Tag Archives: gel

qPCR – Emma’s New 3KDSqPCR Primers

Due to previous contamination issues with Emma’s primers, Emma asked me to order new primers, reconstitute them and run a qPCR for her to see if we could eliminate her contamination issues with this primer set. cDNA template was supplied by Emma (from 2/2/11) and was from a C.gigas 3hr Vibrio vulnificus challenge. Samples were run in duplicate, as requested. Master mix calcs are here. Plate layout, cycling params, etc. can be found in the qPCR Report (see Results). Primer set used was:

Cg_3KDSqPCR_F/R (SR IDs: 1186, 1187)

Results:

qPCR Data File (BioRad CFX96)

qPCR Report (PDF)

The negative controls (NTC) are negative, meaning they do not cross the threshold set by the BioRad software. However, there is clearly amplification in the NTCs, but they come up late enough that they do not cross the threshold and, thus, generate a Cq value. Additionally, the melt curve reveals peaks in the NTCs that are at the same melting temperature as the product produced in the cDNA qPCR reactions. This would potentially imply some sort of contamination, as Emma has experienced.

Honestly, I do no think contamination is the problem. I believe that the “contamination” being seen in the NTCs is actually primer dimer. Increasing the annealing temperature (I’m not sure if Emma tried this during her troubleshooting) could potentially alleviate this issue. However, I’m not sure she’s amplifying the target that she wants to. Based on my analysis, I think she needs to re-design primers for her 3KDS target. Read my analysis and why I came to this conclusion below.

It seems unlikely that two independent people (and multiple primer stock replacements!) would have contamination, so I looked in to things a bit further.

I BLASTed the primer sets (NCBI, blastn, est_others db, C.gigas only) and the BLAST results reveal the primers matching with a C.gigas EST sequence that would produce a band of only 63bp. Here’s a screen capture of the BLAST results:

This result does NOT agree with what is entered in our Primer Database. As entered in our sheet, the expected PCR product would be ~102bp. However, taking in to account the BLAST results, it would be difficult to distinguish the difference between primer dimers and PCR product in a melt curve analysis.

Emma has previously run a conventional PCR with these primers and ran a gel (see below). At the time, it was thought to be contamination, but in retrospect (knowing the results of the qPCRs and the BLAST results) it seems likely that what she’s seeing in the negative controls was actually primer dimer, which was the same size of her PCR product (which she thought should be larger). Additionally, the gel was difficult to interpret because no ladder was run. A ladder might have revealed that her PCR product was half the size that she was expecting:

Colony PCR – Colonies from COX1 Genomic Cloning (from 20110411)

Ran colony PCR on various colonies produced from cloning on 20110411. All colonies were picked, re-streaked on Kan50 plate(s) and PCR’d. Master mix calcs are here. Cycling params:

  • 95C – 10mins

40cycles of:

  • 95C – 30s
  • 55C – 30s
  • 72C – 3mins
  • 72C – 10mins

Results:

Colony PCR – 5’RACE Colony: COX2 (repeat of yesterday’s PCR)

Repeated yesterday’s PCR on the re-streaked colony in order to run the product on a gel with a more appropriate ladder. See yesterday’s entry for all PCR info.

Results:

Lane 1: Hyperladder I

Lane 2: colony PCR

Lane 3: NTC

A band of nearly ~950bp is seen in the colony PCR, suggesting that the cloning reaction was successful. However, this does not match up with the expected size of ~1500bp seen on 20110407. Will sequence this regardless. Also, the gel on 20110407 may not have run properly (see image from that dat), which could possibly explain why we don’t see the “expected” size band of ~1500bp? Will inoculate a liquid culture for mini prep for eventual sequencing.

Colony PCR – 5′ RACE Colony: COX2

One white colony (marked with arrow in image linked) from the two plates from Steven’s cloning (from yesterday) was picked, restreaked on a new Kan50 plate (no X-gal) and PCR’d.

Master Mix:

2x Apex Red Master Mix – 25uL

10uM M13 Forward – 1uL

10uM M13 Reverse – 1uL

H2O – 23

Added 25uL to each PCR tube.

Cycling Params:

  • 95C – 10mins

40 cycles of:

  • 95C – 30s
  • 55C – 30s
  • 72C – 2mins

1 cycle:

  • 72C – 10mins

Results:

Lane 1: Hyperladder IV

Lane 2: colony PCR

Lane 3: NTC

Turns out the Hyperladder IV (this gel was run in the Friedman Lab) only goes up to 1000bp. So, the band we see in the colony PCR reaction could be close to the expected size if the insert is present (~1500bp). Although, we also see a band in the NTC. Will repeat this PCR and run on a gel with a more appropriate ladder…

Colony PCR – 5′ RACE Colonies

Two light blue colonies (there were no white colonies) were picked, restreaked on a new Kan50 plate (no X-gal) and PCR’d.

Master Mix:

2x Apex Red Master Mix – 37.5uL

10uM M13 Forward – 3uL

10uM M13 Reverse – 3uL

H2O – 46.5

Added 25uL to each PCR tube.

Cycling Params:

  • 95C – 10mins

40 cycles of:

  • 95C – 30s
  • 55C – 30s
  • 72C – 2mins

1 cycle:

  • 72C – 10mins

Results:

The two pale blue colonies do NOT contain our desired insert. Despite the presence of a larger, faint band (~950bp), that is far smaller than our 5’RACE insert size (~1500bp). And, clearly, the primary amplicon produced is ~250bp, which is the expected size for empty vector… Ladder is Hyperladder I (Bioline).

Will need to re-do ligation reaction and will do so at the recommended volumes in the TOP TA (Invitrogen) protocol.

5’/3′ RACE PCRs – Nested PCRs for COX2 Sequence

Due to the failure of the primary PCR on both 5′ and 3′ RACE cDNA libraries (from 20080619) yesterday, will perform nested PCR using a nested GSP designed by Steven (CgPGSRACEsrNGSP1; SR ID:1209). The 5uL of PCR reactions that were set aside yesterday were diluted to 250uL with tricine-EDTA (supplied with the Clontech SMARTer RACE cDNA Amplification Kit) as instructed in the Clontech manual. The master mix and tube layouts were exactly the same as yesterday’s, but instead of using 2.5uL of RACE cDNA library as template, I used 5uL of the diluted PCR reaction. Additionally, Universal Nested Primers were used instead of the Universal Primer Mix (both supplied in the kit). Cycling parameters followed “Program 2″ from the Clontech manual for 25 cycles.

Entire PCR rxns were run on a 1.2% gel, as instructed by the Clontech manual.

Results:

So….. What we see here is a melted gel!

But! We also see a successful PCR! The first three lanes (excluding the Hyperladder I) are 5′ RACE rxn, followed by two different negative controls (the negative control in the last lane is the one we’re really concerned with and it’s totally clean). The next three lanes are the 3′ RACE rxn, followed by two different negative controls (the negative control in the last lane is the one we’re really concerned with and it’s totally clean). As hoped/expected, we got a nice, clear product in the 5′ RACE rxn.

The bright band (~1500bp) in the 5′ RACE rxn PCR was excised and purified using Millipore Ultrafree DA columns according to protocol. Will clone and sequence this product.

3’RACE – C.gigas 3’RACE for COX2

Used Cg_COX2_3’RACE_short (SR ID: 1197) & Cg_COX2_3’RACE_long (SR ID: 1196) and the Clonetech SMART RACE cDNA Amplification Kit (unknown acquisition date) to attempt to acquire more 3′ sequence of the C.gigas COX2 isoform. Used Gigas 3’RACE cDNA (from 20080610).

Results:

Gel Loading:

Lane 1: Hyperladder 1

Lane 2: empty

Lane 3: Cg_COX2_3’RACE_long

Lane 4: Cg_COX2_3’RACE_long NTC

Lane 5: empty

Lane 6: Cg_COX2_3’RACE_short

Lane 7: Cg_COX2_3’RACE_short NTC

Lane 8: Hyperladder 1

No products produced. This could be due to a large number of factors. The age of the cDNA (from 20080610) is well beyond what the Clontech manual says for storage term (6 months). Additionally, the Clontech polymerase used was nearly 6 years old. The kit (and its components) are of an unknown age and could factor in to the failure of this procedure. Also, the primers that were designed had less than ideal Tm, per the kit’s recommendations.

May need to sequence some previously purified potential COX2 fragments in order to obtain a more useable region of the gene for RACE.

PCR – New C. gigas COX Primers for Sequencing of Isoforms

Used new primers for obtaining bands for additional sequencing of both COX isoforms in C. gigas. Master mix calcs are here. Master mix shorthand (MM##) is described below:

MM07 – Cg_COX_416_F (SR ID: 1193) + Cg_COX1_qPCR_R (SR ID: 1191) Expected band size (if no intron) = ~1540bp

MM08 – Cg_COX_416_F (SR ID: 1193) + Cg_COX2_454align1_R (SR ID: 1190) Expected band size (if no intron) = ~1540bp

MM09 – Cg_COX1/2_qPCR_F (SR ID: 1192) + Cg_COX1_qPCR_R (SR ID: 1191) Expected band size (if no intron) = ~225bp

MM10 – Cg_COX1/2_qPCR_F (SR ID: 1192) + Cg_COX2_454align1_R (SR ID: 1190) Expected band size (if no intron) = ~225bp

MM11 – Cg_COX_1519_F (SR ID: 1146) + Cg_COX2_454align1_R (SR ID: 1190) Expected band size (if no intron) = ~275bp

MM12 – Cg_COX_982_F (SR ID: 1151) + Cg_COX2_454align1_R (SR ID: 1190) Expected band size (if no intron) = ~812bp

Results:

Ladder is Hyperladder I from Bioline.

Master mixes are indicated underneath each group by the labels MM##. The order within each MM group (from left to right) is: template, NTC, NTC.

All bands boxed with green were purified using Millipore’s Ultrafree-DA spin columns. Samples were stored @ -20C in “Sam’s Misc. -20C Box”.

MM07 – Fails to produce any bands of any size. Suggests the presence of intron(s) causing the size of the potential amplicon to exceed the capabilities of the polymerase under these cycling conditions.

MM08 – Produces a band of ~400bp which is well below the expected 1540bp (if no introns) size. Due to the faintness of the band, the band was not excised. Will consult with Steven to see if he thinks it worth repeating to produce sufficient product for sequencing.

MM09 – Produce a ~500bp band. The band was excised. This band size is ~275bp larger than the expected size of 225bp. This implies the presence of an intron in this region. This band size differs from that produced by MM10, which suggests that this primer set can be used for qPCR AND distinguish between the COX1 and COX2 isoforms.

MM10 – Produced a ~700bp band. The band was excised. This band size is ~475bp larger than the expected size of 225bp. This implies the presence of an intron in this region. This band size differs from that produced by MM09, which suggests that this primer set can be used for qPCR AND distinguish between the COX1 and COX2 isoforms.

MM11 – Produced multiple bands, of which two were excised; a ~3000bp band and a ~600bp band. These bands were excised solely based on their intensity and their immediate useability for sequencing. Will discuss with Steven on whether or not this should be repeated and the other bands excised for sequencing purposes. Both bands that were excised exceed the expected band size of ~275bp, suggesting the presence of multiple introns. Additionally, the presence of so many products suggests that the primers are not very specific, in regards to their target.

MM12 – An extremely faint band of ~350bp can be seen, however, due to it’s faintness and it’s small size (expected size was ~812bp), the band was not excised. Will discuss with Steven to see if this warrants repeating to accumulate sufficient product for sequencing purposes. No amplification of any larger products suggests the presence of introns, causing the size of the potential amplicon to exceed the capabilities of the polymerase under these cycling conditions. This is also confirmed by the MM11 PCR results in which a 3000bp band was produced. Since the primer set in MM12 has an additional 600bp at the 5′ end, this has already exceeded the abilities of the polymerase, even if this addtional 600bp does NOT include an additional intron. However, it is curious that the MM12 primer set does not produce smaller, spurious PCR products as is seen in the MM11 primer set (these two primer sets both use the same forward primer).

Genomic PCR – Repeat of C.gigas COX genomic PCR from 20110118

This was repeated to generate more PCR product for sequencing purposes. PCR master mix calcs and cycling params are here. Master mixes 04 and 05 (MM04 and MM05) were repeated to gain more PCR product from the faint 550bp & 1500bp bands(MM04) and 5000bp band (MM05).

MM04 – Cg_COX_982_F (SR ID: 1151) + Cg_COX_1545_R (SR ID: 1148) Band size w/o intron = ~550bp

MM05 – Cg_COX_982_F (SR ID: 1151) + Cg_COX_2138_R (SR ID: 1149) Band size w/o intron = ~1130bp

Results:

Gel was run on 20110203

Samples on the left portion of the gel are from the MM04 primer combo and those on the right are from the MM05. Boxed bands were excised, purified using Millipore Ultra DA-free spin columns and stored @ -20C in Sam’s “Misc. -20C Box.”

Interestingly in the MM05 set, inconsistent, faint bands of ~400-500bp are visible. These were not visible the first time this PCR was conducted (see 20110118), but the exposure of the gel image wasn’t turned up as high as in this image. Due to their inconsistency and extremely low yield, these bands were not excised.

Genomic PCR – C.gigas cyclooxygenase (COX) genomic sequence

Attempt to obtain full genomic sequence for C.gigas COX. PCR set up/cycling params/etc are here. Primer set combinations(master mixes) are as follows:

MM01 – Cg_COX_5’UTR_3_F (SR ID: 1150) + Cg_COX_1009_R (SR ID: 1147) Band size w/o intron = ~1000bp

MM02 – “” + Cg_COX_1545_R (SR ID: 1148) Band size w/o intron = ~1540bp

MM03 – “” + Cg_COX_2138_R (SR ID: 1149) Band size w/o intron = ~2135bp

MM04 – Cg_COX_982_F (SR ID: 1151) + Cg_COX_1545_R (SR ID: 1148) Band size w/o intron = ~550bp

MM05 – “” + Cg_COX_2138_R (SR ID: 1149) Band size w/o intron = ~1130bp

MM06 – Cg_COX_1519_F (SR ID: 1146) + Cg_COX_2138_R (SR ID: 1149) Band size w/o intron = ~620bp

Results:

Bioline Hyperladder I used for marker. Gel is loaded with template samples at the far left of each master mix group with two no template controls (NTC) in the remaining two wells of each master mix group. All NTCs on the gel are clean.

All bands surrounded by a green box were excised from the gel.

MM01, MM02 and MM03 – The smallest expected band (i.e. no intron present) would have been 1000bp in MM01. Instead, we see faint banding of multiple sizes less than 1000bp in both MM01 and MM02. MM03 fails to produce any bands. This potentially suggests a couple of things. Firstly, the multiple banding produced in MM01 and MM02 suggests that the PCR conditions lead to some non-specific priming and should be optimized. Secondly, the fact that no bands were produced that are equal to or larger than the “no intron size” suggests that intron(s) may exist in the 5′ region of the COX gene and are large enough that the polymerase had insufficient time/ability to amplify.

MM04 – Three distinct bands were produced: 2000bp, 1500bp and 550bp. The size of band that would have been produced had an intron NOT been present would have been ~550bp. A band of this size was produced in this PCR reaction. However, two additional bands were produced. The presence of these two larger bands lends additional evidence for the existence of multiple isoforms of COX (which is also supported by the fact that multiple isoforms of COX are known to exist in most other species). The 2000bp band was excised and purified with Millipore Ultra-free DA spin columns and stored @ -20C until a sequencing plate is readied.

MM05 – A distinct band of ~5000bp was produced. This is significantly larger than the “no intron size” of ~1130bp, suggesting the presence of an intron. This band was excised, but not purified due to the low concentration of DNA in the gel. The gel slice was stored @ -20C until this PCR reaction could be repeated to accumulate sufficient product for sequencing.

MM06 – A distinct band of ~2200bp was produced. This is significantly larger than the “no intron size” of ~620bp, suggesting the presence of an intron. The band was excised and purified with Millipore Ultra-free DA spin columns and stored @ -20C until a sequencing plate is readied.

The PCR reactions reveal the presence of intron(s) in the COX gene we’re investigating as well as providing evidence for the existence of multiple isoforms in C.gigas. Since the PCR products that have been excised for sequencing are so large, additional primers will need to be designed closer to the introns in order to generate smaller products that can be fully sequenced. Additionally, all reactions using the primer designed to anneal in the 5’UTR of COX (SR ID: 1150) failed to produce useful results. This is either due to poor performance of the primer under these reaction conditions or due to the presence of a large intron in the 5′ region of the gene. Additional reverse primers will be designed that anneal closer to the 5′ portion of the COX gene in hopes of characterizing the 5′ genomic sequence better.

After speaking with Steven today about the potential existence/”discovery” of multiple isoforms, he decided to map the newly-released C.gigas 454 NGS data to the existing COX coding sequence in GenBank (FJ375303). The alignment is shown below.

The two 454 reads that map closest to the 5′ end of the COX coding sequence match up nearly perfectly, with periodic SNPs. The remaining 454 reads that map to the COX coding sequence are very different and provide very good evidence of a previously unidentified isoform of COX in C.gigas. Primers will be designed from both the existing COX sequence in GenBank (FJ375303) and the other potential isoform. These primers will likely be used in both qPCR and for sequencing purposes, in order to be able to distinguish and characterize both isoforms. Additionally, BLASTing will be performed with the sequences from both isoforms to evaluate how they match up with existing COX isoforms in other species.