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  • Blaze9
    Junior Member
    • Feb 2013
    • 8

    #1

    Need verification of my Differential Expression pipeline

    This is all gonna be in pseudo code/explanations, but can someone verify my pipeline, or let me know if there's a better method to doing something?

    The project has 10 samples (5 male: 1 control, 2 experiments with a replicate each, same w/ female) of an organism w/o a reference genome. We are using de novo assembly to assemble all 10 samples. (Trinity/Oases/Bridger, etc)

    After we assemble the samples, we want to create a reference so we can use it for Differential Expression. We will merge the 10 assembles together, run CD-HIT-EST to remove redundancy, and then proceed to annotate the fasta. We plan on using blastx, and save the output to an xml. Import the xml into Blast2GO, remove all the non-annotated transcripts, and export the annotated fasta. This fasta will use as our reference for mapping.

    We take the above annotated fasta, and map it back to the raw reads using bowtie2 or BWA, generate SAMs. Then use samtools to sorted BAMs.

    Convert our annotated reference to gff3, and use HTseq-count to evaluate counts. Then run DESeq to get our DE genes.

    Does this sound like a good plan?

    We're currently at the "reference transcript" stage, and we will be submitting the reference to our local blast cluster in the next few days. I just want to verify that what I'm thinking is correct, or if there's something else I should be doing.

    Thank you!
  • Brian Bushnell
    Super Moderator
    • Jan 2014
    • 2709

    #2
    Are you assembling the genome or transcriptome?

    Comment

    • Blaze9
      Junior Member
      • Feb 2013
      • 8

      #3
      It's illumina RNA-seq data, so it'll be a transcriptome.

      My organism has no reference genome at all, so we're doing denovo assembly via Bridger.
      Last edited by Blaze9; 06-30-2015, 10:20 PM.

      Comment

      • fanli
        Senior Member
        • Jul 2014
        • 197

        #4
        I'd evaluate how many non-annotated transcripts get removed after Blast2GO.

        Comment

        • Brian Bushnell
          Super Moderator
          • Jan 2014
          • 2709

          #5
          I suggest merging all of the reads prior to assembling, so you just get one assembly. That should give a better and less-redundant assembly compared to assembling 10x and deduplicating the results.

          Comment

          • GenoMax
            Senior Member
            • Feb 2008
            • 7142

            #6
            Would it be better to assemble male/female data separately?

            Comment

            • Brian Bushnell
              Super Moderator
              • Jan 2014
              • 2709

              #7
              I wouldn't... as long as they're all the same organism, it's easiest to assemble them all together both in terms of recovering low-expression genes and avoiding redundancy, which really is hard to remove without loss of real information.

              The ideal method of assembly (combining first or not combining first) may vary, though, depending on the ploidy and SNP rate. High-SNP-rate haploids, for example, might be better assembled individually.

              Comment

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