosis in tissue culture, providing molecular insights into this fundamental cellular process in a rapid and high-throughput manner. S2 cells have proven amenable to both fixed- and live-cell imaging applications. Notably, live-cell imaging can yield valuable information about how loss or knockdown of a gene can affect the kinetics and dynamics of key events during cell division, including mitotic spindle assembly, chromosome congression, and segregation, as well as overall cell cycle timing. Here we utilize S2 cells stably transfected with fluorescently tagged mCherry:&#945;-tubulin to mark the mitotic spindle and GFP:CENP-A (referred to as &#8216;CID&#8217; gene in Drosophila) to mark the centromere to analyze the effects of key mitotic genes on the timing of cell divisions, from prophase (specifically at Nuclear Envelope Breakdown; NEBD) to the onset of anaphase. This imaging protocol also allows for the visualization of the spindle microtubule and chromosome dynamics throughout mitosis. Herein, we aim to provide a simple yet comprehensive protocol that will allow readers to easily adapt S2 cells for live imaging experiments. Results obtained from such experiments should expand our understanding of genes involved in the cell division by defining their role in several simultaneous and dynamic events. Observations made in this cell culture system can be validated and further investigated in vivo using the impressive toolkit of genetic approaches in flies.

Use of Drosophila S2 Cells for Live Imaging of Cell Division

Cell divisions can be visualized in real time using fluorescently tagged proteins and time-lapse microscopy. Using the protocol presented here, users can analyze cell division timing dynamics, mitotic spindle assembly, and chromosome congression and segregation. Defects in these events following RNA interference (RNAi)-mediated gene knockdown can be assessed and quantified.

Drosophila S2 cells are an important tool in studying mitosis in tissue culture, providing molecular insights into this fundamental cellular process in a ...

Investigation of the Transcriptional Role of a RUNX1 Intronic Silencer by CRISPR/Cas9 Ribonucleoprotein in Acute Myeloid Leukemia Cells

The bulk of the human genome (~98%) is comprised of non-coding sequences. Cis-regulatory elements (CREs) are non-coding DNA sequences that contain binding sites for transcriptional regulators to modulate gene expression. Alterations of CREs have been implicated in various diseases including cancer. While promoters and enhancers have been the primary CREs for studying gene regulation, very little is known about the role of silencer, which is another type of CRE that mediates gene repression. Originally identified as an adaptive immunity system in prokaryotes, CRISPR/Cas9 has been exploited to be a powerful tool for eukaryotic genome editing. Here, we present the use of this technique to delete an intronic silencer in the human RUNX1 gene and investigate the impacts on gene expression in OCI-AML3 leukemic cells. Our approach relies on electroporation-mediated delivery of two preassembled Cas9/guide RNA (gRNA) ribonucleoprotein (RNP) complexes to create two double-strand breaks (DSBs) that flank the silencer. Deletions can be readily screened by fragment analysis. Expression analyses of different mRNAs transcribed from alternative promoters help evaluate promoter-dependent effects. This strategy can be used to study other CREs and is particularly suitable for hematopoietic cells, which are often difficult to transfect with plasmid-based methods. The use of a plasmid- and virus-free strategy allows simple and fast assessments of gene regulatory functions.

Investigation of the Transcriptional Role of a RUNX1 Intronic Silencer by CRISPR/Cas9 Ribonucleoprotein in Acute Myeloid Leukemia Cells

Direct delivery of preassembled Cas9/guide RNA ribonucleoprotein complexes is a fast and efficient means for genome editing in hematopoietic cells. Here, we utilize this approach to delete a RUNX1 intronic silencer and examine the transcriptional responses in OCI-AML3 leukemic cells.

The bulk of the human genome (~98%) is comprised of non-coding sequences. Cis-regulatory elements (CREs) are non-coding DNA sequences that contain binding ...

A FACS-based Protocol to Isolate RNA from the Secondary Cells of Drosophila Male Accessory Glands

To understand the function of an organ, it is often useful to understand the role of its constituent cell populations. Unfortunately, the rarity of individual cell populations often makes it difficult to obtain enough material for molecular studies. For example, the accessory gland of the Drosophila male reproductive system contains two distinct secretory cell types. The main cells make up 96% of the secretory cells of the gland, while the secondary cells (SC) make up the remaining 4% of cells (about 80 cells per male). Although both cell types produce important components of the seminal fluid, only a few genes are known to be specific to the SCs. The rarity of SCs has, thus far, hindered transcriptomic analysis study of this important cell type. Here, a method is presented that allows for the purification of SCs for RNA extraction and sequencing. The protocol consists in first dissecting glands from flies expressing a SC-specific GFP reporter and then subjecting these glands to protease digestion and mechanical dissociation to obtain individual cells. Following these steps, individual, living, GFP-marked cells are sorted using a fluorescent activated cell sorter (FACS) for RNA purification. This procedure yields SC-specific RNAs from ~40 males per condition for downstream RT-qPCR and/or RNA sequencing in the course of one day. The rapidity and simplicity of the procedure allows for the transcriptomes of many different flies, from different genotypes or environmental conditions, to be determined in a short period of time.

A FACS-based Protocol to Isolate RNA from the Secondary Cells of Drosophila Male Accessory Glands

Here, we present a protocol to dissociate and sort a specific cell population from the Drosophila male accessory glands (secondary cells) for RNA sequencing and RT-qPCR. Cell isolation is accomplished through FACS purification of GFP-expressing secondary cells after a multistep-dissociation process requiring dissection, proteases digestion and mechanical dispersion.

To understand the function of an organ, it is often useful to understand the role of its constituent cell populations. Unfortunately, the rarity of ...

Cryopreservation of PGCs for Long-Term Preservation of &lt;em&gt;Drosophila&lt;/em&gt; Strains

Primordial Germ Cell Cryopreservation and Revival of Drosophila Strains

Drosophila strains must be maintained by the frequent transfer of adult flies to new vials. This carries a danger of mutational deterioration and phenotypic changes. Development of an alternative method for long-term preservation without such changes is therefore imperative. Despite previous successful attempts, cryopreservation of Drosophila embryos is still not of practical use because of low reproducibility. Here, we describe a protocol for primordial germ cell (PGC) cryopreservation and strain revival via transplantation of cryopreserved PGCs into agametic Drosophila melanogaster (D. melanogaster) host embryos. PGCs are highly permeable to cryoprotective agents (CPAs), and developmental and morphological variation among strains is less problematic than in embryo cryopreservation. In this method, PGCs are collected from approximately 30 donor embryos, loaded into a needle after CPA treatment, and then cryopreserved in liquid nitrogen. To produce donor-derived gametes, the cryopreserved PGCs in a needle are thawed and then deposited into approximately 15&#160;agametic host embryos. A frequency of at least 15% fertile flies was achieved with this protocol, and the number of progeny per fertile couple was always more than enough to revive the original strain (the average progeny number being 77.2 &#177; 7.1), indicating the ability of cryopreserved PGCs to become germline stem cells. The average number of fertile flies per needle was 1.1 &#177; 0.2, and 9 out of 26 needles produced two or more fertile progeny. It was found that 11 needles are enough to produce 6 or more progeny, in which at least one female and one male are likely included. The agametic host makes it possible to revive the strain quickly by simply crossing newly emerged female and male flies. In addition, PGCs have the potential to be used in genetic engineering applications, such as genome editing.

Author Spotlight: PGC Cryopreservation &amp;#8211; An Alternative Approach Towards Long-Term Preservation of Drosophila Strains 

A long-term preservation method for Drosophila strains as an alternative to the frequent transfer of adult flies to fresh food vials is highly desirable. This protocol describes the cryopreservation of Drosophila primordial germ cells and strain revival via their transplantation to agametic host embryos.