week 2: mRNA seq Flashcards
RNA vs. DNA
Molecular differences
Strand #
DNA is relatively stable and only minor sample degradation is seen with shipping (barring any delays/complications)
RNA is highly UNSTABLE and sample degradation may be seen with shipping (especially if going to China)
RNA
- AGUC
- OH on sugar
- single stranded, and often but not always, linear in shape
DNA
- AGTC
- H on sugar
- two antiparallel, complementary strands form a double helix
central dogma
DNA, RNA, mRNA, protein
transcription: DNA to RNA
polyadenylation: RNA to mRNA
translation: mRNA to protein
mRNA
– polyadenylated mRNA is RNA that is expressed and/or in the process of being expressed. It is therefore an indication of the downstream effects of modifications made to biological control systems that are influenced by both internal and external factors. (i.e. drugs, environmental factors, DNA modifications, etc.)
mRNA vs. “Other” RNA
Other types of RNA are important for many applications as well, however, a main focus within the genomics is on actively expressed transcripts (result of transcription; cell makes RNA out of DNA), that is why mRNA is specifically so important
Other types:
- tRNA, lncRNA, ncRNA, rRNA, miRNA, snRNA, snoRNA
TLDR:
“Gene Expression” study = mRNA Seq
Key feature that differentiates mRNA from other RNA types = polyA tail
QC steps
total RNA
(sample QC)
library construction
(library QC)
sequencing
(data QC)
Bioinformatics analysis
QC & Library Prep
- Starting Material
Cell Pellets or Tissue / Whole Blood / FFPE
- Novogene can extract the total RNA from most cell / tissue
- Novogene can never guarantee the success of an extraction as it’s highly depended on the quality of the starting material
- Extraction costs are $50-$70/sample (variable based on sample count)
- we encourage clients to perform their own RNA extraction is possible
Total RNA
- >100ng of total RNA needed for non-directional library prep (most common)
- >400ng of total RNA needed for directional library prep
- What if the client has less than 100ng?? – we can accommodate it through one our low input pipelines
Sample QC
- QC Method = Agilent 2100 or AATI fragment analyzer
Checks RNA integrity, purity, and quantity
For all normal RNA/DNA pipelines, we allow for 2 library QC’s within the quoted cost. (i.e. 1 sample + 1 backup can be QC’d for no additional cost)
Any additional QC’s that may be needed on top of that
Sample QC
RNA Sample Requirements
Client Facing Sample Requirements
chart of requirements - look in ppt :)
RNA Sample Requirements
- Qubit
Quantification of RNA
- Unit: ng/µL
Not used as part of Novogene internal QC, but is a common tool used by clients.
A qubit fluorometer is a sensitive instrument used to quantify RNA (as well as DNA and protein) based on fluorescence
Fluorescent dye used in the Qubit assay has a high affinity for RNA and binds to it, forming a dye-RNA complex. The amount of light emitted is proportional to the amount of RNA present.
RNA Sample Requirements
- Nanodrop
Quantification & Qualification of RNA
Units: ng/µL & Absorbance Units (A)
Not used as part of Novogene internal QC, but is a common tool used by clients.
Sample Requirements:
OD260/280 ≥ 2.0
OD260/230 ≥ 2.0
260nm: nucleic acids (RNA and DNA)
Because DNA and RNA absorb at the same wavelength, DNA contamination can inflate concentrations
280nm: proteins
230nm: contaminants of Trizol, guanidine thiocyanate, EDTA, phenol and guanidine hydrochloride etc….
RNA Sample Requirements
- Agilent 2100 Bioanalyzer / AATI Fragment analyzer / Tapestation
Quantification & Qualification of RNA
Agilent 2100 Bioanalyzer
Utilizes microfluidics technology to perform electrophoresis on a miniaturized scale.
Highly accurate, well known instrument, produces gel like images
AATI Fragment Analyzer
Capillary electrophoresis system that separates nucleic acids based on size and charge.
Suitable for integration into automated workflows for large-scale projects.
Used by Novogene
TapeStation
Automated electrophoresis system, samples are detected using fluorescence
Moderate resolution compared to Bioanalyzer.
Library Prep Options
bug chart look at ppt :)
Library Prep: PolyA Selection vs rRNA Depletion
Poly-A tail selection: oligo(dT) beads selectively pull down the mRNA, leaving everything else behind
rRNA depletion: rRNA is selectively depleted from the sample. In the prep step, tRNA and sRNA aren’t captured due to small size. Leaving mRNA, lncRNA, and circRNA primarily to be captured in the prep
so it is named after what it eliminates basically
Library Preparation: PolyA Selection vs rRNA Depletion
rRNA-Depletion uses
When other ncRNAs are of interest
Eukaryotic spp from FFPE
For all Prokaryotic spp
Library Prep: Directional vs Non-Directional Prep
Directional = Stranded = Strand Specific
Non-Directional = Non-Stranded
What: Directional mRNA library preparation preserves RNA strand directionality (3’ -5’ orientation); whereas, this information is lost in non-directional prep
How: Stranded/Directional prep uses dUTP in place of dTTP to label the second cDNA strand for selective degradation. This allows the first strand to be the only template left, ensuring that all of the transcripts share a common orientation
Note: rRNA depletion preps are always directional. polyA selection preps can either be directional or non-directional
Library Prep: Directional vs Non-Directional Prep
chart look at ppt :)
Library Prep: Directional vs Non-Directional Prep
- Why Non-Stranded mRNA Library? - so why non-directional?
- Simplicity: Non-stranded library prep is generally less complex and can be more straightforward to perform. It doesn’t require the additional steps needed to preserve strand information, which can simplify the workflow.
- Cost: Because it involves fewer steps and reagents, non-stranded library prep can be less expensive than stranded library prep. This can be an important consideration for clients with budget constraints.
- Experimental Design: Some experiments may not benefit from the additional information that stranded RNA-Seq provides. In cases where the orientation of the transcript does not impact the study’s outcome, a non-stranded will suffice. For example, if the goal is to measure overall gene expression levels rather than to study antisense transcription or overlapping genes, non-stranded RNA-Seq could be appropriate.
Why Stranded mRNA Library?
Strand Specificity: Stranded library prep allows researchers to determine the orientation of the RNA transcripts, which is crucial for understanding antisense transcription and enhancing transcript annotation.
Comprehensive Transcriptome Analysis: Stranded mRNA prep offers a clear and comprehensive analysis across the transcriptome, providing more data per assay, including
1. Full sequence and variant information
2. Higher discovery power to detect known and novel transcripts.
3. More accurate gene expression data
4. Increased alignment efficiency
5. Detecting features like gene fusion and allele-specific expression
Library Prep
- Low Input Options
Watchmaker Kit (San Jose Lab)
- rRNA depletion (directional - better for looking at antisense studies and studies that need direction lol and for understanding the transcriptome). rRNA eliminates rRNA and is used if the client wants ncRNA
- Input: 25ng
- Human Mouse Rat only
Cost: QC (1 time High sensitive QC w/ Bioanalyzer included), rRNA Depletion Lib Prep, & Sequencing at 40M PE150 reads (NovaSeq X Plus), no analysis
< 24 Samples: $329 per sample
24-100 Samples: $309 per sample
100+ Samples: $289 per sample
Takara Kit (Outsourced to ADH)
polyA selection (non-directional, less complex so less expensive and is good if client’s study does not require directionality)
Input: at least 10ng
Success of library prep and downstream results cannot be guaranteed
Cost: QC (1 time High sensitive QC w/ Bioanalyzer included), Takara SMART-seq V4 ultra low input RNA kit, sequencing 20M PE150 reads, no analysis
< 24 Samples: $450 per sample
24-100 Samples: $400 per sample
Prioritize Wachmaker kit for all low input samples (prob. because we need to outsource it and also that it is cheaper), UNLESS
- BSL concern
- Previous batch of samples was processed at ADH
- Non HMR species
Library Preparation: Globin Depletion
What is gmRNA?
- Globin mRNA (gmRNA) is the messenger RNA that encodes globin proteins.
Globulin and gmRNA are highly abundant in whole blood, overwhelming other RNA types. Their presence can interfere with the detection of low-abundance RNA species.
gmRNA-Depletion
- gmRNA is predominantly found in red blood cells. Any RNA samples derived from whole blood must undergo a globin depletion step
- PBMC(s) & plasma does not typically need gmRNA-depletion
peripheral blood mononuclear cells (PBMCs)
