Dr. Umarah Usman


Main Focus

We are interested in understanding how growth signaling works in the model green alga- Chlamydomonas. Using a combination of biomolecular and analytical tools we resolve the cellular response to perturbation in growth signaling. Our focus is on the Target of Rapamycin (TOR) kinase signaling, a highly conserved growth regulator across various eukaryotes. 
We study two main aspects of TOR signaling;  

1. TOR signaling and cell cycle of Chlamydomonas: 
Firstly, we established a robust system for synchronized culturing of Chlamydomonas strain (CC1690) and explored molecular markers for various cell cycle stages. Since TOR pathway is known to regulate the cell cycle in different organisms, we evaluated how inhibition of TOR pathway influences dynamics of different biomolecules as well as physiological features.    
For further details;
  • Jessica Jüppner*, Umarah Mubeen*, Andrea Leisse, Camila Caldana, Henrike Brust, Martin Steup, Marion Herrmann, Dirk Steinhauser and Patrick Giavalisco, Dynamics of lipids and metabolites during the cell cycle of Chlamydomonas reinhardtii. The Plant Journal, 92: 331–343. doi:10.1111/tpj.2017. <https://onlinelibrary.wiley.com/doi/abs/10.1111/tpj.13787>
  • Jessica Jüppner*, Umarah Mubeen*, Andrea Leisse, Camila Caldana, Andrew Wiszniewski, Dirk Steinhauser and Patrick Giavalisco, The target of rapamycin kinase affects biomass accumulation and cell cycle progression by altering carbon/nitrogen balance in synchronized Chlamydomonas reinhardtii cells. The Plant Journal 93(2): 355-376, 2018.   <https://onlinelibrary.wiley.com/doi/full/10.1111/tpj.13642>
  • Mubeen et. al., TOR inhibition alters proteome kinetics affecting growth and cell cycle progression in Chlamydomonas (manuscript in preparation)

2. Resolving proximal and distant targets of TOR signaling 
After noticing the drastic shifts in metabolite, lipids and protein expression upon TOR inhibition, we wanted to identify the key targets of TOR signaling and disentangle the proximal from distal targets of TOR in Chlamydomnas. We used targeted metabolomic and isotope-labelling techniques to follow the time course kinetics to track the utilization/fate of nutrients after TOR inhibition. Moreover, we optimized the method for label free quantification of phosphorylation changes upon TOR inhibition to track immediate post-translational protein modifications.
  • Umarah Mubeen, Jessica Jüppner, Jessica Alpers, Dirk K Hincha and Patrick Giavalisco,  TORC1 inhibition drives de-novo amino acid synthesis by enhancing ammonium assimilation in Chlamydomonas (manuscript in revision).
  • Umarah Mubeen, Krzysztof Bajdzienko and Patrick Giavalisco Label free quantification of phosphorylation changes in Chlamydomonas upon TORC1 inhibition (manuscript in review).
*equal author contribution

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