Tuesday, March 6, 2018

Trascriptome analysis of programmed cell death in Cryphonectria parasitica

This is the first post in series dedicated to my research and project I'm involved in. Also, I'm going to bring here some analysis work I'm doing just to myself. To find out more follow the tags #myresearch and #myanalysis.

This time I'll bring an example of how to use Circos tool to visualize genomic and transcriptomics data. This tool is visually very appealing, but more you put on the graph less useful it becomes.

Before we start I want to introduce one basic concept from mycology, barrage. On figure below barrage shown by arrows and compatible strains' interactions shown by arrowheads.

In a nutshell barrage or incompatibility reaction is a form of innate immune response that causes two genetically distinct fungal strains reject each other. In fungal world most of interactions between strains happen through hyphal fusion or anastomosis. If all immune signals check and no disagreement found two strains fuse and continue to exist as a single individual. But if immune response triggered, two strains form a barrage, a separation wall made out of dead cells. Barrage separates two strains restricting exchange of genetic material. It gives us a glimpse into early evolution of sexual reproduction and immunity. Basically saying if we too different from each other genetically direct exchange of genes may cause more damage than good, so lets have sex instead.

Circular diagram below shows genes differentially expressed in C. parasitica during incompatibility reaction.

This diagram allows to see overall picture of how C. parasitica genes (red dots) behave in relation to genome map. Plus you can compare them to genes of P. anserina (purple) and N. crassa (green) in similar reaction. Not particularly informative, but you certainly can take something out of it.

First of all C. parasitica  has much more upregulated genes (pink area) than other two fungi. Also there are transcriptionally inert areas of genome, showing no gene activation. And finally lack of correlation in expression rate between three species. Basically red dots do not appear together with purple and green, showing different or no expression at all.

Figure caption: Gene differential expression (DE) shown on C. parasitica genome map (11 largest scaffolds).
Diagrams from outside to inside: Black lines show genome map of 11 scaffolds, each tick mark corresponds to 100,000 bp. Inside the outer black lines, blue marks indicate previously annotated genes on JGI C. parasitica genome portal and orange marks indicate novel genes. Novel genes are transcripts which demonstrated detectable level of expression in areas of genome previously not annotated on genome portal. First circle shows expressed genes, and second circle shows DE genes during barrage. Interior to this are C. parasitica gene IDs of DE genes where black IDs indicate genes differentially expressed during barrage only in C. parasitica, green and purple IDs indicate that orthologs of those genes are DE during Heterokaryon Incompatibility (HI) in N. crassa and P. anserina respectively. The inner-most pink, grey and blue bands show plots of individual genes expression. The Y axis indicates genes differential expression in log2 scale. Y axis pink colour indicates upregulated (y> 2), blue – downregulated (y< -2) and grey (2>y>-2) indicate non-DE genes. Red dots indicate C. parasitica genes, green and purple dots indicate DE orthologs during HI in N. crassa and P. anserina respectively.
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