25 Jan

New publication from the lab: How to stabilize a sex-specific gene expression pattern in male flies

New manuscript from the lab published in Nucleic Acids Research: Drosophila Sister-of-Sex-lethal reinforces a male-specific gene expression pattern by controlling Sex-lethal alternative splicing.

In a collboration with the labs of Stefan Schneuwly, Gunter Meister (both at the University of Regensburg), Michael Krahn (Westfälische Wilhelms-Universität Münster), and Oliver Rossbach (Justus-Liebig-University Giessen), we could demonstrate that the protein Sister-of-sex-lethal (Ssx) is required in male flies to suppress production of Sex-lethal (Sxl).


Genomic tagging of the Sex-lethal (Sxl) locus in flies to reveal Sxl protein mis-expression (arrowheads) in male flies mutant for Sister-of-Sex-lethal. Arrows mark expression of a Sxl isoform in neural cell bodies and projections.


Most higher eukaryotes reproduce sexually, increasing the variability in the offspring. This allows e.g. rapid adaption to a new (or changing) environment or the cleansing of harmful mutations from a population. Sexual reproduction in higher eukaryotes usually involves individuals of different sex: males and females. Not surprisingly, the genetic programs that determine sex and control sexual differentiation need to be particularly robust in order to ensure survival of the population.

In Drosophila, a single protein, the master regulator Sex-lethal (Sxl), governs female development by controlling the expression of key factors involved in female morphology and behaviour. Once expressed, it engages in an auto-regulatory, positive feedback loop to ensure its sustained expression. This stably ‘flips the switch’ and commits to female development.

In contrast, in males Sxl expression needs to be shut-off which is achieved by alternative splicing that generates RNA isoforms encoding truncated, non-functional Sxl protein. Fluctuations inherent to gene expression can, however, produce small amounts of functional Sxl protein. When left unchallenged, this protein can trigger a self-enforcing cascade resulting in Sxl protein expression snowballing out of control. Until now, however, it remained unclear how males completely shut off the Sxl expression cascade and protect themselves against runaway protein production to ensure robust sex-specific development.

We have discovered a safeguard mechanism that prevents Sxl production in adult male flies. We identified the protein Sister of Sex-lethal (Ssx) as the first antagonist of Sxl-mediated auto-regulatory splicing that defines a precise threshold level for activation of the auto-regulatory, positive feedback loop that controls Sxl expression. We could show that Ssx exerts function by competing with Sxl for the same RNA regulatory elements thus preventing Sxl from triggering the self-enforcing expression cascade in adult male animals.


8 Jun

NEW FINDING: Purification of Cross-linked RNA-Protein Complexes by Organic Extraction

The advent of interactome capture has allowed the unbiased identification of RNA binding proteins (RBPs) dramatically expanding their number and yielding novel insights into RNA biology (see also our recent review).

For interactome capture, RBPs are photo-cross-linked to their RNA targets. Subsequently, oligo-dT resin is used to capture polyadenylated RNAs and to co-purify with them the covalently bound proteins. RNAs that lack a ploy(A)-tail can, however, not be captured by this approach, limiting its broad application. In particular, prokaryotic organisms that do not polyadenylate their mRNAs are not amenable to interactome capture.

Now three manuscripts have been uploaded to bioRxiv by the Lilley, Krijgsveld, and Beckmann labs (we contributed to one of them). In all cases extraction with organic solvents is employed to purify cross-linked RNPs (see figure) circumventing the requirement of a poly(A)-sequence for RNP capture. Moreover, this approach also captures RBPs that bind to RNA as short as 30 nt.



The manuscripts can be found here:

Purification of Cross-linked RNA-Protein Complexes by Phenol-Toluol Extraction

Unbiased dynamic characterization of RNA-protein interactions by OOPS

The Human RNA-Binding Proteome and Its Dynamics During Arsenite-Induced Translational Arrest

29 Nov

Another manuscript accepted…

Nucleic Acids Research just accepted another manuscript for publication to which we have contributed. In an experimental effort headed by our colleague Sébastien Ferreira-Cerca (University of Regensburg, Biochemistry III), the function of the atypical Rio kinases in ribosomal smal subunit (SSU) biogenesis and maturation was addressed in Archea. This revealed activation of Rio2 by an ancient and conserved mechanism involving ribosomal RNA that stimulates release of the kinase from the nascent 40S particle. Watch out for the next NAR table of contents: there you should find a link to the manuscript, once it is out!

4 Nov

New publication from the lab

Good news: A manuscript from the lab has just been accepted for publication in the RNA Journal!

We have identified the protein Sister-of-Sex-Lethal (Ssx) as a novel repressor of translation. Ssx is a paralog of the master regulator of female development in Drosophila, Sex-lethal (Sxl), that acts as a repressor of male-specific lethal-2 (msl-2) mRNA translation. It employs two distinct and mutually reinforcing blocks to translation that operate on the 5’ and 3’ untranslated regions (UTRs) of msl-2 mRNA, respectively. While 5’ UTR-mediated translational control involves an upstream open reading frame, 3’ UTR-mediated regulation strictly requires the co-repressor protein Upstream of N-ras (Unr) which is recruited to the transcript by Sxl.

Ssx and Sxl have a comparable RNA-binding specificity and both proteins can associate with Uracil-rich RNA regulatory elements present in msl-2 mRNA. Moreover, both repress translation when bound to the 5’ UTR of msl-2. However, Ssx is inactive in 3’ UTR-mediated regulation as it cannot engage the co-repressor protein Unr. The difference in activity maps to the first RNA-recognition motif (RRM) of Ssx. Conversion of three amino acids within this domain into their Sxl counterpart results in a gain-of-function and repression via the 3’ UTR, allowing detailed insights into the evolutionary origin of the two proteins and into the molecular requirements of an important translation regulatory pathway.

Find the full text here.  RNA. 2017 Oct 31. pii: rna.063776.117. doi: 10.1261/rna.063776.117. [Epub ahead of print], PMID: 29089381


11 Aug

Analysis of circRNPs

Are circular RNAs (circRNAs) translated? It is very intriguing to speculate that (at least some) circRNAs might encode functional peptides. So far however, evidence in support of this theory is weak. One might hypothesize that by non-canonical initiation once in a while a ribosome might indeed translate an open reading frame encoded by circular RNA, whether this yields significant amounts of a functional protein still remains to be demonstrated.

In a collaborative effort with the Bindereif lab at the Justus-Liebig-University of Giessen, we have analyzed the sedimentation of circRNAs in sucrose gradients.  If circRNAs are indeed translated this could be revealed by a change of sedimentation behavior after treatment with a drug that releases elongating ribosomes from RNAs (Puromycin). In our experiments however, no significant change in sedimentation behavior of selected abundant circRNPs from HeLa cells could be observed, suggesting that these circRNAs are not (or at best only weakly) translated.

Scientific reportsCircRNAs do however associate with proteins to form ribonucleoproteins (RNPs). In our recent publication ‘CircRNA-protein complexes: IMP3 protein component defines subfamily of circRNPs’ (published in Scientific Reports) we demonstrate that in HeLa cells, circRNAs form distinct, large RNPs. Moreover, we identify the RNA-binding protein and tumor marker IMP3 (IGF2BP3) as a protein component of numerous circRNPs.

(Picture taken from Schneider et al., 2016, Scientific Reports 6, 31313, doi:10.1038/srep31313, CC 4.0)



31 May

Bioinformatics Course at the University of Regensburg



From October 10th to 14th 2016, a methods course on ‘Analysis of NextGen RNA-Seq data for expression profiling and protein binding RNAs‘ will take place here in Regensburg. Insightful lectures will be deliverd by reknown experts in the field, including (in alphabetical order) Simon Anders (FIMM Helsinki), Markus Hafner (NIAMS/NIH Bethesda), Steve Hoffman (University of Leipzig), Stefan Kirsch (Fraunhofer  ITEM, Regensburg), Charlotte Soneson (University of Zurich), Rainer Spang (University of Regensburg), Nicholas Strieder (University of Regensburg), and Grischa Toedt (EMBL Heidelberg). After the lectures, there will be ample time for hands-on training allowing the participants to gain some practical experience with the latest computational approaches. If you are interested in participating, please register before July 13th.

The course is generously supported by the Graduate Research Academy RNA Biology of the Collaborate Research Center SFB960 ‘Ribosome formation: principles of RNP biogenesis and control of their function’.

31 Mar

Review article: The expanding universe of ribonucleoproteins

Soon a special issue with focus on ‘RNA biology in physiology and disease’ will be published by the European Journal of Physiology (Pflügers Archiv). Together with our colleagues Benedikt Beckmann (IRI for the Life Sciences, Humboldt University Berlin) and Alfredo Castello (University of Oxford) we have contributed a review article entitled: The expanding universe of ribonucleoproteins – of novel RNA-binding proteins and unconventional interactions.

We focus on the recent advances in the identification of novel RNA-binding proteins (RBPs) and the unexpected finding that many of the novel RBPs do not contain identifiable RNA-binding domains (RBDs), raising the question of how they interact with RNA. It is surprising that despite the many functions that have been attributed to RNA, our understanding of ribonucleoproteins (RNPs) is still mostly governed by a rather protein-centric view, leading to the idea that proteins have evolved to bind to and regulate RNA and not vice versa. However, RNPs formed by an RNA-driven interaction mechanism (‘RNA-determined RNPs’) are abundant and offer an alternative explanation for the surprising lack of ‘classical’ RBDs in many RNA-interacting proteins (which we discuss in detail in the review article).

HCV-on-40SHCV IRES bound to a 40S ribosomal subunit, structure based on Yamamoto et al., 2015; PDB ID: 5FLX, individual panels represent different orientations (rotated by 90°).

7 Jan

New colleague in the lab: Andreas Horn

AndreasThe new year has just started and already there are some great news: Andreas Horn joined the lab as a PhD student! His PhD project will focus on a novel strategy that we have recently developed which allows to map protein-RNA interaction with high resolution in a parallel fashion. Welcome to the lab!

17 Dec

Season’s Greetings

Lab-Christmas-2015With christmas time approaching, we would like to thank our colleagues and collaborators for a wonderful and productive year! Also we would like to specifically thank the funding agencies for their very generous support that helps us to pursue our scientific goals!

Merry Christmas, a relaxing holiday season and a happy and successful New Year!

16 Dec

Fellowship for Stefan Reich

JHS_Logo_RGBWe are very happy to announce that Stefan Reich was awarded a fellowship from the Joachim Herz Stiftung!

‘I am very happy that my application for an Add-on Fellowship for Interdisciplinary Science from the Joachim Herz Stiftung was successful. This now gives me the opportunity to attend conferences and additional courses in bioinformatics which will support our work. Personally, I hope to gain further insight into data analysis which will pave the way to success in my doctoral thesis. For this reason I want to thank the Joachim Herz Stiftung very much for the generous support and I am looking forward to the first meeting with the other fellows in March 2016.’

-Stefan Reich, PhD student

1 Aug

Great news: Second funding period for Collaborative Research Centre 960 granted

SFB Mitglieder kleinThe Collaborative Research Centre 960 (SFB960) – Ribosome formation: principles of RNP biogenesis and control of their function has been extended for another funding period! We are now part of the SFB960 and we are very grateful for the financial support by the Deutsche Forschungsgemeinschaft (DFG) that allows us to address exciting scientific questions (see project B11).

Pictured above: the principal investigators of the SFB 960