Thought that this was an interesting paper, published recently in PNAS.
The paper shows that alternative splicing produces different transcript isoforms for the 5’UTR region of the human gene encoding α-1-antitrypsin called SERPINA1, such that splicing of 5’UTR modulates the inclusion of long upstream ORFs (uORFs). What’s new with all this I hear you say. Well, the authors go on to show that while SERPINA1 transcripts produce the same protein isoform, they do so with different translation efficiencies. Differences in uORF content and 5’UTR secondary structure combine to differentiate the translational efficiencies of SERPINA1 transcripts.
α-1-antitrypsin is of interest because deficiencies in this protein are associated with chronic obstructive pulmonary disease (COPD), liver disease, and asthma. This work points to the possibility that genetic alterations in noncoding gene regions, such as the 5’UTR region, could result in α-1-antitrypsin deficiency.
The work also reinforces the idea that the amount of protein produced from a gene is not a simple function of the abundance of the transcript.
The reference is: Proc Natl Acad Sci U S A. 2017 Nov 21;114(47):E10244-E10253. doi: 10.1073/pnas.1706539114. Epub 2017 Nov 6.
The image used is their Figure 3. SHAPE-MaP structure probing data for SERPINA1 transcripts.
Loved the whimsical comedy of the ‘Detectorists‘ series with the excellent MacKenzie Crook (as Andy Stone) and Toby Jones (as Lance Stater). It follows Lance and Andy’s lives as their personal situations and ambitions orbit their central obsession with metal detecting.
It made me think of some analogies with Science. Obsession – yeah, tick. Do we ever stop thinking about our research topic? From hours of scanning the landscape only to uncover ‘ring-pull’ duds (yeah tick – see ‘failed experiments, no?). Or is it that we are just centimetres away from that Anglo-Saxon gold hoard. Maybe we have selected the wrong ‘field’ in the first place. I think that, like Lance and Andy, most of us dream of landing ‘the big one’ – maybe that discovery that will be transformative? We can but dream?
Especially loved the concept of the “discovery dance” – what kind of celebration would you do when the the game changing discovery comes your way….can you practice it? should you practice it?…or should it come as a natural reaction?
Here’s a link to a brief YouTube clip:
I think we are all Detectorists at heart. Think I’ll get practicing my dance….
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After overfilling the tubes with the agar/growth media a cross is sliced into the agar with a sterile blade (see clip above). Doing this his will hopefully help the roots find a way down through the agar/growth media.
Then the Arabidopsis seeds (sterilised in bleach and suspended in sterile water) are pipetted onto the surface of the agar one-by-one (ok, maybe sometimes two-by two) – see clip below.
The trays are then sealed with micropore tape and that’s it – now to wait to see if the seeds germinate – should take around a week to see the emergence of the very young shoots.
Setting up the next experiment. It involves pipetting agar growth media into (literally) 100’s of tubes – see movie clip above. I try to overfill the tubes with the molten agar mixture (this is important for a later step….where I place single Arabidopsis seeds on the agar surface…watch this space).
Science is 99% perspiration, and 1% inspiration….and this is the ‘perspiration’ bit.
Ahhh….the best 4 words in scientific research? It’s been a long, arduous trip but finally we shall be adding a few dents to our current knowledge of alternative splicing/splicing factors/temperature and the clock….will keep you posted.
Made me think about the time it takes to publish scientific research, and I came across this commentary article in Nature from 2016.
I think many of us working at the coal-face of research will recognise a lot of what it says, e.g.
“Many….feel trapped in a cycle of submission, rejection, review, re-review and re-re-review that seems to eat up months of their lives, interfere with job, grant and tenure applications and slow down the dissemination of results.”
Also talks about “resetting the clock” – not to do with circadian clocks, but related to the time stamp of submission and resubmission(s).
Is it taking longer to publish? One contributor to the article says that the average time for their group of papers took 9 months…[9 months is good, no?]
Anyway, for the time being lets focus on…”now acceptable for publication” 🙂
This work from the Lab of RNA Biochemistry at the Freie University Berlin shows just how sensitive splicing is to small changes in body temperature.
They looked at alternative splicing (AS) of U2af26 across a physiologically relevant temperature range (35-40oC). [U2af26 is a component of the essential splicing factor U2af (U2 auxiliary factor) where it can substitute for U2af35 in heterodimers with U2af65]
The authors show that U2af26 exon 6/7 skipping showed a very nice linear correlation with the temperature (see their figure below), suggesting that AS is able to react in a thermometer like way to read body temperature changes.
The paper goes on to show an involvement for SR proteins in temperature-regulated U2af26 AS, primarily via modulation of the phosphorylation state of SRs. The authors speculate that there will be a physiological role for temperature-controlled AS in other phenomena, such as hypothermia and fever.
Back to thinking about how to explain alternative splicing in an easy, graphical or pictorial way.
Here’s an attempt at sketching plant cells under a microscope. Grid like arrangement of cells, with chloroplasts (photosynthesis organelles) as greenish circles, and the cell nucleus as dark circles/blobs.
Not entirely sure where this is going…maybe a cartoon. Still hope to include Pandas somewhere along the line…
Are RNA thermosensors more common than we thought? Interesting article in the Journal of Experimental Biology speculating whether RNA thermometers (RNATs), well-studied in Prokaryotes, are prevalent in the other Kingdoms of Life.
Changes in the conformation of RNATs (see their Figure 1, above) typically involve melting of short regions of the mRNA, for example hairpin structures, in response to elevated temperature (a ‘zipper’ mechanism) or a shift between alternative conformations of the mRNA that involve larger regions of the molecule (a ‘switch’ mechanism).
The RNAT contains the Shine–Dalgarno (S–D) sequence (AGGAGG) that, when fully exposed, can bind to the small (30S) ribosomal subunit and allow translation to commence. The start codon (AUG) is often located eight nucleotides downstream from the S–D sequence. Thus melting of the ‘thermometer’ allows the S–D sequence and start codon to interact with the 30S subunit, promoting translation of the mRNA.
Interesting read – I wasn’t familiar with the concept of ‘marginal stability’ – the idea that for RNA secondary and tertiary structures, thermosensor regions must have the right stability – or ‘balancing act’ – to allow temperature-driven changes in shape to take place when (and only when) a signalling function is required.
I particularly liked the section on ‘Differential translation of allelic mRNAs: another way to modulate the proteome?‘ – the concept that natural variants (allozymes) with different thermal optima can provide a species with an opportunity to establish populations with adaptively different thermal optima in regions of its biogeographic range where temperatures differ. Thus a cold-optimised allozyme might be more common in populations living in colder regions of a species’ range, whereas the warm-optimised allozyme would be dominant in warmer regions, and therefore crucially that slight changes in base composition likely alter the thermally sensitive mRNA structures that govern translational ability in a way that ensures differential translation of distinct allelic messages.
The author, George Somero, make an interesting point that we might assume that “changes in temperature often are regarded as having negative influences on macromolecular stability” adding “However, there is also a ‘good’ side to this thermal perturbation: the alteration in conformation of the macromolecule that is caused by a change in temperature can function as a thermosensing mechanism and lead to downstream changes that are adaptive to the cell.”
Exciting times lie ahead for RNA structure and temperature sensing….
Trying to re-learn the language of GATEWAY cloning. ‘BP reactions’, ‘LR cloning’, ‘attB sites’, ‘entry clones’, ‘destination vectors’, ‘binary vectors’…I could go on. Thinking of trying a series of ‘Improved Gateway Binary Vectors (ImpGWBs)‘ to make plants express our genes of interest (GOIs) fused to markers. These are described in this paper:
As for the choice of marker, there is a dizzying choice, so as well as trying to get to grips with GATEWAY, there is the question of what best to use as marker. I’ve had disappointing results fusing our GOIs to green fluorescent protein (GFP) in the past, so maybe time to try something else. As you can see, there is no shortage of choice:
Trying to work out how long to make the upstream promoter region for some plasmid constructs. I’ve been using the SnapGene tool to visually stitch together DNA sequences.
How long is the promoter for a particular plant gene? 500, 1000, 2000 bp? or is it defined by particular features in the promoter? I guess for some genes the upstream region barges into other gene loci.
I tried out this web-tool, plantpromoterdb.
Seems quite useful. It displays some features of the promoter that might be considered when deciding the promoter chunk length e.g. it will show the predicted transcriptional start site, and other cis– features.
Seems, though, that most studies take a nominal 1000 to 2000bp upstream of the translational start codon (ATG). Think it’s good to know some of the promoter ‘landscape’ though. Here’s the reference for plantpromoterdb: