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LSU's Oliver Wessely on microRNAs and Kidney Development

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Name: Oliver Wessely
 
Position: Assistant professor, cell biology & anatomy/genetics, Louisiana State University Health Sciences Center
 
Background: Postdoc, University of California, Los Angeles — 1997-2003
PhD, natural sciences, University of Vienna — 1997
Visiting scientist, German Cancer Research Center — 1996
Magister, molecular genetics, University of Vienna — 1992
 

 
At the LSU Health Sciences Center, Oliver Wessely investigates kidney development in both normal and diseased states, with a particular focus on polycystic kidney disease. Recently, Wessely expanded his research to include microRNAs and their effects on kidney development in the frog, specifically Xenopus laevis, and the mouse.
This week, RNAi News spoke with Wessely about his miRNA efforts.
 
Let’s begin with some background on your lab.
 
We are studying kidney development using two model systems. On the one hand, [we’re studying] early, or pronephric, kidney development in the frog, and on the other hand [we’re studying] the metanephric kidney in mouse.
 
[In addition to kidney development], we’re interested in … what’s going on during disease formation, in particular polycystic kidney disease.
 
As part of [an effort] to explore some unexplored aspects [of the kidney], we’ve decided to look into microRNAs. We’ve been working on this for a year and a half now.
 
Can you give some insight into the work you’ve already done?
 
There are two things we’re trying to do. One is a profiling-type approach [in which we] see what microRNAs are expressed in the kidney and when they are expressed. In particular what we’re interested in, is trying to identify those microRNAs that are conserved in the kidney of frog and mouse. The idea is that you identify those microRNAs that really have fundamental functions … the ones that have really big roles in the regulation of kidney development.

We started out looking through the literature for microRNAs expressed in the kidney and have identified about 30 shown to be present in mouse, rat, and zebrafish kidneys … We now have performed a microarray screen for microRNAs expressed in the kidney.
 
Was this in both frog and mouse?
 
In this case, we have done it only in mouse. The idea is to perform the screen in mouse and then take the promising candidates and look whether they are also expressed in the frog. If we identify an evolutionarily conserved miRNA, then we would study those in more detail.
 
We’ve done one big round of microarray [screening looking for miRNAs in two different stages of early mouse kidney development], but it didn’t give as many positives as we would have expected. … We might have to expand this a little bit to look [for miRNAs expressed later in kidney development] and look at tissue specificity. So far, we only have compared early embryonic kidneys to kidneys of newborn mice; we haven’t yet compared the kidney to other organs such as heart, liver, or to lung.
 
So you were looking at these early stages of kidney development and expected to see more microRNA activity than you did?
 
We thought we would see more expression of different microRNAs during kidney development. We actually got a relatively small subset that is differentially expressed during the two stages we were looking at.
 
Because a lot of microRNAs seem to be expressed at low levels, we were thinking that we would get … more early ones versus late ones.
 
The [microRNAs] that might be there but we don’t pick up in a screen like [the one we ran] are steady state microRNAs — those that don’t change at all or change very slightly during development you wouldn’t pick up. There are very few that really change, either up or down, dramatically.
 
Were the [miRNAs that changed significantly] ones that were already in the literature?
 
Let’s put it like this: they are in the literature, but they are not really studied.
 
What’s next going forward?
 
This was one part of our project — to find and catalogue microRNAs expressed in the kidney. The second [step] is to do loss-of-function studies.
We have identified the Dicer homolog in the frog. What you do in frogs is eliminate genes by antisense morpholino oligomers … [which] interfere with the translation of the protein. We have used this approach to look for kidney defects — in this case we have so far only used the frog kidney.
 
There are clearly kidney defects [associated with the inhibition of miRNA expression]. Now that we have these microRNAs and a defect when we eliminate microRNA biogenesis in the kidney, we should be able to correlate those together. The way we plan to do that would be by performing rescue experiments.
 
The advantage of the frog is that it is very fast. We can do any kind of experiment, and within a week or two we have very reproducible results. Let’s say we have microRNA X and we want to see if it is required for [a particular] kidney phenotype. We can synthesize those microRNAs, inject them, and see if they rescue [the] phenotypes in Dicer morpholino-injected embryos.
 
What we have done so far looks promising. We clearly have phenotypes, and now we’re on our way to find out whether these correlate to certain microRNAs.
One important aspect is that in the kidney many different members of microRNA families are expressed, so you won’t be able to address [their role] with a simple knockout. Let’s say you have a certain microRNA family and you want to see if it is really required for patterning of the kidney. You can’t just make a single knockout of one microRNA and expect to see a phenotype because, in most cases, you have three or four family members expressed in the same tissue, which can be compensatory.
 
So it gets a little bit technically challenging. And that’s the advantage of the frog [where] we can make morpholino oligomers against three or four [members of different families] and then knock them out simultaneously. That works really well.
 
Are you collaborating with anyone on this work, or is it strictly in-house?
 
Right now it is [in-house].

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