Research

The lab is interested in understanding the molecular and physiological functions of mechanisms that regulate gene expression. Our current major interests are linked to the three areas described in more detail below, namely Oscillatory Gene Expression, Cell Fate Control, and MicroRNAs. However, we are happy to let the data guide us and have thus also worked at times on RNA modification, splicing, or transcription termination.

Oscillatory Gene Expression

oscillations_for website_hard_crop

Development of a multicellular organism requires accurate regulation of events in time. Biological ‘clocks’ are thought to orchestrate such timekeeping but their molecular nature and properties have remained elusive. We discovered massive mRNA level oscillations as an apparent clock output during larval development of the nematode C. elegans (Hendriks et al., Mol Cell 2014). Characterized by a shared eight-hour period and a large amplitude (>2.1 fold), oscillations affect 20% of the active genes. These features and the accessibility of C. elegans for genetic screens make this phenomenon a powerful model to study developmental clocks. To achieve this, we have been investing heavily in technology to investigate oscillations and the processes they control at the single animal level. We can thus track developmental progress of animals for 384 animals at a time using a plate reader and examine development and oscillatory gene expression in parallel in tens of animals through long-term imaging. These approaches are complemented by sequencing at high temporal resolution. Using these and more standard molecular biology approaches, we have been able to show that periodic transcription is a major contributor of rhythmic mRNA accumulation, and identify candidate transcription factors. Ongoing genomic and genetic approaches aim not only at finding additional clock components and their wiring, but also at understanding their physiological role and relevance in developmental timing.

Cell Fate Control

cell_fate
Figure adapted from Büssing et al., (2008) 14: 400-409

An ability to self-renew is a key feature of animal stem and progenitor cells, and therefore tightly controlled. It allows these cells to produce both a copy of themselves and a second, more differentiated daughter cell when dividing. Using C. elegans and mammalian cells, we study the mechanisms that promote self-renewal and terminate it when progenitor cells differentiate. We have a specific interest in the let-7 miRNA and its target LIN41/TRIM71, an RNA-binding protein, which regulate self-renewal and differentiation in worms as well as mammals. In C. elegans, we found that LIN41 silences its mRNA targets through distinct mechanisms, depending on the binding location: LIN41 binding to 3’UTRs promotes mRNA degradation, whereas 5’UTR-binding inhibits translation (Aeschimann et al., Mol Cell 2017). We are now working on identifying the players in these distinct silencing mechanisms, as well as the molecular basis of the highly specific target recognition by LIN41. Furthermore, we are studying the developmental functions of the LIN41 targets lin-29 and mab-10, which form a transcription factor complex necessary for several aspects of cell differentiation such as cell cycle control and cell fusion. We use techniques such as CRISPR-Cas9-mediated genome engineering and ribosome profiling in both C. elegans and mammalian cells with the aim of obtaining a mechanistic understanding of how LIN41 and its downstream targets control self-renewal and cell differentiation.

MicroRNAs

miRNA Figure _Rüegger 2012 adpatedai
Figure adapted from Rüegger et al., Trends Biochem Sci (2012): 10:436-446

MicroRNAs (miRNAs) are small regulatory RNAs, ~22 nucleotides in length, that silence target mRNAs to which they bind. Through translational repression and mRNA degradation, they control diverse physiological events, and miRNA dysregulation accordingly contributes to various diseases, most notably cancers. The lab has a longstanding interest in understanding the molecular mechanisms by which miRNAs act (e.g., Ding & Großhans, 2009), the physiological functions that they execute (e.g. Ecsedi et al., 2015), and the mechanisms that regulate miRNAs themselves (e.g., Chatterjee & Großhans, 2009; de la Mata et al., 2015). Current projects revolve around characterization of novel small RNA pathway factors, and mechanisms that control miRNA target specificity under physiological conditions.